Improvement of soybean management practices
The dicamba- and 2,4-D-resistant traits are attractive options for producers with limited POST herbicide options in soybean. Adoption of Xtend and Enlist technologies is expected to continue increasing; however, questions remain regarding weed control and off-target movement of these herbicides.

The objectives of this current proposal are to:
• Further experiments to understand the extent to which dicamba and 2,4-D remain in the environment following application.
• Evaluate weed control with glyphosate plus dicamba across a range of spray tank pH’s.

Results from this research will be shared with other scientists and used across the industry to better understand dicamba and 2,4-D movement.

Results from these experiments will be shared with farmers, farmer-advisors, and other scientists at field days, conferences and professional scientific meetings.

Updated May 11, 2022:
The Roundup Ready® Xtend®, XtendFlex®, and Enlist E3®soybean traits offer options for the control of some of our most problematic herbicide-resistant weed species in soybean. Adoption of these systems is anticipated to continue to increase along with the post-emergent applications of dicamba and 2,4-D. However, questions remain regarding weed control and off-target movement of the herbicides.

Applications of XtendiMax® with VaporGrip® and Engenia® require the addition of a volatility reduction agent (VRA). It
is presumed that FeXapan® with VaporGrip® will also require a VRA once the label is approved. Dicamba is more likely to
volatilize at a pH below 5, and these VRAs, which are also known as pH modifiers, reduce volatility by increasing the pH of the spray solution. We evaluated pH and waterhemp control of spray solutions that included one of three approved VRAs in combination with either XtendiMax® with VaporGrip® or Engenia®. Each mixture included a drift-reduction adjuvant, water conditioner, and glyphosate, and was applied at 15 and 20 gallons per acre (GPA). All three pH modifiers increased pH of the spray solution and each spray solution resulted in greater than 90% waterhemp control by 4 weeks after application. However, it remains unknown how effective the VRAs will be in reducing dicamba volatility when applications are made on a large scale.

Another question is whether the newest formulation of 2,4-D, which is used in the Enlist™ products, is less volatile than
the newer dicamba formulations. In a series of experiments funded by MSMC and the United Soybean Board, we have
found Enlist™ products to be less volatile overall. However, it is important to note that we can still detect 2,4-D in the air
and it is unknown whether this amount of 2,4-D detected in the air could increase as the Enlist™ technology is adopted on a higher percentage of acreage.

Missouri producers are urged to use these products with care and remember to incorporate best management practices
that prevent off-target movement and also the development of herbicide-resistant weeds.

Research results from the proposed objectives will provide additional information pertaining to off-target movement of dicamba and 2,4-D. Results should also help guide recommendations for inclusion of pH modifiers in a dicamba plus glyphosate tank-mix.