carnarvon good agricultural practice guide - Vegetables WA

C arnar vo n G ood Ag r ic ult ur a l P ractice Guide

Department of Agriculture and Food

Introduction

Introduction

Ca rn ar vo n Go od Ag ri cult ural Pr ac tic e Guide

Foreword

‘Good practice’ is all about adopting growing methods that both improve profitability by achieving high yields of quality produce while contributing to a sustainable production system. Increasingly many growers are finding that practices that sustain a healthy environment often boost their bottom line. This Carnarvon Good Agricultural Practice Guide was developed by vegetablesWA and the Carnarvon Growers Association and complements a number of good practice demonstration sites across the Carnarvon growing region. The project was funded by the Commonwealth Government Caring for our Country (CfoC) program. It builds on the success of the Good Practice Guide previously developed for the Swan Coastal Plain, by tailoring it for the unique conditions of Carnarvon. The Guide brings together a range of resources into a user-friendly format across a range of growing topics. We hope it provides the information you need to apply good practice in the field or the impetus to seek further advice. We trust you share our vision of continual improvement within the industry and you find the Guide useful in achieving good practice. John Shannon vegetablesWA

Department of Agriculture and Food

Introducti o n

I

Acknowledgements The Carnarvon Good Agricultural Practice Guide is part of a Caring for our Country (CfoC) project, developed at Carnarvon Horticultural District thanks to Australian Government funding plus the leadership and joint work between vegetablesWA, the Department of Agriculture and Food, Western Australia (DAFWA) and Carnarvon Growers Association (CGA). Carnarvon Growers Association acknowledges and appreciates the support given to this project by vegetablesWA and the staff at the Gascoyne Research Station in Carnarvon, who throughout the project shared their experience to reach the goals. It is important to highlight the generous contribution of growers in Carnarvon, who shared their experiences and invaluable knowledge to enrich this agricultural guide towards the sustainability of this horticultural district. Carnarvon Growers Association would like to recognise the project steering committee, which included Michael Nixon, Mark Bumbak, Robbie Kuzmicich, Malcolm Jones, Henry Van As and John Shannon. We also thank Josephine Eynaud, for the design and layout of the Guide.

© Carnarvon Growers Association Author: Carlos Ramirez, CfoC Project Officer Carnarvon Horticultural District c/o Gascoyne Research Station, 296 South River Road (PO Box 522) Carnarvon WA 6701 ISBN: 978-0-646-904948

Disclaimer Carnarvon Growers Association makes this guide and the information contained within freely available to Western Australian vegetable growers on the understanding that users exercise their own care and judgement with respect to its use. Carnarvon Growers Association and its employees and contributors do not guarantee that the publication is without flaw of any kind or wholly appropriate for growers’ particular purposes and therefore disclaims all liability for any error, loss or other consequence that may arise from any reliance by users on any information contained herein. This publication is intended to inform Western Australian growers of current best practices in the industry at the time of publication. That said, growers are advised to also obtain appropriate professional advice relevant to their particular circumstances.

II

Introduction

NUTRIENT MANAGEMENT

Nutrient management


Contents Section 1 N utri en t m a n a g em en t

1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 The importance of soil pH in crop nutrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Calcium: a key factor in Carnarvon’s crop nutrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Important concepts for adequate soil management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Total Exchange Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Plant Nutrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Macronutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Micronutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Soil laboratory analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Irrigation water testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Nutrient application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Timing application to crop needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Nutrient composition of fertilisers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Developing a fertiliser budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Organic matter in soils – an accurate indicator of soil health and fertility . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Organic fertilisers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Maintaining and Calibrating spray equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Boomspray maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Mixing the chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 When spraying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 After spraying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Fertiliser storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Record keeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Section 1 N utri ent m a nag em ent

1

Nutrient management

Introduction Appropriate soil management is a key factor of both economic and environmental sustainability for vegetable production. Improving soil health improves productivity including lowering input cost for herbicides, pesticides and fuel, reducing wear on machinery and driving more efficient use of water and nutrients. Most of Carnarvon’s soils are alkaline (have a high pH) and contain high levels of sodium (Na). Combined with a lack of water across a variety of sandy to sandy loam soils this makes managing crop nutrition one of the most challenging activities for growers across the region. Fortunately Carnarvon growers recognise the importance of adequate plant nutrition, based on strategies to establish equilibrium in soil bases saturation that makes elements including sulphur (S), phosphorus (P) and potassium (K), more available to the plant. In this chapter we highlight some of the most important practices for growers to follow in order to improve the efficiency of nutrient application while having minimal environmental impacts.

Most of Carnarvon’s soils have high pH levels and a high sodium (salt) content.

Most Carnarvon soils have a pH range of 6.8 to 7.8 and are classified as ‘neutral to slightly alkaline’. At this range of pH the solubility of micronutrients such as manganese (Mn), zinc (Zn) and copper (Cu) falls rapidly and plant availability starts to decline. As pH starts to increase towards being strongly alkaline (pH > 8.5), the availability of phosphorus, iron (Fe), copper, zinc and manganese drops rapidly and regular tissue tests may be needed to identify possible deficiencies of these elements (Washington State University, 2004).

Figure 1 Nutrient availability at different pH levels 4.0 pH 4.5 Extreme acidity

5.0 Very strong acidity

Strong acidity

5.5

6.0

Medium acidity

6.5

Slight acidity

7.0

Very slight acidity

7.5 Slight alkalinity

8.0

8.5

Moderate alkalinity

9.0

9.5 pH10.0

Strong alkalinity

Very strong alkalinity

Nitrogen Phosphorus Potassium Sulphur Calcium

The importance of soil pH in crop nutrition There are two main reasons why it is important to manage soil pH: 1. Vegetables can only absorb minerals when they are dissolved in the soil solution. A slight change in pH can affect the degree of solubility of such minerals. Soil pH indirectly affects the biological and chemical activity of the soil (see Figure 1).

Magnesium Iron Manganese Boron Copper and zinc

Source: Redrawn from Troug. E. (1946)

2. Not all vegetables can grow successfully in soils with the full spectrum of pH.

2

S e c t io n 1 N u t r i e n t ma n a g e me n t


Table 1 Effect of fertilisers in soil pH Material

Analysis N-P-K

Speed of effect

Impact on pH

Ammonium sulphate

20-0-0

Rapid

Very acidifying

Calcium nitrate

15-0-0

Rapid

Minimal

Potassium nitrate

13-0-44

Rapid

Neutralising

Ammonium nitrate

34-0-0

Rapid

Acidifying

Urea

45-0-0

Rapid

Slightly acidifying

Mono-ammonium phosphate

11-48-0

Rapid

Acidifying

Di-ammonium phosphate

18-46-0

Rapid

Acidifying

Triple superphosphate

0-46-0

Medium

Neutralising

Superphosphate

40-20-0

Medium

Neutralising

Potassium chloride

0-0-60

Rapid

Neutralising

Potassium sulphate

0-0-50

Rapid

Neutralising

Limestone

Slow

Minimal

Hydrated lime

Rapid

Minimal

Medium

Neutral

Gypsum (calcium sulphate)

Different fertilisers vary in their impact on soil pH (see Table 1). The following generalisations may be used as a guide: • Ammonium (NH4+) or ammonium-forming fertilisers (e.g. urea) reduce soil pH (acidify) over time. • Nitrate (NO3-) sources carrying a basic cation are less acidifying than ammonium fertilisers. • The presence of calcium (Ca), magnesium, potassium, and sodium in the fertiliser may slightly increase or cause no change in soil pH.

Figure 2 Sodium removal Ca++ Na

Ca++

Calcium: a key factor in Carnarvon’s crop nutrition Calcium plays an important role in the soil as an element, that in balanced proportion with other bases, helps to establish equilibrium in soil base saturation, which makes elements like sulphur, phosphorus and potassium, among others, more plant available. This cationic exchange in soils also helps to liberate sodium, making it easier to be drained out of the system, reducing salinity (see Figure 2). Carnarvon growers commonly use three key sources of calcium: gypsum, lime sand (CaCO3) and crushed lime (Ca(OH)3). Each source has different chemical and physical characteristics (see Table 2).

Clay particles minus charge

Na+ Ca++ Na+ Ca++

Ca++

Na+

• Elemental sulphur, ammonium sulphate, and compounds such as iron or aluminium sulphates can reduce the soil pH. • Gypsum (calcium sulphate — CaSO4) has minimal impact on soil pH. However, in areas where excess sodium is a problem, gypsum can help to improve soil structure.

Ca++

+

Na+

Ca++

= Calcium

Na+

= Sodium

Soil solution

Source: © Jerry Spencer, Pitchcare Online Magazine, 2009

neutralising value, particle size and solubility. Neutralising value measures the alkalinity of the lime source relative to a pure calcium carbonate (100% NV). Particle size, is a physical characteristic that allows the product to dissolve faster and achieve a better distribution throughout the soil.

Table 2 Neutralising value, particle size and solubility of calcium amendments Calcium source

Neutralising value

Particle size

Solubility

Gypsum (CaSO4)

Poor

Finest (5–20 microns)

Highest

Lime sand (CaCO3)

93%

Fine (< 0.24 mm)

High

Crushed lime (Ca(OH)3)

104%

Coarse material

Poor

Both industry and scientists throughout the world accept that the quality of agricultural limes is best measured by

Section 1 Nutri en t m anagem en t

3

a

b

Knowing a soil’s physical, chemical and biological conditions is a priority. Soil test results provide a general overview of soil conditions in terms of texture, pH, cation exchange capacity (CEC) and nutrient levels. As such, a soil sample is a valuable diagnostic tool that allows growers to better understand their soil and gain a realistic expectation about the performance of the next crop. These results also provide a good indication of the type and amount of fertiliser required to achieve optimum growth and yield for a particular crop.

c

Total Exchange Capacity

© Organic Store. www.theorganicstore.com.au/

Gypsum is often used as part of a strategy to correct soil compaction and poor soil structure. Poor soil structure is often associated with too many sodium ions attached to the clay particles. On some occasions excess magnesium can also have the same effect. As gypsum dissolves, calcium replaces sodium and/or magnesium on the exchange sites. This can also counteract excessive salinity levels in soil and has the added benefit of not affecting the pH of soil (Home Depot, 2013).

Important concepts for adequate soil management Some basic concepts follow that will allow growers to organise an efficient fertilisation program that guarantees adequate plant nutrition and a desirable crop yield with minimal or nil negative soil impacts.

Figure 3 Total Exchange Capacity

High TEC (>18 meq/100 gr): — High levels of clay or organic matters — Greater water holding capacity Total Exchange Capacity

Amendments, (a) gypsum, (b) lime sand and (c) crushed lime.

Total exchange capacity (TEC) is the maximum quantity of total cations, of any class, that a soil can hold at a given pH value, and make available for exchange within the soil solution (see Figure 3). TEC is used as a measure of fertility, nutrient retention capacity,and the capacity to protect groundwater from cation contamination (Wikipedia, 2013).

— Larger the quantity of lime must be added to increase the soil pH

Ideal level: 10–18 meq/100 gr

Low TEC (-0.5

-0.5 to -1.5

1.0

Source: vegetablesWA, 2007


13

© Government of Western Australia, www.water.wa.gov.au/Water+regions/Mid+West+Gascoyne/default.aspx

Table 4 Vegetable crop water salinity tolerance (ECw) Vegetable crop

No reduction in yield (dS/m)

10% reduction in yield (dS/m)

Zucchini

3.1

3.8

Cucumber

1.7

2.2

Tomato

1.7

1.9

Grapes

1.0

1.7

Cantaloupe/rockmelon

1.4

2.4

Watermelon

1.3

na

Capsicum

1.0

1.5

Sweet corn

1.0

1.7

Onion

0.8

1.2

Eggplant

0.7

1.6


Nutrient application Plant nutrients applied in proper quantities and at appropriate times will help achieve optimum crop yields. However, improper application of nutrients can cause water quality problems both locally and downstream. Good nutrient management uses nutrients wisely for optimum economic benefit, while minimising impact on the environment. In general, apply nutrients while the crop is actively growing and can use them. Shortly after planting, when the plant’s root system is immature, the crop’s need for fertiliser will be 1% or less of its full-life requirement (vegetablesWA, 2007). At this stage in the growth cycle, it is important fertiliser remains at a shallow depth long enough for the crop to take up what it needs. Later, the crop may be doubling in weight weekly, so larger amounts of fertiliser will be required to meet plant needs. By that time, the plants’ root systems will be more extensive, enabling the crop to recover applied nutrients from a greater volume and depth of soil.

14

© Carlos Ramirez

Soil and leaf analysis are the key elements to understand the nutrition balance in your crop. Talk to your agronomist to guarantee an accurate fertilisation program for your crop.

To minimise leaching of nutrients beyond the crop’s root zone, apply fertilisers frequently in small amounts, especially on sandy soils. Timeliness is most important with nitrogen fertiliser. Much of the nitrogen applied can be lost through leaching and volatilisation if it is applied too early. Phosphorus application is also most efficient when it occurs at or near planting time, especially with soils low in phosphorus. Time of application is less critical with potassium than with nitrogen or phosphorus. Do not apply fertilisers if rain is predicted. Both ammonium and nitrogen in nitrate form are soluble in water and will readily leach past the crop’s root zone. In addition, phosphorus can be lost through surface run-off. Losses of nitrogen through volatilisation (conversion to ammonia gas) can be higher in alkaline soils than in acid soils. Incorporation of urea and ammonium-based fertiliser by irrigation will minimise such losses. Nitrate sources such as potassium nitrate, calcium nitrate and magnesium nitrate are more suitable.



Sulphate of ammonia is useful in alkaline soils, as it helps acidify the soil and thereby enhances the availability of trace elements. Nutrients such as nitrogen, phosphorus and potassium are readily translocated from old leaves to new growth (see Table 5). Hence, symptoms of these deficiencies occur initially in the older leaves. Nutrients such as calcium and boron do not appear to be retranslocated from old leaves to new growth under any circumstances. Hence, for these nutrients, deficiency symptoms occur generally in young growing parts of the plant. For many nutrients, the extent of retranslocation is variable, depending upon the degree of the deficiency, the plant species, and the nitrogen status of the plant. For example, there is little or no movement of copper, zinc, or molybdenum out of old leaves of deficient plants. For these nutrients, symptoms will occur mainly in young tissues. Table 5 Nutrient mobility within the plant Mobile

Variably mobile

Immobile

Nitrogen

Copper

Calcium

Phosphorus

Zinc

Boron

Potassium

Sulphur

Manganese

Magnesium

Molybdenum

Iron Mobile = Retranslocated from old leaves to new growth under all conditions.

© Carlos Ramirez

Some varieties of mango rootstocks tolerate high levels of water and soil salinity. This tolerance is possibly associated with the capacity of this rootstock to restrict the uptake and transport of Cl- and Na+ ions from the root system to the above-ground parts.

Variable mobility = Retranslocated from old leaves to new growth only under some conditions. Immobile = Not retranslocated from old leaves to new growth under any conditions.

© Carlos Ramirez


15

Timing application to crop needs

© Carlos Ramirez

All plants require the same mineral elements; however, the quantity, rate and timing of uptake vary with crop, variety, climate, soil characteristics and management. Timing fertiliser applications so nutrients are available when plants need them increases nutrient use efficiency and reduces potential adverse environmental effects. Nitrogen tends not to accumulate in plants and so needs to be supplied regularly. Ideally, match nitrogen application rates with crop growth. With young crops, which require less nutrients than crops at the mid-growth stage, it is better to apply nitrogen in smaller, more frequent doses because the plants’ root systems are smaller. During the first four weeks of the crop’s growth, application rates may be less than half of those required later during the crop life cycle (vegetablesWA, 2007). To maximise the efficiency of crop nitrogen usage, the first (light) application should occur after planting but before emergence for direct-sown crops, or immediately after planting for transplanted crops. Consider drenching transplants with a dilute nutrient solution in the trays before transplanting and using starter solutions. Managing nitrogen in this way will minimise field losses and will ensure adequate nitrogen availability to the crop during critical growth periods.

Grapes demand high levels of potassium to achieve optimum yields

Crops mainly use phosphorus during the early growth stages (at the seedling stage for annuals and during early regrowth for perennials), but it is still required throughout the crop life cycle. Phosphorus is necessary for early root development, is mobile in plants and can be stored in stems and leaves. Potassium leaches easily in sandy soils. In order to promote optimal early growth, apply sufficient potassium in the early growth stages on such soils. Regular potassium applications are not critical during the later stages of crop growth as, like phosphorus, potassium can be stored in the plants’ leaves and stems (Morgan D, 2013). In most of the eastern states of Australia the best time to broadcast or band potassium is during autumn. Winter rains move the fertiliser into the root zone making it available for uptake during the growing season. In Western Australia, fertiliser is most often applied during spring. © Shutterstock

Potassium is the most abundant nutrient in banana fruit cells. This nutrient is not only important in yield but also to improve fruit quality.

16

Grapes and bananas demand high levels of potassium. Bananas contain about 370 mg/100 g of pulp. Potassium is also removed from vineyards in harvested grapes at a rate of about 1.6–5 kg of actual potassium per tonne of fruit. S e c t io n 1 N u t r i e n t ma n a g e me n t


Sulphur is generally incorporated into fertilisers containing the elements magnesium, potassium and phosphorus in a quantity sufficient to meet crop needs (vegetablesWA, 2007). Calcium is often present in fertilisers such as superphosphate, or in soil improvers such as gypsum or limes. Under Carnarvon’s saline soils, an annual preplanting calcium program is required in order to see the effects on soil exchange capacity and sodium reductions. Calcium nitrate can be applied post-planting to supply calcium and nitrogen (vegetablesWA, 2007). Magnesium is commonly found in adequate to slightly high levels in Carnarvon soils. However imbalances in relation with the soil calcium content are common in some soil analysis. Both calcium and magnesium should be at a proportion of 80% of all bases saturation with magnesium around 20% and calcium 60% as an appropriated equilibrium between these two elements. As with calcium, apply magnesium before planting and through the crop cycle as needed. Boron and zinc are nutrients with a low availability under the alkaline (high pH) Carnarvon soils. To increase availability of these nutrients, apply calcium in the form of gypsum or limes before planting. Timely foliar sprays of these elements will correct any deficiency, but recovery can be slow if spraying is delayed until symptoms are severe.

Nutrient composition of fertilisers A wide range of fertilisers — and hence a wide range of nutrient compositions — is available. However, proprietary mixed products may not contain the correct ratio of nutrients for a particular crop type or growth stage. Understanding the nutrient composition of various fertilisers helps when choosing the most appropriate option for a given situation, saving money and time and preventing wastage (vegetablesWA, 2007). Following is a comparison of some of the most common sources of nitrogen, phosphorus and potassium: Urea [CO(NH2)2]: • Fertiliser grade: 46-0-0. • Soluble, readily available source of nitrogen. • Contains the highest percentage of nitrogen of all dry fertilisers. • Applying too much near germinating seeds can kill seedlings due to release of ammonia (NH3). • Rapid nitrogen losses can occur through volatilisation as ammonia gas when urea is applied to the soil surface and not incorporated. Incorporation or injection of nitrogen into the soil is important to avoid such losses. Ammonium nitrate (NH4NO3): • Fertiliser grade: 34-0-0. • Soluble, readily available source of nitrogen. • Dry fertiliser product. • 50% of the nitrogen is present as ammonium (NH4+). • 50% of the nitrogen is present as nitrate (NO3-), which is susceptible to leaching and denitrification. • Ammonia volatilisation is not an issue unless applied to high pH soils (i.e. >7.5). • Strong oxidizer that can react violently with other incompatible materials. • Should be stored properly to prevent risk of explosion. • A natural affinity to absorb moisture limits bulk storage during summer. Ammonium sulphate (NH4)2SO4: • Fertiliser grade: 21-0-0-24S. • Contains 24% sulphur.

© Carlos Ramirez

Tomatoes remove about 2.2–2.4 kg of nitrogen per tonne of fruit produced. However high rates of nitrogen can reduce yields. Potassium is highly demanded compared with nitrogen with tomatoes using more than 300 kg of potassium per hectare each season.


• Soluble, readily available source of nitrogen and sulphur. • Volatilisation is not an issue unless applied to high pH soils (i.e. >7.5). • Also marketed in a liquid form as 8-0-0-9S.

17

Potassium sulphate (K2SO4):

Diammonium phosphate (NH4)2HPO4:

• Contains 50–53% potassium, 18% sulphur and no more than 2.5% chlorine.

• Fertiliser grade: 18-46-0. • Soluble, readily available source of phosphorus and nitrogen. • Initial soil reaction can produce free ammonia, which can cause seedling injury if too much fertiliser is placed near the seed.

• Major use is for chloride-sensitive crops. Potassium-magnesium sulphate (K2SO4•2MgSO4): • Contains about 22% potassium, 11% magnesium, 22% sulphur and no more than 2.5% chlorine.

• Acid-forming fertiliser.

• Along with the potassium, this product is a good source of magnesium and suplhur.

Monoammonium phosphate (NH4H2PO4): • Fertiliser grade: 11-52-0.

• Often referred to as sul-po-mag or K-mag.

• Soluble, readily available source of phosphorus and nitrogen.

• Water soluble source of nutrients.

• Acid-forming fertiliser.

Potassium nitrate (KNO3): • Contains about 44% potassium and 13% nitrogen.

Concentrated superphosphate [Ca(H2PO4)2•H2O]:

• All nitrogen is in the nitrate (NO3-) form.

• Fertiliser grade: 0-46-0. • Soluble, readily available source of phosphorus. • Also called triple or treble superphosphate. Potassium chloride (KCl): • Most abundantly used form of potassium fertiliser. • Contains 60–63% potassium. • Not recommended for alkaline soils due to its chlorine content. • Water soluble source of potassium.

In the case of sulphur, potassium nitrate is sometimes applied when other fertiliser sources are applied. For example, when ammonium sulphate is applied to supply nitrogen, plant-available sulphur is also applied. Sulphur is taken up by plants as the sulphate ion (SO42-), so most fertilisers applied in the sulphate form will be immediately available for root uptake by plants. Gypsum (CaSO4) is less water soluble than the other sulphate fertilisers, but it can be an effective and efficient source of sulphur, as well as calcium (McCauley A, et al, 2009) (see Table 6).

