Integrated Crop Management Conference

Proceedings of the 23rd Annual

Integrated Crop Management Conference November 30 - December 1, 2011 Iowa State University Ames, Iowa

AEP 0302 - 2011

2 — 2011 Integrated Crop Management Conference - Iowa State University

Prepared by Brent A. Pringnitz, program coordinator

Iowa State University Extension and Outreach Agriculture and Natural Resources Program Services 2101 Agronomy Hall, Ames, Iowa 50011-1010 Phone: (515) 294-6429 FAX: (515) 294-1311 [email protected] www.aep.iastate.edu Copyright © 2011 Iowa State University Extension and Outreach

All trademarks, service marks, registered marks, or registered service marks contained in this document are the property of their respective owners, and their use does not imply endorsement by Iowa State University. Mention of trade names does not imply endorsement of one product over another, nor is discrimination intended against any similar product not named.

… and justice for all The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or family status. (Not all prohibited bases apply to all programs.) Many materials can be made available in alternative formats for ADA clients. To file a complaint of discrimination, write USDA, Office of Civil Rights, Room 326-W, Whitten Building, 14th and Independence Avenue, SW, Washington, DC 20250-9410 or call 202-720-5964. Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Cathann A. Kress, director, Cooperative Extension Service, Iowa State University of Science and Technology, Ames, Iowa.

2011 Integrated Crop Management Conference - Iowa State University — 3

Proceedings of the 23rd Annual Integrated Crop Management Conference November 30 - December 1, 2011 Iowa State University Ames, Iowa

Table of Contents Speaker contact information....................................................................................................................................... 5 Crop management 1. Growin’ good corn: Rocket science or common sense?........................................................................................ 7 RL (Bob) Nielsen, Extension corn specialist, Agronomy, Purdue University

2. Long silks, short pollen…a long year?............................................................................................................... 15 Roger W. Elmore, professor and Extension corn agronomist, Agronomy, Iowa State University

3. Making silage from Iowa’s forage crops.............................................................................................................. 17 Stephen K. Barnhart, professor and Extension forage agronomist, Agronomy, Iowa State University

5. Midwest crop weather 2011-2012: What follows a strong La Niña?.................................................................. 21 Elwynn Taylor, professor and Extension climatologist, Agronomy, Iowa State University

6. Crop and biofuel outlook for 2012................................................................................................................... 23 Chad Hart, assistant professor and Extension economist, Economics, Iowa State University

7. Sustainable production and distribution of bioenergy for the Central US.......................................................... 27 Chad Hart, assistant professor and Extension economist, Economics, Iowa State University

8. Energy management for crop production.......................................................................................................... 31 H. Mark Hanna, Extension ag engineer, Agricultural and Biosystems Engineering, Iowa State University; Dana Petersen, program coordinator, ISU Farm Energy, Iowa State University

Pest management 10. Herbicide resistance in waterhemp: Past, present, and future............................................................................37 Patrick J. Tranel, professor, Crop Sciences, University of Illinois at Urbana-Champaign

11. Weed management for 2012............................................................................................................................. 41 Micheal D. K. Owen, professor and Extension weed specialist, Agronomy, Iowa State University

12. Herbicide-resistant weeds: An evolving problem of importance in Iowa crop production.................................. 45 Micheal D. K. Owen, professor and Extension weed specialist, Agronomy, Iowa State University

13. A reintroduction to soil applied herbicides........................................................................................................ 49 Bob Hartzler, professor and Extension weed specialist, Agronomy, Iowa State University

14. Diversified weed management tactics in diversified cropping systems: ............................................................. 55 Foundations for durable crop production and protection Matt Liebman, professor and H.A. Wallace Chair for Sustainable Agriculture, Agronomy, Iowa State University

16. Update on the soybean aphid efficacy program................................................................................................. 59 Erin W. Hodgson, assistant professor and Extension entomologist, Entomology, Iowa State University; Greg VanNostrand, research associate, Entomology, Iowa State University

17. Japanese beetle biology and management in corn and soybean......................................................................... 63 Erin W. Hodgson, assistant professor and Extension entomologist, Entomology, Iowa State University; Cody Kuntz, graduate student, Entomology, Iowa State University; Matt O’Neal, associate professor, Entomology, Iowa State University; and Greg VanNostrand, research associate, Entomology, Iowa State University

18. Assessing the benefits of pyramids and seed treatments for soybean aphid host plant resistance....................... 67 Michael McCarville, graduate student, Entomology, Iowa State University; Matthew E. O’Neal, associate professor, Entomology, Iowa State University; Walter R. Fehr, distinguished professor, Agronomy, Iowa State University

4 — 2011 Integrated Crop Management Conference - Iowa State University 20. Goss’s wilt: Get the facts.................................................................................................................................... 73 Alison Robertson, associate professor and Extension plant pathologist, Plant Pathology, Iowa State University; Charlie Hurburgh, professor, Agricultural and Biosystems Engineering, Iowa State University; Lisa Shepherd, assistant scientist, Seed Science Center, Iowa State University; Charlie Block, assistant professor, Plant Pathology; Roger Elmore, professor and Extension corn agronomist, Agronomy, Iowa State University

Nutrient management 23. Fertilizer situation and outlook.........................................................................................................................77 David Asbridge, president, NPK Fertilizer Advisory Service

24. Corn and soybean response to soil pH level and liming.....................................................................................93 Antonio P. Mallarino, professor, Agronomy, Iowa State University; Agustin Pagani, graduate research assistant, Agronomy, Iowa State University; John E. Sawyer, professor, Agronomy, Iowa State University

25. Nutrient uptake by corn and soybean, removal, and recycling with crop residue............................................103 Antonio P. Mallarino, professor, Agronomy, Iowa State University; Ryan R. Oltmans, graduate research assistant, Agronomy, Iowa State University; Jacob R. Prater, graduate research assistant, Agronomy, Iowa State University; Carlos X. Villavicencio, graduate research assistant, Agronomy, Iowa State University; Louis B. Thompson, ag specialist, Agronomy, Iowa State University

26. Effect of a rye cover crop and crop residue removal on corn nitrogen fertilization...........................................115 John E. Sawyer, professor and Extension soil fertility specialist, Agronomy, Iowa State University; Jose L. Pantoja, graduate research assistant, Agronomy, Iowa State University; Daniel W. Barker, assistant scientist, Agronomy, Iowa State University

27. Nitrate loss in subsurface drainage as affected by nitrogen application rate and ..............................................123 timing under a corn-soybean rotation system Matthew J. Helmers, associate professor, Agricultural and Biosystems Engineering, Iowa State University; Reid D. Christianson, Extension program specialist, Agricultural and Biosystems Engineering, Iowa State University; John Sawyer, professor, Agronomy, Iowa State University

Soil and water management 29. Can conservation complement agriculture?..................................................................................................... 129 John Doudna, graduate research assistant, Ecology, Evolution and Organismal Biology, Iowa State University; Matt Helmers, associate professor, Agricultural and Biosystems Engineering, Iowa State University; Matt O’Neal, assistant professor, Entomology, Iowa State University

30. Residue biomass removal and potential impact on production and environmental quality.............................. 131 Mahdi Al-Kaisi, associate professor, Agronomy, Iowa State University; Jose Guzman, research assistant, Agronomy, Iowa State University

31. Water quality benefits of perennial filter strips in row-cropped watersheds..................................................... 139 Matthew J. Helmers, associate professor, Agricultural and Biosystems Engineering, Iowa State University; Xiaobo Zhou, assistant scientist, Agricultural and Biosystems Engineering, Iowa State University; Heidi Asbjornsen, associate professor, Natural Resource and the Environment, University of New Hampshire; Randy Kolka, soil scientist, USDA Forest Service, Northern Research Station; Mark D. Tomer, soil scientist, USDA Agricultural Research Service, National Laboratory for Agriculture and the Environment


Speaker contact information Mahdi Al-Kaisi Associate Professor, Agronomy Iowa State University 2104 Agronomy Hall Ames, IA 50011-1010 515/294-1923 [email protected] David Asbridge President, NPK Fertilizer Advisory Service Chesterfield, MO 636/778-8680 [email protected] Steve Barnhart Professor, Agronomy Iowa State University 2104 Agronomy Hall Ames, IA 50011-1010 515/294-1923 [email protected] Madan Bhattacharyya Associate Professor, Agronomy Iowa State University G303 Agronomy Hall Ames, IA 50011-1010 515/294-2505 [email protected] Betsy Buffington Extension Program Specialist, Entomology Iowa State University 9 Insectary Ames, IA 50011-3140 515/294-7293 [email protected] Silvia Cianzio Professor, Agronomy Iowa State University 2017 Agronomy Hall Ames, IA 50011-1010 515/294-1625 [email protected]

Rick Cruse Professor, Agronomy and Director, Iowa Water Center Iowa State University 3212 Agronomy Hall Ames, IA 50011-1010 515/294-7850 [email protected] Matt Darr Assistant Professor, Agricultural and Biosystems Engineering Iowa State University 202 Davidson Ames, IA 50011-3080 515/294-8545 [email protected] John Doudna Graduate Teaching/Research Assistant, Ecology/Evolution and Organismal Biology Iowa State University 251 Bessey Ames, IA 50011-1020 515/294-3523 [email protected] Roger Elmore Professor, Agronomy Iowa State University 2104 Agronomy Hall Ames, IA 50011-1010 515/294-1923 [email protected] Mark Hanna Extension Ag Engineer, Agricultural and Biosystems Engineering Iowa State University 200B Davidson Hall Ames, IA 50011-3080 515/294-0468 [email protected]

Chad Hart Assistant Professor, Economics Iowa State University 468E Heady Hall Ames, IA 50011-1070 515/294-9911 [email protected] Bob Hartzler Professor, Agronomy Iowa State University 2104 Agronomy Hall Ames, IA 50011-1010 515/294-1164 [email protected] Matt Helmers Associate Professor, Agricultural and Biosystems Engineering Iowa State University 209 Davidson Hall Ames, IA 50011-3080 515/294-6717 [email protected] Erin Hodgson Assistant Professor, Entomology Iowa State University 103 Insectary Ames, IA 50011-3140 515/294-2847 [email protected] Laura Jesse Extension Program Specialist, Plant Pathology Iowa State University 327 Bessey Ames, IA 50011-1020 515/294-0581 [email protected] David Laird Professor, Agronomy Iowa State University 2505 Agronomy Hall Ames, IA 50011-1010 515/294-1581 [email protected]

6 — 2011 Integrated Crop Management Conference - Iowa State University Leonor Leandro Assistant Professor, Plant Pathology Iowa State University 325 Bessey Ames, IA 50011-1020 515/294-8855 [email protected]

Ken Ostlie Professor, Entomology University of Minnesota 1980 Folwell Ave, Rm 219 St. Paul, MN 55108-6125 612/750-0993 [email protected]

S. Elwynn Taylor Professor, Agronomy Iowa State University 2104 Agronomy Hall Ames, IA 50011-1010 515/294-1923 [email protected]

Matt Liebman Professor, Agronomy Iowa State University 1401 Agronomy Ames, IA 50011-1010 515/294-7486 [email protected]

Micheal D. K. Owen Professor, Agronomy Iowa State University 3218 Agronomy Hall Ames, IA 50011-1010 515/294-5936 [email protected]

Patrick Tranel Professor, Crop Sciences University of Illinois 320 ERML 1201 W. Gregory Dr. Urbana, IL 61801 217/333-1531 [email protected]

Antonio Mallarino Professor, Agronomy Iowa State University 3216 Agronomy Hall Ames, IA 50011-1010 515/294-6200 [email protected]

Alison Robertson Associate Professor, Plant Pathology Iowa State University 317 Bessey Hall Ames, IA 50011-1020 515/294-6708 [email protected]

M.T. McCarville Graduate Research Assistant, Entomology Iowa State University 113A Insectary Ames, IA 50011-3140 515/294-8663 [email protected]

Erika Saalau Extension Program Specialist, Plant Pathology and Microbiology Iowa State University 351 Bessey Ames, IA 50011-1020 515/294-1741 [email protected]

R.L. Bob Nielsen Professor, Agronomy Purdue University 915 W. State St. West Lafayette, IN 47907-2054 765/494-4802 [email protected]

John E. Sawyer Professor, Agronomy Iowa State University 2104 Agronomy Hall Ames, IA 50011-1010 515/294-1923 [email protected]

Bill Northey Secretary of Agriculture/IDALS Wallace State Office Bldg 502 E 9th St Des Moines, IA 50319 515/281-5321

Kristine Schaefer Extension Program Specialist, Entomology Iowa State University 8 Insectary Ames, IA 50011-3140 515/294-4286 [email protected]

Greg Tylka Professor, Plant Pathology Iowa State University 321 Bessey Ames, IA 50011-1020 515/294-3021 gltylka@ia


Growin’ good corn: Rocket science or common sense? RL (Bob) Nielsen, Extension corn specialist, Agronomy, Purdue University

Background For 70 years, beginning in 1866, national corn grain yields in the U.S. were essentially flat (Fig. 1) and averaged only 26 bpa (bushels per acre) during that entire 70-year time period. The absence of noticeable yield improvement throughout all those years is remarkable given that farmers of the day were essentially also plant breeders practicing a recognized form of plant breeding (mass selection) as they saved the best ears from each year’s crop for planting the next. As the nation began to emerge from the Great Depression and Dust Bowl years of the 1930’s, U.S. corn growers began to replace their traditional open-pollinated corn varieties with the new technology of double-cross hybrid seed corn. Within a few years, a significant shift in national corn grain yield was evident. During the period 1937 – 1955, average corn yields changed from no annual yield improvement to an annual rate of gain equal to roughly three quarters of a bu per ac per year (Fig. 1). Such a shift in the rate of improvement in corn grain yield represented a quantum leap shift in productive capacity. A second quantum leap in the annual rate of yield gain in corn occurred in the mid-1950’s with the greater adoption of single-cross hybrids and other new improved production technologies including mechanization, herbicides, and inorganic fertilizers (especially nitrogen). Beginning around 1956, the rate of annual yield gain dramatically changed from about three quarters of a bu per ac per year to nearly 2 bu per ac per year and has remained at that rate in the succeeding 55 years (Fig. 1). The exponential population growth on this planet mandates that we increase the rate of yield improvement in corn and other major food crops around the world. If the average annual rate of yield improvement remains constant at just under 2 bu per ac per year, then achieving a national average corn yield of 300 bpa would not be expected to occur until about 2086; a far cry from the often quoted promise that biotechnology will result in a national U.S. corn grain yield average of 300 bpa by the year 2030. To reach that lofty goal by 2030, another quantum leap shift in the rate of annual yield gain would have to occur beginning NEXT YEAR that would take us to an annual increase of about 7.5 bu/ac/yr for the next 19 years. Such a quantum leap shift in yield improvement would be unprecedented in the history of corn production. Contrary to the hype and hoopla over transgenic corn traits by the farm press and seed corn industry in recent years, there is little evidence that a third quantum leap shift in corn productivity has yet begun (Fig. 1). Another disconcerting fact is that relative to trend yields, the annual relative rate of yield gain has been steadily decreasing for the past 50+ years (Fig. 2). Shortly after the second quantum leap shift occurred in the mid-1950’s, the relative rate of yield improvement was about 3.5% per year. Since then the absolute rate of yield gain per year has remained unchanged at 2 bu per ac per year. However, since today’s average grain yield is significantly higher than those in the 1950’s, the relative rate of annual yield gain today is only about 1.2% per year.

300 Bushels per acre is achievable today! Even though the goal of achieving a national AVERAGE corn yield of 300 bpa by 2030 is likely out of reach unless a miraculous improvement in technology occurs soon, it is true that individual growers have demonstrated in national corn yield contests that they can produce 300 bpa with today’s technologies and genetics (NCGA, 2010). Furthermore, the physiological yield components necessary to produce a 300+ bu crop are not terribly out of reach today. Potential ear size is easily 1000 kernels with today’s hybrids. That would be equal to an ear with 18 kernel rows and 56 kernels per row. If (admittedly a big IF) that ear size could be maintained at a harvest population of only 30,000 plants per acre and IF kernel weight could be maintained at about 85,000 kernels per 56 lb. bushel (a modest kernel weight), those yield components would multiply to equal a yield potential of 356 bpa!

8 — 2011 Integrated Crop Management Conference - Iowa State University Historical U.S. Corn Grain Yields 1866 to date 180

1866-1936

160

1937-1955 Since 1956

140

y = 1.9135x - 3690.6 R2 = 0.9193

120 100 80 60 40

y = 0.7644x - 1452.4 R2 = 0.7224

20 0

Data source: USDA-NASS

1860

1880

1900

1920

1940

1960

1980

2000

2020

2040

Figure 1. National average corn grain yield since 1866. Data source: USDA-NASS (2011).

Relative annual yield gain (% of trend yield)

Current Annual Rate of Yield Gain As A Percent Of Historical Trend Yield U.S. Corn Grain, 1956 - 2011 4.0% 1956

3.5%

Current (2011) annual rate of yield gain is equal to 1.9 bu/ac/yr or 1.2% of current (2011) trend yield (157 bu/ac)

3.0% 2.5% 2.0% 1.5%

2011

1.0% 0.5% 0.0% 0

50

100

150

200

Trend yield (bu/ac) Data source: USDA-NASS

Figure 2. Relative annual rate of yield gain for U.S. corn since 1956 based on current annual rate of 1.9 bu/ac/yr. Data source: USDA-NASS (2011).


The secret to producing 300+ bushel corn Given that the yield potential of that bag of seed corn is already 300+ bpa, then what is preventing all of us from routinely producing those high yields on our farms? The answer to that question is simple… Once that seed is planted, that crop is subjected to a season-long array of yield influencing factors, most of which are stresses that reduce yield potential. So, the secret to improving yields on your farm is simply to sharpen your focus on identifying the yield-influencing factors specific to the fields you farm. Once you have successfully done that, then you are better equipped to identify the appropriate agronomic management strategies to alleviate those factors holding back your yield and, perhaps, enhance those factors that promote high yields. Pretty simple, eh?

