CORN Newsletter: 2009-12, May 4, 2009

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C.O.R.N Newsletter 2009-12
May 4, 2009 - May 12, 2009

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Are there substitutes for 2,4-D ester in soybean burndown programs
by Mark Loux


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From a weed management standpoint, the good news about delayed planting is that more of the weeds have emerged by the time the ground is tilled or the burndown is applied, compared with early planting, which makes things easier for the in-crop herbicide program. In addition, later-planted crops can develop more rapidly, and be competitive with weeds sooner after planting. The bad news is that the burndown situations get tougher, and the opportunity to use 2,4-D ester becomes more limited as we all rush to get crops in the ground. The problem here is that as weeds get larger, the need for 2,4-D ester becomes greater. Marestail and giant ragweed are good examples of this problem. Populations without herbicide resistance become generally more difficult to control as plants get larger, and glyphosate activity can be variable on large plants. In the absence of 2,4-D ester, populations with resistance to glyphosate and/or ALS inhibitors can be almost impossible to control with soybean herbicides in May as plants get taller and older. We would suggest making every effort to include 2,4-D in burndown programs in fields with these types of problems, even if it means further delays in planting, or substitute tillage for herbicides to ensure that the crop gets off to a weedfree start.

Where it is not possible to use 2,4-D ester due to imminent soybean planting, our research shows that the most comprehensive burndown in soybeans is likely to occur with a mixture of glyphosate and a chlorimuron-containing product (Canopy, Valor XLT, Synchrony, Envive). Next best would be a mixture of glyphosate with a cloransulam-containing product (Firstrate, Sonic, Gangster, Authority First), which can be more effective on marestail and ragweeds than mixtures of chlorimuron and glyphosate, but may be less effective on most other no-till weeds. Where weeds are large, the Valor or Authority that is in some of these products has some potential to antagonize the activity of glyphosate, but there are considerable advantages to these herbicides with regard to residual weed control. Increasing the rates of glyphosate and the herbicide containing chlorimuron or cloransulam should be considered as weed size increases, but increasing rate will not result in control of glyphosate- or ALS-resistant populations.

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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868


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