Table 6 Sources of sulphur and magnesium and their composition Element

Name of material

Chemical composition

S

Elemental sulphur

S

% of element

S

Ammonium bisulphate

NH4HSO4

S

Ammonium polysulphide

(NH4)2Sx

40–50

S

Aluminium sulphate

Al2(SO4)3

14.0

S

Ammonium sulphate

(NH4)2SO4

24.2

S

Ammonium thiosulphate

(NH4)2S2O3•5H2O

26.0

100.0 17.0

S

Gypsum

CaSO4

18.6

S

K-Mag

K2SO4•2MgSO4

22.0

S

Potassium sulphate

K2SO4

18.0

S

Magnesium sulphate

MgSO4

13.0

Ca

Calcitic limestone

CaCO3

32.0

Ca

Dolomitic limestone

CaMg(CO3)2

22.0

Ca

Hydrated lime

Ca(OH)2

45.0

Ca

Calcium oxide

CaO

55.0

Ca

Gypsum

CaSO4

22.3

Ca

Calcium nitrate

Ca(NO3)2

19.4

Mg

Dolomitic limestone

CaMg(CO3)2

3–12

Mg

Epsom salts

MgSO4•7H2O

Mg

Kiserite

MgSO4•H2O

18.3

Mg

K-Mag

K2SO4•2MgSO4

11.0

Mg

Magnesium nitrate

Mg(NO3)2

19.0

Mg

Magnesia

MgO

18

9.6

55–60



© Carlos Ramirez

Sulphur applied in a form other than sulphate, such as elemental sulphur, must be oxidized by sulphur-oxidizing bacteria in the soil before the sulphur can be taken up by plants. The oxidation of elemental sulphur to sulphate creates acidity, so elemental sulphur can be used as an amendment to reduce soil pH. Elemental sulphur is quite insoluble, so it will take several weeks to reduce soil pH. Factors that will influence the rate of oxidation of elemental sulphur include: temperature, moisture, aeration, and fertiliser particle size (McCauley A, et al, 2009). In terms of microelements many different fertilisers are marketed as micronutrients. Usually, micronutrients are mixed with fertilisers containing nitrogen, phosphorus, and/or potassium. Because there are so many brands of micronutrients, it is important to read the label to determine the source of the micronutrient in the fertiliser. The three primary classes of micronutrient sources are: • Inorganic sources • Synthetic chelates • Natural organic complexes. Because micronutrients are needed in such small amounts, the best method to correct a micronutrient deficiency is usually applying the micronutrient as a foliar fertiliser. It is important to remember there is a strong relationship between micronutrient availability and soil pH; therefore, growers can maximise micronutrient availability by keeping the soil pH in the correct range (see Figure 1, page 2).


Manganese, iron, zinc and molybdenum are important for leaf growth in watermelons and are taken up and used during early stages of crop development. Boron and zinc are needed during flowering and early bud development.

Table 7 Sources of boron, copper, iron, manganese, zinc and their composition Element

Trace element

% element

B

Borax

11.3

B

Borate 46

14

B

Borate 65

20

B

Boric acid

17

B

Solubor

20

Cu

Copper sulphate

22.5

Cu

Copper chelates

Variable

Fe

Iron sulphate

19–23

Fe

Iron oxides

69–73

Fe

Iron ammonium sulphate

14

Mn

Manganese sulphates

26–28

Mn

Manganese oxides

41–68

Mn

Manganese chelates

12

Zn

Zinc sulphates

23–35

Zn

Zinc carbonate

52

Zn

Zinc phosphates

51

Zn

Zinc chelates

9–14

19

Developing a fertiliser budget The last part of a well-planned nutrient management program is to calculate the amount of fertiliser needed to supply crop needs — develop a fertiliser budget. Often fertilisers list the nutrient they contain on the container (bag) as a percentage universally following a N–P–K–S sequence. Following are some basic calculations required to develop a fertiliser budget: 1. Calculate the amount of a commercial fertiliser required to supply a specific level of nutrient. For example:

Nutrient (kg/ha) ÷ % of nutrient in fertiliser x 100 = amount of fertiliser to apply (kg/ha) Crop requirement

Fertiliser contribution

25 kg/ha of potassium are needed and the plan is to use potassium nitrate that contains 44% K2O.

25 kg/ha ÷ 44% x 100 = 54.5 kg/ha of potassium nitrate is required.

2. In a different way, the same formula can be used to identify how much of a nutrient is being supplied to the crop using a specific commercial fertiliser.

Amount of fertiliser x % of nutrient in fertiliser ÷ 100 = amount of nutrient applied (kg/ha)

100 kg/ha of potassium nitrate is going to be applied . Composition Potassium nitrate

N

K

13%

44%

100 kg/ha x 13% ÷ 100 = 13 kg/ha of nitrogen will be provided to the crop

100 kg/ha x 44% ÷ 100 = 44 kg/ha of potassium will be provided to the crop


© Shutterstock

20



Organic matter in soils – an accurate indicator of soil health and fertility Maintaining and improving soil organic carbon levels is an increasingly important aspect of modern farming. Compost provides potentially one of the most effective ways to apply organic matter to soils and improve organic carbon levels. Soil organic matter is the third, and arguably the most important, aspect of soil because of its potential to improve the other two (physical and chemical) components and collectively improve soil quality resulting in: • Better crop performance and crop quality. • Improved nutrient and irrigation efficiency. • Increased infiltration and reduced compaction. • Reduced nutrient leaching and increased nutrientholding capacity. • Reduced need for pesticides (Paulin B, et al, 2008). These improvements relate to better soil quality from improved biological activity (soil health), fertility and physical characteristics that include better moisture-holding capacity and drainage, and reduced soil compaction and erosion.

Physical properties

Chemical properties

Organic matter

© Carlos Ramirez

Cover crops can improve soil organic carbon levels.

Improved soil organic carbon is directly related to soil quality and performance. Increased quality reflects improved biological function (soil health), fertility and physical attributes that include better drainage, reduced compaction and erosion, and improved moisture-holding capability, at least for lighter soils (Paulin B, et al, 2008). Compost is not the only option available to increase soil organic carbon. Others include the use of cover or break crops, reducing the use of cultivations, selecting safe pesticides that have little or no impact on beneficial soil biology and adopting practices such as permanent bed systems. Using compost, particularly in intensive industries such as vegetable production, has demonstrated the potential to reduce the need for fertiliser, irrigation and pesticides, and improve marketable yields. It is also likely to improve product quality and extend shelf life. For areas like Carnarvon the most recommended strategy to increase the carbon content in the soil is the use of cover crops. Some species have demonstrated the ability to produce high amounts of dry matter with minimum use of inputs. See Chapter 3: Soil Management.

© Carlos Ramirez

Turf grass under Carnarvon conditions produced 3734 kg of dry matter per hectare— 37% of its biomass.


21

Organic fertilisers A list of some reported advantages and disadvantages related to the use of organic fertilisers: Advantages of organic fertilisers: • Improve soil structure, texture and tilth. • Improve moisture retention. • Can control soil erosion. • Can control weeds. • Can have an effect similar to lime amendment. • Increase nutrient availability. • Can be an effective single source of nutrients. • Provide nutrients for several years after application. • May lock-up off-target pesticide sprays. • Increase populations of soil organisms. • Increase nitrogen fixation. Disadvantages of organic fertilisers: • Slow release of nutrients can cause problems with nutrient leaching. • Phosphorus can be supplied in a form that is more prone to leaching than other forms. • Difficult to transport. • Composition can be highly variable and unpredictable. • Increased likelihood of greenhouse gas emissions. • May contain toxic metals (animal manures). • May be a source of pathogens (animal manures).

© Shutterstock

Organic fertilisers can improve soil structure, texture and moisture retention.

© Carlos Ramirez

Field pea cover crop, left: disc incorporation of biomass, right: biomass rolled down on soil surface.

22



© Josephine Eynaud, Redtail Graphic Design

Maintaining and Calibrating spray equipment All agricultural equipment, including boomsprays, fertigation equipment, spreaders and broadcast machinery, requires careful maintenance and must be recalibrated every season. Machinery wear and tear affects application rates from season to season, even if the same product is put through the machine. Applying the right amount of chemical at the right time is a major factor in ensuring successful pest and disease control. Too many chemicals, particularly herbicides, may damage the crop and harm the environment; it will certainly waste money. Too little will also waste money because it will fail to give proper control (DPI, 2010). The main steps required to control pests include: • Selecting the right chemical and rate for the job. • Spraying at the right time under the right conditions. • Spraying with a well-prepared and accurately calibrated boomspray. • Measuring and mixing chemicals accurately. • Operating the sprayer accurately in the field.

Boomspray maintenance Systematically inspect the boomspray. Inspect all components of the sprayer for wear or deterioration and replace if defective. This includes not only components of the spray equipment, pump, hoses, nozzles, etc, but also the structural elements of the boom, axles, bearings, etc. When using the sprayer, carry out regular maintenance as detailed in the following pages (DPI, 2010).


Applying the right amount of chemical at the right time is a major factor in ensuring successful pest and disease control.

Pump • Fill oil reservoirs or grease caps and use a grease gun on nipples (where fitted) before use. • Re-grease every four hours, or as indicated in the service manual. If the pump has an oil sight tube, check the oil for chemical contamination. Any visible contamination indicates pump seals need replacing as soon as possible. • After spraying, drain the tank and pump using at least 20 litres of clean water to flush out any chemical. • Follow label instructions to dispose of the container and any unwanted contents. Tank and hoses • Check all hose connections for tightness. • Inspect hoses for leaks, wear or deterioration. • Fill only through the strainer to ensure no solids enter to block either the pump or nozzles. • Remove and clean the main filter assembly after each spraying period. Be careful not to damage or deform the mesh while cleaning. Nozzles • It is important to check nozzles regularly and replace nozzles when the variation in flow rate varies greater than 10% from the specified flow rate.

23

• Where a spray unit is in regular, frequent use it may be necessary to change all the nozzles at least once or twice a year.

Figure 5 Typical arrangement for performing a boomspray calibration

• Nozzles of different materials wear at different rates. Brass nozzle tips wear quickly, especially with wettable powders. Stainless steel, ceramic and nylon nozzle tips wear more slowly. • Set the boom height to the nozzle manufacturer’s specification so they overlap appropriately. (For example, 110° flat fans with a nozzle spacing of 500 mm will have a double overlap at 500 mm high or a single overlap at 350 mm high). • Nozzles should all be the same type, material and stage of wear. • Check nozzles for blockages and clear by reversing them and use compressed air or a small brush. Never use metal probes and never blow through nozzles with your mouth. Clean all nozzle filters. • Fit anti-drip valves to nozzle bodies. Check they are working correctly (DPI, 2010). Agitation • Good tank agitation is essential when mixing chemicals and for continued suspension with wettable powders or water dispersible granules. • Provide an adequate agitation system and ensure it is working properly. Usually a by-pass return from the pump is used.

Source: All rights reserved to the Virginia Cooperative Extension from Virginia State University. pubs.ext.vt.edu/442/442-453/442-453.html

Check nozzle outputs Checking nozzles individually can be time consuming. A simple and cheap device makes this job much easier by allowing several nozzles to be tested at once (see Figure 5). For best results all the nozzles on the boom should deliver a flow rate that is within ±5% of the manufacturer’s specified flow rate for the chosen operating pressure.

It is important to check nozzles regularly.

© Carlos Ramirez

24



Calibration Chemicals need to be applied evenly and at the prescribed rate. An accurately calibrated boom will ensure this is achieved. Calibration of boomsprays is not just a once-ayear activity; recalibrate regularly to ensure the prescribed rate is maintained (DPI, 2010).

There are many methods of calibrating a boomspray. An accurate and simple method is explained below. Safety Never calibrate the boom with chemical in the tank. Always use clean water and flush out the boom before checking flow rates.

Calibration steps 1. Determine the ‘boom factor’. Measure the distance between nozzles along the boom in millimetres, then divide by 100. For example, for a 500 mm spacing, divide by 100, giving a boom factor of 5. 2. Time tractor. Run the tractor over a distance 100 metres at a speed and engine revolutions per minute (rpm) suitable for spraying. Record the time taken in seconds, the tractor gear and engine revs. 3. Select spraying pressure. Choose a suitable operating pressure between 200–350 kPa for flat fan nozzles or 300 kPa or more for hollow cone nozzles. Note that while hollow cones can be operated up to 1000 kPa there is an increased risk of spray drift. Set the pressure at the engine rpm to be used. 4. Measure nozzle outputs. Park the tractor and operate at the selected pressure and engine rpm. Measure the outputs of the nozzles (in ml) for the number of seconds it took to travel 100 m. Average the outputs.

Example: Where three nozzles have outputs of 250, 270, 245 ml:

Average output (ml): 250 + 270 + 245 = 255ml 3 5. Calculate the water rate.

Water rate (L/ha) = average output (ml) boom factor

Example: If the boom factor is 5 and the average nozzle output is 255 ml in the time it took to travel 100 m. Water rate (L/ha) = 255 ml = 51 L/ha 5 6. Calculate the chemical requirement. When the water rate is known, the tank mix can be calculated and made up. If the tank is not completely filled, only enter the amount of water used in the equation instead of tank capacity Example: If the tank capacity is 2000 L and the chemical rate from the label is 2 L/ha.

Chemical/tank = tank capacity (L) x chemical rate (L/ha) water rate (L/ha)

Chemical/tank (L) = 2000 L x 2 L/ha = 7 8.4 L of chemical per tank 51 L/ha When spraying always use the same gear, rpm and nozzle pressure. Any changes will alter the applied dose of chemical (DPI, 2010).


25

© Carlos Ramirez

Mixing the chemicals • Read the label directions. • Measure out liquid chemical in a graduated measuring cylinder. • Weigh out wettable powders and mix with enough water to form a slurry in a small container. • Weigh out granular materials and dissolve in a small volume of water. • Mixing hoppers or loaders fitted to the tank make the operation easier and safer and should be used where available according to the manufacturer’s specification.

When spraying observe the speed is correct and keep speed constant.

• Use fresh clean water free of suspended organic matter or clay. Some chemicals are deactivated when they contact these materials. Some water may not be suitable. • Wear suitable personal protective equipment and clothing.

When spraying Continually observe that: • The pressure is correct.

• Add the measured chemical to a small volume of water in the tank with the agitator operating.

• Speed is correct and constant.

• Fill the tank to the required volume.

• Boom height is correct.

• Nozzles are operating correctly. • The agitator is functioning. Do not stop the tractor while the spray unit is spraying as this will result in an overdose on that spot.

After spraying • Do not store chemical in the spray unit because some chemicals break down, or clog up the sprayer. Clean the boomspray 1. Follow any decontamination procedures on the label. 2. Where no directions are given on the label at least carry out the following rinsing process: • Flush clean water through equipment, with nozzles removed, so dirt is rinsed out of lines. • Regularly clean exterior of spray equipment. • Remove nozzles and filters, wash and replace. © Carlos Ramirez

26

• Never leave spray material in spray unit.



Fertiliser storage Ensure fertiliser storage areas are: well-ventilated, appropriate for the type of fertiliser, protected from direct sunlight and rain, designed for easy containment and removal of spillage, and located away from watercourses (such as rivers and creeks) (vegetablesWA, 2007). Fertiliser storage requirements may vary depending on the type of fertiliser, how it is packaged (bulk, bagged, liquid, manure, etc.), local conditions and local government legislation. For appropriated information about correct storage of fertilisers and pesticides in general, please visit the following links: • www.fertilizer.org.au/files/pdf/cop/Fertilizer%20 Handling%20Code%20of%20Practice.pdf • www.health.wa.gov.au/publications/ documents/11627_Pesticides.pdf

It is important to record the following information: • Details of fertiliser application (including location of the block/s fertilised, date of application, type and quantity of fertiliser used, the method of application and by whom, etc.). • Information on soil condition and characteristics. • Results of nutritional analyses (such as soil and tissue/sap testing). • Crop type, variety, planting date and harvesting date. • Crop performance and quality measurements. • Crop health and nutritional disorders, if any. Detailed records provide vital information on production and environmental management, which is important for crop performance, market access and sustainability (vegetablesWA, 2007). n

• www.epa.gov/agriculture/ag101/pestfertilizer.html

Record keeping Keep detailed records — they are essential for soil testing and nutrient management. Monitoring nutrient applications, crop performance and other relevant factors (such as weather patterns) facilitates decision making with respect to the efficiency of fertiliser use. It allows nutrition programs to be fine tuned and any environmental impacts associated with fertiliser use to be minimised (vegetablesWA, 2007).

© Carlos Ramirez

Carnarvon growers.

© Carlos Ramirez


27

References 1.

Anderson H and Cummings D (1999) Measuring the salinity of water. Victorian Department of Sustainability and Environment. Landcare Notes LC0064. www.dpi.vic.gov.au/agriculture/farming-management/ soil-water/salinity/measuring-the-salinity-of-water

2.

Anon. (2012) Nutrient Management. The Environmental Protection Agency. USA. www.epa.gov/agriculture/ag101/cropnutrientmgt.html

10. McCauley A, Jones C and Jacobsen J (2009) Nutrient Management Module No 10: Commercial Fertilisers and Soil Amendments. landresources.montana.edu/NM/Modules/NM10layout.pdf

3.

Berry W (2013) Symptoms of Deficiency in Essential Minerals. Plant Physiology Online. First edition, UCLA. 5e.plantphys.net/article.php?ch=t&id=289

11. Morgan D (2013) What is plant nutrition — The Orchid House Web Page, Dyna-Gro Corporation. retirees.uwaterloo.ca/~jerry/orchids/nutri.html

4.

Cimmyt (2013) Nutrient Mobility. International Maize and Wheat Improvement Centre. wheatdoctor.cimmyt.org/index.php/en/nutrientproblems/list/171?task=view

5.

DPI Victoria (2010) Calibration and Preparation of Boom Sprayers. Victorian State Government. www.dpi.vic.gov.au/agriculture/farming-management/ chemical-use/agricultural-chemical-use/spraying-spraydrift-and-off-target-damage/ag1224-calibration-andpreparation-of-boom-sprayers

12. Paulin B and O’Malley P (2008) Compost production and use in horticulture. Bulletin 4746. Department of Agriculture and Food, WA. www.agric.wa.gov.au/objtwr/imported_assets/content/ hort/compost_bulletin08.pdf

6.

DPI Victoria (2011) Soil Fertility Monitoring Tools. Victoria State Government. www.dpi.vic.gov.au/agriculture/farming-management/ business-management/ems-in-victorian-agriculture/ environmental-monitoring-tools/soil-fertility

7.

Home Depot (2013) Lime & Gypsum Fertilisers. www.homedepot.com/webapp/ catalog/servlet/ContentView?pn=Lime_ Gypsum&storeId=10051&langId=-1&catalogId=10053

8.

Lantzke N, Calder T, Burt J and Prince R (2004) Water salinity and plant irrigation. Farmnote No. 34/2004. Department of Agriculture and Food, WA. www.agric.wa.gov.au/objtwr/imported_assets/content/ lwe/land/acid/f07800.pdf

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9.

Lines-Kelly R (2002) Cation Exchange Capacity. Soil, Health and Fertility. NSW Department of Primary industries. www.dpi.nsw.gov.au/agriculture/resources/soils/structure/ cec

13. vegetablesWA (2007) Good Practice Guide. www.vegetableswa.com.au/goodpractice.asp 14. Washington State University (2004) Soil pH. Tree fruit research & extension centre. soils.tfrec.wsu.edu/webnutritiongood/soilprops/soilpH. htm 15. Wikipedia (2013) Cation Exchange Capacity. en.wikipedia.org/wiki/Cation-exchange_capacity


PEST AND DISEASE MANAGEMENT

Pest and disease management


Contents Section 2 Pes t a n d d i s ea s e m a n ag e m e n t

29

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Common Pests in the Carnarvon Horticultural District . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Sucking pests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Caterpillars, moths and butterflies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Beetles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Flies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Beneficial insects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Vegetable Diseases in the Carnarvon Horticultural District . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Virus diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Bacterial diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Fungal diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Nematodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Section 2 Pes t a nd di s ea s e m a nag e me n t

29

Pest and disease management


Promote beneficial insects that eat target pests.

Introduction Integrated pest management (IPM) is a broad-based approach that integrates a range of practices for economic pest control. The United Nations defines IPM as ‘the careful consideration of all available pest control techniques and subsequent integration of appropriate measures that discourage the development of pest populations and keeps pesticides and other interventions to levels that are economically justified and reduce or minimise risks to human health and the environment’.

Integrated

I

P Pest

Management

M

Monitoring

Identify

Sanitation

Any IPM strategy implemented is based on the following principles: I. Acceptable pest levels: The emphasis is on control, not eradication. IPM holds that wiping out an entire pest population is often impossible, and the attempt to do so can be expensive and environmentally unsafe. IPM programs first work to establish acceptable pest levels, called action thresholds, and apply controls if those thresholds are crossed. These thresholds are pest and site specific. II. Preventive cultural practices: Selecting varieties best for local growing conditions and maintaining healthy crops are the first lines of defence, together with plant quarantine and ‘cultural techniques’, such as crop sanitation. III. Monitoring: Regular monitoring is the cornerstone of IPM. Monitoring is broken into two steps, first; inspection and second; identification. Accurate pest identification is critical to a successful IPM program. Record keeping is essential, as is a thorough knowledge of the behaviour and reproductive cycles of target pests. IV. Mechanical controls: Mechanical methods are the first options to consider. They include simple hand picking, erecting insect barriers, using traps, vacuuming, and tillage to disrupt breeding.

30

Exclusion

Treatment Strategy

Evaluation

V. Biological controls: Natural biological processes and materials can provide control, with minimal environmental impact, and often at a low cost. The main focus here is on promoting beneficial insects that eat target pests. VI. Responsible pesticide use: Synthetic pesticides are generally only used as required and often only at specific times in a pest’s life cycle. There are numerous benefits from using IPM. These include: • Early detection of potential problems as a result of regular crop monitoring. • Maintaining effectiveness of chemicals by delaying resistance. • Encouraging natural enemies to help manage pests. • Development of a more robust cropping system since it doesn’t rely on one control method. • Saving money while producing a high-quality product (SARDI, 2011). S e c t io n 2 P e s t a n d d i s e a s e ma n a g e me n t


Common Pests in the Carnarvon Horticultural District Weather conditions in a semiarid zone like Carnarvon, with a mostly dry climate all through the year and precipitation levels of less than 250 mm a year, seem to be perfect for horticultural development free from many pest and diseases due to the ‘apparently’ tough conditions described previously. Normally areas with a higher annual rainfall and elevated percentages of humidity are more susceptible to fungal development and bacterial diseases and the appearance of multiple pest problems. However, some of the most common pests and diseases have adapted their life cycles to Carnarvon weather conditions and for that reason most of the pests and diseases included in this chapter are similar to those in other horticultural areas of Western Australia. Crops from the solanaceae family in Carnarvon need frequent spraying to produce high yields and fruit quality. Regular spraying every 7–14 days may be needed during certain seasons to control major pests, such as aphids on the whole plant, grubs on the fruits and powdery mildew (Leveillula taurica) and bacterial spot (Xanthomonas campestris) on the leaves (Burt J, 2005). Capsicums, chillies, tomatoes and eggplant are also highly susceptible to soil-borne diseases such as fusarium rot, sclerotinia rot, rhizoctonia stem canker, and root knot nematode. Crop rotation is recommended, with an interval of three years between capsicum crops. Soil fumigation with metham sodium or methyl bromide may also be necessary before planting to control pests and diseases and nematodes (Burt J, 2005). The management of vegetable pests in Carnarvon generally employs the same principles used in other vegetable growing regions in Australia or even around the world. Following is the most relevant information about the important groups of pests causing damage in Carnarvon crops.