Rocket science or common sense? The trouble with the way many folks go about the business of improving yields on their farms is that they always look for the “silver bullets” or the “one-size-fits-all” answer to their problems. They read farm magazine articles that highlight what one guy has done in Timbuktu that supposedly resulted a 20 bpa jump in his corn yields and figure that they ought to try the same thing on their farm in northwest Iowa. They listen to the testimonials of someone in the next county over that used Bob’s High Yield Snake Oil & Emolument on his crop and rush over to their local crop input retailer to buy some of the stuff to try on their farm. They take notes on the best management strategies presented at a crops conference by some guy from Purdue University who has never been on their farm and make plans to adopt those BMPs for next year’s crop. The problem or challenge, you see, is that you need to invest your own time and effort to identify the important yieldlimiting factors that are specific to your own fields. As I stated earlier, once you have successfully identified the yieldlimiting factors specific to your production fields, then you are better equipped to identify the appropriate agronomic management strategies to alleviate those factors holding back your yield and, perhaps, enhance those factors that promote high yields. It ain’t rocket science. It is hard work and common sense, coupled with a sound knowledge of agronomic principles.

Yield influencing factors (YIFs) The process of identifying the YIFs that are important to your specific fields is not an easy one. First of all, these YIFs can be either negative or positive in their effects on yield. Pay attention to both. These YIFs may occur every year in a given field… or they may not. These YIFs often interact with other YIFs to influence yield. Think about the compounded effects of heat + drought + soil compaction. These YIFs often affect different crops differently. For example, most of us do not worry about gray leaf spot disease in soybeans. Frankly, as a corn guy, I don’t worry about soybeans anyway, but that’s another story. These YIFs often interact with soil type / texture / drainage conditions. These YIFs almost always interact with weather conditions. Ultimately, the effects of YIFs on corn yield are equal to their effects on the four components that constitute grain yield. The timing of the occurrence of YIFs relative to crop growth stage greatly determines their effect on these yield components because they develop at different times throughout the season (Fig. 1).

•• Plants per acre (population or “stand”) •• Ears per plant (degree of barrenness) •• Kernels per ear (potential vs. actual) •• Kernel rows per ear •• Kernels per row •• Weight per kernel


Figure 3. Phenological timeline of the development of yield components in corn. (Source: Nielsen’s imagination) Once you sit down to list the possible YIFs that may influence corn yields on your farm, you will easily reach the conclusion that there must be a gazillion YIFs to consider. Where do you begin? If you have farmed a particular field for a while, your own experience in that field is invaluable to identifying the YIFs specific to that field. You can probably come up with a short list of obvious YIFs based on that alone. In future cropping seasons, strive to keep thorough notes on what happens with the crop during the entire growing season. Don’t just plant it and come back at harvest. Visit your fields regularly. Sure, you can hire a crop scout to walk your fields for you, but there is a lot to be said for you walking your fields yourself. Take advantage of the agronomic skills and knowledge of both the private and public sectors. Work closely with the sales or technical agronomists from your crop input retailers. Consider hiring the services of an independent crop consultant. Don’t forget the Extension resources available at your own land-grant university. You say you don’t know the name of your state’s Extension corn or soybean agronomist? Shame on you! You can find them in the following Web directories. These specialists can also put you in contact with other, more specific, content matter specialists at your land-grant university. http://www.kingcorn.org/experts/CornSpec.html http://www.kingcorn.org/experts/soyspec.html Stay up to date during the growing season by reading Extension newsletters from around the Midwest. You can find most of them linked at my Chat ‘n Chew Café Web site: http://www.kingcorn.org/cafe. Yes, I know this is shameless promotion of my own Web activity, but what can I say? Spend time perusing two good university Web sites that focus on corn production issues. Mine at Purdue: http://www.kingcorn.org/news/archive.html Roger Elmore’s at Iowa State Univ: http://www.agronext.iastate.edu/corn Did your wife buy you a smartphone or tablet for your birthday with 3G cellular connectivity? Install a GIS app on it and use the thing to map problem areas in the field for future reference. I have used an app called GISRoam with my Apple iPad to map problem areas or field features with reasonably good success. There’s another app called iGIS that I have not used enough to comment on, but it’s worth checking out. If you use your iPhone, I would recommend considering an after-market phone case that contains an additional battery to provide you with more hours of GIS field scouting. Take advantage of previous year’s yield maps to physically direct you to specific spots in a field to continue your hunt for YIFs. Target those field areas for specific soil sampling. Target those areas to intentionally scout the following crop season. Do you have access to aerial imagery during the growing season? Recognize that aerial imagery by itself often cannot identify the cause of visual differences in a field. That is usually your job using the imagery to guide you to spots in the field. The bottom line with this discussion is… Get out into your fields during the growing season, identify problem areas early while the evidence is still there to aid diagnostics, and figure out what’s going on with your crops!


Key factors to consider Even though I hinted earlier in this treatise that you should not blindly believe any “expert” who has not been on your farm, here are a few key factors I can offer to you for your consideration as you go about the business of identifying the important YIFs for your farm. Because I am “Iowa-challenged”, these factors will by necessity be influenced by my experiences with growing good corn in Indiana.

Field drainage In my area of the eastern Corn Belt, naturally poorly-drained soils constitute a major perennial challenge to establishing vigorous stands of corn by virtue of their effects on the success and uniformity of rooting and plant development. The adequacy of field drainage (tile or surface) greatly influences whether corn will produce 200-plus yields or nothing (ponded out) or somewhere in between. By improving tile or surface drainage in a field, you can reduce the risks of ponding or soggy soils, loss of soil nitrate by denitrification, and soil compaction by tillage and other field equipment. Reducing these risks enables more successful root development and stand establishment of the corn crop, which in turn will enable the crop to better tolerate stresses later in the growing season.

Supplemental water Some soils in the eastern Corn Belt suffer from the opposite problem of drying out too easily when rainfall is inadequate. Obviously, fields with those soils will usually respond to supplemental water provided by above-ground irrigation (center pivots, shotguns, rows) or below-ground supplementation by virtue of pumping water back into tile drains or drainage ditches. Either choice requires informed decision-making relative to irrigation scheduling based on crop demand and soil water availability (Joern & Hess, 2010). Maintenance and proper operation of center pivot irrigation systems is crucial to optimize efficiency in terms of irrigation costs and crop benefit.

Hybrid selection Most of us spend too little time evaluating the documented performance of potential hybrids for use in our operations. Look at any hybrid trial that includes “good” hybrids from a range of seed companies and you will easily see a 50 to100 bushel range in yield between the top and bottom of the trial. Mind you, this spread from high to low occurs in variety trials where supposedly every hybrid entered into the trial is a “good” hybrid. I doubt that seed companies enter “bad” hybrids on purpose. The key challenge is to identify hybrids that not only have good yield potential, but that also tolerate a wide range of growing conditions (Nielsen, 2010). The best way to accomplish this is to evaluate hybrid performance across a lot of locations. University trials are good for this exercise (Iowa State Univ, 2011; Devillez, 2011). If you use seed company trials, be aware that often there are few competitor hybrids included in variety trial results. Recognize that no hybrid wins every trial in which it is entered. Look for hybrids that consistently yield no less than about 90% of the highest yield in the trial no matter where they are grown. For example, if the top hybrid in a particular trial yielded 230 bpa, then look for hybrids in the same trial that yield at least 207 bpa (230 x 0.90). That may not sound like much of a challenge, but you will be surprised how few hybrids will meet that goal when evaluated over a lot of locations. Once you’ve identified some promising hybrids based on their consistency of performance, then concentrate on other important traits like resistance to important diseases in your area of the state.

Manage trash in no-till If you no-till corn on soils that are poorly drained, then you simply must strive to manage surface “trash” to enable drying / warming of surface soils, facilitate effective planter operation, and improve crop emergence / stand establishment. Aim to burn-down winter annual weeds or cover crops before their growth becomes unmanageable. Use row-cleaners on the planter units to remove a narrow band of “trash” from the seed furrow area. Avoid planting “on the wet side” in order to minimize the risk of furrow sidewall compaction or topside compaction.

Avoid soil compaction If you improve soil drainage, you will also minimize the risk of working or planting fields “on the wet side” and, therefore, the risk of creating soil compaction with tillage or other field operations that can limit root development.

12 — 2011 Integrated Crop Management Conference - Iowa State University Minimize the number of tillage trips, consider strip-till or no-till systems. Remember, though, that no-till or strip-till is not immune to the risk of soil compaction.

Continuous corn or not? Frankly, continuous corn simply does not yield as well as rotation corn. Numerous long-term rotation trials have documented this across a number of states. The yield drag is especially likely for no-till corn after corn. Folks who claim to do well with continuous corn are often fairly aggressive with their management of the stover from the previous crop. Corn stover delays the drying / warming of the soil and thus delays crop emergence and development. Corn stover (including old root balls) often interferes with planter operation, causing poor / uneven seed depth or seed-2-soil contact and thus causes delayed or uneven crop emergence. Decomposing corn stover immobilizes soil nitrogen early in the season and can retard corn growth and development early in the season until root development reaches a critical mass. Corn stover can intercept soil-applied herbicide and reduce the effectiveness of weed control. Finally, corn stover harbors inoculum of important diseases like gray leaf spot or Goss’ wilt. Any way you look at it, a continuous corn cropping system is fraught with challenges.

Starter fertilizer or not? Starter fertilizer, especially nitrogen, is important for maximizing corn yields in the eastern Corn Belt. I offer the following explanation and leave it to you to decide whether your situation is similar. A little background: Young corn plants depend heavily on stored kernel reserves until roughly the V3 stage of development (three leaves with visible leaf collars). At that point, the plants begin to “wean” themselves from dependence on the stored kernel reserves (which are playing out) to dependence on the developing nodal root system. If life up to that point has been hunky-dory, the transition to dependence on the nodal roots will go smoothly and the crop will continue to develop into a vigorous and uniform stand that will tolerate future stresses nicely. However, if conditions have been challenging during emergence and early stand establishment, then nodal root development has probably been stunted and the young plants will struggle to “wean” themselves from the kernel reserves. Consequently, the plants will appear to “stall out”, their development will become uneven, they will turn light green to yellow, and the resulting stand will not be as vigorous and uniform as you want. Such a stand of corn will likely continue to struggle the remainder of the season. It is the latter situation wherein a robust 2x2 starter fertilizer program will aid the young plants as they struggle in the transition to dependence on nodal roots. Our experience in the eastern Corn Belt suggests that starter nitrogen is the primary important nutrient and starter N rates should be no less than 20 to 30 lbs actual N per acre; perhaps higher than that for no-till continuous corn.

Nitrogen management Nitrogen management in the eastern Corn Belt is challenging because of our poorly drained soils, ample rainfall, and the risk of N loss by either denitrification or leaching. Consequently, yields are often lower than desired because of inadequate levels of soil N during the growing season, resulting in lower grain income for the grower. Alternatively, growers sometimes apply more N than the crop requires in an effort to mitigate the consequences of excessive N loss on the crop and, thus, incur higher crop production expenses. Best management practices that target the efficient use of nitrogen fertilizers in corn are well documented (Camberato et al., 2011; Sawyer, 2011) and include avoiding fall N applications, avoiding surface application of urea-based fertilizers without incorporation, and adopting sidedress N application programs where practical. These practices, plus the implementation of a robust starter fertilizer program, will help reduce the loss of soil N and maximize the bushels produced per pound of N fertilizer applied.

Disease management Warm, humid conditions typical of the eastern Corn Belt during the summer months are conducive for the development of several important foliar fungal corn diseases, including gray leaf spot and northern corn leaf blight. Goss’s Wilt, a potentially severe bacterial disease, has “migrated” into Indiana in recent years and represents a new challenge for growers in the eastern Corn Belt. Yield losses from these foliar corn diseases can easily decrease corn grain yields by 20% or more.


Best management practices that target efficient management of these important corn diseases are well documented (Wise; 2010a, 2010b, 2011) and include:

•• •• •• ••

Hybrid selection for good disease resistance characteristics. Avoiding continuous corn cropping systems. Avoiding no-till cropping systems. Responsible use of foliar fungicides (except for Goss’s Wilt)

Remember, it ain’t rocket science! It should be obvious at this point that achieving higher, more consistent yields does not require “rocket science”. Rather, we’re talking about a lot of common sense agronomic principles that work together to minimize the usual crop stresses that occur every year and allow the crop to better tolerate uncontrollable weather stresses. Other agronomic practices not discussed in this presentation include a sound weed control program that focuses on the use of residual herbicides and an attitude that you will aim to kill weeds when they are small. Make the effort to identify those yield limiting factors that are most important for your specific farming operation. This requires good crop detective skills and a sound understanding of agronomic principles. Together with your crop advisor(s), work toward identifying and implementing good agronomic management practices that target those yield limiting factors.

References Camberato, Jim, RL (Bob) Nielsen, Eric Miller, and Brad Joern. 2011. Nitrogen Management Guidelines for Indiana. Applied Crop Research Update, Purdue Extension. online at http://www.kingcorn.org/news/timeless/ NitrogenMgmt.pdf [URL accessed Oct 2011]. Elmore, Roger. 2011. Corn Production. Iowa State Univ. online at http://www.agronext.iastate.edu/corn [URL accessed Oct 2011]. Iowa State Univ. 2011. Iowa Crop Performance Tests. online at http://www.croptesting.iastate.edu [URL accessed Oct 2011]. Joern, Brad and Phil Hess. 2010. Irrigation Scheduler. Purdue Research Foundation. download online at http://www.agry.purdue.edu/irrigation [URL accessed Oct 2011]. Devillez, Phil. 2011. Purdue Crop Performance Program. Purdue Univ., online at http://www.ag.purdue.edu/agry/ PCPP/Pages/default.aspx [URL accessed Oct 2011]. NCGA. 2010. Winners Corn Yield Guide. National Corn Growers Association. online at http://www.ncga.com/ uploads/useruploads/ncyc2010.pdf [URL accessed Oct 2011]. Nielsen, RL (Bob). 2010. Hybrid Selection: Where’s the Beef? Corny News Network, Purdue Univ. online at http://www.agry.purdue.edu/ext/corn/news/timeless/HybridSeln.html [URL accessed Oct 2011]. Nielsen, RL (Bob). 2011. Chat ‘n Chew Cafe. Purdue Univ. online at http://www.kingcorn.org/cafe [URL accessed Oct 2011]. Nielsen, RL (Bob). 2011. Corny News Network Archives. Purdue Univ. online at http://www.kingcorn.org/news/ archive.html [URL accessed Oct 2011]. Nielsen, RL (Bob). 2011. State Extension Corn Specialists. Purdue Univ. online at http://www.kingcorn.org/experts/ CornSpec.html [URL accessed Oct 2011]. Nielsen, RL (Bob). 2011. State Extension Soybean Specialists. Purdue Univ. online at http://www.kingcorn.org/experts/ SoySpec.html [URL accessed Oct 2011]. Sawyer, John. 2011. Nitrogen; a sub-section of the Iowa State Univ Soil Fertility Web Site. online at http://www. agronext.iastate.edu/soilfertility/nutrienttopics/nitrogen.html [URL accessed Oct 2011]. USDA-NASS. 2011. QuickStats. United States Dept Agric – Nat’l Ag Statistics Service. Online at http://quickstats.nass.

14 — 2011 Integrated Crop Management Conference - Iowa State University usda.gov [URL accessed Oct 2011]. Wise, Kiersten. 2010a. Goss’s Bacterial Wilt and Leaf Blight. Purdue Extension publication BP-81-W. online at http:// www.extension.purdue.edu/extmedia/bp/BP-81-W.pdf [URL accessed Oct 2011]. Wise, Kiersten. 2010b. Gray Leaf Spot. Purdue Extension publication BP-56-W. online at http://www.extension. purdue.edu/extmedia/bp/BP-56-W.pdf [URL accessed Oct 2011]. Wise, Kiersten. 2011. Northern Corn Leaf Blight. Purdue Extension publication BP-84-W. online at http://www. extension.purdue.edu/extmedia/BP/BP-84-W.pdf [URL accessed Oct 2011].


Long silks, short pollen…a long year? Roger W. Elmore, professor and Extension corn agronomist, Agronomy, Iowa State University Corn harvest is nearly complete in Iowa as I write this, 19 days ahead of the 5-year normal and slightly behind that of last year (USDA-NASS, 2011a). Many farmers already report corn and soybean yields are “better than expected.” Does that mean the crop is turning out better than they expected at planting, in early July, in early August? It depends on the baseline. In early July I heard many talk about being in the ‘garden spot,’ things were looking really good! But then the straight-line winds of July 11th flattened corn across a wide strip of central, eastern and northeast Iowa. Later, hail and wind storms decimated more of our corn even into September. Then, with such a hot July we were very concerned about poor pollination (Elmore, 2011). Reports of long silks suggested we either were short on pollen or we had missed the ‘nick.’ The high temperatures certainly sped up crop development to where it was pushing growth stages faster than we would have liked. Of course, it could have been worse. Some fields were flooded out, some were dried out, many were badly lodged. Not surprisingly, 2011 yields are across the board from ‘lower than expected’ to ‘higher than expected.’ The current state yield forecast (USDA-NASS, 2011b) is for 169 bushels per acre. If realized, that is 4 bushels above last year but 8 below the 30-year trend line (Figure 1). The USDA expects 13,650,000 acres harvested, 600,000 more than last year, and 450,000 less than we planted.

Figure 1. Thirty-year corn yield trendline (tl) & 2011 October Forecast (fc), Iowa and U.S.A. from USDA-NASS, 2011b and previous years.

Yield variation Regional differences are obvious this year. For example, the current estimate of 178 bushels per acre as the average for the Northwest Iowa district is about 7 bushels below that of 2010 but the 135 bushel per acre estimate for Southeast

16 — 2011 Integrated Crop Management Conference - Iowa State University Iowa is 37 bushels above that of 2010!

