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C.O.R.N
Newsletter
2008-32
September 22, 2008 -
September 30, 2008
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Fall Herbicide Treatments in Wheat – Burndown or Early POST
by
Mark Loux
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For the past several years, we have emphasized the importance of a preplant/preemergence application of glyphosate in no-tillage wheat. Many winter annual weeds have emerged by early October, and they can be effectively controlled with relatively low rates of glyphosate prior to wheat emergence. This can be a more effective treatment for winter annuals, compared to the herbicides that can be applied broadcast to wheat in late fall or early spring. Producers who have applied glyphosate at the time of no-till wheat planting report that their fields have been relatively free of winter annuals in the spring. Preemergence application of glyphosate is also an effective and inexpensive tool to control winter annual grasses such as downy brome and cheat. A dense population of winter annuals may have already suppressed wheat growth by the time a spring treatment can be applied. In addition, our research over the past 8 years or so in various crops has led us to the general conclusion that herbicides are most consistently effective on winter annuals when applied in fall. The effectiveness of spring treatments can be extremely variable due to wide swings in weather conditions and the possibility of a late spring.
We have previously suggested that glyphosate applied at this time of the year could provide some of the better control of dandelion in wheat, but producers have indicated that this has not necessarily been the case. While we know that late September is somewhat early for optimum dandelion control, our recommendation was based on the known variability of spring herbicide treatments on dandelion. Late fall herbicide treatments to emerged wheat may be another option that is more effective for dandelion control. We conducted a study last fall and spring to compare various herbicide treatments on dandelion in wheat. This is only one year of data, and we’ll be conducting the study again this year, but the results highlight some of the more effective treatments as well as the issues with dandelion control in spring.
Fall treatments were applied in mid-November, and spring treatments were applied in early April. Results shown here are from a May 13 evaluation. At that time, dandelion control from fall treatments ranged from 63 to 97%, while control from spring treatments ranged from 43 to 78%. Express (0.33 oz/A) was a common component of the most effective treatments in fall or spring. Express plus dicamba (4 oz product/A) applied in the fall resulted in 97% dandelion control the following spring. This treatment also effectively controlled the winter annual weeds in the field. Several other treatments resulted in this level of control, but were more expensive. Examples – WideMatch + dicamba; WideMatch + Express; WideMatch + Harmony Extra. We did not apply the combination of Harmony Extra + dicamba in the fall, since Express is more effective on dandelion than Harmony Extra. Only one spring-applied treatment provided better than 70% control of dandelion - WideMatch + Express + 2,4-D.
We did not apply 2,4-D in the fall, due to its potential to injure wheat and reduce yield. We did apply a premix product that contained dicamba and 2,4-D in fall and spring, but this treatment was less effective than any of the others. We were not able to measure wheat yield at the study location, but we will be able to do so when we repeat the study this year. The results of this study indicate that one approach to dandelion and winter annual weed management may be to skip the preemergence glyphosate treatment, and instead apply herbicides in November to emerged wheat. This may not be the right approach in fields with a history of winter annual grass problems or other perennial weeds that are in the right stage for control by late September. We hope to get a better comparison for dandelion control between the preemergence glyphosate application and the late fall herbicide treatments in the second year of the study.
A final note on burndown - at this time of the year we start to receive questions about the safety and legality of 2,4-D applied prior to wheat planting. We do not know of any 2,4-D product labels that support this use of 2,4-D. There is some risk of stand reduction and injury to wheat from preplant applications of 2,4-D. We question why producers would want to use 2,4-D, when glyphosate can be applied for about the same cost to obtain a similar level of weed control (better on some species). One argument in favor of the use of 2,4-D would be to avoid overuse of glyphosate and slow the development of herbicide resistance. However, 2,4-D can be used with glyphosate in fall and spring herbicide treatments prior to corn and soybean planting, and would probably be best avoided prior to wheat planting.
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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,
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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.
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