Sucking pests Sucking pests, are a group of insects that insert their mouth parts into plant cells and suck out the sap, generally causing the cells to collapse and die. Those pests that attack the leaves can leave white stippling or fine brown spotting as evidence of their presence. They are generally found on the underside of the leaves. The most important pests classified in this category are thrips, aphids, mites, mealy bugs and scales. Some cause serious economic damage to crops unless appropriate and timely action is implemented.


Chillies are highly susceptible to soil-borne diseases such as fusarium rot, sclerotinia rot, rhizoctonia stem canker and root knot nematode.


31

Thrips

in silvery white streaks on the petals. Fruit damage varies according to the crop. For instance, on cucumbers, feeding results in severe distortion and curling and is evident by white striations on the fruit. Control Insect pests can sometimes be controlled solely by chemical application, but this is not the case with thrips as they rapidly develop resistance to insecticides. There are a number of general strategies growers can follow to control thrips in greenhouse and outdoor crops.

© Pennsylvania Department of Conservation and Natural Resources — Forestry Archive, bugwood.org

Thrips feed on leaves, flowers and fruit and some carry plant viruses. They are slender, tiny (1–2 mm long) and only just visible to the naked eye. Growers may be able to see thrips if they shake flowers or leaves onto white paper, or if thrips are caught on sticky traps (DAFWA, 2004). Thrips pierce plant cells with their mouthparts and feed on plant juices. The collapse of plant cells can result in the formation of deformed flowers, leaves, fruit, stems and shoots. Thrips can attack ornamentals, vegetables, strawberries and fruit tree crops and some species are also vectors for plant viruses such as tomato spotted wilt virus (TSWV) (vegetablesWA, 2007). Thrips that affect vegetable production in Australia include: • Western flower thrips (WFT, Frankliniella occidentalis) cause feeding damage and are a vector for TSWV.

There are currently few biological control options for thrips in Australia. For greenhouse growers, predatory mites such as Neoseiulus cucumeris or Typhlodromips montdorensis that feed on thrip larvae and Hypoaspis mites that feed on the pupae, are commercially available (see www.beneficialbugs.com.au or www.biologicalservices.com.au). Adopt the recommended chemical spray program Spray applications are only effective when the thrips are actively feeding (larvae or adults). It is necessary to apply a series of the same spray at regular intervals depending on temperature. It is then advisable to change chemical groups for the next series of sprays to reduce the chances of the thrips developing resistance to pesticides. Always use a recommended spray program and only when thrips have been accurately identified (HAL, 2002).

• Tomato thrips (Frankliniella schultzei); a vector for TSWV. • Onion thrips (Thrips tabaci); a vector for TSWV. • Plague thrips (Thrips imaginis); a native species that is not a vector for TSWV. The WFT is the most damaging thrip and the most efficient vector of TSWV. TSWV is mainly of concern in tomatoes, capsicum and lettuce where it can cause up to 100% crop loss. (DAFWA, 2004).

© Graeme Murphy, Ontario Ministry of Agriculture and Food, www.omafra.gov.on.ca/english/crops/facts/03-077.htm

Thrip damage in capsicum.

Symptoms The adult and larval thrip stages feed by piercing the plant surface with their mouthparts and sucking the contents of plant cells. This causes white or brown spots on the leaves where the plant cells have been destroyed. These spots are also speckled with dark faecal droppings from the thrips feeding (HAL, 2002). Thrip damage is noticed first on the lower leaves of cucumbers and tomatoes, while in sweet peppers it is evident in the upper, youngest leaves. Heavy infestations reduce the photosynthetic ability of the plants and, as a result, the yield. On vegetable flowers, thrip feeding results

32

© Graeme Murphy, Ontario Ministry of Agriculture and Food, www.omafra.gov.on.ca/english/crops/facts/03-077.htm

Thrip damage in cucumbers.

S e c t io n 2 P e s t a n d d i s e a s e ma n a g e me n t



Thrip damage in Haas avocados.

Monitoring for thrips Use yellow sticky traps (one per 200 m2 or at least one trap per glasshouse) suspended 10 cm above the plant canopy. By monitoring thrip numbers growers can determine if thrip populations are increasing or decreasing and decide whether or not to apply an insecticide. Routine trapping is important as WFT are inconspicuous and the damage they cause may not be immediately visible (HAL, 2002). Weed control It is important to control weeds within the immediate crop and surrounding crops. Weeds can provide an environment for thrips to feed on and reproduce in, especially when no crops are being grown (HAL, 2002). © D. Thomas Lowery, Agriculture and Agri-Food Canada, www.agf.gov.bc.ca/cropprot/grapeipm/thrips.htm

Thrip damage in grapes.

For WFT follow the ‘three-spray’ strategy: three consecutive sprays three to seven days apart with an insecticide from one chemical class, followed by three consecutive sprays with another insecticide from a different chemical class (see www.dpi.nsw.gov.au/ agriculture/horticulture/pests-diseases-hort/multiple/ thrips/wftresistance).


Infested crops Remove infested crop and weed debris from the greenhouse or field between crops as thrips can live and breed on this material until the new crop is planted. This is achieved by removing and burning, or ploughing in a harvested or abandoned crop. If this debris is not destroyed, all the thrips including the eggs and pupae in the plants will survive, and transfer into the next crop (HAL, 2002).

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Aphids

© Joseph Berger, bugwood.org

Adult aphids on tomato leaf.

Aphids are small, pear-shaped soft-bodied insects, usually about 2–4 mm long. Aphids often cluster on young shoots and flower buds or underneath older leaves. There are many different species of aphids, which vary in colour from green to yellow and black. Aphids attack fruit trees, ornamental flowers and a wide range of vegetables. Aphids also transmit virus diseases such as broad bean wilt. Small aphid colonies multiply rapidly during warm weather and large infestations can develop in a number of days. Symptoms Aphid damage isn’t usually noticeable until there is a large population of aphids on the plant, but their numbers can build rapidly. Aphids can reproduce asexually and the time from hatching to adulthood may be as little as 7–10 days under optimum conditions. Aphid feeding will rarely kill a healthy or mature plant. Control is usually initiated due to the visual effects of foliar damage represented by distorted, curled or yellow leaves.

Aphids also release a sugary liquid called honeydew. The honeydew can be seen glistening on the lower foliage of the plant or on anything under the infested plant. Sometimes a black fungus called ‘sooty mould’ will grow on the honeydew. Although sooty mould doesn’t infect plant leaves it can block sunlight from reaching the leaves, inhibiting photosynthesis. Control Insect pests can sometimes be controlled solely by applying chemicals, but this is not the case with aphids as they rapidly develop resistance to insecticides. Apply a strong spray of water and mild soap to remove sooty mould from plants or anything else it is growing on. Some plants may be harmed by soap, so before using any kind of soap on a plant, first test a small area of the plant with the solution. Spray the mixture on a few leaves and wait 5–7 days to see if any adverse reaction occurs (Godfrey LD, 2005).

© Clemson University, bugwood.org

© Jane, kids.nationalgeographic.com/archive-blogs/jane-of-thejungle-gym/2011/09/little-pests.html

Aphid symptoms on a tomato leaf.

Aphid in capsicum plant.

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Mites

© Frank Peairs, CSU, bugwood.org

Spider mite (Tetranychus urticae).

Mites are not insects, but more closely related to spiders and ticks. They are usually found in the growing tips on the underside of newly-formed leaves and under the calyx of flowers and fruit or in protected depressions. The life cycle from egg, through two nymphal stages to adult takes between 4–10 days depending on temperature. Adults are oval, usually transparent to yellowish green or red in colour, stationary when feeding and moving slowly when disturbed (Godfrey LD, 2005). In the case of spider mites, they live in colonies that can contain hundreds of individuals. The names ‘spider mite’ and ‘web spinning mite’ come from the silk webbing most species produce on infested leaves. The presence of webbing is an easy way to distinguish these mites from all other types of mite and small insects, such as aphids and thrips, which can also infest leaf undersides. Symptoms At first, the mite damage shows up as a stippling of light dots on the leaves; sometimes the leaves take on a bronze colour. As feeding continues, the leaves turn yellowish or reddish and drop off. Often, large amounts of webbing cover leaves, twigs, and fruit. Damage is usually worse when compounded by water stress.

Cultural practices can have a significant impact on spider mites. Dusty conditions often lead to mite outbreaks. Water-stressed trees and plants are less tolerant of spider mite damage. Be sure to provide adequate irrigation. Mid-season washing of trees and vines with water to remove dust can help prevent serious late-season mite infestations. Be sure to get effective coverage, especially on the undersides of leaves. If more control is required, use an insecticidal soap or oil in the spray, but test the product on one or two plants to be sure it doesn’t damage them (Godfrey LD, 2005). Spider mites frequently become a problem after applying insecticides. Such outbreaks are commonly a result of the insecticide killing off the mites’ natural enemies, but also occur when certain insecticides stimulate mite reproduction. For example, spider mites exposed to carbaryl (Sevin) in the laboratory have been shown to reproduce faster than untreated populations. Carbaryl, some organophosphates, and some pyrethroids also favour spider mites by increasing the level of nitrogen in leaves. Insecticides applied during hot weather usually appear to have the greatest effect, causing dramatic spider mite outbreaks within a few days of application. (Godfrey LD, 2005). If a treatment for mites is necessary, use selective materials, preferably insecticidal soap or insecticidal oil. Both petroleum-based horticultural oils and plant-based oils such as neem, canola, or cottonseed oils are acceptable. Sulphur sprays can be used on some vegetables, fruit trees, and ornamentals. Use liquid products such as sulphur and potash soap combinations (for example, Safer Brand 3-in-1 Garden Spray) rather than sulphur dusts, which drift easily and can be inhaled. Don’t use sulphur if temperatures exceed 32.2ºC (90°F), and don’t apply sulphur within 30 days of an oil spray. Sulphur is a skin irritant and eye and respiratory hazard, so always wear appropriate protective clothing (Godfrey LD, 2005). Only use insecticides registered for the crop being sprayed and strictly observe the label or permit directions.

Control Spider mites have many natural enemies that can limit populations. A monitoring program for the pest and its predators will help achieve responsible cost-effective control of pest mites. Some mites have developed resistance to many miticides which were previously effective. Use remaining miticides discerningly so as to minimise the build-up of resistance in the mite population. Do not apply sprays at the first sign of mites, but only when numbers reach a critical level, and insufficient numbers of predatory mites exist to bring them under control.

© Lesley Ingram, bugwood.org

Mite damage in grapes.


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Scales and mealy bugs

Honeydew, sooty mould and waxy deposits may cover leaves, reducing photosynthetic efficiency and can lead to leaf drop. Contamination of fruit with honeydew and sooty mould reduces its market value. The honeydew attracts ants, which collect the honey and indirectly protect mealy bugs from natural enemies. Some mealy bugs inject toxic substances while feeding deforming the plant. Some mealy bug species transmit viruses. Severely infested plants may wilt due to sap depletion; leaves turn yellow, gradually dry and ultimately fall off. Feeding on fruit results in discoloured, bumpy, and scarred fruit, with low market value, or unacceptability for the fresh fruit market.

© Teotzlcoatl, www.shaman-australis.com/forum/index. php?showtopic=20367

Mealy bugs.

Mealy bugs attacking roots, as in the case of the citrus mealy bug, cause stunted roots, rotting of roots and subsequent wilting of the plants. Control

Although scales and mealy bugs belong to different insect families, they have a many similarities in their life cycles and feeding behaviours that make them complex to treat, but similar in the strategies for control. In both cases females are wingless and often retain legs providing mobility. In the case of mealy bugs, females do not change completely, they attach themselves to plants and secrete a powdery wax layer used for protection while they suck the plant juices. Scales follow the same strategy to suck plants but instead of a soft powdery wax, scales form a harder waxy cover that protects their soft body. Soft scales do not produce a hard cover, but some become quite tough and leathery when they mature. Males on the other hand, are short-lived as they do not feed at all as adults and only live to fertilise the females. Males transform completely during their lives, changing from wingless, ovoid nymphs to ‘wasp-like’ flying adults.

The control of these pests, especially mealy bugs, often requires the control of caretaking ants. Without specific ants, mealy bug and scale populations are small and slow to invade new areas and the field would be free of a serious infestation. However, not all ants have a positive relationship with mealy bugs and scales. Instead, some ants are important general predators of a wide range of insects and also play a role in soil development through their underground nesting activity (DPI, 2007).

Symptoms Mealy bugs and scales damage plants by sucking sap from roots, tender leaves, petioles and fruits. They excrete honeydew on which sooty mould develops. Badly infested leaves turn yellow and gradually dry. Severe attack can result in shedding of leaves and clusters of flowers, reduced fruit setting and shedding of young fruit. The foliage and fruit may become covered with sticky honeydew, promoting the growth of sooty moulds.

© Shutterstock

Polyrhachis sp. ant forming a herd of mealy bugs.

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© Carlos Ramirez

Scales on mango.

© Don Ferrin, LSUAC, bugwood.org

Sooty mould in citrus.

The best time to monitor most soft scales to determine population levels and timing of reproduction is mid–late spring (mid-October to November) and late spring–early summer (February to March). Inspect leaves, twigs and fruit stalks, depending on the scale species. For hard scales, inspect fruit from fruit set to harvest. The one exception is citrus snow scale, for which the trunk and branches should be inspected during November–December. In grapes, sticky bands like ‘track-trap’ or ‘bird tangle foot’ on arms or on main stem will prevent crawlers of mealy bugs and prevent ants reaching the bunch. Collection and proper destruction of the pruned material from infested grape areas along with the removal and destruction of loose bark after pruning will reduce populations significantly. In general, chemical products provide limited control of these pest because of their habit of hiding in crevices and the presence of a waxy covering over the body. Integrated management includes physical barriers, such as ant sticky bands, timely removal of crop residues from infested fields and an effective control of weed and debris that support mealy bugs between plantings. Weeds also provide an alternative host for ant populations between periods where mealy bug infestations are small. Ploughing the orchards during November exposes the eggs to sun’s heat supporting further out-of-season control (DPI, 2007). Section 2 Pes t a nd di s ea s e m a nag e me n t

© Whitney Cranshaw, CSU, bugwood.org

Beetles such as the Australian ladybird (Cryptolaemus montrouzieri), are important predators of nymphs.

The biological control of these insects is commonly effective. Mealy bugs and scales are attacked by a wide range of parasites and predators including parasitic wasps, and predatory ladybirds, mites, wasps, caterpillars, lacewings and hoverflies. In tree orchards, these natural enemies make a significant contribution to the control; often more than 50% of scale and mealy bugs are parasitised.

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Bugs

Symptoms These pests insert their snouts underneath the fruit skin. An enzyme they leave at the sting point turns that area of under the skin into liquid and then the bug drinks the liquid. Sting points produce dark pinprick marks on the skin and discoloured areas appear where fluid is removed. The nymphs excrete honeydew, a sugary liquid on which sooty mould develops. If this coating becomes dense it decreases photosynthesis, further reducing the plant’s health.

© Ministry of Agriculture Food & Rural Affairs, www.omafra.gov. on.ca/IPM/english/tomatoes/insects/stink-bug.html

Tomato bug damage.

Bugs belongs to the order hemiptera and are characterised by mouthparts that originate from the tips of their heads which suck the sap of their host. Their life cycle stages include the egg, adult-like nymphs, and winged adults.

Control Bug damage is usually not serious enough to implement control measures. A little damaged foliage can be pruned, and minor occurrences do not harm the plant seriously. If bug population and damage is significant consult with an agronomist to develop and implement an appropriate control scheme.

As with mealy bugs and aphids, bug nymphs produce a sugary substance that acts as a growing point for secondary fungal problems, which will reduce plant’s photosynthetic efficiency. Lace bug damage can be distinguished by the presence of cast skins. Both nymphs and adults can cause early feeding damage to flower buds resulting in their abortion. Losses can be up to 100% in severe cases. Symptoms on capsicum and eggplants fruit are less common. Cloud spotting similar to that seen on tomatoes can occur on both capsicum and eggplants. In tomatoes, adults and nymphs feed on the fruit and pierce the skin with their mouth parts. Damage to green fruit causes fruit to be malformed and dimpled. On ripe fruit, the effects of their feeding toxin leads to white, circular spots on the fruit.

© Johnny N. Dell, bugwood.org

Green vegetable bug (Nezara viridula).

Large numbers are normally present during November and December.

© Natasha Wright, Florida Department of Agriculture and Consumer Services, bugwood.org

Rutherglen bug (Nysius vinitor).

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Caterpillars, moths and butterflies Moths and butterflies are grouped together in the order lepidoptera, which means ‘scaly wings’. The main difference between moths and butterflies is that moths do not fly during the day unless disturbed. Butterflies also have clubbed antennae and hold their wings vertically when at rest, whereas moths sit with their wings flat (CSIRO, 2006). Moths and butterflies undergo a complete life cycle that includes four stages: egg, caterpillar (larvae), pupae and adult. It is in the caterpillar stage (larval stage) where damage increases in both the foliage and fruit of a number of vegetables. These insects chew holes in foliage and fruit and leave excrement and silk on plants. The most important moths and butterflies reported in WA also damage crops in Carnarvon and include the following:

© Gerald J. Lenhard, Louisiana State University, bugwood.org

Saddleback caterpillar.

Diamondback moth (Plutella xylostella)

© David Cappaert, Michigan State University, bugwood.org

© Russ Ottens, University of Georgia, bugwood.org

© Whitney Cranshaw, Colorado State University, bugwood.org

© Natasha Wright, Florida Department of Agriculture and Consumer Services

Description Caterpillars are light brown at hatching and bright green when fully grown. Adult moths are 8 to 10 mm long and fold their wings over their body, forming a tent-like shape. Numbers increase steadily from October to December, then diminish in the heat of summer and climb again when the weather cools during autumn (vegetablesWA, 2007). Host vegetable crops Brassica vegetables including broccoli, cauliflower, cabbage, Brussels sprouts, Asian leafy brassicas, for example, bok choy, gai lan. Primary damage Most destructive insect pest of brassica crops worldwide. Eats holes in leaves (making feeding windows by leaving the upper surface of the leaf intact), tunnels into heads and contaminates produce by pupating inside broccoli florets and cauliflower curds.


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Heliothis — corn earworm (Helicoverpa armigera) native budworm (Helicoverpa punctigera)


© W. Billen, Pflanzenbeschaustelle, Weil am Rhein, bugwood.org

© Paolo Mazzei, bugwood.org


Description Older caterpillars vary in colour and can be green, pink, buff, or brown. They have distinct side stripes and visible hairs. Most active from October to April. Host vegetable crops Sweet corn, beans, peas, lettuce, brassica vegetables, greenhouse vegetables and a wide range of other crops. Primary damage In sweet corn, heliothis caterpillars chew leaves and tunnel down the silk channel of the cob to chew the kernels. Feed on leaves, buds, flowers and pods. Older caterpillars burrow into fruit, pods, and heads of crops. Cluster caterpillar (Spodoptera litura)

© Merle Shepard, Gerald R.Carner, and P.A.C Ooi, bugwood.org

© Natasha Wright, Florida Department of Agriculture and Consumer Services, bugwood.org

© University of Georgia Archive, bugwood.org

Description Young caterpillars are smooth-skinned and vary in colour from green to brownish purple, with a row of triangular spots on each side of the body. When disturbed, the caterpillar curls into a tight spiral with the head protected in the centre. Host vegetable crops Brassica vegetables, leafy vegetables, tomatoes, leeks, beans and a wide range of other crops. Primary damage Young larvae feed close together and skeletonise leaves. Older larvae feed separately and chew holes in leaves. Older caterpillars also attack flowers and pods.

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Loopers (Chrysodeixis spp.)




Description Caterpillars are green and move with a distinctive looping action. Host vegetable crops Leafy vegetables, brassica vegetables, greenhouse vegetables, beans, tomatoes. Primary damage Chew large ragged holes in leaves and bore into the heads of crops. May also feed on flowers and pods. Cutworm caterpillars (Agrotis spp. and other species)

© Mark Dreiling, bugwood.org


© W.M. Hantsbarger, bugwood.org

Description Caterpillars are usually dark-grey to brown in colour. When disturbed they curl into a distinct ‘C’ shape. Caterpillar pupates can be found in the soil and emerge as a medium-sized, grey-bodied moth with dark wings. It may be active throughout most of the year but it’s the autumn, and more especially the spring generations, that do the most damage. They have a wide host range and can damage almost all vegetable crops; young seedlings are especially vulnerable. Host vegetable crops Brassica vegetables, tomatoes, leafy vegetables, cucurbit vegetables, beans, parsley. Primary damage Small caterpillars skeletonise leaves or leave small holes. Older caterpillars feed on stems and may cut off seedling stems at ground level.


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Cabbage white butterfly (Pieris rapae) © Russ Ottens, University of Georgia, bugwood.org




© Whitney Cranshaw, Colorado State University, bugwood.org

Description At hatching caterpillars are orange, but become a dark velvety green with a thin yellow stripe on sides and on top. It normally sits on the upper surfaces of leaves in broad daylight. The adult female butterfly is distinctive, with white wings and a black spot on each forewing. Host vegetable crops Brassica vegetables. Primary damage Large irregular areas of the leaf edge are eaten. Dark green caterpillar droppings contaminate leaves.

Control There is a wide range of strategies available to control caterpillars. Compared with other pests, caterpillar life cycles are quite bit longer providing an opportunity to monitor their population and select a strategic control to reduce their impact through their different stages. Adults are usually attracted to sweet baits made of ripped fruits. This characteristic may be used to elaborate poisoned bait traps to track and reduce adult population (see Figure 1). There is also a range of biological control options for caterpillars in Australia. Naturally-occurring beneficials include insect predators, such as assassin bugs, tachinid flies, paper wasps, lacewings and ladybirds. Parasites include Trichogramma wasps which parasitise moth eggs and other wasps such as Apanteles and Cotesia spp. which parasitise the caterpillar. Trichogramma are available commercially for release against heliothis eggs in sweet corn (vegetablesWA, 2007).


Caterpillar predators.

