Glyphosate-Resistant Kochia in Montana Herbicide Recommendations and Best Management Practices for Growers Prashant Jha Weed Scientist Kent McVay Extension Cropping Systems Agronomist Aruna Varanasi Post Doctoral Research Associate Vipan Kumar Graduate Research Assistant
Research Bulletin No. 4602 1
Kochia Emergence Flushes
Glyphosate-Resistant Kochia in Montana: Herbicide Recommendations and Best Management Practices for Growers Prashant Jha, Weed Scientist Kent McVay, Extension Cropping Systems Agronomist Aruna Varanasi, Post Doctoral Research Associate Vipan Kumar, Graduate Research Assistant Montana State University, Southern Agricultural Research Center, Huntley, MT 59037
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Kochia Biology Kochia (Kochia scoparia (L.) Schard.) is one of the most troublesome annual broadleaf weeds in crop fields, pastures, roadsides, wastelands, and ditch banks across the Northern Great Plains (NGP). If not controlled early, kochia causes severe yield reductions (up to 60%) in crops, including wheat, barley, corn, and sugar beet, and can be a major problem weed in chemfallow. Kochia seed survives in soils only 1-2 years. Seeds have little-to-no dormancy, and the majority (> 90%) of the seeds lying on or near the soil surface in a no-till condition germinate early in the spring, with two to three emergence flushes through the summer. Kochia exhibits rapid growth and flowers in late summer. The weed is capable of self- and cross-pollination, and reproduces by seed. A single kochia plant is capable of producing up to 50,000 seeds that can spread by wind, water, contaminants in hay, agricultural equipment, or by on-farm vehicles. At maturity, the plant breaks off at the base of the stem and “tumbles” across the landscape with the prevailing wind, a unique and rapid mechanism of seed dispersal. Furthermore, kochia is well adapted to drought, salt, heat, and cold conditions.
Development and Spread of Glyphosate-Resistant Kochia
Glyphosate (Roundup® or other generics) is an effective, nonselective, broad-spectrum herbicide used for weed control. However, various factors concerning the use of glyphosate for more than a decade for burndown weed control prior to planting, in chem-fallow, and for in-crop applications in Roundup Ready® crops, have resulted in the evolution of glyphosate-resistant weeds (presently 24 species in the United States), including kochia. Glyphosate-resistant kochia was first reported (Drs. Curt Thomson and Phil Stahlman, KSU) in western Kansas in 2007, and subsequently has been found in Nebraska, Colorado, North Dakota, South Dakota, and southern Alberta. During the summer of 2012, glyphosate (Roundup® or other generics)resistant kochia populations were first detected in chemfallow fields in northern Montana with a history of repeated glyphosate use in chem-fallow prior to winter wheat planting and postharvest in wheat stubble. Use of glyphosate at rates below the recommended field-use rate and at weed heights greater than 4 inches have potentially Herbicide-Resistant worsened the problem. Based on our research, a 5- to Kochia in Montana 11-fold level of glyphosate Enhanced selection pressure (Roundup®)-resistance has from repeated use of herbicides been documented in kochia with the same mode of action populations from Hill and has resulted in evolution of Liberty Counties in Montana. herbicide-resistant kochia Glyphosate inhibits populations across the the activity of the EPSPS northwestern region, including (target-site gene) enzyme in Montana. Aatrex® (Atrazine)Kochia Plant plants and blocks protein resistant kochia was first synthesis, resulting in growth reported in Montana along inhibition and plant death. railroads in 1984. Kochia Very recently, we discovered that the glyphosate-resistant kochia resistant to sulfonylurea (SU) herbicides, Glean® (chlorsulfuronpopulations from Montana had multiple copies of the target-site methyl) and Ally® (metsulfuron-methyl), was detected in gene compared with a known susceptible kochia population. wheat fields in 1988, and is believed to occur in nearly 70% Overproduction of the gene increases the number of target of Montana farm fields today. Kochia resistance to auxinic sites where glyphosate binds; thus, the resistant plant functions herbicides (Banvel® and Starane®) was found in a few Montana normally despite normally-lethal doses of glyphosate. Increasing wheat fields in 1995, although the extent of the rate of glyphosate to control resistant kochia is not a good infestation is limited. Very recently (fall of 2012), strategic option, as it may result in plants with even higher levels glyphosate-resistant (GR) kochia was found in chem-fallow fields of resistance. in Hill and Liberty Counties in Montana and suspected in Toole County (2013), suggesting a potential risk of further spread in Montana if not managed.
