New Extension Publication on Differentiating 2,4-D and Dicamba Injury on Soybeans

Adoption of Xtend soybeans is expected to reach 70-80% of the soybean acres in the U.S. in 2019. The approval of Enlist E3 soybean imports by China and the Philippines earlier this year has allowed for full commercialization in the U.S. and provided farmers with another auxin herbicide (2,4-D choline) in their soybean weed management programs. The approval of these technologies allows farmers to spray dicamba or 2,4-D herbicides postemergence for management of glyphosate resistant weeds such as horseweed, giant ragweed, waterhemp, and Palmer amaranth. However, the use of Xtend technology resulted in an increased number of herbicide off-target movement complaints across the Midwest from farmers growing non-dicamba tolerant crops. Differentiating between 2,4-D and dicamba symptomology will become increasingly important for farmers and ag professionals as they evaluate complaints of off-target movement of these two herbicides. The purpose of this publication is to provide some guidance on how to accomplish this diagnosis.

Although it is not the objective of this publication to discuss potential yield reduction from off-target movement of these herbicides, it is important to understand that soybeans are more sensitive to dicamba than 2,4-D. Therefore, it will require higher doses of 2,4-D to cause the same levels of injury caused by off-target movement of dicamba. Differences in soybean injury levels and yield reduction in response to 2,4-D and dicamba exposure from a multi-state study are described in Table 2. Keep in mind that the level of injury and yield reduction in response to these herbicides will vary depending on time of exposure and the environmental conditions after exposure. Therefore, it is difficult to accurately predict soybean yield reduction from visual injury ratings.

In conclusion, differentiating 2,4-D and dicamba symptomology is challenging, however, subtle differences do exist and are key for accurate herbicide injury diagnostics.

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