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Figure 1 Number of adult cluster caterpillars captured on traps in the Carnarvon Horticultural District

Cluster caterpillar number

2,500 2,000 1,500 1,000 500

/1 3

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11

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Date

Bacillus thuringiensis (Bt) and nuclear polyhedrosis virus (NPV) are highly effective and selective biological controls. Bt is a bacterial stomach poison for all caterpillars, which is sprayed onto foliage like other insecticides. NPV is a virus registered in Australia for use on heliothis. It attacks the cell structure of the caterpillar, forming ‘crystals’ that kill the caterpillar after a few days. Both Bt and NPV are applied to foliage where they are eaten by actively-feeding caterpillars that die three to five days later. Bt and NPV are safe to use around beneficial insects, bees and mammals (AUSVEG, 2013). Manage all chemical control options carefully to reduce the development of resistance and harm to beneficials. See the Australasian Biological Control website www.goodbugs.org.au/Chemicals.htm for a useful list of pesticides and their effects on common beneficial insects (vegetablesWA, 2007).

© Butterfly Fun Facts, www.butterflyfunfacts.com/nuclearpolyhedrosis-virus.php

Nuclear Polyhedrosis Virus — NPV.

Resistance to synthetic pyrethroid insecticides has been detected in populations of diamondback moth in all Australian states. Helicoverpa armigera has developed resistance to organochlorines, synthetic pyrethroids and carbamates. Only use insecticides registered for the crop in question and strictly observe the label or permit directions. Inspect crops two to four days after spraying to ensure the spray has killed enough caterpillars to prevent economic loss (vegetablesWA, 2007).

© Joseph LaForest, University of Georgia, bugwood.org

Spraying crop.


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Beetles Adult beetles are usually hard-bodied insects with thick forewings. The young are grubs, borers, or wireworms. Often adults feed on different host plants than the larvae, although both stages may be destructive to vegetables. Some beetle larvae live underground (for example, wireworm, African black beetle). Their life cycle includes the egg, larval, pupal and adult stages (vegetablesWA, 2007). Symptoms Beetle damage to vegetable crops is regarded as rare. However, beetles cause the most damage by feeding on foliage, cotyledons, and stems. They create shallow pits and small rounded, irregular, holes (usually less than 3 mm) in the leaves, resulting in a shot hole appearance. The damage is unique and similar for nearly all species. A heavy flea beetle attack can result in wilted or stunted plants. Control According to the vegetablesWA Good Practice Guide, there are no biological control options currently available to control beetles. If chemicals are required, only use insecticides registered for the crop being treated and strictly observe the label or permit recommendations. More than one treatment may be required.

To control beetles, it is important to monitor their populations using yellow sticky traps. Seedlings do not tolerate high population of beetles. After crops reach the four-leaf or five-leaf stage the plants are usually well established and can easily tolerate feeding damage. Also, the number of adult flea beetles often starts to decline throughout the summer. Other additional beetle control measures include: • Effective weed control in and around planting sites to deprive flea beetle larvae of food sources needed for successful development. • Remove old crop debris and other surface trash to deprive overwintering beetles of protective cover. African black beetle (Heteronychus arator), vegetable beetle (Gonocephalum elderi) or false wireworm and vegetable weevil (Listroderes difficilis) are the most important species reported making damages to several crops in WA (see Figure 2). These species concentrate damage at ground level or just beneath the soil surface damaging roots and seedling stem necks.

Figure 2 Reported pest distribution

Vegetable beetle (Gonocephalum elderi).

Carnarvon

Vegetable weevil (Listroderes difficilis).

African black beetle (Heteronychus arator) © Pest and Diseases Image Library, bugwood.org

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© Atlas of Living Australia, bie.ala.org.au/species/BRENTIDAE



Flies Flies are an exceptionally diverse group of pests across many regions around the world and for agricultural activities they represent one of the most significant phytosanitary threats. Flies can significantly reduce the capacity of an agricultural region to trade competitively in local or international markets. Effectively managing flies requires everyone to be involved in controlling the insect and restricting its spread (NSW DPI, 2007).

© M. K. Billah. icipe, www.infonet-biovision.org/default/ images/93/pests

Mango fruit affected by fruit fly.

© Florida Division of Plant Industry Archive, bugwood.org

Fruit fly in orange.



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Fruit fly The Tephritid fruit flies are pests of fresh fruits and vegetables, laying eggs in the growing tissues of fruit. The eggs normally hatch in a few days and the young larvae burrow into the fresh tissues and inoculate the fruit with bacteria causing secondary fruit rot. The mature larvae leave the fruit and pupate in the soil where they emerge two weeks later as young adults. Sexually mature males and females mate and the cycle is then repeated. The Mediterranean fruit fly (Medfly) is a pest in many areas of WA. It was first detected at Claremont in 1895 and is now found as far south as Esperance and as far north as Derby. The main area of infestation extends from Carnarvon to Bunbury (Broughton S, et al, 2001).

Medfly is known to infest more than 200 fruit and vegetable species. In WA, stone fruit, pome fruit, citrus, loquats and guavas are particularly susceptible (Broughton S, et al, 2001). The onset of Medfly activity is temperature dependent. In the south-west of the State Medfly is active in late spring, summer and autumn. Medfly can overwinter as adults, as eggs and larvae (in fruit), or as pupae in the ground. Adult Medfly are active in winter when temperatures exceed 12ºC. As temperatures increase in spring, adults start to emerge from the ground and overwintering flies become active. If control is not started at this time, Medfly populations will increase to cause problems later in the season.

Figure 3 Mediterranean fruit fly a

(a) Adult The adult fly is 3-5 mm long, with a light brown body. The wings are mottled with distinct brown bands. The abdomen is brown, encircled by two light-coloured rings. The female has an ovipositor; the male does not. Adult Medfly may live for 2–3 months and are often found in foliage of fruit trees. (b) Eggs After mating, females search for a suitable host. Fruit such as apricots are preferred hosts. However, when Medfly populations are high, females become less choosy and will infest less preferred hosts. The eggs hatch within 2-4 days.


b

(c) Larvae The larvae are white with a flat, pointed head. It is this stage of the life cycle that is most often seen. They are about l mm long, but quickly grow to 8 mm. The larvae feed on the flesh of the fruit, causing it to decompose. When fully grown, larvae stop feeding and leave the fruit, burrowing into the soil to pupate. (d) Pupae Pupae resemble a small brown capsule or barrel about 4 mm long. The adult fly cuts through the pupal case and burrows up through the soil. Source: Broughton S, et al, 2001.


c

d



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Control It has been estimated that if uncontrolled, Medfly would infest 100% of susceptible fruit such as apricots, nectarines, peaches and mandarins and to a lesser extent, fruits such as apples and pears. All citrus is susceptible during warm winters. Only early-maturing varieties of stone fruit or fruit-fly-tolerant varieties of fruit such as some lemon cultivars and avocados can be grown without insecticide applications (Broughton S, et al, 2001). Control strategies are under pressure due to the restricted use of some of the chemicals that have been effective in reducing the population of fruit flies, due to the potential health risks of consumers worldwide. However, as with other cases, a program following IPM strategies is the only way to effectively reduce the negative economic impact of this threat (Broughton S, et al, 2001). The integrated control strategy for this pest is based on the following principles: • Hygiene: It is essential to properly dispose of all unwanted fruit in both commercial and home gardens. For control to be effective, fly-infested or unwanted fruit, including fruit left on the tree, must be disposed of (see Figure 4). Acceptable disposal methods include: ——Boiling and then feeding cooked fruit to poultry or pigs. ——Solarising by placing fruit in plastic bags. Seal bags and leave them in the sun for a few days. ——Freezing affected or unwanted fruit for at least one day. ——Burying is not ideal as larvae can survive. If no other option is available for large amounts of fruit, bury it at least one metre deep. • Chemical control: This includes two main techniques — baiting, and lure and kill. Baiting consists of applying coarse droplets of protein laced with insecticide to leaves. Male and female Medfly are attracted to the protein as they forage for food, feed on it and acquire a lethal dose of insecticide. Start baiting during the early stages of fruit development and continue until all fruit has been harvested. Baiting may not control Medfly on crops that are highly susceptible or in high-pressure areas. Apply the bait to the foliage as a coarse spot spray of 60–100 ml for each tree depending on size. Droplet size needs to be at least 2 mm across to ensure efficacy. As the insecticide used in baits has a short residual life, baits need to be re-applied at weekly intervals. They also need to be re-applied if there is more than 5 mm of rain.



Medfly trap.

Lure-and-kill devices work in a similar way to baits, exploiting the need of female Medfly to obtain dietary protein for egg production. Traps are hung on trees and the protein in the device attracts both male and female flies. Depending on the trap, the flies drown or obtain a lethal dose of insecticide (Broughton S, et al, 2001). • Trapping: Even though is not recommended as a control method because it does not control the adult population, trapping is a useful tool for detecting Medfly populations and will help reduce the number of Medfly in backyards. Traps provide information about what flies are present in the immediate areas and do not attract flies into your orchard. • Physical exclusion: A baseline option is the use of physical barriers such nets, bags, or nylon flyscreen to keep the adults out of contact with fruits (Broughton S, et al, 2001). For detailed information about Medfly control strategies and technical information visit the DAFWA website and/or visit the following links: • www.agric.wa.gov.au/action/ Search?s=2099799233,SearchMode=SRCH,sv_ DoWordSearch=Y • agspsrv34.agric.wa.gov.au/ento/medfly.htm • www.dpi.nsw.gov.au/agriculture/pests-weeds/ insects/qff • www.fruitfly.hawaii.edu/

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Figure 4 Medfly IPM Scheme

POPULATION MONITORING

Baseline trapping: Male lures and food-based attractants are used to monitor fluctuations in populations of the four species of economic importance Grid trapping: Grid trapping consists of the target agricultural and surrounding areas. Male lure traps are placed in every square kilometre to identify the fluctuation in populations within the 40–50 square kilometre grid. Flies are collected and identified to species and recorded in a database.

SUPPRESSION TECHNIQUES

Field sanitation: Sanitation is the process of disposing of infested fruit so the fruit fly larvae will not survive. Male annihilation: The annihilation process consists of putting out a sufficient number of male lure traps per a given area to catch most males in the population. Lowering the number of males in a population will minimise the chances of successful reproduction and regeneration. Protein bait applications: Attractant-based protein bait sprays using environmentally safer toxicants are used at low volumes in growing areas and border crops to further ‘protect’ economically important crops from fruit fly damage. Biological control: Male-only sterile fly releases and augmentative releases of natural enemies (parasitoids) provide another method for maintaining fruit fly populations at economically acceptable threshold levels.


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Whitefly Whitefly are small hemipterans that belongs to the Aleyrodidae family. More than 1550 species have been described feeding mainly on the underside of plant leaves. They derive their name from the mealy white wax covering the adult’s wings and body. Adults are tiny insects with yellowish bodies and whitish wings. Although adults of some species have distinctive wing markings, many species are most readily distinguished in the last nymphal (immature) stage, which is wingless. While several species of whitefly cause crop losses through direct feeding, a species complex, or group of whiteflies in the genus Bemisia are important in the transmission of plant diseases. A major problem is that whiteflies, and the viruses they carry, can infect many different host plants, including agricultural crops, palms and weeds. Whiteflies develop rapidly during warm weather, and populations can build up quickly in situations where natural enemies are destroyed and weather is favourable. Whiteflies normally lay their tiny, oblong eggs on the undersides of leaves. The eggs hatch and the young whiteflies gradually increase in size through four nymphal stages called instars. The first instar (crawler) is barely visible even with a hand lens. The crawlers move around for several hours, then settle and remain immobile. Later instars are oval and flattened, like small scale insects (Flint ML, 1998). The legs and antennae are greatly reduced, and older nymphs do not move. The winged adult emerges from the last nymphal stage. All stages feed by sucking plant juices from leaves and excreting excess liquid as drops of honeydew as they feed (Flint ML, 1998). Whiteflies suck phloem sap causing leaves to turn yellow, appear dry, or fall off plants. As a consequence of excreted honeydew, leaves may be sticky or covered with black sooty mould losing its photosynthetic activity. The honeydew attracts ants, which interfere with the activities of natural enemies that may control whiteflies and other pests (Jelinek S, 2007).

© Scott Bauer, USDA Agricultural Research Service, bugwood.org

Whitefly adults.

Control The control of whiteflies is a process where natural enemies play a significant role given their large availability. There are many chemicals registered for whitefly, but as a general rule pesticides rarely provide more than moderate reductions in population size. It is important to get thorough spray coverage including the undersides of leaves. Follow chemical pesticide treatment with a thorough visual inspection a few days after treatment (Flint ML, 1998). Some of the active constituents registered for whitefly control include acephate, bifenthrin, carbaryl, chilli spray, chlorpyrifos, cyfluthrin, dimethoate, endosulfan, fenitrothion, garlic spray, maldison, omethoate, permethrin, pyrethrins and soap sprays. It is important to observe label directions and seek advice from experienced advisers if unsure of the best choice(s) (Flint ML, 1998).

Even though, whiteflies are not reported as a serious pest in Carnarvon Horticultural districts, it is important for growers to monitor them in order to act efficiently against a progressive increase in population. Whiteflies have a wide host range, including: avocado, banana, cabbage, capsicum, cassava, cauliflower, citrus, coconut, cotton, eggplant, garlic, guava, legumes, mango, mustard, onion, peaches, pepper, radish, squash, soybean, tomato, and tobacco. © Susan Salisbury, www.palmbeachpost.com/news/news/ whiteflies-hit-palm-beach-county-homeowners-trees-/nRChk/

Whitefly in banana leaves.


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Trapping whiteflies using yellow sticky cards is another practice used to monitor populations as well as to control adults. Some of the naturally-occurring enemies of whiteflies include parasitoid wasps and pathogenic fungi. These are probably more accessible for a field crop than a greenhouse situation. There is a commercially available parasitoid wasp called Encarsia formosa (supplied by Biological Services) as well as a predatory mite Typhlodromips montdorensis Monty (supplied by Beneficial Bug Company) and Mallada signata Green lacewing (supplied by Bugs for Bugs) (Jelinek S, 2007). For further information visit: • www.dpi.nsw.gov.au/__data/assets/pdf_ file/0009/339588/Whitefly-management-ingreenhouse-vegetable-crops.pdf

© Frank Peairs, Colorado State University, bugwood.org

Lacewing larvae.

• www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7401. html


Lacewing adult.

Beneficial insects In the following link you will find information relating to the most effective beneficial insects commercially available in Australia and a list of commercial suppliers of bio-control agents and the products they sell with all the technical information for the proper use in your crop. ABC — Australasian Biological Control website www.goodbugs.org.au © M.A. van den Berg, Institute for Tropical and Subtropical Crops, bugwood.org

Sooty mould damage in citrus caused by whiteflies.

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Vegetable Diseases in the Carnarvon Horticultural District Successful control of vegetable diseases requires an integrated program that includes the use of resistant varieties, crop rotation, balanced soil fertility, weed and insect control, and proper cultural strategies, as well as the proper selection, timing, and method of applying fungicides, bactericides, or nematicides. Economic control depends on establishing an overall disease management system for the entire supply chain. The first step in an effective disease-management program is proper identification of the problem. This is often the most difficult, but most important step. Make every possible effort to ensure the disease is accurately diagnosed. Failure to accurately identify the problem can lead to severe consequences. Keeping accurate records of the crops planted, the problems encountered and the pesticides used forms a key baseline tool in the implementation of any IPM program.

Virus diseases There are many viruses that affect vegetable crops in the Carnarvon Horticultural District, with solanaceous crops and cucurbits the most affected. Symptoms vary depending on the plant host, age, variety, weather conditions and nutritional status. Viruses often have a number of alternative hosts including vegetables, ornamentals, weeds and native plants and are usually spread from plant to plant by insects (for example, aphids, thrips) or fungal vectors (vegetablesWA, 2007).

Symptoms Tomato spotted wilt virus symptoms include irregular necrotic (dead) spots on leaves, black or purple stem streaks, chlorosis (yellowing), chlorotic blotching, chlorotic or necrotic ring spots and line patterns on leaves and fruits, leaf distortion and deformation, dropping of leaves or shedding of buds, dieback and leaf collapse, stripes on petals, and plant death caused by wilting. Cucumber mosaic virus in plant tissue makes characteristic hexagonal viral inclusion bodies that can be diagnosed under laboratory conditions. The inclusions can also be rhomboidal and may appear hollow and form larger aggregates (Broughton S, et al, 2004). Control To control viral diseases it is critical to control the vectors and reduce potential sources of infection. This means pest management, on-farm hygiene and biosecurity are critical. • Promptly destroying or removing old crops will help eliminate virus reservoirs. • Avoid sequential plantings side by side of susceptible crops. • Use healthy planting material. • Sow virus-resistant varieties when available. • Plant non-host barriers between plantings to reduce the movement of vectors.

Tomato spotted wilt virus (TSWV) and cucumber mosaic virus (CMV) are the most common viruses affecting crops in Carnarvon. Both viruses are spread by thrips and aphids. © Gerald Holmes, Valent USA Corporation, bugwood.org and Edward Sikora, Auburn University, bugwood.org

© Paul Bachi, University of Kentucky Research and Education Center, bugwood.org

© Gerald Holmes, Valent USA Corporation, bugwood.org and Edward Sikora, Auburn University, bugwood.org

TSWV symptoms in tomato fruit.

TSWV symptoms in tomato leaves.


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© Gerald Holmes, Valent USA Corporation, bugwood.org

TSWV symptoms in capsicum fruit.

Bacterial diseases in plants are difficult to control. The emphasis is on preventing the spread of the bacteria rather than curing the plant. Integrated management measures for bacterial plant pathogens include the use of genetic host resistance cultivars or hybrids as one of the most important control methods. Sanitation and particularly disinfestation of pruning tools is compulsory in areas affected by bacterial diseases as the most effective way to reduce or eliminate bacterial contamination of healthy plants. In terms of chemical products, applications of copper-containing compounds or Bordeaux mixture (copper sulphate and lime) and some antibiotics like streptomycin and/or oxytetracycline may also help kill or suppress plant pathogenic bacteria prior to infection and reduce spread of the disease, but they will not cure plants that are already diseased.



TSWV symptoms in capsicum leaves.

Bacterial canker in tomato fruit.

• Remove and destroy plants with virus symptoms. • Remove all weeds to minimise virus and vector sources. • Rotate different insecticides effective against vectors. • Break the disease cycle by not growing susceptible crops for three months. For detailed information visit: www.agric.wa.gov.au/ objtwr/imported_assets/content/pw/ins/pp/hort/ fn069_2004.pdf

Bacterial diseases Although considered structurally simple, bacteria are extremely diverse and are found almost everywhere on Earth in vast numbers. There are both beneficial and pathogenic bacteria. Beneficial bacteria are involved in such diverse processes as digestion in animals, nitrogen fixation in the roots of certain legumes, the decomposition of animal and plant remains, and sewage disposal systems. Pathogenic bacteria, on the other hand, cause severe and often destructive diseases in plants.

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© Mary Ann Hansen, Virginia Polytechnic Institute and State University, bugwood.org

Marginal browning or necrosis also called ‘firing’.



© Paul Bachi, University of Kentucky Research and Education Center, bugwood.org

The most common bacterial disease in the Carnarvon Horticultural District is bacterial canker (Clavibacter sp), which is a serious disease in tomato production areas worldwide and outbreaks occur annually. It is a particularly difficult disease to manage because not only is there no cure, but the pathogen can be hard to eradicate once it has been introduced into a greenhouse, garden, or field. However, preventive measures can be taken at all stages of production to avoid losses (Ellis SD, et al, 2008). Tomato plants of all ages are susceptible to bacterial canker; all above-ground parts are susceptible. Symptoms on seedlings include small, water-soaked lesions on foliage; stunting; and wilting. Seedlings affected by bacterial canker will die in many cases. Wilting is also evident in field plants and is often the first symptom to be observed. Infected stems split, resulting in the open cankers that give this disease its name. When cut lengthwise, diseased stems show a reddish-brown discolouration of the vascular system. The pith may be discoloured and grainy (mealy) or pitted. Wilting and vascular discolouration indicate a systemic infection of the tomato plant (Seebold K, 2008). Control Control of bacterial canker can be difficult once symptoms are observed. A preventive disease management program is the best defence. The most important strategies for integrated control are: • Planting stock: Use certified pathogen-free seed and transplants. Avoid saving seed from previous crops unless necessary. If seed must be saved, avoid collecting seed from obviously diseased plants. • Sanitation: Remove symptomatic seedlings in the greenhouse as quickly as possible and destroy them.


Bacterial canker and wilt of tomato.

Clean and sterilise greenhouses thoroughly. Sterilise containers, benches (and other surfaces), and tools with a solution of 1 part bleach to 9 parts water (10%). In the field, remove symptomatic plants and their immediate neighbours from the production area and bury or incinerate them; however, this may not be practical if more than a few plants are affected (Seebold K, 2008). Stone fruit are important in the Carnarvon Horticultural District and are susceptible to bacterial spot, caused by Xanthomonas campestris pv. Pruni. In this case the main symptoms are greenish-yellow spots in leaves, that can enlarge in wet weather into angular water-soaked areas, often with a yellow halo on plums, sunken twigs, initially dark green, but becoming tan, fruits with many tan spots less than 1 mm diameter, often becoming cracked and pitted, with gum formation Recommendations to control this problem are as follows: • Avoid winter pruning: Pruning during summer or early autumn (before the seasonal break) provides less opportunity for the bacteria to enter wounds. Disinfect secateurs in bleach solution between trees. • Chemical: Copper hydroxide is registered in WA for the control of Pseudomonas only on cherries and apricots. However, the use of copper hydroxide to control bacterial diseases has been obtained on other stone fruit in the eastern states. Bacterial black spot in mango is also an issue that, although it doesn’t cause important fruit losses in Carnarvon,it appears permanently through the harvest season. This bacterial disease is caused by Xanthomonas campestris pv. mangiferaeindicae, and also affects leaves and twigs in the tree.

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Generally, bacterial black spot has a seasonal variation in its severity. This observation is in line with reports from Queensland where the disease is most severe in southern areas but losses occur in the north with unseasonally wet conditions during fruit development. Symptoms are associated with black and raised leaf spots. They tend to be angular in shape because they are confined by the larger veins. Twig and stem lesions are black and cracked and can be an important means of survival for the black spot bacterium. © Clemson University — USDA Cooperative Extension Slide Series, bugwood.org

Several copper spray formulations may be used if they are registered. In the Northern Territory, a treatment with 500 g/kg of copper oxychloride is applied at the rate of 250 g/100L (or 4 kg/ha) or a 400 g/L formulation of copper oxide is applied at the rate of 300–400 ml/100L. Either formulation is applied every four weeks from flowering to fruit-set. Both have a withholding period of one day. Always use chemical control in conjunction with the following management practices, which will help keep the pathogen at bay, prevent its dispersal or minimise the initiation of infection: • Prune to remove infected branches (sources of inoculum) and to improve aeration within the tree. • Practise hygiene such as sterilisation of pruning and harvesting implements. • Provide windbreaks to minimise wind damage (creation of infection sites) and the spread of the bacterium by wind (Pitkethley R, 2006).