Lessons from 2011 Is there anything we should take away from their 2011 corn growing experience? What can we learn from this year and do differently next year to try to improve their yield? There are always things to learn, I’m always on the learning curve. We need to keep thinking, comparing and learning year-to-year. This year with the extremely high heat in July, I’m not sure we could have avoided a yield reduction, even with good hybrid selection, management practices, etc. In any case, it’s wise to plant a diverse set of hybrids the crop silks at different times. That way you can avoid the consequences of a week or several days perhaps of stress occurring during the pollination period. But when we have three or four weeks of extremely hot weather like we did in July this year, there’s not much gained by having different silking dates resulting from different hybrids planted. They were all stressed! Nevertheless, always plant a diversity of corn hybrids, in order to spread out the silking dates and maturity dates. It may not help in a year like 2011, but there is a good chance it will in other years. “Better than expected…,” that’s something for which to be thankful. Let’s try to do what we can to do much better than expected next year!

References Elmore, R. 2011. Long silks? Integrated Crop Management News. Iowa State Univ. Extension. 9 August 2011. http://www.extension.iastate.edu/CropNews/2011/0729elmore.htm Elmore, R. and S. Taylor. 2011. August 2011 Iowa corn yield forecast. Iowa State Univ. Extension. 12 August 2011. http://www.extension.iastate.edu/CropNews/2011/0812elmoretaylor.htm Taylor, E. and R. Elmore. 2011. Weather impact on Midwest corn 2011. Integrated Crop Management News. Iowa State Univ. Extension. 29 July 2011. http://www.extension.iastate.edu/CropNews/2011/0809elmoretaylor.htm USDA-NASS. 2011a. Crops & Weather. 31 Oct. 2011. http://www.nass.usda.gov/Statistics_by_State/Iowa/Publications/Crop_Progress_&_Condition/2011/ Vol35__10_31_11.pdf USDA-NASS. 2011b. Crop Production. 12 October 2011. http://usda01.library.cornell.edu/usda/current/CropProd/CropProd-10-12-2011.pdf


Making silage from Iowa’s forage crops Stephen K. Barnhart, Extension forage agronomist, Agronomy, Iowa State University Proper ensiling is a controlled fermentation, which converts perishable wet forage plant material to a stable, stored feed energy source. Good ensiling management is required for high silage quality and dry matter (DM) recovery. To guide silage management practices, it is important to understand the biological and chemical processes that occur during ensiling, their effects on silage quality, and how these processes can be managed to help produce a more consistent feedstuff.

The ensiling process There are four phases during the ensiling process: Aerobic phase or the pre-seal management, fermentation phase, stable phase, and the feed-out phase.

Aerobic, pre-seal phase During the aerobic phase, forage is cut, chopped, moved to the site of ensiling, packed, and sealed. Management practices at each step will influence the success of the final ensiling. The management goal(s) during the aerobic phase is to store the chopped forage and create an anaerobic environment as soon as possible. In the presence of oxygen, plant and microbial respiration dominates, causing changes and nutrient losses from the chopped crop. Respiration is a necessary step, because it uses the oxygen trapped in the chopped forage material, but at the same time is a wasteful process, because it uses some of the plant sugars needed for further fermentation, thus, wasting some energy and dry matter (DM). An important, first step is to harvest the forage crop(s) at the proper time. In making this decision, several plant maturity-related and livestock needs factors must be considered. Table 1 provides descriptive harvest maturities for several commonly used forage crops. When harvested at these stages, there is generally a good compromise for yield and nutritive quality. Some of these corps can be chopped directly as a standing crop at these stages, some may require cutting, windrowing and wilting to a more appropriate whole plant moisture content before chopping. Table 1. Maturity stages at which commonly used forage crops are chopped for silage Crop

Stage of maturity

Corn

Proper ‘whole plant moisture’; or kernels at ¼ to 2/3 milk- line

Sorghum, grain and forage

Kernels at mid- to late-dough

Cereal grains

Late boot to early-flowering, or kernels at mid- to late-dough stage

Alfalfa

Late-bud to early-bloom

Red Clover

Late-bud to early bloom

Summer annual grasses

Late vegetative to late-boot

Grass mixtures, orchardgrass, smooth bromegrass, and timothy

Boot to early-heading

Legume - grass mixtures

Grasses at boot early-heading

The next important practice during pre-seal management is to chop the forage at the proper particle length. The recommended cutting length is 3/8 to 1/2 inch. Forage chopped in this particle size range packs well. When forage is too coarsely chopped, it is difficult to pack tightly, maintains excess trapped air, and allows respiration to continue for an extended period. Chopping too finely wastes fuel and may adversely affect the normal rumen function of cattle that eat the silage. Forage chopper knives are adjusted to cut at 3/8 to 1/2 inch, however, there will be some longer particles, which are actually useful in ruminant feeding.

18 — 2011 Integrated Crop Management Conference - Iowa State University To further reduce respiration losses during the aerobic phase, fill the silo or silage bag quickly, pack the chopped forage well, cover and seal the chopped material as soon as possible. If managed well, the aerobic phase will last about one day. The heat produced as a product by respiration raises silage temperature and increases the rate of microbial processes, both good (fermentation) and bad (respiration). A noticeable increase in temperature is normal, and it is not uncommon for 50 and 70 percent moisture forage to reaches a temperature as high as 115°F during ensiling. Forage chopped and stored at moisture contents lower than 50 percent is more difficult to pack, thus providing more oxygen for a longer period during this initial, aerobic phase. More oxygen generally results in temperatures above about 120°F which can lead to an undesirable high-temperature reactions that causes heat-damage-browning, and decreased silage protein and DM digestibility. Silage producers can reduce excessive respiration losses by chopping the forage crop at the appropriate (60 to 70 percent) moisture content. The appropriate moisture content is the same for all crops, but each forage crop being used will require slightly different growth stages or management to achieve the desirable moisture content.

Fermentation phase During the fermentation phase, the goal is for desirable bacteria to ferment sugars and carbohydrates to lactic acid, and to lower the pH of the ensiled forage to around 3.8-4.2, a level normally required for good quality silage. Processes during this phase occur under anaerobic (oxygen-free) conditions and should be dominated by growth of lactic acid-producing bacteria. This period lasts for two to four weeks. During the first days of ensiling, however, plant enzymes and acetic acid producing bacteria compete with lactic acid bacteria for sugars and proteins. Plant enzymes also break down some plant proteins to soluble non-protein nitrogen (NPN). Protein breakdown is highest during the first day after sealing and decreases rapidly as oxygen is used up. Very little protein breakdown occurs after one week under proper ensiling conditions. After ensiling, NPN in the silage can range from 20 percent to as much as 85 percent of total N. Fermentation is carried out by two main groups of lactic acid bacteria are homofermenters, which produce only lactic acid from sugar; and heterofermenters, which produce carbon dioxide, ethanol, acetic acid, and lactic acid. The homofermenters are the most desirable because their activity does not cause DM loss as do heterofermenters. High levels of less desirable acetic acid and ethanol reduce the palatability of silage and, thus, animal intake. Large numbers of lactic acid bacteria, and other types of bacteria, occur naturally on plants and grow under warm, humid conditions. As a result, corn and other forage crops, chopped at appropriate moisture contents, finish fermenting within 2 to 3 weeks. Fermentation occurs faster at silage mass temperatures between 80° and 100°F, but may require several more weeks if the chopped forage is < 50°F.

Stable phase When lactic acid bacteria have reduced the silage pH sufficiently to stop their growth (pH 4.0 - 4.2 or lower), the stable phase begins. As long as the silo remains sealed and anaerobic, little biological activity occurs during this period.

Feed-out phase After the silo is opened and during feed-out, the surface is reexposed to oxygen where yeast, mold, and aerobic bacteria can again degrade the silage. These organisms convert remaining plant sugars, lactic acid, or other energyrich nutrients in the silage to carbon dioxide, water, and heat. In addition, residual plant proteins can be converted to ammonia. Because fermentation acids can be broken down during aerobic spoilage, silage pH can increase to levels sometimes exceeding 7.0. Heating and a yeast aroma are the most common symptoms of aerobic deterioration of silages. Thus, feed-out spoilage causes increased DM losses, degraded feed, and a higher risk of toxic organisms and their spoilage products. When good feed-out management is practiced, aerobic feed-out losses are minimal. Recommended management is to remove a minimum of 2 to 3 inches of silage per day in the winter and 4 inches of silage per day in the summer from tower silos. For bunker silos, it is best to remove at least 4 inches per day in the winter and 6 to 10 inches per day from the silage surface in the summer. Also, feed silage to the livestock in small amounts two to four times per day instead of in one large feeding.


Silage additives Producers hear and read advertisements and promotions about products to help make better silage. To determine whether to use a silage additive or which one is best, it is important that you know how the additive influences silage fermentation. Remember that an effective additive may help make good silage a bit better, but it will not make poor silage good. The most commonly used silage additives can be divided into five categories: bacterial inoculants, nonprotein nitrogen (NPN) sources, and sugar sources.

Bacterial inoculants These are the most common silage additives in the United States and are primarily homofermenter lactic acid bacteria. Effectiveness of the applied inoculant depends on the natural lactic acid bacterial population, the sugar content of the crop, and strains of bacteria in the inoculant. The inoculant must provide at least a tenfold increase in the lactic acid bacteria numbers in the silo to be economically practical. Currently there is no method for quick determination of natural lactic acid bacteria numbers on the chopped crops. A common recommendation for the addition of inoculant lactic acid bacteria is to add a minimum of 100,000 colonyforming units (CFU) of lactic acid bacteria per gram of fresh forage. Inoculants are most consistently effective when the chopped forage has low numbers of naturally occurring bacteria, or when the chopped forage has low concentrations of fermentable sugars and carbohydrates, as is more often the case with chopped forage grasses and legumes, particularly when chopped at 70 percent moisture or higher. Some strains of a bacterial species have been selected for use on particular crops. Therefore, buy the inoculant product that is selected for the crop you are ensiling. If that is not possible, try a product for a similar crop within the same classification (i.e. legumes and grasses). A relatively new approach in silage inoculant additives is to include an inoculant to direct the fermentation, aid in preventing spoilage during feed-out, and to improve ‘feed bunk stability.’ The bacteria Lactobacilus buchneri has been demonstrated to improve aerobic stability of silages by reducing the growth of yeasts. The beneficial impact of L. buchneri appears to be related to the production of some acetic acid in addition to lactic acid during fermentation. Aerobic stability is likely improved because acetic acid inhibits growth of specific species of yeast that are responsible for heating and spoilage upon exposure to oxygen as compared to untreated silages. Treating silage with inoculants including L. buchneri most likely would be beneficial under circumstances where problems with aerobic instability are expected. Corn silage, small grain silage and high moisture corn are more susceptible to spoilage once exposed to air than legume or grass silage, and therefore L. buchneri inoculation may be a benefit.

Non-protein nitrogen sources (NPN) Both ammonia and urea are common additives for improving corn, sorghum, and other cereal silages with low protein concentrations. These additives are used to increase the total crude protein and NPN concentration of silage and to improve aerobic stability during feed-out. Application rates are typically 5 to 10 pounds of an hydrous ammonia or 10 to 20 pounds of urea per ton of fresh chopped forage. Addition of NPN can raise the pH of the crop, with ammonia having the greatest effect. Urea is preferred over ammonia because urea is safer and easier to handle since no special application equipment is required. NPN must be carefully managed in ruminant animal diets. Its feeding value varies and must be balanced with the other constituents in rations

Added carbohydrate sources Whey, molasses, and starchy cereal grains are sometimes used to improve preservation of low energy crops. Additions of 1 to 10 percent dried whey of fresh silage weight have been successful in improving fermentation of low sugar forage crops, such as alfalfa and grass. Molasses, applied at 2 to 5 percent of fresh silage weight, improves fermentation in high moisture (> 70 percent) crops and in crops with naturally low sugar content, such as alfalfa. The addition of molasses combined with an inoculant to a low sugar crop may improve conditions for fermentation of sugar to lactic acid.

20 — 2011 Integrated Crop Management Conference - Iowa State University When the ensiling process goes wrong! Ensiling is usually successful. However when important steps are mismanaged, it can lead to undesirable results. Plant material chopped too dry and inadequate packing can trap excess oxygen. As the aerobic phase stretches too long, some naturally occurring bacteria produce less lactic and more acetic acid and, This can also occur in the absence of enough sugars for proper fermentation. This condition can also occur when a silo is opened mid-way through the fermentation phase, as when a producer puts additional forage on the existing fermenting silage. Rexexposure to added oxygen can cause a gradual growth of undesirable bacteria, a reduction in lactic acid and increased acetic acid concentrations, reducing silage palatability Clostridium bacteria and other undesirable bacteria that may be present on the chopped crop can convert already formed lactic acid to foul smelling butyric acid and produce ammonia from plant protein. This is called a secondary fermentation, and is characterized by butyric acid levels greater than lactic acid levels, ammonia-N levels greater than 10 percent of total N, pH above 5.0, and a “rancid butter” odor. Clostridial fermentation may sometimes dominate in silage with a moisture content above 70 percent. Other problems can develop during the ‘stable phase’ if oxygen slowly enters through silo walls and through plastic covers. This can reactivate aerobic microorganisms. The growth of yeasts, molds, and other aerobic bacteria, including Listeria bacteria, grow in silage exposed to oxygen. Listeria can become a serious animal health concern.

Summary To achieve good silage fermentation, the crop must be harvested at the proper moisture (60 to 70 percent) level. Silage that is too wet causes seepage losses from the silage and growth of undesired microorganisms, which result in a less palatable feed for ruminants. Too dry (< 50 percent moisture) silage, however, increases DM losses due to respiration and heating and reduces the opportunity for lactic acid bacteria to grow. The key for successful ensiling is to chop the forage to a minimum cutting length of 3/8 to1/2 inch, pack the forage tightly in the silo, and seal the silo well to prevent air passages through covers and walls. When these conditions are met, silage quality can be further improved with silage additives. Bacterial inoculants can increase the number of lactic acid bacteria in the silage. The desirable lactic acid bacteria use sugar to produce lactic acid, which decreases pH to 4.0 to 4.2. A rapid pH drop results in stable, high quality silage. Fermentable sugar concentration can be raised with molasses, whey, or cereal grains. Non-protein nitrogen products are used in crops with low protein concentrations, such as corn and sorghum, to increase their crude protein level and to improve silage stability during feed-out.


Midwest crop weather 2011-2012: What follows a strong La Niña? Elwynn Taylor, professor and Extension climatologist, Agronomy, Iowa State University The abnormal 2011 weather for much of the Earth turned out very much as it had been during the previous La Niña events of like strength (1952-5/1974). Temperatures in the Midwest tended to alternate from warmer than usual for a week or two to colder than usual for a week or two through the Winter and the Spring. The winter was wet in Montana and dry in Texas. Melting snow brought floods (mainly to the Missouri river basin). Heat exacerbated the Texas drought. Early spring tornadoes brought death and destruction on a scale not known since the previously strong La Niña events. Wet conditions at planting threatened crop establishment and hot/dry spells in the summer reduced yield potentials. Tropical storms had favorable conditions to make landfall on the continental US. All in all 2011 was a year with extreme weather just as expected from previous Strong La Niña Year experience. The previous strong events weakened in late spring then strengthened to persist into a 2nd year leaving forecasters scrambling to discern if 2012 will be a “normal” year or a re-run of the past winter and spring.

• • • • • • • •

Subsoil moisture for Iowa in November 2011 was lower than during the past 3 years A strong La Niña was the likely cause The La Niña is expected to persist into March 2012 and perhaps longer Argentina drought risk is increased by La Niña La Niña Winters tend to be Wet in Montana, Dry in the Western Corn Belt, Wet in the East Winter may have extremely warm and extremely cold weeks as did the past winter. Summer drought risk is increased by low subsoil moisture in the Fall If La Niña continues into spring and summer drought risk is further increased.

References Long-lead weather forecasts are found at: http://www.cpc.ncep.noaa.gov/products/predictions/90day/ The La Niña / El Niño outlook is found at: http://www.esrl.noaa.gov/psd/enso/mei/ The temperature anomaly of the sea is found at: www.osdpd.noaa.gov/ml/ocean/sst/anomaly.html The current SOI is found at: http://www.longpaddock.qld.gov.au/ The US Drought map is found at: http://droughtmonitor.unl.edu/



Crop and biofuel outlook for 2012 Chad Hart, assistant professor and Extension economist, Economics, Iowa State University Crop agriculture has been on a roll. Corn and soybeans have provided positive returns three of the past four years. The 2011 crop year is shaping up to be the most profitable year on record. And futures prices for 2012 are offering sizable returns over projected production costs. So 2012 is shaping up to be an exciting market year for crop agriculture. The story over the past few years has been of large supplies, but even larger demands. While the 2011 crops are not as large as anticipated and the global economy continues to struggle, crop markets remain relatively strong. Biofuels have been the leading source of crop demand and new production platforms are being explored. Exports have been supportive, especially for soybeans, during the last three years. And livestock feed remains a critical part of the demand picture. The supply picture for 2011 has been weaker than hoped, but that weakness has supported prices. Corn area increased by 3.7 million acres in 2011. That should have boosted production, but pretty much every weather event that can lower corn yields has hit this corn crop in at least some part of the country. From floods and droughts to wind and hail to heat and frost, we have seen it all. Yields are off, even in comparison with last year. So 2011 corn production is roughly in line with 2010 production. Soybeans suffered through many of the same weather factors. That, combined with a drop in planted acreage, has put 2011 soybean production between 250 and 300 million bushels below last year. Despite the problems, both the corn and soybean crops in 2011 will be in the top 5 crops the U.S. has ever seen. The demand picture for 2011 has also been weaker than hoped. Global economic concerns press on the markets. The slide in crop prices throughout September was mainly driven by worries about the debt crisis in Europe and the effects a Greek default could have on other economies. These concerns not only hit the crop markets, but impacted stock, currency, and metal markets as well. The economic news through October has soothed the markets and crop prices have rebounded a little. For corn, the headline over the past year was the passing of the torch as ethanol passed domestic livestock feed as the #1 use of U.S. corn. Corn demand via ethanol topped the 5 billion mark for the 2010 crop. The outlook for the 2011 and 2012 corn crops suggests ethanol will continue to use roughly 5 billion bushels per year. While oil prices have had their ups and downs this year, overall the energy price pattern continues to support biofuel production. Based on ethanol production data, roughly 95 million bushels of corn are converted into ethanol each week. Figure 1 shows ethanol blending margins from January 2007 through October 2011 and margin projections based on futures prices out through mid-2014. The historical margins show that ethanol blending has been economically worthwhile for the vast majority of time over the past five years. And the projections indicate margins will remain positive even after the ethanol tax credit expires at the end of this year. For 2012, the keys for the ethanol industry will be the response of the industry to the loss of the tax credit and any movement on the introduction of E15 blends in the fuel sector. Corn feed and residual demand for the 2011 crop is projected at 4.7 billion bushels, as feed demand continues to shift lower. Returns to the livestock industry have been on the mend over the last couple of years. But the pattern has been a few months of profit followed by a few months of loss. Cattle production remains in decline, while hog and poultry production have returned to positive territory. A big issue for 2012 is price competition in feeds. Given corn’s relatively high price in comparison to other feeds, livestock feeders have moved to replace corn in part of the ration with lower cost feed. As Figure 2 shows, at the end of October wheat prices are actually below corn and remain close to corn over the next year. Normally, wheat futures run around $1.50 above corn futures. So wheat may be an attractive feed option for some U.S. livestock producers. We usually do not feed a lot of wheat, but other parts of the world do. So this same feed price competition is also affecting the corn export outlook.