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Best Management Practices (BMPs) for Reducing the Risk of Glyphosate-Resistant Kochia
2. Integrate Cultural and Mechanical Weed Management Practices. Growers should aim to reduce herbicide selection pressure on weeds by adopting diversified cultural practices that reduce sole reliance on herbicides. Some of these approaches include:
Kochia is the first weed known to develop resistance to glyphosate in Montana. Growers should adopt recommended BMPs for containment and management of resistant weed populations, with the inclusion of diversified cultural, mechanical, and chemical control options effective on kochia. The emphasis of resistance management efforts should not be limited to minimizing the crop yield loss, but also to reducing the resistant weed seed bank. Below are the recommended BMPs:
• Plant crops in weed-free fields to eliminate the risk of competition from established weeds. • Use high crop-seeding rates, narrow row spacing, and optimum fertilization and irrigation methods to enhance crop competition against weeds. • Diversify crop rotation. Rotate Roundup Ready® (RR) crops like RR sugar beet or RR corn with small grains (spring wheat/ barley) or dry beans in irrigated regions of Montana. Include legumes (peas and lentils) and oilseeds (canola, sunflower, and safflower) into the continuous wheat-fallow dryland systems of Montana. Diverse crop rotations inherently include the use of multiple management tactics and herbicides with different modes of action.
1. Understand the Weed Biology. A sound knowledge of kochia biology is necessary to understand the evolution and spread of herbicide-resistant kochia. Growers need to be aware of the routes of resistance spread (through pollen and seed) across fields and landscapes. To prevent spread of herbicide resistance through cross-pollination, kochia plants that have escaped herbicide applications should be eliminated before flowering. Seed-mediated dispersal of herbicide resistance Uncontrolled Kochia Trail in a Chem-Fallow Field in can be avoided by adopting the Northern Montana following practices: • Always plant crop seeds that are certified and weed-free. • Prevent weed seed movement within and between fields through irrigation, manure applications, and spreading crop residue. • Clean the tillage, planting, mowing, spraying, and harvesting equipment, and on-farm vehicles thoroughly before moving from one field to another to avoid introduction of resistant seeds into new fields.
• Use tillage as a management option where appropriate. Since kochia seedlings emerge from very shallow soil-depths (less than 1/2-inch), tillage can potentially reduce the soil seed bank by burying short-lived seeds. Additionally, targeted tillage can be used to manage escaped or resistant kochia plants occurring in patches, before they start producing seed.
• Other cultural practices such as cover crops may be utilized as an integrated weed management strategy.
• Use targeted tillage to uproot kochia plants that escaped herbicide applications before those plants produce seed. • Collect and destroy seeds of any uncontrolled/escaped kochia plants postharvest in crop stubble. • Control kochia populations at field borders, fence lines, roadsides, and other non-crop areas to minimize the movement of resistance into crop fields.
Control Kochia in Field Borders and Fence Lines
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3. Add Herbicide Diversity. Although herbicides are the most effective and economical weed control options, growers should use diversified effective chemical control tactics to manage the evolution and spread of herbicide-resistant weeds. The following recommendations can help achieve this goal: • Scout fields regularly prior to and following herbicide applications to assess herbicide performance and promptly destroy weed escapes. Timely scouting is essential to maintain a record of weed species abundance or shifts and early detection of on-farm weed control failures. • Apply herbicides at full labeled rates for effective weed control. Do not apply herbicides at below-label rates.Repeated exposure to low herbicide rates allows survival of rare resistant weed individuals and subsequent development of herbicide resistance over generations. Make sure that the sprayer equipment is in good condition (no worn out or plugged nozzles) and properly calibrated. Check for proper ground speed, boom height, spray coverage, and weather conditions at the time of herbicide application. Use of adjuvant(s), when recommended, may potentially overcome high pH (>7) and hard water (high levels of Ca, Mg, or Fe ions) problems, which are believed to reduce herbicide effectiveness. For example, addition of ammonium sulfate in the spray tank can overcome adverse effects of hard water on glyphosate efficacy. Addition of adjuvants, when recommended, may also improve herbicide efficacy and weed control under heat and drought stress conditions.