© U. Mazzucchi, Università di Bologna, bugwood.org

Bacterial spot (Xanthomonas arboricola pv. pruni) of stone fruits. Bacterial black spot in mango.

© Carlos Ramirez

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Fungal diseases Collectively, fungi and fungal-like organisms (FLOs) cause more plant diseases than any other group of pests with more than 8000 species shown to cause disease. The importance of fungi has spurred scientists worldwide to study their biology. The impact fungi have with regards to plant health, food loss, and human nutrition is staggering (Ellis SD, et al, 2008). Damping-off causing sudden death of seedlings as well as downy mildew and powdery mildew are the most common fungal diseases growers have to face in Carnarvon. However, other fungal diseases, such as banana speckle, also affect banana leaves on Carnarvon farms. The impact on yield hasn’t yet been analysed under Carnarvon dry conditions and the permanent fraying effect of wind across banana leaves has lead to this diseases passing unnoticed. Damping-off, usually associated with the fungi pythium, rhizoctonia, phytopthora, fusarium or aphanomyces, generally occurs under cold, wet conditions. High salt

concentrations in the soil also cause damping-off. While a range of fungicides is registered to control dampingoff, an integrated approach is required. The incidence is significantly reduced by careful irrigation management, avoiding over wetting areas during the seedling establishment, and the use of appropriate fungicides when required. Downy mildew is a collective term for diseases that affect a wide variety of plants, with different species infecting different plant groups. For example, downy mildew is caused by Bremia lactucae in lettuce, Peronospora destructor in spring onions and Peronospora parasitica in brassicas. In some instances, control can include using resistant varieties. Always ensure the right control measures are implemented for the right crop and conditions. In table grapes, the disease first appears on the upper surface of leaves as small yellow oil spots. The spots may enlarge or merge to cover most of the leaf. After warm humid nights, the downy growth appears on the undersides of the oil spots.


© Yuan-Min Shen, Taichung District Agricultural Research and Extension Station, bugwood.org

© Julie Beale, University of Kentucky, bugwood.org

© Yuan-Min Shen, Taichung District Agricultural Research and Extension Station, bugwood.org

Downy mildew symptoms in table grapes.

Powdery mildew symptoms in table grapes.


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An integrated management program for this disease in table grapes must start with a series of actions that stop the pathogen spreading around the farm. These actions include avoiding distribution of infected soil and plant matter by equipment and machinery (for example, mechanical harvesters, leaf pluckers, trimmers and utilities), by soil still adhered to rootlings, or by potted vines from nurseries (Nicholas P, et al, 2005). Canopy management practices that encourage air movement will help dry out leaves and improve sunlight and spray penetration. Such practices include: lower planting density, trellising and pruning to open the canopy, shoot training to open the canopy, vine trimming and hedging, lateral shoot thinning and leaf plucking. In terms of chemical control alternatives, pre-infection (protectant) fungicides help prevent downy mildew zoospores from entering the green vine tissue. Spray coverage needs to be good enough to protect all of this green tissue. A pre-infection spray program often requires application on a 7 to 14 day schedule. This may be expanded to a 21 day program later in the season as shoot growth slows and possible infection events lessen (Nicholas P, et al, 2005). © Carlos Ramirez

As flowering is the critical period to prevent crop loss, the spray program may need to be tightened to every 5–7 days to coincide with possible infection events (DAFWA, 2007). Post-infection (eradicant) fungicides are systemic and penetrate the vine tissue killing the downy mildew fungus from within the tissue. Post-infection fungicides work best when applied as soon as possible after an infection event — within five days of infection and before oil spots appear. No additional spraying should be required until weather conditions favour another possible infection event. In this situation, pre-infection fungicides may be used again. When the fungus is visible it is difficult to kill. A single post-infection spray is usually not effective, although it may reduce the number of spores and limit spread of the disease (DAFWA, 2007).

© Shutterstock

Carnarvon table grapes.

As soon as the disease progresses, infected parts of flower clusters, bunches and young berries may be covered with white downy growth. As the spot grows, the halo fades (Nicholas P, et al, 2005). The earliest sign is a single leaf spot every 50 m of vine row after primary infection. Later, diseased bunches blacken and fall. Berries infected after flowering develop a purple hue, shrivel and fall.

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The key factor when dealing with pathogenic issues, is accurate identification of the causal agent. This provides the basis of the most appropriated management tools for a given crop.

DAFWA provides a commercial horticultural disease diagnostic service through the AGWEST Plant Laboratories in South Perth. More information about taking and delivering samples for further pathogen or nematode identification is available at: www.agric.wa.gov.au/PC_90014.html



Nematodes Nematodes, also known as ‘eel worms’, are colourless and microscopic worm-like animals. Scientists have described about 20,000 species of nematodes and some specialists estimate there could be more than a million species. Most nematodes are harmless to plants, and some are even beneficial (Coleby J, 2009). Nematodes have a resistant cuticle (skin) and an ability to adapt well to environmental change, which has enabled them to become the most abundant multicellular animals on Earth. Nematodes are classified in three functional groups: 1. Saprophytic nematodes break down organic matter in the soil, release nutrients for plant use and can improve soil structure, water-holding capacity and drainage. They are important in mineralising, or releasing, nutrients in plant-available forms.

Figure 5 Root knot nematodes a

When nematodes eat bacteria or fungi, ammonium (NH4+) is released because bacteria and fungi contain much more nitrogen than the nematodes require. 2. Predaceous nematodes feed on soil microbes including other nematodes. 3. Parasitic nematodes are the most important due to their negative impact in crop yield. Within the last group of parasitic nematodes, Meloidogyne spp. are one of the three most economically damaging genera of plant-parasitic nematodes to horticultural and field crops, They are reported to cause problems in about 2000 plants responsible for about 5% of global crop losses, mainly in agricultural areas with hot climates or short winters. Root knot nematodes enter the roots as larvae (see Figure 5a), causing the plant roots to form galls or knots (see Figure 5b). These galls or knots block the transport of water and nutrients through the plant. Nematode larvae mature in the roots where they mate. Female adults remain in the roots and lay eggs into an egg sac that exudes into the soil. The eggs hatch and the young larvae go on to infect more roots (vegetablesWA, 2007). Symptoms are mainly related, with yellowing plants and mid-day wilting, similar to symptoms of water and nutrient stress; sometimes death, especially if interacting with other organisms; gall formation and root branching as the most representative symptoms.

© Bruce Watt, University of Maine, bugwood.org

b

Radopholus similis, or burrowing nematode, is one of the most damaging and widespread nematodes attacking bananas, causing toppling or blackhead disease. It is considered to be the main nematode problem of intensive commercial bananas, especially Cavendish types. Radopholus is a migratory endoparasite nematode, spending its adult life in the root and corm tissues where it completes its life cycle in 20–25 days. Males have an atrophied stylet and are considered to be non parasitic but juveniles and adult females are active and have mobile forms that cause the damage and easily invade new roots (see Figure 6a). After entering the roots, the nematodes occupy an intercellular position in the roots where they suck the internal celular sap of nearby cells, as such destroying them and causing cavities. These cavities coalesce and are continually enlarged by the nematodes, feeding and tunnelling laterally and towards the root tissues (see Figure 6b).


Nematode infections are difficult to diagnose without looking at underground symptoms, but some aboveground symptoms can give some indication.

(a) Root knot nematode. (b) Nematode damage in tomato roots.


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Figure 6 Burrowing nematode a

c


b © Nemapix Archive, bugwood.org

(a) Burrowing nematode (Radopholus similis). (b) Banana roots affected by R. similis. (c) Banana plant affected by R. similis.

Control © Michael McClure, University of Arizona, bugwood.org

High populations of this nematode, mainly associated with sandy soils, will cause symptoms such as stunted plant growth and lack of vigour; reduction in the number and size of leaves; leaf yellowing; premature defoliation; increased susceptibility to wilt; reduced yield, small bunches; increased harvest-to-harvest time and plant toppling (see Figure 6c). Collecting root samples and looking at the underground symptoms will provide useful information. If a root is cleared of soil and cut in half longitudinally, reddish-brown necrosis can be seen extending from the surface extending towards the centre, but not entering the stele. Other important nematodes that damage vegetables, vines and fruit trees include: • Beet cyst nematode (Heterodera schachtii) : Causes considerable yield loss to cruciferous vegetable crops like cabbage, Chinese cabbage, cauliflower, Brussels sprouts, broccoli, turnip, radish and swede. • Root lesion nematode (Pratylenchus species) • Dagger nematode (Xiphinema species) • Ring nematode (Criconemella xenoplax)

Successful management of parasitic nematodes requires an integrated approach. The use of cover crops like fumigator sorghum and/or forage brassicas is been reported as an effective strategy to improve soil structure by the addition of extra organic matter into the soil while reducing most soil-borne pathogens, such as fungi, and is particularly useful in combating pest nematodes. Recent CSIRO research has shown that forage brassicas can control nematodes in the soil thanks to an aromatic compound of which sulphur is a major part. This compound has been found in higher concentrations in Nemcon fumigation brassica. Glycosinolate breaks down in the wet soil and produces a cyanide-like gas, which pervades soil pores helping to control of parasitic nematodes (Barnett D, 2000). Appropriated use of phosphorus in fertiliser programs promotes root generation and elongation, especially important immediately following planting when seedlings are more susceptible to nematode damage. Crop rotation, improvements in soil organic matter and correct irrigation are all part of an integrated approach to manage nematodes. Nematicides are registered for use in some crops. Always check for registration before use and follow label instructions. n

• Pin nematode (Paratylenchus species) • Stubby root nematode (Paratrichodorus species) • Stunt nematode (Tylenchorynchus species) • Citrus nematode (Tylenchulus semipenetrans)

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References 1. ASTA (2013) Bacterial Canker of Tomato. A Commercial Growers Guide, American Seed Trade Association. www.lincolnu.edu/c/document_library/ get_file?uuid=585aefcc-b271-46d3-878e0ab895232094&groupId=145912 2. AUSVEG (2013) Caterpillars. National Peak Industry Body For Vegetables & Potato Growers. ausveg.com.au/intranet/technical-insights/ cropprotection/caterpillars.htm 3. Barnett D (2000) Nematode Control. Fact Sheet. ABC: Gardening Australia. www.abc.net.au/gardening/stories/s124457.htm 4. Broughton S and De Lima F (2001) Control of Mediterranean Fruit Fly (Medfly) in Backyards. Department of Agriculture and Food, Western Australia. agspsrv34.agric.wa.gov.au/ento/medfly.htm 5. Broughton S, Jones R and Coutts B (2004) Management of thrips and tomato spotted wilt virus. DAFWA Farmnote 69/2004. www.agric.wa.gov.au/objtwr/imported_assets/content/ pw/ins/pp/hort/fn069_2004.pdf 6. Burt J (2005) Growing capsicums and chillies. DAFWA. Farmnote 64/99: www.agric.wa.gov.au/objtwr/imported_assets/content/ hort/veg/cp/capsicums/f06499.pdf 7. Coleby J (2009) Nematodes. Fact Sheet. ABC: Gardening Australia. www.abc.net.au/gardening/stories/s2534493.htm 8. CSIRO (2006) Moth and butterfly (Lepidoptera) research. www.csiro.au/en/Organisation-Structure/Divisions/ Ecosystem-Sciences/Moth-and-butterfly-Lepidopteraresearch-at-CSIRO.aspx 9. DAFWA (2007) Downy Mildew in Vineyards – Bulletin 4708. www.agric.wa.gov.au/objtwr/imported_assets/content/ hort/vit/bulletin4708.pdf 10. NSW DPI (2005) Integrated Pest and Diseases Management for Australia Summerfruits. Summerfruit Australia Inc. www.dpi.nsw.gov.au/__data/assets/pdf_ file/0008/184526/summerfruit-fulla.pdf 11. DPI Victoria (2007) Organic Farming: Managing Scale insects on Citrus. Note Number: AG1302. Department Of Primary Industries, Victoria, Australia. www.dpi.vic.gov.au/agriculture/farming-management/ organic-farming/organic-fruit-and-vegetables/ managing-scale-insects-on-citrus


12. Ellis SD, Boehm MJ and Coplin D (2008) Bacterial Diseases of Plants. Fact Sheet. Ohio State University. Department of Plant Pathology. Agricultural and Natural Resources. ohioline.osu.edu/hyg-fact/3000/pdf/PP401_06.pdf 13. Ellis SD, Boehm MJ and Mitchell TK (2008) Fungal and Fungal-like Diseases of Plants. Fact sheet. Ohio State University. Department of Plant Pathology. Agricultural and Natural Resources. ohioline.osu.edu/hyg-fact/3000/pdf/PP401_07.pdf 14. Flint ML (1998) How to Manage Pests – Pests in Gardens and Landscapes – White flies. UC IPM Online – Statewide Integrated Pest Management Program. University of California Agriculture & Natural Resources. www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7401.html 15. Godfrey LD (2005) How to Manage Pests. Pests in Gardens and Landscapes. UC Statewide Integrated Pest Management Program, University of California, Davis. www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7405.html 16. HAW-FLYPM (2013) Hawaii Areawide Fruit Fly Pest Management Program. Collaborative Project between the UH CES, USDA ARS and HDOA. www.fruitfly.hawaii.edu/ 17. Horticulture Australia (2002) Western Flower Thrips and Tomato Spotted. Wilt Virus National Strategy for the Management Western Flower Thrips and Tomato Spotted. www.vgavic.org.au/pdf/WFT_Introduction.pdf 18. Jelinek S (2007) Whitefly management in greenhouse vegetable crops. Prime Fact 1007. NSW Department of Industry and Investment. www.dpi.nsw.gov.au/__data/assets/pdf_ file/0009/339588/Whitefly-management-in-greenhousevegetable-crops.pdf 19. Murphy G, Ferguson G and Shipp L (2003) Biology of Thrips in Greenhouse Crops. Fact Sheet. Ontario Ministry of Agriculture And Food. www.omafra.gov.on.ca/english/crops/facts/03-077.htm 20. Nicholas P, Magarey P and Wachtel M (2005) Downy mildew in grapes. Information from the Grape Production Series Number 1 Diseases and Pests. Department of Agriculture and Food, Western Australia. www.agric.wa.gov.au/objtwr/imported_assets/content/ hort/vit/pw/downymildew.pdf 21. NSW DPI (2007) Queensland fruit fly. www.dpi.nsw.gov.au/agriculture/pests-weeds/insects/qff

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References continued 22. Pitkethley R (2006) Bacterial Black Spot of Mango. Agnote No I24. North Territory Department of Primary Industry Fisheries and Mining. 23. Plantwise (2013) Burrowing nematode (Radopholus similis). Plantwise Knowledge Bank. www.plantwise.org/KnowledgeBank/Datasheet. aspx?dsID=46685 24. SARDI (2011) Integrated Pest Management. Government of South Australia. www.sardi.sa.gov.au/pestsdiseases/horticulture/ horticultural_pests/diamondback_moth/integrated_ pest_management 25. Seebold K (2008) Bacterial Canker of Tomato. Plant Pathology Fact Sheet. University of Kentucky – College of Agriculture. Cooperative Extension Service. www.ca.uky.edu/agcollege/plantpathology/ext_files/ PPFShtml/PPFS-VG-6.pdf 26. Sorensen KA (1988) Insect Pests of Vegetables. North Carolina Agricultural Extension Service AG-404. Centre for Integrated Pest Management, NCSU. ipm.ncsu.edu/vegetables/pests_vegetables.html 27. vegetablesWA (2007) Good Practice Guide. www.vegetableswa.com.au/goodpractice.asp

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Soil Management

Soil management


Contents Section 3 So i l m a n a g em en t

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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Soil Quality In Carnarvon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Managing Soil Quality in Carnarvon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Organic Matter (OM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Cover Crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 Calcium amendments and soil salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

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Soil management Introduction Appropriate soil management is critically important for the long-term production of high-quality and high-yielding fruit and vegetables around arable areas worldwide. In terms of the local conditions in the Carnarvon Horticultural District, good soil management increases the soil water holding capacity and carbon content, reduces soil salinity and minimises erosion. To determine the most appropriate soil management activities, it is important understand the history of Carnarvon soils, where they come from and what they consist of. This provides the necessary information to allow growers to increase the efficiency of their cropping practices by implementing strategies that boost soil productivity in Carnarvon. Such practices will help reduce yield-limiting factors such as soil salinity, unfavourable soil moisture conditions and extreme soil temperatures among others.

© Karan A. Rawlins, University of Georgia, bugwood.org

Characteristic salty environment with scarce vegetation development, mainly covered by shrubs adapted to this salty condition.

According to Green RSB, et al, 2001, stable soil structure is essential to ensure adequate water infiltration and drainage, aeration, crop root penetration, optimum soil temperature conditions and adequate nutrient supply. For Carnarvon, our focus in soil management strategies will be directed to highlight the most appropriated practices reported to increase carbon content and to force sodium replacement in order to improve the natural nutrient balance.

Soil Quality In Carnarvon The quality of soils dedicated to agricultural activities is closely related to the physical and chemical characteristics of the soil. These characteristics can be summarised as: texture, structure and fertility. In terms of fertility, this concept will be addressed using the content of organic matter in the soil as the main indicator of fertility. Soil texture is qualitative classification, which depends on how much sand, silt and clay is present in a particular soil. The combination of these three aggregates classifies soil into a number of textural classes.

© Phil Crawl, USDA Forest Service, bugwood.org

Analysis of soil profile showing characteristic layers will give us a good understanding of soil genesis and physical and chemical conditions.

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Soil structure, on the other hand, is a concept related to the aggregation of the particles themselves. In the broadest sense, structure includes the size, shape and arrangement of soil particles and aggregates. A wellstructured soil allows free air and water movement and easy penetration of the soil by the crop root system. Soils in the Carnarvon Horticultural District were formed on alluvial flats adjoining the Gascoyne river. The soils closest to the river (known as the Gascoyne Association) are generally brown and have a uniform profile of loamy fine sand to silty loam and silty clay loam texture (Green RSB, et al, 2001). S e c t io n 3 S o i l ma n a g e me n t


Managing Soil Quality in Carnarvon According to Green RSB, et al, 2001, the most important components of soil structure that need to be managed to increase soil quality in Carnarvon are: levels of organic carbon and exchangeable sodium (relative to other exchangeable bases), and salinity. The relationship between these factors in Carnarvon presents a particular imbalance characterised by low levels of organic matter in the profile combined with high levels of exchangeable sodium. Nevertheless, growers can manage this imbalance with a persistent strategy of adding organic matter, calcium amendments and effective irrigation techniques.

© Carlos Ramirez

Gascoyne river.

Soils adjacent to the Gascoyne Association, but further from the river (known as Coburn Association), generally have a gradational or duplex profile. In a gradational soil the clay and silt content gradually increases with increasing depth. On the other hand, a duplex soil has an abrupt change in texture with increasing depth, for example a loam over a light clay. The Gascoyne Association soils are free draining and well structured, while the Coburn Association soils are generally poorly drained and structured (Wells MR, et al, 1990).

© Carlos Ramirez

Typical Carnarvon soil.

Carnarvon Horticultural District.

© Google earth


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Organic Matter (OM) Organic matter is the third and arguably the most important component of soil and provides an indirect measure of the total soil carbon contained within the soil. It has the potential to improve both the physical and chemical soil components. The amount of soil organic matter is primarily determined by the climate of a region. Particularly important is the amount and annual distribution of rainfall in relation to temperature. Native vegetation in Carnarvon is sparse due to low annual rainfall levels and high summer temperatures. As a result soil organic matter levels are inherently low (Green RSB, et al, 2001). Increasing soil organic matter is central to improving soil performance as it will improve soil tilth, structure and water infiltration, which provides a safeguard against the adverse effects of salinity. An adequate level organic matter will also benefit the soil in other ways including: • Improving physical conditions. • Improving crop performance and crop quality. • Increasing water infiltration and water holding capacity. • Improving nutrient holding and reducing nutrient leaching. • Increasing nutrient and irrigation efficiency. • Decreasing erosion losses. • Improving pesticide efficiency. It is also important to recognise that not all forms of soil carbon improve soil performance. Carbon derived from the action of bushfires is often not active, however biochar, produced from pyrolysis (incineration of organic materials in the absence of oxygen), is both stable and active and could prove to be a valuable additive to Carnarvon’s sandy soils (vegetablesWA, 2007).

© Shutterstock

Compost.

Compost is the result of a managed decomposition process involving successions of naturally-occurring microorganisms that break down and transform organic matter into a range of increasingly complex organic substances, many of which are loosely referred to as humus. Humic materials are responsible for many of the important quality characteristics of soils that include increased soil organic carbon, soil fertility and the ability to hold plant-available nutrients and moisture. In this dynamic process, rates of 20 to 30 m3/ha are initially recommended. Long-term rates will be determined by a combination of management practices (vegetablesWA, 2007). With regular application, compost will increase soil nitrogen and carbon levels, increase soil cation exchange capacity, increase water holding capacity, reduce bulk density and stabilise pH. The greatest benefits arise when regular use of compost effectively ‘buffers’ the soil against climatic events, equipment failure or human error that would otherwise result in loss of potential yield. This buffering effect is due to increased soil organic carbon, which increases the soil’s ability to hold crop-available nutrients and water (vegetablesWA, 2007). For detailed information about compost in WA please visit: www.compostforsoils.com.au

Table 1 Changes in soil quality resulting from increasing soil organic carbon levels Soil carbon (%)

Volumetric water (%)

Bulk density (t/m3)

CEC (c mole/kg)

pH (CaCl2)

Total nitrogen (%)

0.54

10.12

1.43

2.71

5.85

0.03

0.79

12.00

1.36

6.17

6.80

0.05

0.95

14.17

1.32

8.53

6.85

0.07

LSD P 6), to be classified as sodic. This situation is probably due to salty water inclusion, weathering of the parent materials plus a salt build-up due to irrigation with water containing sodium. Another source may be sodium chloride (NaCl) particles blown in from the ocean (Green, RSB, et al, 2001).

In summary, sodic soils contain high levels of sodium and prevent plants from absorbing essential nutrients on the soil, while saline soils contain high levels of salt in the soil solution and many plants cannot tolerate these levels of salt. © Carlos Ramirez

Carnarvon soil showing signs of sodium build-up on soil particles.


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© Carlos Ramirez

Gypsum application.

The use of calcium as a soil amendment is a priority to ameliorate sodic soil conditions. Calcium is made up of two positive charges (cations) and attracted to negatively charged particles, such as clay. Luckily, sodium has only one positive charge and is weaker than calcium, allowing calcium to act like a thug and push the sodium off the CEC site (Bolton S, 2009). There are different sources of calcium available for use in agriculture. The three most commonly used sources for growers in Carnarvon are gypsum (CaSO4), lime sand (CaCO3), and crushed lime (Ca (OH)3). One of the most important characteristics to consider when selecting calcium amendments is solubility. The higher the solubility, the faster the calcium is released into the soil to start the exchange with the sodium cations. According to Green RSB, et al, 2001, gypsum is 170 times more soluble than lime and it doesn’t increase the soil pH, which is a consideration in the high pH soils of the district.