24 — 2011 Integrated Crop Management Conference - Iowa State University 0.16 0.14 0.12

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Figure 1. Ethanol blending margins Corn export demand is estimated at 1.6 billion bushels, down significantly from last year. Weakness in the dollar supports the export outlook. But the feed competition and increases in worldwide corn production offset that effect. Figure 3 displays export sales so far this marketing year. Current corn export sales pace is just ahead of last year, as importing countries have taken advantage of the September price dip. Exports remain the big story for soybeans, especially exports to China. With China shifting some purchases to South America, USDA lowered its export estimate to 1.375 billion bushels. This is well below the record from the last couple of years, but is still a strong export amount. The early sales data definitely shows the slowdown in exports. As Figure 3 shows, current soybean exports are significantly lower. As of mid-October, sales were down to all of the top 5 soybean importing countries. Domestic crush demand is projected at 1.635 billion bushels, down just over 100 million from last year. USDA projections have domestic use of soybean oil on the increase, while export demand is expected to fall. Biodiesel demand for soybean oil will be a key variable to watch in 2012. Biodiesel production has surged in 2011. In fact, the latest monthly figures (for July) from the U.S. Department of Energy show record production in the U.S. USDA expects another surge in biodiesel production in 2012 as the industry ramps up to meet the biodiesel portion of the Renewable Fuels Standard. From their early October outlook, USDA had projected ending stocks for corn at 866 million bushels, over 250 million bushels less than last year. Soybean ending stocks were estimated at 160 million bushels, down 55 million bushels from last year. So U.S. ending stocks remain tight. Currently, USDA projects 2011/12 season-average prices at $6.70 for corn and $13.15 for soybeans. The futures markets have backed off from those levels though. Current futures prices (as of Oct. 28, 2010) point to 2011/12 season-average prices around $6.40 per bushel for corn and $12 per bushel for soybeans.


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26 — 2011 Integrated Crop Management Conference - Iowa State University With the sustained high prices for both crops, the acreage competition for 2012 should be interesting again. Corn looks to have the upper hand in the competition. Futures (as of Oct. 28) indicate 2012/13 season-average prices in the $6 range for corn and $12 range for soybeans. Crop input costs are headed up again, much like the scenario we saw in 2008 and 2009. With the prevented planting we saw last spring in the Dakotas and the eastern Corn Belt, we could see another sizable shift of land into corn production. Both corn and soybeans continue to offer significant positive returns. And corn is holding a roughly $150 per acre advantage on soybeans, about the same advantage as it had this time last year.

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Soybeans

Figure 4. Projections for 2012 season-average prices based on futures. As they stand right now, the 2011 and 2012 crop years look to be profitable ones for Iowa corn and soybeans. That would make it three profitable years in a row. As I wrote last year “With cash prices above $5 per bushel for corn and $11 per bushel for soybeans, there are strong marketing opportunities currently. And futures are showing strong marketing opportunities for both crops in the future as well.” That picture still holds. So as you prepare for 2012, analyze your production costs and take advantage of marketing opportunities that cover those costs and offer additional returns.


Sustainable production and distribution of bioenergy for the Central U.S. Chad Hart, assistant professor and Extension economist, Economics, Iowa State University Global demand for energy continues to increase as the planet’s population grows past 7 billion and incomes rise, especially in developing countries. The increasing demand for energy has spurred many countries to explore alternative energy platforms. Over 50 countries throughout the world have active bioenergy programs. The U.S. has moved to the front of this activity as we have grown to become the largest producer of biofuels and as we alternate between the world’s largest importer and exporter of ethanol. In 2007, the federal government provided a blueprint for biofuel development over the next decade with the Renewable Fuels Standard (RFS). Figure 1 shows the RFS and details targets for various types of renewable fuels. Looking forward over the next decade, the government is seeking significant expansion of cellulosic biofuels. The target for cellulosic biofuels expands from 250 million gallons in 2011 to 16 billion gallons in 2022.

40 35

Billion Gallons

30 25 20 15 10

2022

2021

2020

2019

2018

2017

2016

2015

2014

2013

2012

2011

2010

0

2009

5

Conventional Biofuels

Cellulosic Biofuels

Biodiesel

Additional Advanced Biofuels

Figure 1. Renewable fuels standard. As part of the government’s efforts to meet the RFS targets, USDA recently called for proposals to investigate the development of sustainable bioenergy platforms. Iowa State University and collaborators from several other states have been awarded funds for a project that will: 1) explore the feasibility of producing advanced transportation fuels derived from perennial grasses grown on land that is unsuitable or marginal for row crop production and 2) improve the sustainability of existing corn/soybean systems by reducing agricultural runoff of nutrients and soil and increasing carbon sequestration.

28 — 2011 Integrated Crop Management Conference - Iowa State University The project, known as CenUSA, is a multi-state and multi-disciplinary effort being led by Iowa State University Agronomy professor Ken Moore. Project activities will take place in Iowa, Indiana, Wisconsin, Minnesota, Nebraska, Illinois, Vermont and Idaho by researchers from Iowa State University, Purdue University, University of Illinois, University of Minnesota, University of Nebraska, University of Wisconsin, University of Vermont, Idaho National Laboratory and from USDA Agricultural Research Service offices in Wisconsin, Nebraska, Illinois, Pennsylvania, and Iowa.

Figure 2. CenUSA team.

CenUSA has 9 broad platforms within the project:

• • • • • • • • •

Feedstock Development Sustainable Production Systems Feedstock Logistics System Performance Feedstock Conversion Markets and Distribution Health and Safety Education Extension and Outreach

Each platform has specific goals. For feedstock development, the goal is to develop improved perennial grass cultivars and hybrids that can be used on marginal cropland in the Central U.S. for the production of biomass for bioenergy. Sustainable production systems are set to conduct comparative analyses of the productivity potential and the environmental impacts of promising bioenergy crops and management systems using a network of fields strategically located across the Central U.S. For feedstock logistics, the goal is to develop systems and strategies to enable sustainable and economic harvest, transportation, and storage of biomass feedstocks to meet the needs of the energy industry. The goal within system performance is to provide detailed analyses of feedstock production options to help policymakers, farmers, and the bioenergy industry make informed decisions about biomass production (amounts and locations); environmental impacts; and the interaction among biomass production, climate change, or other environmental shifts. In feedstock conversion, the goal is to perform a detailed economic analysis on the biorefinery performance using pyrolytic processing of biomass into liquid fuels and to provide biochar to researchers on the project. The markets and distributions platform will examine farm level adoption decisions, exploring the effectiveness of policy, market and contract mechanisms that facilitate broad scale voluntary adoption by farmers; and evaluate impacts of expanded advanced biofuel system on regional and global food, feed, energy and fiber markets. The health and safety platform will conduct a detailed analysis of all tasks associated with biomass production for hazard targets of personnel, equipment, environment, downtime, and product and will determine potentially


hazardous respiratory exposure limits associated with the production of biomass. The education platform will provide rich interdisciplinary training and engagement opportunities for undergraduate and graduate students in all areas of the bioenergy value chain to meet the workforce challenges of the bioeconomy. The extension and outreach platform will deliver science-based informational and educational programs for agricultural producers, general public, and youth audiences regarding perennial grass and biochar agriculture and biofuels production.

Figure 3. CenUSA grand vision.



Energy management for crop production H. Mark Hanna, Extension ag engineer, Agricultural and Biosystems Engineering, Iowa State University; Dana Petersen, program coordinator, ISU Farm Energy, Iowa State University

Introduction and overview Almost all direct energy used during field operations is consumed by an engine during operation of tractors or selfpropelled equipment such as combines, forage harvesters, or sprayers. Transmitting engine power as efficiently as possible for the task (pulling implements through soil, cutting plants, pumping, etc.) has significant effects on the amount of energy being used. Before investigating specific ways to increase efficiency during these tasks, a first question to ask is if the field operation is necessary. Increased fuel efficiency may gain five, ten, twenty percent or more whereas omitting the operation and leaving the tractor parked saves 100 percent of fuel. Some type of seeding, harvest, and weed or pest control operation is nearly always necessary. However, the type and frequency of tillage operations to prepare or weed a seedbed are often variable. Row crops such as corn or soybeans may be produced with one or no tillage passes prior to planting. Establishment of perennial alfalfa and small grains traditionally used primary and secondary tillage operations. New no-till seeders with better seed bed preparation and seed placement have resulted in yields equal to stand established using conventional tillage. Factors in choosing tillage operations include comfort with a specific management style along with local soil, crop, and weather conditions. Successful reduced and no-till operations are often found in the same neighborhood as fields with more aggressive tillage schemes suggesting that options to reduce tillage frequently exist. For example, although surface cornstalks from the previous year can appear daunting, no-till soybean yields are frequently equal to those of full-width tillage systems in yield trials. If tillage is required, consider using only a single-pass tillage system prior to planting. Strip-till systems till only a part of the field in the row zone for the subsequent crop to be planted. Ridge-till systems use row-crop cultivation for weed control to build ridges, then plant into the ridge the following year. Even when tilling the entire field area, consider why the tillage is being done and don’t till any deeper than necessary. For example, chisel plow operation at a six or eight inch depth requires less drawbar pull and tractor energy than operation of a subsoiler or ripper at depths of a foot or more. Drawbar pull is directly related to tillage depth for many specific tillage implements. Aggressive primary tillage operations such as a moldboard plow or subsoiler often require around 1.5 gallon diesel fuel per acre or more, whereas chisel plowing may require about 1 gallon per acre depending on depth, soil conditions, and speed. Other cultural or production schemes that generally increase efficiency also potentially reduce energy use for the amount of crop harvested. Narrow corn rows can help stimulate vegetative growth and increase potential harvested yield, particularly in northern areas of the Corn Belt. A leguminous cover crop can supply nitrogen to a subsequent crop, reducing the need for fertilizer nitrogen as well as field trips for transport and application.

Tractor use Because so many field operations are tractor-powered, special attention must be given to optimizing how tractor engine power is generated and transmitted for work. For higher horsepower tractors, many operations are drawbar work that involves pulling tillage and seeding implements through the soil. Efficient transfer of engine power through the tractor’s transmission, along with proper attention to ballasting and tire inflation, are important issues. Other tasks require transfer of engine power through the power-take-off (PTO) shaft (e.g. baling) or hydraulic or electrical systems (e.g., some spray pumps or planter seed metering drives). Taking time to assess how tractor engine power is being transferred and used for field operations allows focus on management strategies that can make a difference. Major areas affecting tractor fuel consumption include tractor selection, transmission, maintenance and ballasting/slip/tire inflation.

32 — 2011 Integrated Crop Management Conference - Iowa State University Tractor selection Although matching available tractor power to the task at hand is desirable, moving a smaller tractor several miles to perform a limited task usually does not save fuel. Diesel tractors are generally efficient in fuel use for partial loads of 75 percent or even 50 percent if the throttle is reduced and a higher gear selected. For example, tractor test data on the Case IH Magnum 275 show fuel use efficiency is not reduced (from 100 percent loading) at 75 percent drawbar load and reduced only 14 percent at 50 percent drawbar load. The fuel efficiency of a smaller tractor properly sized to handle the reduced load is often not great enough to justify moving unless the new application is only 10 – 30 percent of tractor power and involves significant hours of use. If a new or used tractor will be acquired, obtain and read Organization of Economic Cooperation and Development (OECD) tractor tests done at the Nebraska Tractor Test Laboratory for tractors being considered. Fuel use efficiency as measured in tests is listed as Hp-hr/gal under fuel consumption. Greater numbers indicate better fuel efficiency. Fuel efficiency values are listed for several levels of PTO and drawbar loading. Because tractor use is often at a partial load, using fuel efficiency from a 50 percent pull and reduced engine speed may serve as a good overall estimate. When comparing tractor models, compare fuel efficiency values with similar loading conditions. As with EPA automotive fuel efficiency estimates, fuel use will vary and depend on actual operation, but test values give an indication of relative efficiency between tractors.

Transmission If the tractor is using only part of its power when pulling a lighter drawbar load, significant fuel savings are possible by shifting the transmission up to a higher gear and pulling the throttle back (reducing engine RPM). Pulling a sprayer or a smaller field cultivator, disk, or planter that is not well matched to the total tractor power available are common examples. Unless the implement requires PTO operation at a specific engine speed, shifting up and throttling back to reduce engine speed saves fuel. Avoid lugging the engine by only reducing speed to a point somewhat above where the engine starts to lug. Some newer, higher-horsepower tractors manufactured in recent years offer infinitely or continuously variable transmissions using electronic control to automatically set the transmission at the most fuel efficient point for a given speed and drawbar load. Taking advantage of this new technology as a tractor is replaced saves fuel. An example of actual fuel savings can be found from an (OECD) tractor test done on a Case IH Magnum 275 rated at 227 hp. Fuel use at 75 percent of maximum drawbar power was reduced 8 percent when the transmission was shifted from 9th to 11th gear and engine speed was reduced from 2091 to 1589 rpm. In similar conditions, fuel use was reduced by 21 percent when only 50 percent of drawbar power was used. Average fuel savings as indicated by tractor tests from 1979 to 2002 indicate fuel savings of 13 percent at 75 percent load and 21 percent at 50 percent load are possible by reducing engine speed and operating in a higher gear (Grisso et al., 2004).

Maintenance Following a prescribed schedule for tractor maintenance is often a source of pride for agricultural tractor owners. Earlier studies with owner operators indicate that on average many operators are timely with maintenance and filter replacement. Still one study indicates that following scrupulous maintenance results in measurable savings. In a University of Missouri study 99 tractors were brought in to be tested “as is” at six locations in the state. Tractor horsepower was measured on a PTO dynamometer. Primary and secondary air and fuel filters were then replaced on each tractor before re-testing tractor power. Average engine horsepower increased 3.5 percent after filter replacement. Factory tractor specialists indicated such increase was normal and expected. In a check of maintenance records on the tractors, most operators were current on filter replacement. Although some were near the end of the service interval, others were near the beginning. Such results suggest that an average increase of 3.5 percent power can be easily obtained by being scrupulously vigilant on air and fuel filter replacement or setting the throttle/fuel supply back 3.5 percent to obtain the same engine power with less fuel. Researchers at the time (1988-9) estimated fuel savings to be 105 gallons of diesel annually per tractor tested. Increases in average engine horsepower since then suggest that vigilant tractor maintenance may save more than this depending on annual hours of tractor use.


Ballasting/slip/tire inflation Excessive wheel slippage during drawbar pull operations creates an obvious waste of labor, fuel, and tractor hours. Conversely, a tractor ballasted so heavily that there is little or no wheel slip sinks too far into the soil causing rolling resistance as the wheel tries to climb out of the track and extra energy use as tire sidewalls flex. Optimum wheel slip range for maximum tractive efficiency (equal to the ratio of drawbar power to power available at the drive axle) depends on surface conditions (Figure 1). Higher-horsepower tractors often have sensors allowing drive wheel slip to be monitored from the cab. Slip can be conveniently checked during fieldwork with significant drawbar loads. On tractors without slip measurement, slip can be approximated by measuring the distance a tractor covers during 10 wheel revolutions under drawbar load and comparing this with the distance traveled during 10 wheel revolutions without drawbar load. For example, if loaded wheel distance is 180 feet and unloaded wheel distance is 200 feet, the tractor under load is covering only 90 percent of the unloaded distance, or experiencing a 10 percent wheel slip. As a quick visual test, optimal wheel slip on soil usually occurs when wheel lug marks near the tire centerline are obliterated but lug marks at the outer edge are reasonably distinct.

Tractive efficiency, %

100 90 80

Concrete

70

Firm soil

60

Tilled soil Soft/sandy

50 40 0

10

20 30 Wheel slip, %

40

Figure 1. Tractive efficiency of transferring axle power to drawbar as affected by wheel slip for various surface conditions.

