Updated February 1, 2021:
Final Report
The commercial launch of Xtend (dicamba-resistant) and Enlist (2,4-D-resistant) soybean in 2017 and 2019, respectively, provided farmers with alternatives to glyphosate for control of weeds with multiple forms of herbicide resistance. However, applications of dicamba in Xtend soybean have annually resulted in off-target movement (OTM) to sensitive plants, with most of the injury occurring to sensitive soybean varieties. The long-term goal of this project is to reduce the threat OTM of dicamba represents to soybean farmers in terms of their freedom to operate, profitability, and sustainability. By characterizing the factors influencing the greatest movement of dicamba and evaluating practices to help mitigate movement, we can move closer to this goal. Research was conducted in 2018 through 2020 to meet these objectives.

One of the key findings thus far in our large-scale field research is that air concentrations of dicamba were usually higher than 2,4-D and dicamba also caused more soybean injury to adjacent sensitive soybean varieties. The data analyzed thus far also indicate that dicamba (Xtendimax with VaporGrip) applied with glyphosate had 6 times greater movement via volatilization than 2,4-D choline (Enlist One) applied with glyphosate. In small-scale volatility testing in the field, dicamba (Engenia or Xtendimax) applied alone resulted in the lowest level of dicamba volatility and significantly greater levels of volatility were observed when these dicamba formulations were tank-mixed with Roundup and Liberty. Overall, the first year of research in 2020 suggests that 2,4-D choline applications in Enlist soybean pose a dramatically lower threat for secondary movement (i.e. volatility), in which the risk is further reduced by the fact that soybeans are around 10 times less sensitive to 2,4-D than dicamba.

The research conducted in 2020 did not include volatility reducing agents (VRA) which are now required by the current dicamba labels. Thus, a VRA will be included in the large-scale field research to be conducted in 2021 to determine if these adjuvants can reduced dicamba volatility, OTM, and soybean injury to similar levels as observed with 2,4-D.

All investigators participated in a meeting with the U.S. EPA in Arlington, VA on January 16, 2020 to discuss our research and the continued consideration of dicamba application regulations. Of course, the focus of our discussion was on the research conducted previously in 2018 and 2019. Subsequently, webinars that were driven by our research activity were delivered to a live audience and recorded to post on the Take Action website: “Drift Reduction Agents: Influence on Drift Management, Weed Control, and Dicamba Volatility”, Bryan Young, Purdue University; “Application Factors Influencing Dicamba Volatility” Bryan Young, Purdue University. Later in the spring of 2020 all members of our research team were active in supplying the U.S. EPA with data on the off-target movement of dicamba by their May 1, 2020 deadline. This data was considered in regulatory decisions on dicamba use in Xtend soybean for five-year label registrations that were announced by the EPA in late October 2020. Preliminary data from our 2020 field research has been presented at both grower and crop consultant virtual conferences, and virtual professional conferences.