Trials carried out at the Gascoyne Research Station in Carnarvon, showed that gypsum initially decreases the soil pH by about 0.5 pH units and also reduces the soil dispersion. The decrease in dispersion improves water infiltration and drainage, promoting better paddock tillage. However, these effects diminished with time due to gypsum’s high solubility and crop irrigation (Green, RSB, et al, 2001). At 2 t/ha of gypsum, the amount of irrigation that dissolved a tonne of gypsum was 120 mm. At a higher dosage of 10 t/ha, due to more contact between the gypsum particles with the water, only 100 mm were required to dissolve a tonne. Therefore, the most economical way to apply gypsum is at low rates (2 t/ha) and relatively frequent for example every one or two crops. (Green, RSB, et al, 2001).

© Carlos Ramirez

© Carlos Ramirez

Crushed lime on soil at a rate of 5 t/ha.

Crushed lime on soil at a rate of 10 t/ha.

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S e c t io n 3 S o i l ma n a g e me n t


For tomato production under Carnarvon conditions, the use of gypsum increased structural stability of the soil and infiltration. With high irrigation rates, gypsum also increased yield and total soluble solids. Deep ripping increased yield only when combined with low irrigation and gypsum, probably because of better water penetration down the soil profile after removal of the hardpan. The data indicate that high irrigation level and reduced dispersion after using gypsum are the most important factors in positive yield responses in tomatoes (Muller AT, 1993). In conclusion, to effectively reduce salinity by leaching sodium out of the root zone, the application of gypsum or a mix of gypsum plus lime should be linked with an adequate irrigation rate. In areas with poor water movement this task can be difficult and that is when the addition of organic matter into the soil comes to play an important role in the improvement of soil structure and salinity reduction. n

© Carlos Ramirez

Trickle irrigation. Solubility of calcium amendments is an important characteristic to keep in mind before use. Increase application rates when using highly soluble amendments to facilitate sodium exchange in a permanent way.

Similar outcomes were found by Ramirez C, 2012, when dosages of 2.5, 5.0 and 10 t/ha of gypsum, lime and mana lime were compared on a seedless watermelon crop. In general, all areas treated with calcium had a decreasing tendency in the yield as the calcium dosage increase, in other words, the highest yields were produced with the lowest dosages of calcium (2.5 t/ha). A chemical comparison between gypsum and limes let us see that the first is basically an hydrated calcium sulphate while limestone is the parent material of all lime products, including agricultural lime, composed of calcium carbonate plus other minerals like magnesium that can occur with limestone. Mixes of 2.5 t/ha of gypsum plus 2.0 to 2.5 t/ha of lime are also commonly used by growers in Carnarvon.


© Carlos Ramirez

An integrated scheme of calcium amendments plus appropriate irrigation and cover crops in summer and winter breaks is the best way to improve soil health in Carnarvon.

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References 1. Bolton S (2009) Addition of Gypsum and other Calcium Products to soil to solve second class water problems. Environmental Imaginers, Melbourne. tgaa.asn.au

7. NSW DPI (2007) Vegetables SOIL pack — Sodic Soil Management. www.dpi.nsw.gov.au/__data/assets/pdf_ file/0009/127278/Sodic-soil-management.pdf

2. Castalanelli C and Nulsen B (2008) Minimising salt damage in home gardens. Gardennote. www.agric.wa.gov.au/objtwr/imported_assets/content/ lwe/salin/sman/minimisesalinity.pdf

8. Ramirez C (2012) The use of Cover Crops in Vegetable Production. WA Grower Magazine Vol 47 No 4. www.vegetableswa.com.au/wagrower_magazine.asp

3. DAFWA (2009) Salinity in Western Australia. www.agric.wa.gov.au/PC_92418.html 4. Glendinning JS (1999) Australian Soil Fertility Manual. Fertiliser Industry Federation of Australia, Inc. 5. Greene RS, Lin AJ and Parr DC (2001) Management of soil organic matter and gypsum for sustainable production in the Carnarvon horticultural district of Western Australia. Miscellaneous Publication No 7. DAFWA.

9. vegetablesWA (2007) Good Practice Guide. www.vegetableswa.com.au/goodpractice.asp 10. Wells MR and Bessell-Browne JA (1990) Horticultural capability of soils adjacent to plantations at Carnarvon, Western Australia. DAFWA — Land Resources Series, Resources Management Division.

6. Muller AT (1993) Effect of gypsum, deep ripping and irrigation on determinate tomatoes. Australian Journal of Experimental Agriculture, 33:803–6. www.publish.csiro.au/?act=view_file&file_ id=EA9930803.pdf

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S e c t io n 3 S o i l ma n a g e me n t

Water Management

Water management


Contents Section 4 WATER MANAGEMENT

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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Irrigation design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 System hydraulics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Calculating Distribution Uniformity (DU) for your irrigation system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Calculating Coefficient of Uniformity (CU) for your irrigation system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Measuring system pressure and pressure variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Measuring the discharge from outlets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Frequency of watering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

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Water management

© Carlos Ramirez

Sprinkler irrigation at the Gascoyne Research Station after cover crop planting.

Introduction Irrigation is a widespread practice required in many areas of Australia, to supplement low rainfall with water from other sources to assist in growing crops and pasture. In general, water for irrigation comes from two main sources, river systems and underground aquifers. Major river systems used for irrigation in Australia include the MurrayDarling system, the Ord River in the Kimberley region of Western Australia and many rivers along the east coast of Australia. A major source of ground water in Australia is the Great Artesian Basin. Given the limited water availability across the Carnarvon Horticultural District, this chapter will focus its attention on all the basic information required to assess and maintain your irrigation system for optimum performance. It’s not necessarily about using less water but, rather, about using it more efficiently to achieve high yields of quality produce. The aim, then, is to encourage positive changes as part of a process of continual improvement. Efficient irrigation minimises water wastage and leaching of nutrients and chemicals. Vital considerations here are the design of the irrigation system itself and the way in which the watering program is scheduled (vegetablesWA, 2007).

Irrigation design Nowadays, all farmers are under pressure to demonstrate they are making effective use of irrigation water, a resource which is becoming increasingly scarce. This doesn’t necessarily mean using less water; it means achieving a reasonable level of production from the water you do use. You need to apply the right amount of water at the right time to plants that are being managed so they can use the water effectively.

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Uneven watering, makes it almost impossible to schedule irrigation to save water or improve yields. It is also difficult to find a site that represents the whole plantation if the system applies water unevenly (Luke G, 1990). Common problems in irrigation systems arise when: • too many sprinklers are placed on one lateral, • sub-mains are too small, • laterals are too long, • ineffective filters are used, • different sprinkler nozzles are used in one irrigation section, or • nozzles are blocked or damaged. In Carnarvon the soils do not readily absorb water. This low infiltration is the reason why large amounts of water can lie around after an irrigation. This can result in either the water running off to wet non-target areas, or excessive evaporation before the water is absorbed into the soil (Luke G, 1990). To prevent this, the designed application rate of the system should be no more than 4 mm per hour. It is important to know what the daily peak water requirements are, so the system can be designed to apply the correct amount of water (Luke G, 1990). In Carnarvon, crops need most water during January, when average daily Class A pan evaporation reaches around 11.5 mm. On hot dry days it can go much higher. Evaporation rates are reasonably predictable, and an analysis of records shows the chances of achieving the daily rates given in Table 1.

S e c t io n 4 WAT E R MA N A G E ME N T


Table 1 Chances of reaching evaporation rates at Carnarvon in January Daily Class A pan evaporation

Frequency of occurrence

11.5 mm

15 days each January

14.1 mm

10 days each January

15.8 mm

3 days each January

16.8 mm

1 day every 3rd January

Source: Luke, G. 1990.

Clearly, to design for 14.1 mm per day will mean the system will not supply enough water on almost 10 days each January. To design for 15.8 mm means the system will not supply sufficient on about three days each January. In deciding what peak evaporation rate you will allow for in the design, it is a matter of choice between having higher costs and taking the risk of greater crop loss (Luke G, 1990). Carnarvon soils hold a considerable amount of water. Therefore to allow the crop to use slightly more than you can apply is satisfactory, providing the deficit does not last too long. Allowing for a peak daily water requirement of 15.8 or 16 mm/day should be satisfactory. It is important to remember that different crops use different amounts of water. Bananas for example, may use 100% of evaporation (that is, up to 16 mm/day), while mangoes use up to 60% (nearly 10 mm/day). Therefore the peak daily requirement to allow for would be 16 mm/day for bananas, and 10 mm/day for mangoes (Luke G, 1990).

System hydraulics There are internationally accepted design standards that will ensure the system operates effectively. Your designer should be able to guarantee the system meets these minimum standards (Campbell-Clause J, 1994). These standards are: 1. Maximum pressure variation in a lateral plus or minus 10%. 2. Maximum variation in output along a lateral plus or minus 5%. 3. Coefficient of uniformity (CU) 84% or higher. 4. Distribution uniformity (DU) 75% or higher. Standards 1 and 2 deal with the hydraulic characteristics of the laterals. They provide a check to ensure the laterals are of the correct size to handle the flow required for the number of outlets. If the pressure loss is less than 10% (that is, if working pressure is 150 kPa, pressure variation should be less than 15 kPa above or below this), the variation in output should then be less than 5% above or below the design output (Luke G, 1990). Standards 3 and 4 refer to the output of the nozzles throughout the field. These figures are available for most sprinklers, given particular spacing, nozzle sizes and operating pressures. Internationally, the design standards for irrigation uniformity are a CU greater than 85% and a DU greater than 75% (1). The system only needs to satisfy either standard 3 or 4. Generally if standard 3 is met, so is standard 4, and vice versa (Luke G, 1990).

© Carlos Ramirez

Pumpkin crop with no plastic mulch and medium flow (3.4 L x m x hr.) drip irrigation.

© Carlos Ramirez

Wetting bulb in dripper irrigation after half and hour of medium flow rate.

© Carlos Ramirez

Wetting bulb after 1 hour irrigation with medium flow (3.4 L x m x hr.) drip irrigation.

Section 4 WATER M ANAGE M E NT

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Calculating Distribution Uniformity (DU) for your irrigation system DU measures how uniformly an irrigation system applies water to the crop. It is calculated as the ratio of the average irrigation volume applied to the driest quarter of the field (or grid) and the average volume applied across the whole field (or grid) (Queensland Government, 2007).

DU tests should be done to ensure your system is applying irrigation water evenly to your crop. Simple catch-can trials can be carried out on any type of irrigation system and the data used to calculate the distribution uniformity for the system.

Example data Assume a catch-can trial, using 25 cans arranged in a grid pattern, was carried out on a sprinkler irrigation system and the following can readings (depths or volumes from same size cans both work) were measured (Queensland Government, 2007). Can readings (mm): 25 15 20 10 15 20 25 28 22 18 17 10 14 7 18 19 14 12 9 18 16 15 23 13 22 Example calculation Step 1. Order these can results from the smallest number to the largest number (mm): 7, 9, 10, 10, 12, 13, 14, 14, 15, 15, 15, 16, 17, 18, 18, 18, 19, 20, 20, 22, 22, 23, 25, 25 and 28. Step 2. Take the lowest quarter (in this case the lowest six can readings) and find their average. Lowest ¼ readings are: 7, 9, 10, 10, 12 and 13. The average of these numbers is: (7+9+10+10+12+13) ÷ by 6 = 10.2 mm Then find the average of all the can readings: 17.0 mm Step 3. Calculate DU using the equation. DU = 10.2 ÷ 17.0 = 0.6 or 60% In this case, the DU is below the minimum target performance standards for horticultural crops. These target levels are 85% for fixed sprinkler and travelling gun systems, 90% for centre pivots, lateral moves and booms, and 95% for micro-sprinkler and drip systems. Low irrigation uniformity often produces large variations in crop yield and quality. It is also a major factor contributing to low water use efficiency and excessive leaching of nutrients and fertiliser out of the root zone. Improving DU to target levels can also lead to better economic returns (Queensland Government, 2007).

© Carlos Ramirez

Distribution of cans in a grid pattern to measure DU. INSET: Beaker.

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Calculating Coefficient of Uniformity (CU) for your irrigation system Step 1. Using a calculator or computer, work out the average deviation of all applied depths (in Microsoft Excel, if all values are put into column A, this might appear as = AVEDEV(A1:A25) Average deviation = 4.32 Step 2. Work out the average of all applied depths (in Excel, this might appear as AVERAGE(A1:A25). Average = 17 Step 3. Divide the results of step 1 by the results of step 2. Average deviation ÷ Average = 4.32 ÷ 17 = 0.2541 Step 4. CU = 1 minus the answer to step 3 x 100. (1 – 0.2541) x 100 = 74.59% CU = 74.59%

A CU of less than 80% will require an adjustment and correction of individual sections of the sprinkler package (water flow pressure, space between sprinklers, overhead high) to ensure sprinklers are working to design specifications. Since the operating pressure of the system was determined at the design stage, increasing or decreasing the pressure to improve uniformity is useful only when the overall design has changed. Changing the nozzle size is useful only when making minor adjustments to the system.


Measuring system pressure and pressure variation The first important task to achieve an accurate pressure adjustment is to ensure pumps and motors are performing according at optimum capacity. A measurement of pump performance is usually a job for qualified, experienced personnel such as local dealers or consultants. This, and corrective action where necessary, are essential parts before you evaluate the rest of your irrigation system (vegetablesWA, 2007). When checking pressures, first adjust any sub-main or internal valves to the pressure shown on the irrigation plan. Do this at the start of each irrigation season by carefully adjusting each valve several times until steady, correct pressure is achieved (Luke G, 1990). If the system is working properly, the valves will be adjusted so the average pressure across the whole unit is as close as possible to the pressure stated on the irrigation plan. None of the emitters should be operating at more than 10% above or 10% below this average pressure (Luke G, 1990). After the internal pressures are properly set, measure the operating system in at least 10 locations spread across each irrigation unit. These must include the points nearest the valve, at the start and ends of laterals, and at points of high and low elevation (Luke G, 1990). In the case of small low-level sprinklers, frequently used on bananas and some tree crops in Carnarvon, pressure reading should be done in at least 10 or more sprinklers. Then calculate the average pressure by adding all the pressures together, and dividing them by the number of Section 4 WATER M ANAGE M E NT

© Carlos Ramirez

Micro sprinkler irrigation in banana crops in Carnarvon.

sprinklers used in the test. The result should be close to the sprinkler pressure stated on the irrigation plan. If the variation is greater than 10% above or below this, try to fix it by adjusting any internal valves installed in the system (Luke G, 1990). In trickle irrigation systems, the pressure at 10 different places in a trickle system should also be taken. These can be at the end of laterals, or at the start, high and low points, as for sprinkler tests. For these mid-lateral readings, cut the fine and insert the threaded take-off. After the reading is complete, repair the lateral with the barbed joiner (Luke G, 1990). Information on irrigation system design in general, and CIDs in particular, is available from irrigation suppliers, as well as the Irrigation Association of Australia’s website at www.irrigation.org.au.

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© Rohan Prince

© Rohan Prince

Measurement of discharge from outlets on a dripper irrigation system.

Styrofoam tray to collect discharge from emitters on a drip irrigation system.

Measuring the discharge from outlets It is essential to periodically measure discharge and compare this with the manufacturer’s performance chart. Collect the discharge from a sprinkler or emitter in a bucket for 30 seconds and measure the water collected in litres, using a measuring jug (Luke G, 1990). In the case of small low-level sprinklers, hold back, the arm or spinner and direct the stream into the bucket for 30 seconds. With large sprinklers, place the end of three to four meters of plastic tubing over the nozzle, and direct the stream into a bucket for 30 seconds. Where the sprinkler has a rear nozzle, repeat the test on the second nozzle to determine the total discharge. Trickle emitters can be held over the collecting container (Luke G, 1990). Discharge, L/h = (Litres collected in 30 seconds) x 120 Repeat the test on at least 10 outlets across the irrigation unit. Compare the discharge measured across your block with the manufacturer’s specifications. If yours are more

than about 15% higher, it is likely that substantial nozzle wear has occurred, and you should consult your supplier about nozzle replacement (Luke G, 1990). On drip irrigation check the system pressure in order to guarantee the system is working accordingly to recommendations. Other important aspects to periodically measure in your irrigation system are the outlet wear, the irrigation distribution and uniformity and removing blockages. For detailed information on these topics visit the following links: • Design guidelines for fixed sprinklers and microirrigation systems. www.agric.wa.gov.au/PC_92490.html • Blockages in irrigation lines. www.agric.wa.gov.au/PC_92488.html • Evaluating sprinkler and trickle irrigation systems. www.agric.wa.gov.au/PC_92491.html

Frequency of watering Having in mind that water is a limiting resource in Carnarvon, then an efficient use of the water allocation for vegetable crops is essential. The answer to how often irrigate a crop is closely related with multiple variables like soil characteristics in texture and structure, rain and evaporation rates, type of crop and growing stage, among others. But one of the most important variables is the tension at which the water is attached to the soil particles. A tensiometer measures how hard the root system of a plant must work to extract water for its needs. All tensiometers read in centibars (cb). One hundred cb equals one bar. The higher the reading on the gauge, for example 40 cb, the harder it is for the plant to extract water from the soil. The lower the reading, for example 10 cb, the easier it is for the plant to extract water from the soil (Luke G. 1990).

© Rohan Prince

Repeat the exercise at least 10 times per hectare to have an accurate measurement of the discharge per emitter.

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Most of the water in the soil available for plant growth occurs as a thin film on the soil particles or as droplets within the soil pores. The amount of water held in pores one to two days after an irrigation is known as field capacity.



A similar study for bananas on a sandy loam soil in Carnarvon, showed that 25 to 30 mm (250 to 300 kL/ha) of water should be applied when the tensiometer at 30 cm depth reads 22 to 25 cb. This reflects the point at which the available soil moisture in the main root zone is depleted by one-third. In this crop, the tensiometer at 60 cm depth should be at field capacity most of the time (15 to 25 cb) (Foord G, 1993). © Carlos Ramirez

A tensiometer is an important tool to ensure adequate irrigation scheduling.

At field capacity, tensiometer readings can range from 6 cb to 10 cb for sandy soils, and 10 cb or more for the heavy-textured soils. Readings less than field capacity indicate the soil is saturated. A tensiometer reading between 25 cb (in light-textured soils) and 60 cb (in heavy-textured soils) tells you it is time to irrigate. High tensiometer readings such as these, show the soil moisture has been depleted to a level where the crop could be stressed and needs water (Luke G, 1990). It is not possible to set out instructions on when to irrigate for all crops, soils, methods of irrigation and climatic conditions. However, by plotting your tensiometer readings and keeping them within the desirable range, you will gain confidence in using these instruments and will be able to decide when to irrigate and how much water to apply (Luke G, 1990). Trials developed for tomatoes on sandy loam soils in Carnarvon, showed that this sort of tomatoes can use 70% of the available soil moisture, without suffering significant yield loss. At this point, the soil moisture tension in Gascoyne fine sandy loam is at 40 cb (Luke G, 1990).

The amount of water a crop requires can be determined with reference to the growth stage of that crop and daily evaporation rates. The latter, can be measured directly or calculated from weather station data on temperature, wind speed, solar radiation and relative humidity. The proportion of daily evaporation that must be replaced by irrigation is referred to as the ‘crop factor’, which will vary according to the type, vigour and growth stage of the crop in question (vegetablesWA, 2007). For capsicums in Carnarvon when using trickle irrigation, water at 25% daily evaporation replacement rate should be irrigated during early growth and at 40–50% daily evaporation replacement rate from flowering onwards. For this crop, tensiometers may be used for irrigation scheduling to apply irrigation at a suggested soil tension of 30–35 cb (Burt J, 2005). In the case of table grapes, research using a system of scheduling based on crop factors and soil moisture monitoring using tensiometers, showed the timing and amount of water applied is important because the shoot and berry development growth stages are affected differently by availability of water. In Carnarvon excessive vigour (which may reduce fruitfulness) is a problem. Water stress will limit growth. Therefore, when shoot growth is active; impose water stress. When berry growth is active; maintain optimum soil moisture (Campbell-Clause J, 2005). Pre-flowering to bunch closure — about 55 days, maintain optimum soil moisture conditions. Yield is being determined during this period, so avoid moisture stress. Maintain tensiometer readings below 30 cb. From bunch closure to veraison (berry colour change) — about 20 days, impose a slight moisture stress by letting tensiometer climb to about 45 cb. This will check vine vegetative growth but have no effect on berry development (Campbell-Clause J, 2005). From veraison to harvest — about 30 days, maintain optimum soil moisture by maintaining tensiometer readings below 30 cb. Under hot Carnarvon conditions this will help improve the quality and storage life of table grapes (Campbell-Clause J, 2005).

© Carlos Ramirez

Tensiometers recording tension at three different depths (15, 30 and 60 cm) in a tomato irrigation trial at the Gascoyne Research Station.


There is a root flush post-harvest, so do not let soil dry out excessively or rapidly then. Tensiometers will break down when irrigation is reduced after harvest (Campbell-Clause J, 2005).

79

Table 2 Irrigation schedule for table grapes grown in Carnarvon Pruning to harvest period Growth stage

Irrigate at tensiometer reading

Pruning to inflorescence visible

40–45

Inflorescence visible to bunch closure

30

Bunch closure to veraison

40–45

Veraison to harvest

30

Harvest to leaf fall period Month

Irrigate using crop factors

January

40

February

40

March

30

April

30

May

25

June

0

Source: Campbell-Clause J, 2005

We recommend a steadily declining moisture availability, to slow vine growth and induce dormancy. Do this by applying irrigation based on evaporation replacement and using crop factors as in Table 2. Table 3 Basic infiltration rates and water-holding capacity for various soil types Soil type

Basic infiltration rate Readily available water (mm/hour)

(mm/metre)

> 30

30–40

Sandy loam

20–30

45–70

Loam

10–20

50–90

Clay loam

5–10

30–80

Clay

1–5

25–70

Sand


© Carlos Ramirez

Tensiometers linked to a data logger for remote analysis of tensions on drip irrigation in capsicums at Carnarvon Horticultural District.