If wheel slip is outside the optimal range of about 9–15 percent (depending on soil conditions) or if there are questions regarding whether the tractor is ballasted properly to use power available from the engine, the tractor operation manual or various references can be checked for advice on ballasting (e.g.,Table 1). Specific amounts of total tractor weight per tractor horsepower are generally suggested depending on tractor style (two-wheel drive, front-wheel-assist, four-wheel drive) and operational speed. Tractors using faster field speeds (e.g. six to seven mi/h instead of four or five mi/h) have optimal fuel efficiency using slightly less weight as they don’t need to pull quite as much load to accomplish an equivalent amount of fieldwork in a given time. Because power is efficiently transferred from engine to drawbar over a

34 — 2011 Integrated Crop Management Conference - Iowa State University range of slip, some variation in weight is allowed. Because most tractors spend a significant amount of time requiring only 70 – 90 percent of rated power available, weight values in Figure 1 are near the low side of the appropriate range. Carrying extra ballast for unused horsepower during operations with light drawbar loads (e.g., pull-behind sprayer, mower/conditioner, or baler) results in small amounts of slip. If the tractor is used for long periods of time for light drawbar loads but has been optimally ballasted for full drawbar horsepower, consider removing ballast to avoid burning fuel to carry dead weight. Table 1. Gross tractor weight, lb/Hp Tractor type 2WD & MFD (lb/Hp) 4WD (lb/Hp)

5.5 110 90

Just as important as total tractor weight is splitting weight appropriately between front and rear axles. The correct percentage of total weight on each axle depends on tractor style (two-wheel drive, front-wheel-assist, four-wheel drive) and whether any rear implement weight is transferred to wheels on the rear axle (pull-type/mounted implement, significant tongue weight, etc., table 2). Table 2. Front-to-rear axle weight ratio as percentage of total weight. Towed/drawbar

Semi-mounted

Fully-mounted

%Front/%Rear

%Front/%Rear

%Front/%Rear

2WD

25/75

30/70

35/65

MFD

35/65

35/65

40/60

4WD

55/45

55/45

60/40

Tractor type

Tires should be correctly inflated for the load they carry to maximize the ability for lugs to engage soil and develop pull. Contrary to ensuring automotive tires are well inflated to minimize fuel consumption, off-road tires operating on soft soil surfaces increase pull by exposing more of the lug surface at lower tire pressure. Over-inflated tires can create excessive slip as lug surfaces near the tire sidewall do not penetrate the soil surface. Knowing weight carried by the front and rear axles when making ballasting decisions allows the weight carried by each tire to be known. Correct pressure can be determined from tire load and inflation tables of the tire manufacturer or in the tractor operation manual. Maintaining correct rather than ‘low’ pressure is important as under inflation causes premature tire failure.

Other issues Adding new technology such as auto-steering or auto-swath control for seed, pesticide, and fertilizer inputs can help to avoid wasting time and materials in the field. Auto-steering allows global positioning system (GPS) information to steer the tractor and avoid excessive overlap of swaths that wastes field time and energy. Auto-swath control allows sections across the implement swath to be turned off when previously treated areas would be overlapped. These technologies can be added to existing tractors and equipment but may be more cost effective to purchase as options as equipment is upgraded and replaced. Manufacturers are starting to embed this type of technology into new equipment, further decreasing prices. Cost for auto-steering can range from $5,000 to $50,000 depending on the accuracy desired. A recent study at Auburn University indicated input savings from one percent to 12 percent for each pass across a field when using automatic section control. This study indicated that, on average, a 4.3 percent savings on seed cost could be observed for a farm while some operations could see as high as a 7 percent savings. Savings are dependent upon field shape and size with the highest benefits occurring in small, irregular shaped fields or fields containing conservation management structures such as grass waterways and terraces. Generally, automatic section control technology can pay for itself within two years.


Modern diesel engines require less idling time to cool the engine. Recommendations for specific equipment can usually be found in the operation manual or through the dealer. Don’t let newer engines idle for periods of many minutes and waste fuel. Check with state regulatory officials regarding proper fuel storage. Vacuum/pressure relief valves protect fuel from water condensation. Reflective white or aluminum paint on the fuel supply barrel and supplemental shading from trees or buildings reduce fuel losses occurring due to evaporation. If an engine block heater is used to assist starting during cold weather, use a timer to avoid heating for many hours before start-up. A typical engine block heater can warm the engine up in about two hours. A low cost timer used to control swimming pool pumps can be used for most 120 volt heaters and pay for itself in about two months or less depending on the heater size and the amount of time currently being used. Diesel fuel mixtures are different for summer and winter. Don’t purchase fuel ahead in late summer if it can’t be used up before cold weather sets in. Use a fuel conditioner or fuel-line antifreeze in equipment that isn’t used much during the winter.

Other individual equipment operations Because a tractor powers most tillage, seeding, and many application operations and also because total energy available from the engine rapidly dissipates if there are significant losses in transmission, drives, and at the tire/soil interface, primary attention for energy saving should be done with the tractor. Look for ways to combine field operations into a single pass such as tilling and applying fertilizer with a strip-till implement or using one-pass tillage. Many individual points regarding saving energy with tillage, seeding, application, and other types of field equipment involve good management and maintenance practices to ensure a good field job is accomplished and avoid the need for another field pass. If objectives of the desired amount of seed, fertilizer, or pesticide being applied or soil tilled to a certain condition are not met, fuel and perhaps additional crop inputs are needed for a second pass. On tillage equipment, worn bearings, scrapers, or cutting edges affect soil manipulation and potentially draft (drawbar pull). Good planter operation involves a pre-field check of seed and fertilizer metering components along with in-field checks of seed placement, proper operation of soil-engaging components, and periodic lubrication.

For further information and references Field operations - general Svejkovsky, C. 2007. Conserving fuel on the farm. National Sustainable Agriculture Information Service/National Center for Appropriate Technology. Available at: http://attra.ncat.org/attra-pub/PDF/consfuelfarm.pdf Hanna, M., J. Harmon, and J. Flammang. 2010. Limiting field operations. Iowa State University Extension publication PM 2089D. Available at: http://www.extension.iastate.edu/Publications/PM2089D.pdf

Tractor - general Staton, M., T. Harrigan, and R. Turner. 2010. Improving tractor performance and fuel efficiency. Michigan State University Extension publication.

Tractor ballasting/slip/tire inflation Hanna, M., J. Harmon, and D. Petersen. 2010. Ballasting tractors for fuel efficiency. Iowa State University Extension publication PM 2089G. Available at: http://www.extension.iastate.edu/Publications/PM2089G.pdf

Tractor transmission Hanna, M., and D. Petersen. 2011. Tractor maintenance to conserve energy. Iowa State University Extension publication PM 2089L. Available at: http://www.extension.iastate.edu/Publications/PM2089L.pdf Sawyer, J. E., M. Hanna, and D. Petersen. 2011. Shift up and throttle back to save tractor fuel. Iowa State University Extension publication PM 2089M. Available at: http://www.extension.iastate.edu/Publications/PM2089M. pdf

36 — 2011 Integrated Crop Management Conference - Iowa State University Tractor selection Hanna, M., and D. Petersen. 2011. Fuel efficiency factors for tractor selection. Iowa State University Extension publication PM 2089O. Available at: http://www.extension.iastate.edu/Publications/PM2089O.pdf Download Nebraska Tractor Test Laboratory reports at: http://tractortestlab.unl.edu/index.htm

Other tractor issues Fulton, J., A Winstead and S Norwood. 2010. Automatic Section Control (ASC) Technology for Planters. Alabama Cooperative Extension System. Available at: http://www.aces.edu/anr/precisionag/Section_Control.php

No-till seeding Schneider, Nick. 2006. No-till Planting of Alfalfa with Italian Ryegrass, field research study report. University of Wisconsin. Available at http://winnebago.uwex.edu/ag/documents/ No-TillPlantingofAlfalfawithItalianRyegrass.pdf Duiker, S.W., J.C. Myers. 2006. Steps Towards a Successful Transition to No-Till. Pennsylvania State University Bulletin No. UC192.Available at: http://pubs.cas.psu.edu/FreePubs/pdfs/uc192.pdf Wolkowski, R.,T. Cox, J. Leverich. 2009. Strip-tillage: A conservation option for Wisconsin farmers. University of Wisconsin Extension Bulletin No. A3883. Available at: http://learningstore.uwex.edu/Assets/pdfs/A3883.pdf


Herbicide resistance in waterhemp: Past, present, and future Patrick J. Tranel, professor, Crop Sciences, University of Illinois at Urbana-Champaign

Introduction Over the last couple of decades, waterhemp has transitioned from being a relatively unknown weed species to one of the worst weeds in the Midwest (Steckel 2007). Its recent success as a weed can be attributed both to its biological characteristics and to changes in weed management practices (Costea et al. 2005). Notable biological characteristics of waterhemp include: rapid growth rate (in part due to its use of the C4 photosynthetic pathway), prolific seed production (up to or exceeding 500,000 seeds per plant), extended emergence period throughout much of the growing season, and dioecious reproductive habit. The latter – which means that plants are either male or female – ensures that plants outcross and, thus, increases genetic diversity of the species and effectively moves genes within and among populations. The adoption of no-tillage and reduced-tillage cropping systems has favored small-seeded weedy species, such as waterhemp; these small seeds germinate most effectively when they are at or near the soil surface. Further contributing to waterhemp’s success as a weed has been its ability to rapidly evolve resistance to various herbicides (Tranel et al. 2011). Its proclivity to evolve herbicide resistance can be attributed to its biological characteristics mentioned above. Of particular importance are high seed production and genetic diversity, which provide the raw materials on which selection can act. Couple the abundant waterhemp “raw material” (i.e., its high reproductive output and genetic diversity) with the intense selection pressure provided by herbicides, and the evolutionary outcome of herbicide-resistant waterhemp populations is not surprising. The problem of herbicide-resistant waterhemp is further exacerbated by waterhemp’s dioecious habit and the potential for long-distance dispersal of resistance via windborne pollen. Herbicide resistance easily moves between populations and can become “stacked” with other herbicide resistance traits, leading to populations with multiple herbicide resistance.

History of herbicide resistance in waterhemp Waterhemp has thus far evolved resistance to herbicides from five different site-of-action groups (Figure 1). The initial reports of herbicide-resistant waterhemp populations were to the triazine herbicides (PSII inhibitors) and the ALS inhibitors during the early 1990s. Subsequently, waterhemp populations were identified with resistance to the PPO inhibitors (e.g., the diphenylethers) and then to glyphosate. Recently, waterhemp populations with resistance to the HPPD inhibitors were identified in both Illinois and Iowa (Hausman et al. 2011; McMullan and Green 2011).


Figure 1. Timeline of resistance and multiple resistance to herbicides/herbicide groups in waterhemp (adapted from Tranel et al. 2011). The mechanisms by which waterhemp is resistant to the five different site-of-action groups are numerous and diverse (Table 1). In some cases, waterhemp exhibits different resistance mechanisms even within a particular herbicide siteof-action group. For example, resistance to triazine herbicides may be conferred by either a resistant target site or by enhanced herbicide detoxification. Similarly, although all known cases of resistance to ALS inhibitors in waterhemp are due to an altered target site, the specific mutation present within the target site may differ among resistant biotypes. Table 1. Mechanisms of herbicide resistance in waterhemp. Herbicide or group

Resistance mechanism(s)

Mutation

Resistant target site

Ser264Gly in D1 protein

Herbicide metabolism

Unknown

ALS inhibitors


Trp574Leu, Ser653Asn, or Ser653Thr in ALS

PPO inhibitors


Deletion of Gly210 in PPO2

Glyphosate

Target site amplification

Multiple genomic copies of EPSPS

HPPD inhibitors

Unknown

Unknown

Triazines

Multiple herbicide resistance in waterhemp Resistance in a weed species to a single herbicide (or to a group of herbicides with a common site of action) is cause for concern. However, this typically will not present an unmanageable problem in a major crop such as corn or soybean, because multiple herbicides are labeled for such crops and, thus, alternative chemical options are available. Unfortunately, for some of our most troublesome weeds, including waterhemp, we are increasingly encountering populations that possess multiple herbicide resistance. That is, these populations possess resistance to herbicides spanning multiple site-of-action groups. In fact, as can be seen in Figure 1, all new cases of herbicide resistance in waterhemp subsequent to resistance to triazines and the ALS inhibitors were cases of multiple herbicide resistance.


For example, the first population of waterhemp identified with resistance to the PPO inhibitors also was resistant to ALS inhibitors. The first glyphosate-resistant waterhemp population also had resistance to ALS and PPO inhibitors, and both waterhemp populations reported resistant to HPPD inhibitors also contained resistance to triazines and ALS inhibitors. In the most extreme case of multiple resistant waterhemp reported to date, a single population is resistant to triazines, ALS and PPO inhibitors, and to glyphosate (Tranel et al. 2011). Coworkers and I recently have conducted surveys to determine the extent of multiple herbicide resistance in waterhemp. We have asked producers to send us tissue samples from waterhemp plants suspected of being resistant to glyphosate. We then perform molecular tests on DNA from the tissue samples to determine if the plants are resistant to glyphosate, PPO inhibitors, and/or ALS inhibitors. We have focused on these three herbicide/herbicide groups since they represent the options for POST control of waterhemp in glyphosate-resistant soybean (and from a technical standpoint, availability of molecular tests for these three resistances enables rapid screening). Using this approach in 2010, glyphosate-resistant waterhemp was confirmed in 20 of 24 fields sampled. As expected, ALS resistant waterhemp was widespread among the fields. Less expected, however, was that a third of the fields were found to contain waterhemp resistant to PPO inhibitors. Not only was multiple herbicide resistance found at the field level, but, as depicted in Figure 2, multiple resistance also was found at the individual plant level. For example, 36% of the plants were resistant to glyphosate and ALS inhibitors, 9% were resistant to glyphosate and PPO inhibitors, and 7% were resistant to all three herbicide/herbicide groups. These data indicate that resistances to all of the major soybean POST herbicides are being stacked into individual waterhemp plants, which poses a serious threat to our ability to effectively manage this weed.

Figure 2. Venn diagram depicting the occurrence of multiple herbicide resistance to ALS inhibitors, PPO inhibitors, and glyphosate in waterhemp. The numbers indicate the percentage of plants resistant to one (in the non-overlapping part of each circle), two of the three (where two circles overlap) or all three (where the three circles overlap) of the herbicide/herbicide groups. Plant tissue from individual plants (122 total) was collected during 2010 from 24 fields suspected of containing glyphosate-resistant waterhemp. Resistant profiles of each sampled plant were determined from molecular tests. Thirteen percent of the plants were found to be sensitive to all three herbicides.

Future implications The consensus in the weed science industry is that herbicides with new sites of action are unlikely to be commercialized in the near future. Thus, we essentially will have to make do with our current arsenal of herbicides. Multiple-resistant waterhemp will continue to expand, both in frequency at which multiple-resistant populations occur, and in the number of herbicide/herbicide groups to which populations are resistant. For example, I fully expect that a waterhemp population with resistances to triazines, ALS, PPO, and HPPD inhibitors, and to glyphosate will be identified during the 2012 or 2013 growing season. It is also expected that waterhemp will evolve resistance to herbicides from additional site-of-action groups if such herbicides are relied upon extensively for waterhemp management. In fact, a very recent report suggests a waterhemp population in Nebraska has evolved resistance to 2,4-D (Bernards et al. 2011). If confirmed, this will represent the sixth site-of-action group to which waterhemp has evolved resistance.

40 — 2011 Integrated Crop Management Conference - Iowa State University Perhaps the most immediate impact of multiple-resistant waterhemp will be an end to the “one-size-fits-most” approach to weed management in the Midwest. The most effective and economical weed management strategies will vary from field to field, depending on the spectrum of resistant waterhemp biotypes present in a given field. In extreme cases, selective cultivation may have to augment chemical control. The occurrence of multiple-resistant waterhemp also will impact our ability to effectively implement resistance mitigation strategies for herbicides to which waterhemp has not already evolved resistance. For example, tank mixing herbicide A with herbicide B will not delay the evolution of resistance to herbicide B if the population is already resistant to herbicide A.

References Bernarnds, M., Crespo, J., Kruger, G., Gaussoin, R. 2011. 2,4-D resistant waterhemp found in Nebraska. CropWatch http://cropwatch.unl.edu/web/cropwatch/archive?articleID=4669108. Costea, M., Weaver, S. E., Tardif, F. J. 2005. The biology of invasive alien plants in Canada. 3. Amaranthus tuberculatus (Moq.) Sauer var. rudis (Sauer) Costea & Tardif. Canadian Journal of Plant Science 85:507-522. Hausman, N. E., Singh, S., Tranel, P. J., Riechers, D. E., Kaundun, S. S., Polge, N. D., Thomas, D. A., Hager, A. G. 2011. Resistance to HPPD-inhibiting herbicides in a population of waterhemp (Amaranthus tuberculatus) from Illinois, United States. Pest Management Science 67:258-261. McMullan, P. M., Green, J. M. 2011. Identification of a tall waterhemp (Amaranthus tuberculatus) biotype resistant to HPPD-inhibiting herbicides, atrazine, and thifensulfuron in Iowa. Weed Technology 25:514-518. Steckel, L. E. 2007. The dioecious Amaranthus spp.: here to stay. Weed Technology 21:567-570. Tranel, P. J., Riggins, C. W., Bell, M. S., Hager, A. G. 2011. Herbicide resistances in Amaranthus tuberculatus: a call for new options. Journal of Agricultural and Food Chemistry 59:5808-5812.


Weed management for 2012 Micheal D. K. Owen, professor and Extension weed specialist, Agronomy, Iowa State University

Introduction While there have not been many new things in weed control/management for 2012, some that have occurred are not necessarily good. Herbicide resistance, particularly in common waterhemp has escalated significantly for populations with evolved resistance to glyphosate and resistance to HPPD herbicides has predictably has been identified in a number of locations across Iowa. Unfortunately, again as predicted, no new “silver bullets” have surfaced and in fact, it is unlikely that new herbicide mechanisms of action will be introduced in the foreseeable future. Thus it comes that much more important to recognize the tactics that are available and establish a diverse long-term approach to using the tools in a sustainable manner.

“New” products and changes While there have not been any new products introduced for 2012 (at this time), there are several products pending registration, “new” generic herbicides and changes in herbicide labels. The following is a partial list of these changes; the inclusion of products should not be construed as an endorsement by Iowa State University or exclusion considered a lack of support.

Ignite (Bayer Crop Science) The Ignite label now describes a single application dose of up to 36 fluid ounces per acre. This application can be followed by one additional application of a maximum 29 fluid ounces per acre for a seasonal maximum Ignite application of 65 fluid ounces per acre. The Ignite applications to corn have not changed; the maximum amount of Ignite in any single application is 22 fluid ounces per acre with a seasonal total of 44 fluid ounces per acre.