• Rotate herbicides with different modes of action over multiple growing seasons in all fields (this is also possible by rotation of crops in the same field). Consecutive applications of herbicide of the same families (same Group number) with the same mode of action have greater potential to develop crossresistance for a weed population. For example, extensive use of sulfonylureas (Ally® or Harmony Extra®) and imidazolinones (Pursuit® or Beyond®) on a given field could lead to the selection of weed populations that are resistant to both herbicide families. • Within each crop or chem-fallow field, use herbicide mixture(s) (tank-mixed or sequential applications) that include multiple effective modes of action to control weeds. This practice reduces the risk of herbicide-resistance. It is important to mix herbicides that target the same weed with similar efficacy and similar persistence. Furthermore, efficacy of the herbicide mixture can be increased by selecting mixture components that degrade differently, and may be synergistic in their activity on weeds. Always use full labeled rates of the tank-mix partners and follow proper tank-mix order. • Target herbicide applications at the recommended weed sizes. For instance, kochia plants should be targeted as early as 3-4 inch height for effective control with postemergence herbicides (not shorter or taller). • Include soil-residual herbicides in the fall or spring burndown program(s), or in chem-fallow to reduce the resistant seed bank and selection pressure from repeated postemergence herbicide applications.
Control Kochia Post-Harvest in Wheat Stubble
Herbicide Programs for Glyphosate-Resistant Kochia Management Growers should include preemergence (PRE) soil-residual and postemergence (POST) herbicides with multiple modes of action in their weed management program to control resistant kochia. Effectiveness of alternative herbicide programs to control glyphosateresistant kochia in Montana cropping systems have been listed in Tables 1 and 2. These herbicides should be used in conjunction (tank-mixed) with glyphosate to obtain broad-spectrum weed control. 5
Table 1. Efficacy of Preemergence (PRE) Soil-Residual Herbicides on Kochia Control. Kochia control Group
Herbicide
Rate/Acre1
Estimated Cost/acre3 6 WAA2
8 WAA
10 WAA
Major Crop(s)
2, 27
Corvus
4.5 oz
9
8
7
$28
Corn
4
Banvel
4-16 oz
8-10
6-8
4-5
$2-7
Chem-fallow, cereals (4 oz/a), corn
4, 3 4, 2,15 5
Banvel + Prowl H2O
8-16 oz + 1.5 pt
9-10
9
6
$16
Chem-fallow, corn
Tripleflex
1 qt
8
5
3
$22
Corn
Sencor
8 oz
10
10
9
$8
Chem-fallow, tolerant varieties of winter wheat, soybean
$16-20
5, 7
Sencor + Linex
8 oz + 16-24 oz
10
10
9
Chem-fallow
5, 14
Authority MTZ
8 oz
10
10
10
$11
Soybean
5, 15
Harness Xtra
3 qt
10
10
10
$32
Corn
5, 15
Aatrex 4 L + Zidua
1 pt + 2 oz
10
9
8
$17
Corn
1 qt
10
10
10
$18
Corn Sugar beet
5, 15, 27
Lumax EZ
8, 8
Ro-Neet SB + Eptam
3.2 pt + 2.3 pt
2-3
2-3
2-3
$64
14
Sharpen
1-2 oz
6
5
3
$5-10
14
Spartan
6 oz
10
10
10
$30
Soybean, field pea
14
Valor
2 oz
7-8
5
4
$12
Corn, soybean, wheat
Chem-fallow, soybean, corn, cereals
14, 15
Verdict
15 oz
7-8
6
5-6
$25
Corn
14, 15
Fierce
3.2 oz
9-10
9
8
$19
Corn, soybean
15
Warrant
48 oz
4
3
2
$15
Corn, soybean
15
Outlook
21 oz
5
3
2
$30
Sugar beet, corn, soybean
15
Zidua
2 oz
6
4
3
$14
Corn, soybean
16
Nortron SC
1-3.75 qt
2-7
2-6
2-6
$24- 89
27
Balance Flexx
3.6 oz
9
8
6
$20
Sugar beet Corn
PRE soil-residual herbicides were applied in early spring (April); Soil pH = 7.8; Organic matter = 2.2 1 Recommended adjuvants were added according to the herbicide label. For all herbicides in the list, follow label use directions for crop use and rotational intervals. Sencor, Linex, or Valor can cause injury to following wheat crop in Montana. Herbicides were applied at 10 GPA. 2 WAA refers to week after application (WAA). 3 These are approximate costs. Costs have been converted to nearest decimal. Specific prices of the herbicides should be obtained from your local dealer. Kochia Control Rating: 10 (96-100%), 9 (90-95%), 8 (85-89%), 7 (80-84%), 6 (70-79%), 5 (60-69%), 4-2 (