80

Period of time 28 June to 7 August (about 40 days) Early August to early October (about 65 days) Early to mid-October (10 days) Mid October to mid-December (32 or more days)

Soil type and texture affect the amount of water readily available for crops, as well as the rate of water infiltration. A well-designed irrigation system increases watering efficiency by minimising evaporation. It also avoids soil erosion, which can occur if the application rate exceeds the infiltration rate of the soil. Thus, the application rate of the system should be slightly less than the infiltration rate of the soil (Luke G, 1990). The infiltration rates of different types of soil are shown in Table 3. On a sandy to sandy loam soil close to the Gascoyne river in Carnarvon, classified as poorly to imperfectly drained, a complete root wetting for tomatoes was reached after two hours of irrigation using a medium flow rate. At this time, wetting bulbs overlapped at 15 cm depth showing good moisture distribution in the root zone for vegetables in this type of soil. As shown in Table 4, longer irrigation times in this type of soil in Carnarvon using a medium flow rate, will cause soil wetting at depths greater than 36 cm, which may be understood as an over irrigation in most vegetables with a target root zone at the first 30 cm depth. In the same infiltration trial but on a different kind of soil, described as loamy to clay loamy texture, the same irrigation rate reached just 24 cm deep and the wetting bulbs didn’t overlap after two hours of irrigation at 3.4 L/m x hr. (medium flow). In this sort of soil, it was necessary to irrigate for four hours to reach the first 30 cm of depth (see Table 5). For optimum water usage, it is important to be aware of the water-holding capacity of the soil in the root zone of a crop. This is the amount of water in the soil between field capacity and the ‘refill point’ (the point at which soil moisture is so low it slows crop growth and stresses the plants). Thus, the water-holding capacity of the soil indicates how much water is readily available for the crop. If the amount of water applied to a crop exceeds ‘field capacity’, then the extra will be lost as drainage water. Soilmoisture monitoring equipment — which allows correlation between the soil-moisture reading and the point at which the soil ceases to drain rapidly after irrigation — makes for easy estimation of the water-holding capacity of an area of land (vegetablesWA, 2007).



Table 4 Depth and width of wetting bulbs in trickled irrigation on a sandy to sandy loam soil in Carnarvon after five different irrigation times with three different flow rates L/m x hr. (flow rate)

Irrigation time (hr) 0.5

1.0

2.0

4.0

8.0

0.5

1.0

Bulb width (cm) 2.5 (low flow)

19

18

26

2.0

4.0

8.0

34

40

Bulb depth (cm) 33

54

13

20

24

3.8 (medium flow)

18

22

34

62

63

15

22

30

36

43

5.0 (high flow)

22

35

43

68

70

20

23

32

38

47

Table 5 Depth and width of wetting bulbs in trickled irrigation on a loamy to clay loamy soil in Carnarvon after five different irrigation times with three different flow rates L/m x hr. (flow rate)

Irrigation time (hr.) 0.5

1.0

2.0

4.0

8.0

0.5

1.0

Bulb width (cm) 2.5 (low flow)

17

22

27

2.0

4.0

8.0

22

28

Bulb depth (cm) 40

57

12

14

17

3.8 (medium flow)

20

24

35

48

67

14

18

24

30

37

5.0 (high flow)

25

25

40

65

76

16

18

20

28

42

For detailed information visit these links: • Irrigating vegetables on sandy soils. www.agric.wa.gov.au/objtwr/imported_assets/ content/lwe/water/irr/fn066_1995.pdf • Irrigation scheduling how and why. www.agric.wa.gov.au/PC_92495.html • Soil moisture monitoring equipment. www.agric.wa.gov.au/PC_92499.html • Tensiometers: Preparation and installation. www.agric.wa.gov.au/objtwr/imported_assets/ content/lwe/water/irr/fn068_2004.pdf • Evaporation figures from the automatic weather stations are available by logging on to www. vegetableswa.com.au — simply follow the ‘Grower information’ link to ‘Weather station information’. n

© Carlos Ramirez

On a poorly drained, sandy to sandy loam soil in Carnarvon, irrigated with 3.4 L/m per hour (medium flow), it was necessary to run the system for at least 2 hours to reach the first 30 cm depth and 30 cm width in order to guarantee a good irrigation pattern for vegetable crops in this kind of soils.


© Carlos Ramirez

Control gear to provide power and cell phone communication to remotely access information from different kind of moisture sensors.

81

References 1. Burt J (1999) Growing capsicums and chillies. Farmnote No. 64/1999 (Reviewed 2005). Department of Agriculture and Food, WA. www.agric.wa.gov.au/objtwr/imported_assets/content/ hort/veg/cp/capsicums/f06499.pdf 2. Campbell-Clause J (1994) Irrigating table grapes in Carnarvon. Farmnote No. 48/1994 (Reviewed 2005). Department of Agriculture and Food, WA. www.agric.wa.gov.au/objtwr/imported_assets/content/ hort/vit/cp/tg/fn048_1994.pdf 3. Foord G and Hills T (1993) Using tensiometers for effective banana irrigation in Carnarvon. Farmnote No. 09/1993 (Reviewed 2005). Department of Agriculture and Food, WA. www.agric.wa.gov.au/objtwr/imported_assets/content/ lwe/water/irr/fn009_1993.pdf 4. Hoffmann H (1990) Efficient irrigation for determinate tomatoes in the Gascoyne River area. Farmnote No. 27/1990 (Reviewed 2007). Department of Agriculture and Food, WA. www.agric.wa.gov.au/objtwr/imported_assets/content/ lwe/water/irr/fn027_1990.pdf 5. Luke G (1990) Efficient irrigation designs for Carnarvon growers. Farmnote No. 12/1990 (Reviewed August 2006). Department of Agriculture and Food, WA. www.agric.wa.gov.au/PC_92492.html 6. Luke G (1990) Evaluating sprinkler and trickle irrigation systems. Farmnote No. 35/1990 (Reviewed August 2006). Department of Agriculture and Food, WA. www.agric.wa.gov.au/PC_92491.html 7. Queensland Government (2007) Water for Profit — Calculating distribution uniformity (DU). www.saiplatform.org/uploads/Library/%235Calculating_distribution_uniformity.pdf 8. vegetablesWA (2007) Good Practice Guide. www.vegetableswa.com.au/goodpractice.asp

82


Caring for our Country Project in Carnarvon

CfoC project in Carnarvon


Contents Section 5 Ca ri n g fo r o ur Co un try p r o je c t at C a r n a r v o n H o rt ic u lt u r a l D is t r ic t

84

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 A BASE LINE TO APPROACH GOOD AGRICULTURAL PRACTICE UNDERSTANDING AND ITS USE in the CARNARVON HORTICULTURAL DISTRICT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

GAP in fertilisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 GAP in irrigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 GAP in soil protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 Project 1: Analysis of different sources of calcium at three different dosages on yield and fruit quality parameters of seedless watermelons (Royal Armada) Project 2: The use of cover crops to improve soil conditions for vegetable production in Carnarvon . . . 96 Project 3: Biofumigant crops for soil pathogen control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Section 5 CFOC Pro j ect AT C ARNARVON HORTI CULTUR A L D I STR I CT

83

Caring for our Country (CfoC) project at Carnarvon Horticultural District

Introduction Caring for our Country (CfoC) is a national strategy being implemented across Australia to achieve a measurable difference to Australia’s environment. Through the Australian Government, CfoC funds projects across the country to achieve national targets with an special focus on projects that improve biodiversity and sustainable farm practices. This funding supports regional natural resource management (NRM) groups, local, state and territory governments, indigenous groups, industry bodies, land managers, farmers, Landcare groups and communities (CfoC, 2012). The CfoC program aims to achieve an environment that is healthy, better protected, well-managed, resilient and provides essential ecosystem services in a changing climate.

Issues related to water use efficiency, soil protection and salinity, virus control in vegetable production and the compilation of the most recommended agricultural practices for Carnarvon conditions were linked to the national priorities within the CfoC strategy to develop the project (see Table 1). This chapter provides the most relevant information about the CfoC project in Carnarvon, which together with this Good Agricultural Practice Guide will provide an important tool to help growers make appropriate decisions with regard to practices such as the use of calcium amendments, cover crops, biofumigants, and irrigation. A second round of funds was approved for the following season and more field works will be developed to progress strategies to improve the sustainability of the agricultural businesses in the Carnarvon Horticultural District.

With the support of the Carnarvon Growers Association (CGA), VegetablesWA and DAFWA leading growers in the Carnarvon Horticultural District received CfoC funding to develop a strategy to start implementing good agricultural practices in key District areas.

84

Secti o n 5 C f o C P r o je c t AT C A R N A RV O N H ORT I C U LT U R A L D I S TR I C T


Table 1 CfoC National Priorities and Carnarvon Project Strategies

CfoC NATIONAL PRIORITies

Sustainable farm practices

Community skills, knowledge and engagement

TARGETS

TARGETS

Improving management practices

Increase the engagement and participation rates of urban and regional communities in activities to manage natural resources

Increase the number of farmers who adopt stewardship, covenanting, property management plans or other arrangements to improve the environment both on-farm and off-farm Improving knowledge and skills

Position all regional natural resource management organisations to deliver best practice landscape conservation and sustainable land planning to communities and land managers within their regions Improve the access to knowledge and skills of urban and regional communities in managing natural resources sustainably and helping protect the environment Ensure the continued use, support, and reinvigoration of traditional ecological knowledge to underpin biodiversity conservation

CARNARVON Project STRATEGies Gypsum soil improvement demonstration Insect-proof netting for virus disease control Biofumigant crops for soil pathogen control Demonstration of best practice irrigation techniques Use of cover crops to improve soils for vegetable production in Carnarvon Visit from soil expert Dr Neal Kinsey Demonstration of best practice pesticide preparation and application Compile and distribute Carnarvon Good Agricultural Practice Guide

Section 5 C F OC Pro j ect AT C AR NARV O N H ORTICULTURA L DIS TRICT

85

2

Excellent Excellent

Very good Very good

Good Good

0

Poor

0

Poor

10

Non-existing Non-existing

Pe

20 10

50

A BASE LINE TO APPROACH GOOD AGRICULTURAL PRACTICE UNDERSTANDING AND ITS USE in the 2 50 CARNARVON HORTICULTURAL DISTRICT 40 8070 7060 Percentage Percentage

Excellent Excellent

Very good Very good

0

Good Good

0

Poor

10

Poor

Questions required growers to score themselves on a range 30 of values from 1 to 5 according to their point of view. The 20 results shown on the following pages provided important 20 input10to help us effectively assess the needs of growers and develop a relevant and useful CfoC project. Non-existing Non-existing

Question 1 How would you rate your knowledge of good agricultural practice (GAP) strategies?

Percentage Percentage

One of the most important tools when developing any project is to determine an accurate base line that helps to analyse the current performance against an expected level, including within the project scope. This base line was developed, based on a survey carried out with 25% of Carnarvon growers, randomly selected from a complete list of association members.

80

40 30

6050 5040 4030 3020 2010 10 0

Question 3 Do you think following GAP strategies on your farm does, or could benefit?

0

1 3 3

20 30 10 20

10 0

3020

All of them All of them

Business Business sustainability sustainability

Yield Yield

Product quality Product quality

The environment The environment

10 0 0

40 60 30 50 20 40

10 1 2 30 Unsuccessful 0 20 1 2 Unsuccessful 10

3 3 No

4 4

5 Very successful 5 Yes Very successful

No

Yes

30 10 20 0 Twice a year Other Other

0

Once a year

Lack of capital Lack of capital

10

of appropriate Lack of appropriate ry/technology chinery/technology




4030

50 70

Lack of time Lack of time

of them All of them

Business Business ainability sustainability

Yield Yield

t quality Product quality

ronment The environment

0

0

5040

2010

100% of growers consider they are using GAP in their 40 farms, which 50 is consistent with the first two questions, 35 60 40 and 93% believe 40 this implementation has had a 30 35 successful result 50 on their farms. However, only 4.3% 25 30 30 of the growers directly link GAP implementation with 20 40 25 business sustainability. 20 15 20 10 15 5 10 0 5

6050

60 80

0

15 5

86

7060

70

60

73.3% of growers consider they have a good or 12 very 30 good understanding of GAP. There is a 100% 12 35 25 consistency between their opinion about their knowledge and their confidence that this knowledge 30 20 is being applied on their farms. In summary these 25 15 questions let us conclude that “What they know is 20 10done”. being

5

0

2010

8070

80



Excellent Excellent

Very goodVery good

Good Good

Poor

Poor

20 10

3020

80


50 40

35

10 0

Business profit Business profit

Excellent Excellent

Very goodVery good

Good

10 20

4030

0

50

30 20

5040

10 0

40 30



3

1510

Question 4 How successful have the strategies been on your farm?

4

20 30

0

2015

0

30 40

0 10

3

Poor

40 50

2

2520

50

Question 2 How would you rate your skills in applying GAP 50 4 strategies?

ss profit Business profit

2

Good

0

3025

10 5

Poor

0 10

6050

3530 Percentage Percentage

30 40



40 50

f information/ ackknowledge of information/ knowledge

1

60

35


50

Never

Secti o n 5 C f o C P r o je c t AT C80 A R N A RVOnce O N aHyear ORT I CTwice U LT U R A L D I S TR ICT a year Never 70

Ve

Non 50

Ca rn ar vo n Go od Ag ri cult ural Pr ac tic e Guide 80

30 5

70

Percentage

Excellent

Good

Very good

Percentage

20

Poor

25

0

10 0

15

No

10

30 20

0

Use of gypsum

Soil analysis

Use of technical advise

Organic fertilisers

Following test recommendations Percentage

Fertirrigation cutting edge technology

Use of frequent small doses of fertilisers

40 30

0 No

No

Yes

Yes

Question 9 How often do you take your leaf test?

60 35

50 60 1

3

4

5 Very successful

30 40 20 30

25 20 15 10

10 20

5

Never

No

66.7% of growers are actively using the soil and leaf analysis service through CGA. There is a big advance in this point. Growers consider this as an important tool for good crop management and returns. However 33.3% of growers still do not use these important tools. Yes

0 Section 5 C F OC Pro j ect AT C AR NARV O N H ORTICULTURA L DIS TRICT No

Never

Twice a year

Twice a year

Once a year 80

0 Quarterly

Never

Once a year

Twice a year

Monthly

Once a year

0

Before flowering

0 10

70 80 60 70 50 60 40 50 30 40 20 30 10 20 0 10

30 Percentage


2

Other

5

50

10

Lack of capital

10

70

20

Lack of time

15

80

Yes Question 7 How oftenNodo you test your soil?

Percentage Percentage Lack of information/ knowledge

20

Never

60

Unsuccessful 40 50

25

Twice a year

0

0

30

10

Question 8 Do you use leaf tests?

Percentage

70 80 60 70 50 60 40 50 30 40 20 30 10 20 0 10

Lack of appropriate machinery/technology

Percentage


80

35

20

Once a year

All of them

Business sustainability

Yield

Product quality

The environment

Business profit

Question 6 Do you use soil tests?

40

30

0

0

12

Fertilisation according with crop phases

5

Record keeping

10

pH buffering

Keeping high humus contents

Nothing

Percentage

15

40

Equipment calibration

50

0

20

10

Yes

5

25

40

30 20

30

50

40

60

35

4

50

Question 5 What GAP strategies do you frequently use on your farm in terms of fertilisation?

10

3

60

GAP in fertilisation

20

Non-existing

Percentage

40

Percentage

All of them

2

Yes

87

2

50 40 Percentage

80 30

70 60

20 Percentage

GAP in irrigation 10

50

Excellent

Very good

25 35

30 20 10 0 No

20 30

Yes

15 25

30 20 10

Tensiometers Tensiometers

5

Digging

10

Crop signs Crop signs

015

Weather Weather informationinformation

520

Percentage Irrigation according Irrigation according with crop phases with crop phases

40

Digging

0 25 10

Cutting edge Cutting edge technology technology

50

Base on Base on knowledge knowledge

5 30 15

Use of evaporation Userates of evaporation rates

60

10 2035

Percentage

3

PercentagePercentage

30

Good

Non-existing

35 0

Poor

40 Question 10 What GAP strategies do you frequently use on your farm in terms of irrigation?

All of them

Business sustainability

GAP 50 in soil protection

Yield

Product quality

The environment

Business profit

Even though 57% of growers agreed that lack of water is an obstacle in GAP implementation and crop expansion, 0 Onceother a year 4.5% Twice a year Never 31.8% 0are irrigating their farms based on their knowledge, 4.5% based on crop signs and used to dig the ground to decide whether or not irrigate, that means that 40.8% of polled growers are not using any technology to manage their irrigation systems. 80 70

60 Question 11 What GAP strategies do you frequently use on your farm in terms of soil protection? Percentage

30 50 40

40 30

10

10 30 20

0

5 Very successful

Nothing

Fallow

Yes

Nothing

4

Shade house Shade house

3

Not work Not when work when soil is wetsoil is wet

2

Fallow

1 Unsuccessful

Crop rotation Crop rotation

10 0

Crop highCrop high densities densities

Use/incorporation Use/incorporation of organicof organic materials materials

Cover crops Cover crops

No

0 20 10

0

50

20

20 40 30 Percentage

4


40 50

Question 12 What is holding you back in implementing GAPs? 12

40

Lack of information and knowledge, capital to invest among other factors, are the most important reasons for growers to explain what is hindering GAP implementation.

35 Percentage

30 25 20 15 10

88

Other

Lack of capital

Lack of appropriate machinery/technology

Lack of time

0

Lack of information/ knowledge

5

As soon as the “Other” column is open, the lack of water appears as the main factor blocking GAP, such as the use of cover crops and the increase of the area under crop. Within these “other” factors is also an important 29% of growers that express they are not interested or motivated to change their way of doing things.



Project 1 Analysis of different sources of calcium at three different dosages on yield and fruit quality parameters of seedless watermelons (Royal Armada) A Research Project included within the overall Caring for our Country (CfoC) project for the Carnarvon Growers Association August – December 2012

INTRODUCTION Horticulture production in seasonally-arid areas such as Carnarvon, WA it is not an easy task. Soil salinity, lack of water and market expectations related to high standards of fruit quality make horticultural production a challenge for all the people involved in this activity. Soil calcium plays an important role in relation to these challenges, as an element that in balanced proportion with other bases helps to establish equilibrium in soil base saturation, which makes elements such as sulphur, phosphorus and potassium, among others more plant available. The cationic exchange capacity (CEC) of soils also helps to liberate sodium, making it easier to be drained out of the system to reduce salinity. For that reason, a trial was established to evaluate three different sources of calcium, used at three different rates, across a watermelon crop at the Gascoyne Research Station in the Carnarvon Horticultural District. A total of 10 different treatments were compared against a control in order to establish which had the greatest impact on the yield of seedless watermelon (variety Royal Armada).

Treatments were applied in plots of 10m by 75 m long. The first 25 m contained 2.5 t/ha of product, the second 25 m contained 5.0 t/ha and the last 25 m was spread with10 t/ha. Treatment N consisting of 2.5 t/ha of gypsum plus 2.5 t/ha of crushed lime received a blanket rate across the full length of the plot (see Figure 1). Plots were randomly set within the trial area with two replications to validate the results. Soil samples were taken and analysed before calcium sprays. Two weeks after calcium was applied, seedlings of seedless watermelon variety Royal Armada were planted in rows in a north-south direction following a ratio of one pollinator row to every three female (seedless) rows. A distance of 1.2 m between plants in the same row and 2.0 m between rows was used for a total of 4,166 plants/ha (see Figure 2). Figure 1 Trial design

In addition, a post-harvest evaluation was performed to identify whether or not there were differences in brix grades and pulp pressure between fruits from different treatments. Watermelons from each treatment were stored in a cool room at 4ºC for four weeks with weekly analysis of the mentioned variables.

METHODOLOGY Three commonly-used sources of calcium were selected for evaluation. Lime sand (CaCO3), gypsum (CaSO4) and crushed lime (Ca (OH)3) were applied at rates of 2.5, 5.0 and 10 t/ha. A fourth treatment consisting of 2.5 tonnes of gypsum plus 2.5 tonnes of crushed lime per hectare was also included within the comparison versus a control treatment, which had no additions of any source of calcium.


89

According to market information, the ideal size for watermelons at the market is between 12 and 14 kilograms per fruit. Based on this information fruit weights were classified in histograms of frequency to identify which treatment produced the most fruit within the preferred range size. According to Table 3, areas treated with crushed lime at 10 t/ha produced the highest amount of fruit within the desired market weight, followed by the areas treated with 2.5 t/ha of lime sand and fruits from areas treated with 5 t/ha of crushed lime came in third place.

© Carlos Ramirez

Calcium application.

Results and Discussion Analysis of productivity per hectare On average all treatments yielded between 29 t/ha, as the lowest value using 10 t/ha of lime sand, up to 59 t/ha as the highest yield obtained using 2.5 t/ha of crushed lime (see Table 1). In general, yield decreased as calcium rates increased across all treatments, except the control (nil treatment). The yield obtained using 2.5 t/ha across all three products was significantly higher than those for the control plots (see Table 2).

Analysis of fruit quality To analyse whether or not there were differences in the fruit quality of watermelons coming from the different treatments, a reference was taken for three main fruit characteristics — fruit size, brix grades and flesh pressure. Brix grades and flesh pressure were measured throughout four weeks of storage in a cool room at 4ºC.

In the case of crushed lime, an increase in 1.68% in the amount of fruit within specification by doubling the rate from 2.5 to 5 t/ha is not an economically feasible decision for growers, keeping in mind that the highest yields were obtained using 2.5t/ha of this source of calcium (see Table 1). In terms of brix grades and pulp pressure the statistical analysis didn’t show any clear relationship between treatments and these characteristics. On average, brix grades were slightly higher at the lowest dosages of calcium with a marked difference at weeks one and four (see Table 4). During the test, in weeks two and three the differences in brix grades were insignificant. A tendency for brix grades to increase as clearly observed across almost all treatments through the first three weeks, and then the lines tend to curve downwards with a most visible tendency at 10 t/ha. In the case of gypsum, the fruit coming from areas treated with 10 t/ha of this product kept the rising tendency in brix grades even after the third week of post-harvest storage (see Figures 3–5).

© Carlos Ramirez

Seedless watermelon crop, variety Royal Armada.