Vida (Gowan) Vida (pyraflufen-ethyl) is an inhibitor of the PPO enzyme and a potent contact herbicide that can be applied to soybean and corn as a preplant burndown, at planting burndown and after planting burndown but prior to crop emergence for the control of many broadleaf weeds. Vida is now registered as a postemergence directed application in corn (conventional, glyphosate-tolerant, Liberty Link, popcorn, seed corn, corn silage, and corn stover). Sweet corn is not registered for a postemergence directed application. Refer to the label for specific restrictions and directions.

Flexstar GT 3.5 (Syngenta) Flexstar GT 3.5 is a different premixture formulation of fomesafen and glyphosate. This premixture contains 5.88% fomesafen and 22.4% glyphosate for a total of 0.56 pounds of fomesafen and 2.26 pounds (acid equivalent) of glyphosate per gallon product. The use rate in Iowa (Region 4) is 2.8 pints per acre.

Medal herbicides (Syngenta) Medal herbicides are a new S-metolachlor series of products with 7.62 pounds of active ingredient per acre (Medal and Medal EC), 7.64 pounds of active ingredient (Medal II and Medal II EC) and a premixture Medal II AT which is atrazine and S-metolachlor at 3.1 and 2.4 pounds active ingredient respectively.

Warrant (Monsanto) Warrant is an encapsulated formulation of acetochlor that is now labeled for application to field corn as a postemergence application. Applications can be made until the corn is 30 inches in height either broadcast or as a directed treatment (e.g. drop nozzles) to minimize interference of the crop with spray coverage. Warrant should be applied prior to weed emergence and will provide residual control of annual grasses and some small-seeded annual broadleaf weeds.

Roundup Ready Plus weed management solutions (Monsanto) Monsanto has partnered with a number of companies to improve weed management in glyphosate-resistant corn and soybean and has incentivized the addition of products other than their proprietary herbicides to provide stewardship

42 — 2011 Integrated Crop Management Conference - Iowa State University to glyphosate and the trait. Additions to the previously listed products are Cobra/Phoenix in soybean and Impact in corn.

Basis Blend (DuPont) Basis Blend is a premixture of rimsulfuron (20%) and thifensulfuron (10%) which is suggested to be a better formulation that is easier to handle, mix and clean out of the sprayers than Basis 75% DF. Basis Blend can be applied any time after harvest but prior to ground freeze-up. It can be applied with other herbicides (e.g. 2,4-D) and is registered for application to fields that wil be planted to corn or soybean.

Valor (Valent) Valor has a modification of the label that describes planting corn seven days after application in no tillage and minimum tillage production systems.

Pyroxasulfone (several) Pyroxasulfone is a “new” product that has been included in the ISU herbicide research program for many years under the KIH-485 description. Considerable research was conducted on corn and soybean and a variety of application timings (e.g. early preplant) and rates were included in this extensive evaluation series (www.weeds.iastate.edu/ research/default.htm). Pyroxasulfone was first included in the ISU research program in 2003 as a 3.57 SC formulation and was a Kumiai experimental product. This herbicide is an inhibitor of very long chain fatty acids similar to the mechanism of action demonstrated by S-metolachlor and acetochlor (Group 15). Agreements have been made with BASF, FMC and Valent to market pyroxasulfone in different proprietary products, either alone or in combination with other herbicides. These registrations are pending.

New genetically engineered traits (several) The development of new genetically engineered (GE) crop traits continues with regard to dicamba-tolerant soybean (Monsanto) and the DHT soybean and corn (Dow AgroSciences). According to these companies, these new crop traits are on track for commercialization mid-decade. There has been considerable discussion about the utility of these traits and labeled herbicides as tools to better manage weeds, particularly those weeds (e.g. common waterhemp) that have evolved resistance to glyphosate. Currently, there are concerns about the movement of the herbicides used in these GE crops to sensitive crops (e.g. grapes) and also whether or not the use of the systems will result in new resistant weed biotypes. The companies are expending considerable time and money developing robust stewardship programs and use guidelines in an attempt to proactively mitigate these concerns. However, it is critically important for growers and applicators to recognize that the adoption of crop systems based on these technologies have concomitant risks and limitations; they do not represent the new “silver bullet” as some uninformed people have been suggesting. The development of Optimum GAT crops has been delayed indefinitely according to DuPont.

New herbicide resistant weed concerns New herbicide resistant weed biotypes have been identified in Iowa and the Midwest and weed biotypes with multiple resistances are increasing. HPPD-resistant waterhemp was identified in 2010 in Southeast Iowa in a seed corn production field. Since then, numerous seed corn production fields with putative HPPD resistant common waterhemp have come to the attention of ISU. Extensive infield research was established in 2011 and research efforts are escalating for 2012. The evolution of HPPD resistance in seed corn production fields can be attributable to the intensity of HPPD use in these fields and the identified problems ascribed to the level of observation and management in the seed production fields. Importantly, given the strategies used in seed corn production, multiple resistances to glyphosate have also been identified in the weed populations under investigation. It is assumed that the extent of HPPD resistance in Iowa, given the likely movement of the resistance trait via pollen, is greater than in just seed corn production fields but masked in commercial production fields. The occurrence of HPPD resistance in seed corn fields is not unlike the canaries in the mines which were used to detect problems for the miners. ISU will continue to monitor HPPD resistance in Iowa common waterhemp populations is conduct research to describe solutions to the problem. Glyphosate resistance in Iowa common waterhemp, as predicted, has increased dramatically in 2011 and is widely distributed across the state. Through collaboration and support from the Iowa Soybean Association, an extensive


collection of field weed populations has been cataloged and these populations will be evaluated for evolved resistance to glyphosate and the other herbicide mechanisms of action commonly used in Iowa. A previous collection of approximately 200 common waterhemp populations selected arbitrarily three years ago was evaluated in the greenhouse for response to glyphosate; approximately 1/3 of those populations were not effectively controlled by glyphosate. It is anticipated that the percentage of Iowa common waterhemp populations with evolved resistance to glyphosate has increased considerably. Furthermore, populations with resistance to PPO inhibitors are also becoming more common. Note that Nebraska recently announced the identification of a population of common waterhemp with resistance to 2,4-D. While common waterhemp is the weed about which most Iowa growers and applicators are concerned, issues with herbicide resistant giant ragweed and horseweed/marestail are also escalating. It is clear that the systems currently used for the production of corn and soybean in Iowa, specifically for weeds, is problematic and inevitably will fail unless changes (other than different herbicides) are included soon.

Weed management tactics: Knowledge and diversity The need for better information is paramount for effective weed management; simplicity and convenience as experienced during the last 16 years of glyphosate-resistant crop systems has run the course and integrated weed management is necessary for the protection of crop yields, the mitigation of existing herbicide resistant weed issues and the proactive tactics needed to keep additional herbicide resistant weed populations from evolving. Unfortunately, while many (and possibly a majority) growers understand that herbicide resistant weeds are an increasing problem, they seem to still be in denial; they fail to recognize that the problem likely exists “close to home” and that action to manage the problem is needed immediately. Recall that typically a weed population must have about 30% of the individuals with evolved resistance to a herbicide before a grower recognizes that the issue exists. The information that must be acquired includes a cursory understanding about weed biology and ecology, the herbicide resistance(s) that are likely to evolve or have evolved, and what tactics are effective to manage these weeds. Part of the problem is the marketing of herbicides; many companies are now describing premixtures of products that include more than one herbicide mechanism of action. The concept of multiple mechanisms of herbicide action effectively helping control herbicide resistant weeds and delay the evolution of future herbicide resistances has gained some traction with growers. However, without better knowledge of the mechanisms of action that are in the premixtures, the marketing of these products is misleading at best. Consider that most of the premixtures available for soybeans includes a PPO herbicide and the other product is an ALS inhibitor herbicide; given that common waterhemp in Iowa already evolved ALS resistance, these products have only one effective mechanism of action and thus do not represent an effective resistance management program. While redundancy of tactics (multiple herbicide mechanisms of action in each application) is an important strategy, the herbicides included must have activity on the target weeds. Another strategy that has gained acceptance for herbicide resistant weed management is the rotation of herbicide mechanism of action. Indeed, this can be the start of a herbicide resistant weed management program, but if that is the only tactic used, herbicide resistance will be delayed one year for every year of herbicide mechanism of action rotation but resistance will inevitably evolve. Another common strategy that is marketed is the need for multiple herbicide mechanisms of action in a weed management program. This typically is established by using different herbicides for sequential applications. Unfortunately, the use of this strategy is diminished as it is the last herbicide applied that imparts the selection for resistance. Again, the most effective way to resolve this problem is to use multiple mechanisms for every herbicide application timing. The most important consideration for weed management in crop production, whether herbicide resistant weed populations exist or not, is the need for diversity in weed management strategies. If diverse strategies beyond simply adding different herbicides are not included, the crop system may not be sustainable. History has proven time and again that herbicide-based weed management will inevitably fail. Mechanical and cultural strategies need to be included in a crop production system. The greater the diversity, the more ecologically sound and economically profitable the crop production system will be. Herbicides will continue to be a key feature of Iowa corn and soybean production, but without other integrated weed management (IWM) strategies, weed management will soon become increasing difficult and crop yields will dramatically decline.

44 — 2011 Integrated Crop Management Conference - Iowa State University Conclusions The future of weed management in the relatively near future is better utilization of existing technologies and the inclusion of older herbicide chemistries (when and where appropriate) and mechanical and cultural tactics. The key to profitable and sustainable weed management is diversity. If a diverse suite of weed management tactics is not used, economic losses attributable to weeds will escalate and herbicide resistant weed populations will become more widely distributed. No new herbicide mechanisms of action have been identified for the short and longer term future. While new herbicide-resistant crop traits may possibly become available in the three to five year future, these traits are not the answers to existing weed management concerns; they are good tools for weed control but must be used in an appropriate fashion to maximize the benefits and minimize the risks.


Herbicide-resistant weeds: An evolving problem of importance in Iowa crop production Micheal D. K. Owen, professor and extension weed specialist, Agronomy, Iowa State University

Introduction The changes in Iowa agriculture over the last three decades have been monumental and the implications of these changes often overlooked during the course of developing the plans for next year. Consider that in the 1970’s, aggressive tillage predominated the production systems in Iowa, conservation tillage was an interesting but not generally practiced idea and herbicides had to be mechanically incorporated into the soil. In the 1980’s, the acetolactate synthase (ALS) inhibiting herbicide families were introduced. The imidazolinone and sulfonyl urea herbicide families were applied to an estimated 90% of the soybean acres and more than 65% of the corn acres. In many instances, these herbicides were applied repeatedly on fields during the year and certainly recurrently from year to year. Despite warnings that this production practice would result in significant problems (e.g. evolved ALS-resistant weed biotypes), commercial agriculture continued with the unsustainable practice of using one type of herbicide exclusively and the inevitable resistant weed problem evolved as predicted. By the time glyphosate-resistant (GR) crops were introduced, ALS resistance was widespread and much of the utility of these important products had been lost. However, the GR crop technologies and concomitant use of glyphosate became available and adoption in global agriculture was unprecedented. Importantly, the trends toward conservation tillage practices were strongly supported by the “new” system. Usage of glyphosate rose to the point that there were no other herbicides used on more than 10% of the soybean acres and only atrazine continued to demonstrate a strong presence in corn (Young, 2006). Once again, naysayers suggested that because the GR-based crop production systems were essentially devoid of diversity for weed management, glyphosate-resistant weeds would evolve (Owen, 1997). These warnings were again unheeded and the inevitable resistant weeds did indeed evolve to the extent that the GR technologies are threatened. Unfortunately, this time, given the unprecedented adoption of GR-based crop systems and glyphosate utilization, the industry had essentially withdrawn from herbicide discovery and development such that no new answers would come forward. Given the dire straits that currently exist in weed management, now is the time to objectively review the sustainability of the system and determine if perhaps it is time to change perspectives on a more diverse management plan for weeds.

What are the options? In Iowa corn and soybean production, there are a number of effective, but sparingly utilized, tools and tactics available to manage the ever increasing herbicide resistant weed problem. This is unlike the situation in the Mississippi Delta and Southeastern states where cotton production is threatened (Culpepper and York, 2007). The rhetorical question as to why the plethora of tools and tactics available to Iowa agriculture have not been used, even when it was correctly suggested that the evolution of GR weeds was inevitable, is a function of demographic changes in agriculture (i.e. size of farms and time availability) as well as a desire for the convenience and simplicity that the GR crop-based systems provided (Owen et al., 2009; Owen et al., 2010). Growers continued to maintain a position of denial that these ever increasing problems would ever impact their farms; it should now be clear that the problems are here and changes must occur now or potentially Iowa agriculture will experience the same severe consequences that growers in Georgia are now facing.

Herbicide options There are numerous “alternate” herbicides that can help resolve the glyphosate resistance in weeds. “Alternate” is another way of saying “old” and these established herbicides are indeed useful if properly included in a longer-term weed management plan. The list of herbicides currently registered for corn and soybean is long and represented by a number of herbicide families and mechanisms of action (MOA). Generally, the more herbicide diversity that is included in a long term weed management plan, the better. However, many of these herbicides have already been improperly used and thus have selected for resistant weed biotypes. Thus, the simple inclusion of other herbicides

46 — 2011 Integrated Crop Management Conference - Iowa State University will not necessarily resolve weed management problems. A partial list of available “alternate” herbicides is presented in Table 1. Table 1. Corn

Soybean

Atrazine

Sencor

Prowl (and others)

Prowl (and others)

Balance Flexx

Authority (and others)

Callisto (and others)

Pursuit

Sharpen

Valor (and others)

Basis

Cobra (and others)

Dual (and others)

Warrant (and others)

Banvel, Clarity

Basagran

2,4-D

Select (and others)

Ignite

Ignite

The point is not to list all the available “alternate” herbicides but rather to provide an indication of the number and diversity of products available for weed control in corn and soybean. There are also a number of premixtures available and often these products are advertised as effective strategies to manage herbicide resistant weeds. Be advised however, that many of these products contain herbicides for which weeds have already evolved resistance (i.e. ALS herbicides and common waterhemp). Thus it is critically important to identify the preexisting weed resistances in the field and also to know the specific MOA of the herbicides under consideration.

Herbicide use concepts The concept of herbicide rotation of MOA has gained considerable traction in Iowa agriculture. While rotation of herbicide MOA is a tactic that can help mitigate the evolution of herbicide resistance, it has, over time, limited utility. Consider the recent identification of HPPD-resistant common waterhemp in a seed corn production field; the company rotated herbicide MOA but still selected for resistance (McMullan and Green, 2011). Again, the more diversity in herbicide use, the better the weed management in the longer-term. Another option is to incorporate other available crop technologies with the herbicide options. The inclusion of the glufosinate-resistant crops and glufosinate as a topically applied herbicide is an excellent option to manage many herbicide-resistant weed biotypes that are present in Iowa crop systems. Proper use of glufosinate is important; recognize that the application requirements are different than those for glyphosate and thus it is important to closely follow the requirements to optimize the weed control provided by the trait/herbicide combination in a diverse weed management system. However, the inclusion of the trait/herbicide combination will inevitably result in the same fate as glyphosate if it is the only adjustment towards a more diverse system made by growers. Consider that resistance to glufosinate has been identified (Heap, 2011). An important herbicide use tactic that has benefits is the inclusion of different herbicide MOA each year. The doctrine of “start clean” reflects the importance of using a soil-applied herbicide that provides residual weed control. This application strategy is typically supplemented by another herbicide with a different MOA applied topically to the crop and weed. However, the relative importance of the soil-applied herbicide for the mitigation of herbicide resistance in weeds is overshadowed by the importance to deter the early season interference of weeds on the crop thus protecting potential yield. No herbicide, despite the advertising rhetoric, will provide season-long weed control. Thus, when another herbicide MOA is applied to another cohort of recently-emerged weeds in the crop, it is that herbicide MOA that selects for resistance and the soil-applied herbicide MOA has limited resistance management value in this scenario. The best strategy for using multiple herbicide MOA is to make each application of herbicides redundant. Redundancy in this context suggests that more than one herbicide MOA should be included each time an herbicide application is made. Again, simplicity is not a consideration when choosing the candidate herbicides; an understanding of existing


resistances in the field, the specific MOA of the herbicides and the need to have diversity in MOA for the overall system must be a core principle of the choices. Furthermore, only considering year to year herbicide diversity is shortsighted. A longer-term herbicide use plan, focusing on a diversity of herbicide MOA and application tactics, must be developed. However, if a change in herbicides use is the only strategy that is included in an attempt to diversify crop production systems and weed management, weed management and thus the crop production system will inevitably fail (Owen, 2011).

Diverse strategies An objective assessment of weed management should make it very clear that herbicide-based systems are destined to ultimately fail. Simple and convenient is a mantra that must be forgotten and while time use considerations are a major factor that has guided agriculture to that which is simple and convenient, more diverse weed management must be included. As suggested, while the need of new “widgets” is important for the short-term, greater diversity in the Iowa crop production system must be established for the long term sustainability of weed management. The primary objection to increasing diversity in weed management appears to be the inability of growers to fully appreciate the consequences of not diversifying the production system. This objection is closely followed by concerns for the time the diverse tactics require. Finally, according to the author, another important objection is the fact that the “institutional knowledge” on how to manage weeds without focusing solely on glyphosate is lacking. Diversity includes, but is not limited to crop rotation, tillage, cover crops, other cultural strategies and mechanical control. A more complete list of tactics and a discussion on the need for diversity is available (Green, 2011; Green and Owen, 2011). The key to a diverse weed management program is a basic understanding of the biology of the system, the interactions of weeds and crops, and a truly objective assessment of the production system (Knezevic et al., 2002; Swanton and Weise, 1991). Integrated weed management (IWM) is crucial to the sustainability of agriculture and diversity of tactics is the basis of IWM. A reasonable objection to the adoption of IWM is time availability. For example the inability to cultivate several thousand acres of row crops because of the time requirement is a real and rational objection. However, consider that growers do not typically use the same corn hybrid on all the acres under their management. Similarly, it is not a common practice to use the same fertility program on every field. The reasons for these examples of production diversity are intuitively obvious; the diversity exhibited by these production decisions minimize risks and maximize economic benefits. The same strategies of managing fields in the smallest unit should be included for IWM; cultivate only the fields that require this tactic and use a diversity of herbicides and crop technologies on individual fields. The greater the diversity in an IWM program, the greater the environmental, economic and ecological benefits.