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Table 1 Estimated watermelon yield across calcium treatments Estimated yield (t/ha) Rate (t/ha)

Treatment A

Treatment C

Treatment D

Treatment N

Treatment B

Lime sand

Gypsum

Crushed lime

Gypsum+lime

Control

Section A

2.5

55

52

59

52

43

Section B

5.0

40

34

48

53

48

Section C

10.0

29

50

42

48

40

Table 2 Number of fruits harvested per plot Number of fruits harvested per plot Treatment A

Treatment C

Treatment D

Treatment N

Treatment B

Rate (t/ha)

Lime sand

Gypsum

Crushed lime

Gypsum+lime

Control

2.5

89

82

92

89

66

Section B

5.0

65

55

74

84

80

Section C

10.0

47

85

66

79

68

Section A

Table 3 Percentage of fruit within a weight range between 12 to 14 kg at different calcium application rates Fruit within a weight range of 12–14 kg (%) Treatment A

Treatment C

Treatment D

Treatment N

Treatment B

Rate (t/ha)

Lime sand

Gypsum

Crushed lime

Gypsum+lime

Control

Section A

2.5

10.11

9.76

11.96

8.00

9.00

Section B

5.0

12.31

7.27

9.46

8.00

9.00

Section C

10.0

2.13

5.88

13.64

8.00

9.00

Table 4 Variation of brix grade within different rates of calcium Weeks after harvest

Rate (t/ha)

1

2

3

4

Average

2.5

11.1

11.3

11.4

12.1

11.5

5.0

9.3

11.3

11.6

11.3

10.8

10.0

9.6

11.3

11.7

11.4

10.9

To measure the flesh pressure, watermelons were cut horizontally and four points proportionally distributed throughout the fruit flesh were tested, starting in the centre and finishing at 2 cm from the peel. The statistical analysis of the flesh pressure variation within treatments was carried out bases on the average of the four values obtained for each treatment. For this characteristic, as with the previous brix grades, the statistical analysis didn’t show a clear relationship between treatments and the variations in flesh pressure (see Figures 6–8). Another important quality standard in melons that can cause significant loss of marketable fruits is hollow heart (HH). According to the Yara’s Melon Plantmaster, this physiological pulp disorder is the result of environmental

© Carlos Ramirez

Methodology to measure flesh pressure.


91

Figure 3 Changes in brix grades across four weeks of monitoring in fruit treated with 2.5 t/ha of different sources of calcium 15 1510 5 10 15 50 10

1

05

2

3

4

TA — lime sand 2 3 4

1 0 1


1

2

3

4

TC — gypsum 2 3 4

1 1

TA — lime sand

TC — gypsum 2 3 4

1

2

3

4

TD — crushed lime 2 3 4

1 1


TC — gypsum

1

2

3

4

TN — gypsum+lime 2 3 4

1 1


TD — crushed lime

1

2

3

4

TB — control 2 3 4

1 1

TB — control 2 3

TN — gypsum+lime

4

TB — control

Figure 15 4 Changes in brix grades across four weeks of monitoring in fruit treated with 5 t/ha of different sources of calcium 1510 5 10 15 50 10

1

05

2

3

4


1 0 1


1

2

3

4

TC — gypsum 2 3 4

1 1

TA — lime sand

TC — gypsum 2 3 4

1

2

3

4


1 1


TC — gypsum

1

2

3

4


1 1


TD — crushed lime

1

2

3

4


1 1

TB — control 2 3

TN — gypsum+lime

4

TB — control

15 10

15 Figure 5 Changes in brix grades across four weeks of monitoring in fruit treated with 10 t/ha of different sources of calcium 5 10 15 50 10

1

05

2

3

4


1 0 1


1

2

3

4

TC — gypsum 2 3 4

1 1

TA — lime sand

TC — gypsum 2 3 4

1

2

3

4


1 1


TC — gypsum

1

2

3

4


1 1


TD — crushed lime

1

2

3

4


1 1

TB — control 2 3

TN — gypsum+lime

4

TB — control

1.5 1.0 1.5 0.5 1.0 1.5 0 0.5 1.0

1

0 0.5 1 0 1

92 1.5

2

3

4

TA — lime sand 2 3 4 TA — lime sand 2 3 4 TA — lime sand

1 1 1

2

3

4

TC — gypsum 2 3 4 TC — gypsum 2 3 4 TC — gypsum

1 1 1

2

3

4

TD — crushed lime 2 3 4 TD — crushed lime 2 3 4 TD — crushed lime

1 1 1

2

3

4

TN — gypsum+lime 2 3 4 TN — gypsum+lime 2 3 4 TN — gypsum+lime

1 1 1

2

3

4

TB — control 2 3 4 TB — control 2 3

4

TB — control


15 15 10 15 10 5 10 5 Ca rn ar vo n Go od Ag ri cult ural Pr ac tic e Guide 0 5 0

1

0

1 1

2

3

4

2 3 4 TA — lime sand 2 3 4 TA — lime sand

1 1 1

TA — lime sand

2

4

1

2 3 4 TC — gypsum 2 3 4 TC — gypsum

3

1

2

3

4

2 3 4 TD — crushed lime 1 2 3 4 TD — crushed lime

TC — gypsum

1

2

3

4

1

2 3 4 TN — gypsum+lime 1 2 3 4 TN — gypsum+lime

TD — crushed lime

1

2

3

4

1

2 3 4 TB — control 1 2 3 4 TB — control

TN — gypsum+lime

TB — control

Figure 6 Changes in flesh pressure across four weeks of monitoring in fruit treated with 2.5 t/ha of different sources of calcium 1.5 1.5 1.0 1.5 1.0 0.5 1.0 0.5 0 0.5 0

1

0

1 1

4

1


2

3

1 1

TA — lime sand

4

1


2

3

1

2

3

4


TC — gypsum

1

2

3

4

1


TD — crushed lime

1

2

3

4

1

2 3 4 TB — control 1 2 3 4 TB — control

TN — gypsum+lime

TB — control

Figure 7 Changes in flesh pressure across four weeks of monitoring in fruit treated with 5.0 t/ha of different sources of calcium 1.5 1.5 1.0 1.5 1.0 0.5 1.0 0.5 0 0.5 0

1

0

1 1

2

3

4


1 1 1

TA — lime sand

2

4

1


3

1

2


3

4

1

2


3

4

TC — gypsum

TD — crushed lime

TN — gypsum+lime

1

1

2

3

4

1

2 3 4 TB — control 1 2 3 4 TB — control TB — control

Figure 1.5 8 Changes in flesh pressure across four weeks of monitoring in fruit treated with 10 t/ha of different sources of calcium 1.5 1.0 1.5 1.0 0.5 1.0 0.5 0 0.5 0

1

0

1 1

2

3

4

2 3 4 TA — lime sand 2 3 4 TA — lime sand TA — lime sand

1 1 1

2

4

1


3

1

TC — gypsum

2

3

4


1

2

3

4

1


TD — crushed lime


TN — gypsum+lime

1

2

3

4

1

2 3 4 TB — control 1 2 3 4 TB — control TB — control

93

b

c

© Carlos Ramirez

Hollow heart damage (a) severe, (b) moderate, (c) light.

and growth stress, including lack of calcium and boron. Other studies have also indicated HH is caused by a rapid growth of the fruit where the rind expands faster than the internal flesh, mainly due to excess nitrogen rates and over-watering along with favourable growing conditions (Johnson, 2009).

Plant hormones are also thought to play a role. It is thought that with inadequate pollination, there is reduced release of the plant hormone that controls the development of storage tissue leading to HH (Johnson, 2009), (YARA, 2013). Analysing the incidence of HH in this trial, there appears to be a relationship between higher dosage of calcium and less HH incidence. However, the differences in HH 5.0 t/ha between 10 t/ha treatments were not wide enough to incidence assert that increasing rates of calcium will reduce the HH problems under acceptable limits (see Figure 9).

However, there is growing evidence that HH is not directly tied to nitrogen, calcium, boron and water management but is related to pollination and weather conditions during 2.5 t/ha pollination. Several researchers have found no increase in HH with increases in nitrogen; even in varieties know to have HH problems.

Figure 9 Percentage of watermelons affected by hollow heart (HH) in fruit treated with four different sources of calcium at three different application rates

Percentage of fruit affected

2.5 t/ha

5.0 t/ha

10 t/ha

25 TC — gypsum 20

TD — crushed lime

TN — gypsum+lime

TB — control

Treatments 15 10 5 0 TA — lime sand

TC — gypsum

TD — crushed lime

TN — gypsum+lime

TB — control

Treatments

Figure 10 Hollow heart incidence in watermelons at different dosages of calcium 18 16 14 12 10 8 6 4 2 0

94

2.5



me sand

a

18

16 5.0 10 14 Tonnes per hectare 12

Control

10 8 6 4 2



Table 5 Rating system to identify the best treatment Measure of impact

TA — lime sand

TC — gypsum

Rate (t/ha) 2.5 Yield (t/ha) Biggest average fruit size Number of fruits/ha Biggest % of fruit within market size specification Brix grades Flesh firmness Total score

5

TD — crushed lime

TN

Rate (t/ha)

2.5 lime + 2.5 gypsum

Rate (t/ha) 10

2.5

5

10

2.5

5

10

TB control

10

3

1

9

2

7

11

6

4

8

5

7

5

4

9

8

1

2

11

10

3

6

10

3

1

7

2

9

11

6

4

8

5

8

9

1

7

3

2

10

6

11

4

5

11

4

3

7

5

2

9

1

6

8

10

2

4

1

9

6

10

11

3

7

8

5

48

28

11

48

26

31

54

33

42

39

36

Looking at each treatment, the percentage of fruit affected by HH at different dosages has an erratic trend that did not make it possible to conclude which rate of each product is the best one to prevent or reduce this quality problem (see Figure 10).

Conclusion Understanding that parameters like yield, fruit size, number of fruits per hectare and quality issues like brix grades, flesh firmness and HH had different responses within treatments, a score system was developed to identify, in general, which source of calcium and which application rate was most consistent across all the appointed parameters (see Table 5). To do this, all the treatments were ranked from 11 to 1, giving 11 points to the treatment with best performance for each selected parameter and 1 point for the treatment with the worst results. According to the yield, 11 points were assigned to the 2.5 t/ha crushed lime treatment. This treatment yielded 56 t/ha, while 10 t/ha of the same product scored only 1 point because it yielded lowest at 29 t/ha. This classification process was carried out across all crop parameters included in this analysis.

Watermelons produced in areas treated with 10 t/ha of crushed lime had the largest fruit, but one of the lowest amount of fruits per hectare. This was consistent with areas treated with 10 t/ha of lime sand, which also had low yields and numbers of fruits per hectare. This treatment consistently showed the lowest scores in all the evaluated parameters proving to be the treatment with the worst crop performance. The weak statistic correlation between variables such calcium source, application rate and crop yield among others, is explained by the fact that both calcium sulphate and calcium carbonates are solid, insoluble amendments with a slow release of small amounts of calcium into the soil solution. An application of these amendments will produce few short-term benefits, but significant long-term benefits. For that reason, in the next cropping season, the project will establish vegetables in the same plots previously treated with calcium. In time, vegetables with a longer life cycle may show a stronger variability within the treatments.

In general, crushed lime, lime sand and gypsum at application rates of 2.5 t/ha seem to be the best options for growers in the Carnarvon area. As observed in Table 5, this application rate scores gave the highest yields per hectare with a good fruit size, brix grades and flesh firmness according to market expectations.


95

Project 2 The use of cover crops to improve soil conditions for vegetable production in Carnarvon. A Research Project included within the overall Caring for our Country (CfoC) project for the Carnarvon Growers Association August – December 2012

INTRODUCTION The use of cover crops in farming systems is not a new practice. Researchers around the world highlight them as the cornerstone of sustainable agriculture. Prior to the development of manufactured fertilisers, cover crops were commonly used to improve soil structure and productivity. Today, they appear as one of the most efficient strategies to guarantee farm sustainability due to their multiple positive impacts on soil protection, increased water infiltration into the soil, reduced evaporation and soil temperature, protection against erosion, accumulation of organic matter in the soil, addition and recycling of nutrients and improved soil structure among others. At DAFWA’s Research Station in Carnarvon 14 different species of grasses, clovers, beans, vetch and biomulch brassica were evaluated as cover crops in order to measure their ability to produce biomass, dry matter (DM), adapt to Carnarvon conditions and compete against weeds with minimum irrigation and no fertiliser.

© Carlos Ramirez

Areas planted with grasses such as rye corn rapidly generated biomass and dry matter.

In general, grasses produced 53% of the total amount of DM produced in the trial. Thanks to this group of plants 34,681 kilos of DM per hectare were incorporated into the soil at the Gascoyne Research Station. Despite this, some other species like vetch produced an amazing amount of DM that placed this species in the second place after fumigator sorghum with 11,127 kilos of DM per hectare. Other groups of plants, including white clover, despite having the worst germination percentage, biomass generation and soil coverage, their efficiency to generate DM was among the best across the 14 species evaluated.

© Carlos Ramirez

These cover crops were planted during August 2012 with a difference of two weeks between the first planted rows and the last ones. This difference in planting time had a significant impact on DM accumulation between the first and last planted species, such as white clover.

Area planted with lupins.

96



Figure 1 Percentage of dry matter at soil incorporation 40 35

Percentage

30 25 20 15 10 5 Vetch

Teff grass

Bounty white clover

Kupu II white clover

Cover crop

Rye corn

Lupins

Annual ryegrass

Bladder clover

Persian clover

Fumigator sorghum

Oats

Fava bean

Field peas

Biomulch Brassica

0

According to Sattel R et al. 1999, non-legumes tend to grow more quickly and take up a higher proportion of nitrogen during the autumn and early winter than legumes. Thus, they are more suitable for nitrogen scavenging. Legumes can fix substantial amounts of atmospheric nitrogen, some of which becomes available to the following crop. In general, the fastest period of legume and non-legume cover crop growth is mid to late spring as temperatures increase. Therefore, nonlegumes are more suitable for soil protection and nitrogen scavenging than legumes.

© Carlos Ramirez

Oats had the fourth highest dry matter production within the group of plants tested in this trial.


97

Despite there not being much information available on the negative impacts of cover crops, some information states that despite residues providing many benefits; it is not always desirable to maximise DM production. Excessive residue can negatively affect field operations (for example, tillage). In terms of carbon:nitrogen (C:N) ratios, the ideal amount of DM depends, in part, on the type of residue, the tillage system used, planting schedules, and needs or limitations of the following crop. Legume residues decompose quickly because they have a relatively low C:N ratio; therefore, excessive DM accumulation generally is not a problem. An exception is crimson clover, which can be difficult to flail and incorporate when stands are heavy and stems are mature and tough (Sattell R et al, 1999). At the end, three different strategies to incorporate the biomass were tested at the Gascoyne Research Station. Incorporation using discs, mulch and rolling down after herbicide application were used to mix the biomass into the soil. Discing and rolling effectively killed the crops, while in the mulch treatment, sorghum regrew and some areas of clovers remained intact due to the short development height at incorporation. One month after biomass incorporation, the mulched area was partially covered by weeds and some of the grasses were still growing, while the disc and rolled areas remained clean even until two months later. Discing has a more disturbing effect on soil structure and leaves the soil completely nude. Rolling down the biomass after treating with a herbicide provides better soil protection for a longer time while planting conditions are optimum at the start of the next season.

© Carlos Ramirez

Sorghum produced the most dry matter per hectare but one of the lowest dry matters per kilogram of biomass.

In this treatment, a layer of DM remains on the soil protecting it against wind erosion and controlling weeds in a more efficient way than the other two strategies. Cover crop selection and management depends on many factors, among them the cover crop’s ability to accumulate DM (i.e., residues) and nitrogen. DM provides energy for soil organisms, contributes to soil organic matter, improves tilth and acts as a sink for nutrients. In relation to the capacity to produce high kilograms of DM per hectare with minimum water requirements, the most recommended species for Carnarvon according to the results in this trial are: fumigator sorghum, vetch, rye corn, oats and field peas in the fifth place. Depending on the season, some cover crops may perform better if planted during late spring or early summer while others, such as clovers, are reported to perform better as cover crops in winter. In relation to the methodology to incorporate the biomass into the soil, the treatment rolling down the biomass on soil surface two weeks after a herbicide application had a better effect killing the cover crop, maintaining adequate weed control for a longer time and protecting the soil against wind erosion. Investigations in South California are recommending this methodology as a way to replace the use of plastic layers in tomato crops.

© Carlos Ramirez

At the end of the trial, sorghum generated 12,916 kilos of dry matter per hectare to be incorporate into the soil.

98



Project 3 Biofumigant crops for soil pathogen control A Research Project included within the overall Caring for our Country (CfoC) project for the Carnarvon Growers Association August – December 2012

Introduction Biofumigation is defined as suppression of soil-borne pests and pathogens by the use of plants that contain inhibitory chemicals. The plants can be harvested as rotation crops or ploughed back into the soil as green manure (Appleby M, 2012). Land limitations often make long-term rotations difficult. Shorter rotations lead to a build-up of pests, with soil-borne diseases being a major challenge for many vegetable crops. One approach to tighter rotations is to fumigate soils using commercially-available chemical fumigants. Methyl bromide has been phased out and can only be used for certain exempted critical uses. Other fumigants such as chloropicrin; dicloropropene + chloropicrin; metam-sodium, metam-potassium, and iodomethane + chloropicrin are still being used in some regions where registered. A major drawback to chemical fumigation is material cost. There are also application requirements and equipment considerations to take into account (Johnson G, 2009)

There has been considerable interest in the use of certain crops as biological fumigants ahead of vegetable production to reduce the need for chemical fumigation, especially in tight rotations. Plants from the mustard family produce chemicals called glucosinolates in plant tissue (roots and foliage). These glucosinolates are released from plant tissue when it is cut or chopped and they are further broken down by enzymes to form chemicals that behave like fumigants. The most common of these breakdown products are isothiocyanates. These are the same chemicals that are released from metam-sodium (Vapam) and metam-potassium (K-Pam), commonly used as chemical fumigants. Sorghums produce a cyanogenic glucoside compound called dhurrin that breaks down to release toxic cyanide when plant tissue is damaged (Johnson G, 2009) To evaluate these biofumigant properties under Carnarvon conditions, areas planted with fumigator sorghum as a cover crop were compared against areas under no crop rotation. Soil samples were taken in five different locations to analyse the presence of soil-borne pathogens like phytophtora sp., phityum sp. and rhizoctonia sp. The level of parasitic nematodes was also assessed. Areas where fumigator sorghum was incorporated into the soil using different alternatives were also compared against a control area where no biofumigant crop was used. The population of helicotylenchus sp. was not different in areas where fumigator sorghum was used compared with the control areas. In all soil samples this nematode was detected in medium to low levels. In terms of fungal feeding nematodes, their populations were higher in areas where no sorghum was used compared with the sorghum areas.

© Carlos Ramirez

In addition of its contribution of dry matter, F. sorghum has been proven to control soil pathogenic organism.


99

The previous results didn’t show a clear benefit in terms of the effectiveness of fumigant sorghum as a biocontroller under the evaluated conditions. As reported by Johnson G, 2009, despite some promising characteristics of sorghum as biofumigant crop, results in other different regions have been inconsistent, often with minimal benefits. It is important to note that success with biofumigant crops depends on a number of factors. The following are some suggestions to achieve the best results: • Choose biofumigant crop varieties selected or bred for higher levels of active compounds if available. • Produce as much biomass of the biofumigant crop as possible. The more biomass produced and incorporated, the more chemical is released. However, as plants mature, they will reach a point where levels of these active chemicals will decline. Do not allow the cover crop to go to seed.

© Carlos Ramirez

Mulch of fumigant sorghum.

Populations of fungal feeding nematodes show a decreasing tendency according to the way the sorghum was incorporated into the soil. The higher populations were found in lots where the sorghum was sprayed with herbicide before it was laid down on soil surface. Medium levels of these nematodes were found in areas where sorghum was disced into the soil and the lowest levels came from areas where the sorghum was mulched. According to Nyczepir A P 1998, the use of sorghum as a biofumigant to manage ring nematode on peach does not seem to be a feasible alternative to chemical fumigation at this time. Although, there was some indication of nematode suppression by the sorghum green manure in the early stages of the experiment, it did not last as long as methyl bromide fumigation (i.e., 12 months vs. 24 months, respectively). In terms of soil fungal pathogens, phytophtora sp. was not detected in any area, while phytium sp. and rhizoctonia sp. were always detected in all the areas under study.

100

• The plant material must be thoroughly damaged so the enzymes can convert glucosinolates into isothiocynates or so that the dhurrin is converted into cyanide. This means chopping the material as much as possible and incorporating it into the soil as quickly as possible so as to not lose the active compounds to the air. A delay of several hours can cause significant reductions in biofumigant activity. The finer the chop, the more biofumigant is released. • Incorporate the material as thoroughly as practical to release the biofumigant chemical throughout the root zone of the area that is to be later planted to vegetables. • Sealing with water or plastic after incorporation will improve the efficacy (as with all fumigants). Soil conditions should not be overly dry or excessively wet. Biofumigant crops can suppress soil-borne pests but do not replace chemical fumigants. Several previously detailed conditions must be met to ensure a certain level of control that is not likely to match the control reached using chemical soil fumigants. n



References 1. AC greenfix (2003.) Grow your own nitrogen. Dakota Frontier Seeds LTDA. www.acgreenfix.com/

7. Johnson G (2009) Weekly Crop Update. Fumigation Alternatives – Biofumigants. http://agdev.anr.udel.edu/weeklycropupdate/?p=837

2. Appleby M (2012) Biofumigation. Ontario Ministry of Agriculture and Food. www.omafra.gov.on.ca/english/crops/hort/news/ allontario/ao0612a1.htm

8. Johnson G (2010) Weekly Crop Update. Hollow Heart in Watermelon. University of Delaware Cooperative Extension. http://agdev.anr.udel.edu/weeklycropupdate/?p=1841

3. Bolton S (2010) Addition of Gypsum and other Calcium Products to soil to solve second class water problems. Environmental Imagineers, Melbourne. http://tgaa.asn.au/states/vic/pdf/

9. YARA (2013) Melon Plantmaster. YARA International ASA. www.yara.com 10. Michigan Cover Crops (2010) Michigan State University. www.covercrops.msu.edu/

4. Desmond A and Chant A (2001) Carnarvon 2 (CAR2 – Wooramel subregion). www.calm.wa.gov.au/pdf/science/bio_audit/ carnarvon02_p87-102.pdf

11. Nyczepir AP and Rodriguez-Kabana R (1998) Biofumigation and Management of Ring Nematode on Peach. http://mbao.org/2002proc/089nyczepira%20mbr02orlando.pdf

5. Endress+Hauser (2007) Coriolis meter used for Brix measurement. Flow Measurement & Control. www.instrumentation.co.za/article. aspx?pklarticleid=4657

12. Sattel R, Buford T, Murray H, Dick R and McGrath D (1999) Cover Crop Dry Matter and Nitrogen Accumulation in Western Oregon. http://ir.library.oregonstate.edu/xmlui/bitstream/ handle/1957/15719/em8739.pdf;jsessionid =14F45ADDC246AD15FD59E01C15A5AF18?sequence=1

6. Hugo Núñez K, Marco Schwartz M, Muñoz AM (1999) Effect of three storage temperatures on the quality of kiwi fruit pulp concentrated at a reduced pressure. Departamento de Agroindustria y Tecnología de Alimentos, Facultad de Ciencias Agrarias y Forestales, Universidad de Chile. www.ncbi.nlm.nih.gov/pubmed/10883300

13. Watermelons Strategic Marketing Plan Overview, Melons Conference July 2011. www.melonsaustralia.org. au/0f3113590c8c31d9730497ec184c8d31/David%20 Weisz%20Watermelons%20Strategic%20Plan%20-%20 June%202011.pdf


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Notes

102