Conclusions It should be clear to anyone who reviews the historic perspectives of weed control objectively that the system is not working. Weeds have evolved resistance to all of the available herbicide MOA. Many weeds have evolved multiple resistances; consider that common waterhemp populations have evolved resistance to glyphosate, ALS herbicides, triazine herbicides, PPO herbicides, HPPD herbicides and most recently, 2,4-D. Specific populations of common waterhemp in Illinois have multiple resistances to five herbicide MOA and in Iowa, all common waterhemp should be considered resistant to all ALS herbicides. While herbicides will continue to be the primary tactic to selectively control weeds in row crops, if only herbicides are used, weeds will inevitably adapt to the tactic and weed control will fail. There is a need to change the crop production systems and more specifically, how weeds are managed. Diversity is the key to economic, environmental and ecological sustainability in weed management and thus crop production, regardless of the lack of simplicity and convenience.

References Culpepper, A. S., and York, A. C. Glyphosate-resistant Palmer amaranth impacts Southeast agriculture. Pages 61-63 in Proceedings of the Illinois Crop Protection Technology Conference. Champaign, IL: University of Illinois Urbana-Champaign. Green, J. M. 2011. Outlook on weed management in herbicide-resistant crops: need for diversification. Outlooks on Pest Management 22: 100-104.

48 — 2011 Integrated Crop Management Conference - Iowa State University Green, J. M., and Owen, M. D. K. 2011. Herbicide-resistant crops: Utilities and limitations for herbicide-resistant weed management. Journal of Agricultural and Food Chemistry 59: 5819-5829. Heap, I. 2011. The international survey of herbicide resistant weeds. Available at www.weedscience.com. Accessed 21 October 2011. Knezevic, S. Z., Evans, S. P., Blankenship, E. E., Van Acker, R. C., and Lindquist, J. L. 2002. Critical period for weed control: the concept and data analysis. Weed Science 50: 773-786. McMullan, P. M., and Green, J. M. 2011. Indentification of a tall waterhemp (Amaranthus tuberculatus) biotype resistant to HPPD-inhibiting herbicides, atrazine and thifensulfuron in Iowa. Weed Technology 25: 514518. Owen, M., Boerboom, C., and Sprague, C. Convenience and Simplicity? An illusion and a detriment to integrated weed management. Pages 127 in Proceedings of the 6th International IPM Symposium. Portland, Oregon. Owen, M., Dixon, P., Shaw, D., Weller, S., Young, B., Wilson, R., and Jordan, D. 2010. Sustainability of glyphosatebased weed management: The Benchmark Study. Pages 1-4 Information Systems for Biotechnology. Blacksburg, VA 24061: Virgina Tech. Owen, M. D. K. 1997. Risks and benefits of weed management technologies. Pages 291-297 in R. De Prado, J. Jorrin, and L. Garcia-Torres, ed. Weed and crop resistance to herbicides. London: Kluwer Academic Publishers. Owen, M. D. K. 2011. Weed resistance development and management in herbicide-tolerant crops: experiences from the USA. Journal of Consumer Protection and Food Safety 6: 85-89. Swanton, C. J., and Weise, S. F. 1991. Integrated weed managment: the rationale and approach. Weed Technology 5: 648-656. Young, B. G. 2006. Changes in herbicide use patterns and production practices resulting from glyphosate-resistant crops. Weed Technology 20: 301-307.


A reintroduction to soil applied herbicides Bob Hartzler, professor and Extension weed specialist, Agronomy, Iowa State University Although the growth regulator herbicides (2,4-D; dicamba, etc.) were responsible for ushering in the chemical era of weed control in the late 1940’s, it was the introduction of the triazine, dinitroaniline and amide herbicides that transformed weed control in corn and soybean. These products were the backbone of weed control systems until the mid-80’s when the introduction of ALS inhibitors and other postemergence products provided more consistent postemergence weed control. The introduction of glyphosate resistant crops in the late 1990’s completed the transition from soil-applied to postemergence programs for the majority of Cornbelt farmers. The heavy reliance on glyphosate for over a decade has created a situation where soil-applied products will once again be an essential component of weed management systems due to herbicide resistance. This paper will discuss factors that influence the performance of soil-applied products for those who have little experience with these products, or simply need a refresher. Preemergence herbicides are most effective when they are absorbed by weed seeds initiating the germination process; however, only a small portion of the applied herbicide actually is taken up by the intended target. The majority of herbicide degrades within the field, but a portion of the herbicide may be lost from the field due to leaching, runoff, or volatilization. The ultimate fate of an herbicide is largely dictated by adsorption of the herbicide molecules to soil colloids.

Herbicide adsorption to soil colloids There are two pools of herbicides present in the soil: the larger pool is the herbicide bound to soil colloids, the smaller pool is the herbicide that is dissolved in the soil water. An equilibrium (the percentage of herbicide present in each pool) is maintained between these two pools, thus herbicide molecules are able to move back and forth (sorption:desorption) between the two pools as herbicide is lost from one of the pools. The equilibrium is determined primarily by the adsorptive capacity of the soil and the chemical characteristics of the herbicide. Since only the herbicide in the soil solution is available to plants, a basic knowledge of herbicide adsorption is essential to understand the behavior and performance of preemergence herbicides. Although adsorption places the majority of herbicide into a ‘bank’ where it cannot be immediately absorbed by weeds, it is critical since it maintains the majority of herbicide near the soil surface where weed seeds germinate, and adsorption protects groundwater from herbicide leaching through the profile.

Soil factors influencing adsorption The adsorptive capacity of a soil is determined by its clay and organic matter content. For most Iowa soils, organic matter is responsible for the majority of herbicide binding. It is important to distinguish between the different types of soil organic matter found in soil. Herbicides bind to the highly degraded, stable forms of organic matter referred to as humic matter or humic acids. The humic acid content of a soil is usually closely related to the organic matter content. Crop residue present on the soil surface in conservation tillage systems or mixed within the soil profile by tillage is not involved in the binding of soil-applied herbicides. Herbicide rates found on the product label take into account herbicide adsorption and are designed to insure that sufficient herbicide is present in the soil solution to control susceptible weeds. Rates of soil applied herbicides generally increase as clay and organic matter increase. For example, the recommended rate for Dual II Magnum increases approximately 10% for each 1% increase in soil organic matter. Many herbicide labels prohibit use on high organic matter soils, such as peats, due to inactivation of herbicide by excessive binding of the herbicide to the soil. Herbicides with a low margin of crop safety often prohibit use on soils with low adsorptive capacity due to the potential for crop injury due to high availability of the herbicide within the soil. Soil pH influences binding of herbicides that are classified as basic chemical compounds (versus acidic or non-ionic compounds). These molecules have a neutral or positive charge depending on the soil pH. In neutral or basic soils (pH ≥ 7) a basic herbicide will have a neutral charge, whereas under acidic soil conditions (pH < 7) the herbicide takes on a positive charge. Due to the positive charge on the molecule in acid soils, basic herbicides are more tightly bound to soil colloids in soils with a low pH. The triazine herbicides are the primary examples of herbicides with a basic nature. The metribuzin label warns that use of the product on soils with pH of 7.5 or higher may result in crop injury. The

50 — 2011 Integrated Crop Management Conference - Iowa State University increased risk of injury in alkaline soils is due to the greater amount of herbicide in soil solution.

Herbicide factors influencing adsorption The degree of soil adsorption of a herbicide is determined by its chemical characteristics. The sorption coefficient (K) is a measure of the tendency for an herbicide to be adsorbed by the soil. It is usually expressed either as Kd or Koc. The K value for an herbicide will vary among soils due to the different binding capacity of soils. The Koc is adjusted for the organic matter content of a soil, whereas the Kd takes into account binding to clay and organic matter. The K values determined on different soils or under different laboratory conditions will vary somewhat, but they are still very useful in predicting herbicide behavior. A simple description of the K value is that it is a ratio of the herbicide bound to soil colloids to the herbicide present in the soil solution. K=

Herbicide (soil) Herbicide (water)

Thus an herbicide that has a high K value will have a high percentage of the herbicide bound to soil colloids, and thus less is dissolved in the soil solution where it would be available for absorption by plants. Herbicides with low K values have more of the herbicide in the soil solution, thus have greater availability to plants and are more mobile in the soil profile. A second parameter that can influence herbicide behavior is an herbicide’s water solubility; however, water solubility usually is relatively insignificant compared to the sorption coefficient. Initially this may not seem logical since the fraction of herbicide dissolved in soil water is responsible for herbicide activity. Consider that most herbicides are applied at a pound or less per acre and that an acre inch of water weighs approximately 220,000 lbs. For most herbicides, water solubility is not a limiting factor due to the large volume of water present in the soil compared to the low rate that herbicides are applied. The sorption coefficient helps explain the performance of herbicides applied to the soil (Table 2). Both glyphosate and paraquat have very high K values compared to other herbicides. Neither product has significant soil activity since they are bound so tightly to soil colloids that they are unavailable to plants. The labels of both products state that the use of water containing soil sediments as a carrier will reduce performance due to inactivation of the herbicide by binding to the colloids. Pendimethalin has a high Koc compared to other preemergence herbicides, which explains why it requires more rainfall to provide consistent control than herbicides with lower sorption coefficients. Dicamba has one of the lowest sorption coefficients of commonly used herbicides. Although dicamba is registered for preemergence use in corn, applications made prior to germination of the corn seed have a relatively high risk of crop injury due to dicamba’s mobility in the soil. Applications made before or shortly after corn planting may allow dicamba to reach the depth of the corn seed and be absorbed as the seed imbibes water and result in damage to the seedling. Table 2. Chemical properties of several herbicides. Common name

Tradename

Koc

H2O Solubility (ppm)

acetochlor

Harness

156

282

atrazine

Aatrex

100

35

dicamba

Banvel/Clarity

2

250,000

glyphosate

Roundup

24,000

10,500

mesotrione

Callisto

122

160

metolachlor

Dual

200

530

paraquat

Gramoxone

1,000,000

620,000

pendimethalin

Prowl

17581

0.33

Source: WSSA Herbicide Handbook; IUPAC Pesticide Properties Database

Environmental factors influencing adsorption Since adsorption is a physical process, temperatures within the range experienced in the field have little impact on binding of herbicides to soil colloids. Rainfall impacts herbicide


performance by facilitating movement in the soil profile (leaching) and by influencing soil moisture content. As soil moisture decreases the film of water surrounding soil particles becomes thinner, resulting in less volume to dissolve herbicide molecules and greater adsorption to soil colloids. Preemergence herbicides are less active during periods when soil moisture is limiting.

Absorption by plants To be effective, preemergence herbicides must be present in the soil solution surrounding weed seeds as the seed initiates germination. Thus, an herbicide must be positioned within the soil profile at the depth of weed establishment. Since most weeds have small seeds, the majority of seeds germinate in the upper inch of the soil profile. The term activation is commonly used to describe movement of a soil-applied herbicide from the soil surface into the soil profile. For most situations, a half inch rain is sufficient to move the chemical to the soil depth required for effective weed control. However, the rainfall required for activation will increase slightly with increasing adsorptive capacity of the soil and sorption coefficient of the herbicide. In addition, more rainfall will be needed in situations where an herbicide is applied to a very dry soil. With the exception of the dinitroaniline herbicides (pendimethalin, trifluralin), differences in the sorption coefficient (K) of commonly used preemergence herbicides are not sufficient to result in significant differences in the amount of rain required for activation. Herbicide absorption from the soil is a passive process. The initial step in seed germination is imbibition of water from the soil. Herbicide molecules present in the soil solution are carried into the seed with the water. Since weeds are most vulnerable to preemergence herbicides just as they initiate germination, having the herbicide present in the germination zone at this time is critical. Herbicide applications made at planting generally are dependent upon rainfall within three to five days to ensure effective control of weeds that germinate shortly after planting and herbicide application. A few preemergence herbicides can be absorbed by roots of emerged seedlings and provide control of established plants. This phenomenon typically occurs when weeds are able to establish due to dry conditions that minimize herbicide availability. Rain shortly after the weeds emerge releases herbicide bound to soil colloids into the soil solution, allowing absorption of the herbicide by the established weeds. It takes higher concentrations of herbicides to kill established weeds than a germinating seed, thus chemicals with low K values and the ability to translocate within the plant are more likely to kill established seedlings than herbicides without these characteristics. The bleaching herbicides (HPPD inhibitors) are promoted for their ability to control established plants through ‘recharge’, whereas amide type and dinitroaniline herbicides have little effect on emerged weeds. While the ability to control emerged weeds can on occasion improve weed control, this type of activity is much less consistent than an herbicide acting on a germinating seeds. Thus fields with escaped weeds should be monitored closely to determine the need for remedial control measures. Herbicide degradation The persistence of an herbicide is typically described in terms of half-life (t½), the time required for 50% of the herbicide present in the soil to break down. Herbicides begin to degrade as soon as they are introduced in the environment, but the rate of breakdown varies widely among chemicals and environmental conditions (Figure 1). In this example, the half-life for the chemicalwas 5 weeks under favorable conditions, but increased to 9 weeks under unfavorable conditions. The primary factors that influence degradation rate are soil characteristics, temperature and rainfall. Herbicides may be broken down by chemical or biological mechanisms, or both. Biological degradation is more responsive to environmental factors than chemical processes. The range of soil temperatures encountered during the growing season typically do not have a major influence on degradation rates, but extended dry periods can result in prolonged persistence of a herbicide. Ideally a preemergence chemical could be applied in early spring and would control weeds until the crop canopy closes. After that it would dissipate quickly so that it would not interfere with future cropping plans or move into water resources or other areas where it is not wanted. Unfortunately, the dynamics of herbicide degradation and environmental variability prevent such a simple solution to weed management. The initial rate of degradation in spring is relatively rapid compared to degradation rates later in the season. This is due to a combination of greater initial herbicide availability and more favorable conditions for biological degradation in the spring (temperature, moisture) than occurs later in the season. Since herbicide degradation rates slow as the season progresses, a product that persists long enough to provide full-season weed control may pose a threat to susceptible rotational crops the following growing season.


Figure 1.

Soil pH influences degradation rates of several herbicides that are used in Iowa corn and soybean production. The persistance of atrazine and chlorimuron increases with soil pH, and this limits their use in areas of the state with alkaline soils due to carryover risks to rotational crops. Atrazine degrades more rapidly when bound to soil colloids, thus the greater availability of atrazine in high pH soils increases the half-life of the chemical. Chlorimuron and other sulfonylurea herbicides are degraded by both chemical and biological processes in acidic or neutral soils, with chemical hydrolysis being the most important mechanism. In alkaline soils, only biological degradation is involved and the persistence is greatly increased. Like atrazine, mesotrione binds to soil colloids less under alkaline conditions; however, mesotrione breaks down more rapidly when in solution than when bound to colloids. Thus, mesotrione is more persistent under alkaline conditions. The imidazolinone herbicides (Pursuit, Scepter) also have increased persistence in acid soils.

Application timing impacts on herbicide performance Preemergence herbicides can be applied over an extended period of time, from fall applications made more than six months prior to crop planting, until after the crop has emerged. The primary influence of application timing is in determining the time period when the herbicide will be present at effective concentrations in the soil. Application timing also influences the probability of the herbicide being activated by rainfall before weeds become established. Several preemergence herbicides are registered for fall applications. Fall applications are most appropriate for controlling winter annual weeds such as marestail/horseweed, field pennycress and henbit in no-till fields. Fall applications can also control early-emerging summer annuals; however, degradation of the product between application and establishment of the crop significantly reduces the length of in-season weed control. The only advantage of fall applications for inseason weed control is eliminating a field operation in the spring, thus the benefit of this strategy should be carefully evaluated. The potential success of this approach increases as one moves north in the state due to the longer winter which reduces the time the herbicide is vulnerable to degradation. Early preplant applications (EPP) are made several weeks ahead of planting. This strategy increases the probability that the herbicide will be moved into the soil profile by rainfall before annual weeds begin to germinate compared to at planting applications. EPP generally require higher use rates than applications made at planting to provide equivalent periods of weed control. The difference in length of control between EPP and at planting applications is magnified when planting is delayed due to wet springs. A factor to consider with EPP treatments is the impact of final seedbed preparation and planting operations on the distribution of the herbicide within the soil profile. In systems where tillage is used to prepare the seedbed after the EPP has been made, improper tillage can either leave a streaky pattern of herbicide across the field or place the herbicide too deep within the profile, effectively diluting the chemical to


non-effective concentrations. Planters that move significant amounts of soil from the row can displace the herbicide, leaving an unprotected strip within the row for weeds to establish. Preemergence applications made within a few days of planting provide the greatest likelihood of full-season weed control since the herbicide is placed in the field when it is needed. It is important to provide the crop with an even start with weeds, so any emerged weeds present at planting should be killed as close to planting as possible. The primary disadvantage of at planting applications is the need for timely rainfall to activate the herbicide. Assuming soils have reached temperatures favorable for germination at planting, failure to receive activating rainfall within three to five days of application may allow early germinating weeds to escape control. In no-till where burndown herbicides are used to kill established weeds rather than tillage, the window for rainfall is narrower due to the lack of soil disturbance to kill weeds that have initiated germination but have yet to emerge. Fields should be monitored closely when limited rainfall following application increases the likelihood of escapes. Rotary hoeing can be effective at reducing control failures due to lack of timely rain, but this tillage operation needs to be completed before weeds have emerged to be most effective. Many preemergence herbicides allow application after the crop has emerged, but some products prohibit this use due to foliar activity that can result in crop injury. Preemergence herbicides applied after planting extend the period of weed control later into the growing season than applications made earlier in the season. This extended control can be valuable for weeds with prolonged emergence periods such as waterhemp. Since these applications are often made during peak weed emergence periods, lack of activating rain soon after application can result in inconsistent performance.

Crop injury In the era of Roundup Ready crops, farmers have become accustomed to herbicides that have a large margin of crop safety. Although most preemergence herbicides used today have less risk of significant injury than some that were used in the past, there is the potential for adverse crop response with many products. The factors that influence this risk are: 1) crop tolerance to the herbicide, 2) soil characteristics, and 3) environmental conditions. Each herbicide has a specific margin of safety on an individual crop, and ratings of crop tolerance to herbicides are provided by most land grant universities. Certain herbicide formulations include a safener that enhances tolerance. ‘Safened’ products include Dual II Magnum, Harness, Balance Flexx, etc. There can be varietal differences within a crop, but these differences are usually relatively small compared to the other factors that determine crop response. The adsorptive capacity of a soil often influences crop response due to increased availability of the herbicide in soils with a low affinity for herbicides. Some products recommend not using the product on soils with low adsorptive capacity due to injury risk. The rate structure specified on herbicide labels is designed to avoid overwhelming the crops tolerance mechanisms, but variability of soil types within a field often makes it difficult to adjust rates accurately according to soil type. Environmental conditions influence both the availability of the herbicide and a crop’s tolerance mechanisms. Excess soil moisture increases the availability of the herbicide by increasing the amount of herbicide in soil solution. Herbicide selectivity normally is achieved by differential metabolism: the crop is able to metabolize the herbicide more rapidly than weeds, thus the weed dies due to toxic concentrations accumulating within the plant, whereas the crop detoxifies the herbicide before it is harmed by the herbicide. When a crop is under stress due to weather, disease, exposure to other chemicals, or other factors its ability to metabolize the herbicide may be compromised. A reduced rate of metabolism can allow the herbicide to reach toxic concentrations within the plant. Determining the impact of injury on yield potential is difficult. Since preemergence herbicides cause injury early in the season, plants often have time to recover from the setback and yields will not be reduced unless significant stand loss occurs.

Summary Preemergence herbicides will play an increasingly important role in weed management due to the evolution of glyphosate resistant weeds, either to reduce the risk of these weeds invading fields or to manage resistant populations. The keys to successful preemergence weed control are: 1) select a product that is effective against the weeds present in the field, 2) select a rate that is appropriate for the target weeds and soil properties of the field, and 3) apply the

54 — 2011 Integrated Crop Management Conference - Iowa State University herbicide uniformly across the field and at an appropriate time. The availability of the herbicide within the soil profile determines the effectiveness of weed control and the risk of crop injury. Thus, knowing the soil characteristics of the field and the adsorptive characteristics of the herbicide is critical in diagnosing problems with performance of soilapplied herbicides.


Diversified weed management tactics in diversified cropping systems: Foundations for durable crop production and protection Matt Liebman, professor and H.A. Wallace Chair for Sustainable Agriculture, Agronomy, Iowa State University One of the key questions facing Iowa’s agricultural community is how to produce sufficient amounts of food and farm income while improving and protecting environmental quality. Because synthetic fertilizers and pesticides constitute important expenses in Iowa farming systems (Duffy 2011; National Agricultural Statistics Service 2011) and because their use can be linked to environmental damage (U.S. Geological Survey 1999; Dinnes et al. 2002; Gilliom et al. 2006), learning how to reduce reliance on these materials without compromising farm productivity and profitability is a key priority for Iowa and other parts of the U.S. Corn Belt. Fossil energy costs associated with farming have increased over the last decade and reducing reliance on non-renewable energy sources is also an important priority for improving profitability (Economic Research Service 2008). With regard to biological challenges to productivity and profitability, weed resistance to commonly used herbicides, including glyphosate, is a growing problem in Iowa and other Corn Belt states (Heap 2011; Tranel et al. 2011). Addressing weed resistance effectively will require approaches that integrate multiple control tactics (Beckie 2006). To address these issues and other related challenges, a 22-acre field experiment was initiated in 2001 at the Iowa State University Marsden Farm in Boone Co., IA. The experiment is designed to test the hypothesis that diversifying a corn-soybean rotation with small grain and forage crops can maintain or improve yields, weed suppression, and profitability, while allowing large reductions in chemical inputs. In addition to a conventionally managed 2-year cornsoybean rotation, the experiment includes a 3-year corn-soybean-small grain + red clover rotation, and a 4-year cornsoybean-small grain + alfalfa-alfalfa rotation. After uniformly cropping the site with oat in 2001 and tuning the three rotation systems in 2002, intensive data collection began in 2003. Spring triticale was used as the small grain in 2003-2005, whereas oat was used in 20062010. During 2003-2010, manure was applied before corn production in the 3-year and 4-year rotations at a mean dry matter rate of 4 tons acre-1, providing a mean of 106 lb N acre-1 once every three years in the 3-year rotation system, and once every four years in the 4-year rotation. Corn in the 2-year rotation received 100 lb N acre-1 as urea at planting, whereas corn in the 3-year and 4-year rotations did not. The late spring nitrate test (Blackmer et al. 1997) was used to determine rates for post-emergence side-dress N applications (as urea ammonium nitrate) for corn in all rotation systems. Weed management in the 2-year rotation was based largely on herbicides applied at conventional rates. In the 3-year and 4-year systems, herbicides were applied in 15-inch-wide bands over corn and soybean rows rather than broadcast, greater reliance was placed on cultivation, and no herbicides were applied in small grain and forage legume crops. Choices of herbicides used in each system were based on the identities, densities, and sizes of weed species observed in the plots. Sampling procedures and other details of farming practices used in the different cropping systems during 2003-2010 are described in Liebman et al. (2008), Cruse et al. (2010), and Gómez et al. (in review). Over the years 2003-2010, synthetic N fertilizer use was 76% and 84% lower in the 3-year and 4-year rotation systems, respectively, than in the 2-year rotation; similarly herbicide use was reduced 85% and 89% in the 3-year and 4-year rotation systems, respectively, relative to the 2-year rotation (Table 1). Over the period 2007-2010, reductions in N fertilizer and herbicide use were greater: compared with the 2-year rotation system, fertilizer N use was 89% and 93% lower in the 3-year and 4-year systems, respectively, and herbicides inputs were 96% and 97% lower in the 3-year and 4-year systems. The conventional 2-year system used the largest amount of fossil fuel energy, the 4-year system used the least, and the 3-year system was intermediate (Table 1). Gas for drying corn grain, fertilizer, and fuel for farm machinery were responsible for the majority of fossil energy consumption (Cruse et al. 2010).

56 — 2011 Integrated Crop Management Conference - Iowa State University Table 1. Inputs, crop yields, weed dry mater production, net returns, and selected soil characteristics for the three cropping systems in the Marsden Farm rotation experiment, Boone Co., IA. Within rows, means followed by different letters are significantly different (P < 0.05); means not followed by letters are statistically equivalent. Data are from Liebman et al. (2008), Cruse et al. (2010), Gómez et al. (in review), and Wander and Lazicki (unpublished).

Cropping system 2-year rotation: Corn-soybean

3-year rotation: Corn-soybeansmall grain†/ red clover

4-year rotation: Corn-soybeansmall grain†/ alfalfa-alfalfa

Fertilizer N inputs, lb N acre-1 year-1 (2003-2010)

68 a

16 b

11 c

Herbicide inputs, lb a.i. acre-1 year-1 (2003-2010)

1.71 a

0.25 b

0.19 c

Fossil energy inputs, barrels of oil equivalent acre-1 year-1 (2003-2008)

1.06 a

0.63 b

0.47 c

Labor requirements, hr acre-1 year-1 (2003-2010)

0.73 c

1.13 b

1.42 a

Net returns to land and management‡, $ acre-1 year-1 (2003-2010)

279

286

284

Corn, bu acre-1 (2003-2010)

194 b

200 a

203 a

Soybean, bu acre-1 (2003-2010)

51 b

55 a

57 a

Small grain†, tons acre-1 (2003-2010)

–––

1.7

1.7

Alfalfa, tons acre-1 (2003-2010)

–––

–––

4.0

In corn, lb acre-1 (2003-2010)

1.8

4.1

3.3

In soybean, lb acre-1 (2003-2010)

1.3

3.4

3.2

Particulate organic matter-C, mg C cm-3 soil, 0-20 cm depth (2009)

2.0 b

2.3 a

2.2 a

Potentially mineralizable N, mg N cm-3 soil, 0-20 cm depth (2009)

33.9 b

39.4 a

39.3 a

Whole rotation

Crop yields

Weed dry matter production

Soil characteristics

† Triticale was grown as the small grain crop in 2003-2005; oat was used in 2006-2010. ‡ Crop subsidy payments were not included as sources of revenue. Despite large reductions in N fertilizer, herbicide, and fossil fuel inputs, corn and soybean yields were higher in the more diverse systems than in the conventional corn-soybean system (Table 1). Weed dry matter production in corn and soybean was low (< 5 lb acre-1) in all systems (Table 1). Weed seed densities in the soil declined in all of the rotation systems during 2003-2010, indicating that reductions in herbicide inputs were not contributing to a build-


up of long-term weed problems. In 2010, when soybean sudden death syndrome was prevalent in central Iowa, the incidence and severity of the disease were lower in the 3-year and 4-year rotations than in the 2-year rotation. Soil particulate organic matter carbon concentrations were significantly greater in the 3-year and 4-year rotation systems than in the conventional 2-year system (Table 1), suggesting that soil organic carbon is increasing in the more diverse rotation systems. Soil potentially mineralizable nitrogen levels were also higher in the 3-year and 4-year rotations than in the 2-year rotation (Table 1), indicating that the more diverse rotation systems had greater capacity to supply crops with N. Net returns to land and management for 2003-2010 were essentially equivalent for the three rotation systems, with the diversified 3-year and 4-year systems providing a few dollars more than the conventional 2-year system (Table 1). Labor requirements increased with increases in rotation length, but labor costs were only a small fraction of total production costs. Energy gain in crop products per unit of fossil fuel energy invested and net economic returns per unit of fossil energy input were greatest in the 4-year system, least in the 2-year system, and intermediate in the 3-year system. Taken together, results of this study indicate that diversified crop rotation systems can produce high yields of corn and soybean, suppress weeds effectively, and improve soil quality, while substantially reducing requirements for synthetic N fertilizer, herbicides, and fossil energy. The mixture of chemical, mechanical, and cultural weed control tactics used in the 3-year and 4-year rotation systems is likely to retard the evolution of herbicide resistance in weeds and provide more options for effective control over the long term.

References Beckie, H.J. 2006. Herbicide-resistant weeds: management tactics and practices. Weed Technology 20: 793-814. Blackmer, A.M., R.D. Voss, and A.P. Mallorino. 1997. Nitrogen fertilizer recommendations for corn in Iowa. Publication PM-1714. Iowa State University Extension, Ames, IA. On-line at: http://www.extension.iastate. edu/Publications/PM1714.pdf. Dinnes, D.L., D.L. Karlen, D.B. Jaynes, T.C. Kaspar, J.L. Hatfield, T.S. Colvin, and C.A. Cambardella. Nitrogen management strategies to reduce nitrate leaching in tile-drained Midwestern soils. Agronomy Journal 94:153-171. Duffy, M. 2011. Estimated crop production costs in Iowa—2011. Iowa State University Extension, Ames, IA. Online at: http://www.extension.iastate.edu/publications/fm1712.pdf. Cruse, M.J., M. Liebman, D.R. Raman, and M. Wiedenhoeft. 2010. Fossil energy use in conventional and lowexternal-input cropping systems. Agronomy Journal 102: 934-941. Economic Research Service. 2008. Agricultural projections to 2017. USDA-Economic Research Service, Washington, DC. On-line at: http://www.ers.usda.gov/Publications/OCE081. Gilliom, R.J., J.E. Barbash, C.G. Crawford, P.A. Hamilton, J.D. Martin, N. Nakagaki, L.H. Nowell, J.C. Scott, P.E. Stackelberg, G.P. Thelin, and D.M. Wolock. 2006. The quality of our nation’s waters: pesticides in the nation’s streams and ground water, 1992-2001. Circular 1291. U.S. Department of Interior and U.S. Geological Survey, Reston, VA. On-line at: http://pubs.usgs.gov/circ/2005/1291/. Gómez, R., M. Liebman, D.N. Sundberg, and C.A. Chase. In review. Comparison of crop management strategies involving crop genotype and weed management practices in conventional and low-external-input cropping systems. Renewable Agriculture and Food Systems. Heap, I. 2011. International survey of herbicide resistant weeds. On-line at: http://www.weedscience.org/in.asp. Liebman, M., L.R. Gibson, D.N. Sundberg, A.H. Heggenstaller, P.R. Westerman, C.A. Chase, R.G. Hartzler, F.D. Menalled, A.S. Davis, and P.M. Dixon. 2008. Agronomic and economic performance characteristics of conventional and low-external-input cropping systems in the central Corn Belt. Agronomy Journal 100: 600-610. National Agricultural Statistics Service. 2011. 2010 State Agriculture Overview - Iowa. NASS-U.S. Department of Agriculture, Washington, D.C. On-line at: http://www.nass.usda.gov/Statistics_by_State/Ag_Overview/ AgOverview_IA.pdf.

58 — 2011 Integrated Crop Management Conference - Iowa State University Tranel, P.J., C.W. Riggins, M.S. Bell, and A.G. Hager. 2011. Herbicide resistance in Amaranthus tuberculatus: a call for new options. Journal of Agricultural and Food Chemistry DOI: 10.1021/jf103797n. United States Geological Survey (USGS). 1999. The quality of our nation’s waters: nutrients and pesticides. Circular 1225. U.S. Dept. of Interior and USGS, Washington, DC. On-line at: http://pubs.usgs.gov/circ/circ1225/.


Update on the soybean aphid efficacy program Erin W. Hodgson, assistant professor and Extension entomologist, Entomology, Iowa State University; Greg VanNostrand, research associate, Entomology, Iowa State University The confirmation of soybean aphid, Aphis glycines (Hemiptera: Aphididae), in 2000 has drastically changed soybean pest management in the United States. Outbreak populations (i.e., 1,000’s per plant) can significantly reduce yield by 40 percent, and reduce seed size, seed coat quality, pod number and plant height (Ragsdale et al. 2007). As a result of the yield loss potential, soybean aphid quickly became the primary soybean pest in Iowa and the north central region. A soybean efficacy evaluation was started at ISU in 2005 and continues to grow with the availability of new products and management tools. Insecticides have been the primary control strategy for soybean aphid during the first decade. Two major classes of insecticides, organophosphates and pyrethroids, are the most common types of foliar insecticides for soybean aphid, but foliar neonicotinoids have also been recently released. Although most labeled products are effective now, we have concerns with managing a persistent pest like soybean aphid solely with insecticides. Aphids can develop genetic resistance to major classes but growers can help delay these events in soybean by minimizing exposure to aphid populations and only treating when populations exceed the economic threshold. Also, rotating modes of action (e.g., pyrethroids, organophosphates, neonicotinoids) will prolong the effectiveness of available products. Host plant resistance is the newest soybean aphid management tool, and is complementary to existing chemical control. Aphid-resistant varieties have the potential to simultaneously reduce insecticide usage and associated production costs, and preserve natural enemies in soybean (Tilmon et al. 2011). To date, host plant resistant genes for soybean aphid are prefixed with “Rag,” which is an abbreviation for “Resistant Aphis glycines.” The Rag1 gene expresses antibiosis and has been commercially available since 2010. Antibiosis is type of resistance where exposed insects do not live as long or produce as many offspring as they could on susceptible plants. The objective of the efficacy program is to evaluate labeled and proprietary foliar insecticides alone and in combination with seed treatments and host plant resistance. We assessed knockdown and residual of foliar insecticides and monitored for potential genetic resistance to insecticidal chemistries.

Comparison of soybean aphid treatments In 2011, soybean aphid efficacy evaluations were established at three ISU Research Farms (Northwest, Northeast, and Johnson). Each location had plots (15 x 45-50 feet) in a randomized complete block design with four replications per treatment. The number of treatments varied between locations, but included at least the same seven controls: untreated, Rag1, seed treatment (ST), ST + Rag1, ST + Rag1 + threshold spray, aphid-free spray, and threshold spray. Two types of seed were used (Rag1 and susceptible). See the 2011 Yellow Book for a complete list of treatments and application rates; this summary only includes data from the Northwest Farm (Table 1). Soybean aphids were counted in plots weekly from June to early September. To estimate the total exposure of soybean plants to soybean aphid, we calculated cumulative aphid days (CAD) based on the number of aphids per plant counted on each sampling date. Yield was determined by weighing grain with a grain hopper and corrected to 13% moisture. One way analysis of variance (ANOVA) was used to determine treatment effects within each experiment. Means separation for all studies was achieved using a general linear mixed model and a least significant difference (LSD) test (α < 0.10) using SAS software (2011).

60 — 2011 Integrated Crop Management Conference - Iowa State University Table 1. List of treatments, rates, and application timings for the Northwest Farm in 2011 Treatment

Active Ingredient

Rate

Timing

Untreated Control

-----

-----

-----

Rag1

-----

-----

-----

CruiserMaxx Beans

thiamethoxam + mefenoxam + fludioxonil

56g/100 kg seed

ST

CruiserMaxx Beans + Rag1

thiamethoxam + mefenoxam + fludioxonil -----

56g/100 kg seed + -----

ST -----

CruiserMaxx Beans + Rag1 + Warrior II

thiamethoxam + mefenoxam + fludioxonil ----lambda-cyhalothrin

56g/100 kg seed + ----- + 1.6 fl oz

ST ----10 Aug

Warrior II

lambda-cyhalothrin

1.6 fl oz

10 Aug

Warrior II + Lorsban Advanced

lambda-cyhalothrin + chlorpyrifos

1.6 fl oz + 16.0 fl oz

29 Jul + 10 Aug

Cobalt Advanced

lambda-cyhalothrin + chlorpyrifos

13 fl oz

10 Aug

Endigo ZC

thiamethoxam + lambda-cyhalothrin

4.5 fl oz

10 Aug

Results Aphid colonization at all three locations was low in June, but gradually increased in July and August. Overall seasonal aphid pressure varied between locations, but the Northwest Farm had the highest abundance. We would expect to see economic loss when the CAD value exceeds 5,000-6,000 (Ragsdale et al. 2007). There were significant differences in CAD between foliar treatments (F=32.335; df=3,8; P