Farmers and others in the agricultural community have waited patiently since June for a decision regarding the labeled use of approved dicamba containing herbicide formulations for use within the Roundup Ready 2 Xtend® (X2) and XtendFlex® (XF) soybean systems. The wait is finally over, and farmers now have another valuable tool to combat herbicide resistance.

In October 2020, the EPA announced the registration of XtendiMax® and Engenia® herbicides as well as the re-registration of Tavium® herbicide for use in dicambatolerant crops (X2/XF soybeans and XF cotton). The new labels for XtendiMax and Engenia include several additional measures to further reduce the potential for off-target movement.

One key component is the requirement of a volatility reducing agent (VRA) to diminish the potential for dicamba volatility. In conjunction with US Academic Weed Scientists, Bayer has evaluated the VRA of VaporGrip® Xtra and its effectiveness through low-tunnel trials simulating a commercial application (Figure 1.) These VRAs serve as pH buffer additives to the spray solution to aid in preventing dicamba acid formation, minimizing the potential for off-target movement after an application.

The approval of these dicamba-containing herbicides means that in 2021, farmers will have more effective herbicide options to combat weed resistance in soybeans than ever before. While the comfort level and familiarity of many herbicide platforms is high, newer technologies such as XtendFlex® and Enlist E3® may not be as well understood.

While Enlist herbicides (Enlist One® and Enlist Duo®) and the approved dicambacontaining herbicides mentioned above are all growth regulators or auxin herbicides, they do not share the same advantages. Enlist One and Enlist Duo contains 2,4-D choline. Both 2,4-D choline and dicamba target the same sight of action (SOA) to terminate weeds; however, they will not produce the same results.

Specific management will be essential to maximize the strength of each herbicide system.

KEY LEARNINGS AND DIFFERENCES:

Spring Burndown: Dicamba herbicides typically offer more consistent performance than Enlist or 2,4-D in cool weather or during significant temperature fluctuations, particularly on marestail. Spring daily highs compared to daily lows can vary 25° to 35°F, resulting in reduced efficacy.

Soil Activity: Dicamba products such as XtendiMax have documented soil activity of up to 14 days. Dicamba complements a pre-emergence residual program to prevent weed emergence further, thus reducing pressure on the POST application.

Enlist E3® System: The greatest efficacy of tough-to-control weeds and glyphosateresistant (GR) weeds can be achieved by tank-mixing Enlist One with Liberty® rather than glyphosate in a post-emergence application. This is especially important for waterhemp and marestail control. Enlist One plus glyphosate or Enlist Duo will provide very effective control of giant ragweed if GR marestail or waterhemp are not an issue. Tank-mix Enlist One with Liberty at a 1:1 ratio (32 oz./A. Enlist One to 32 oz./A. Liberty).

Bookmark the link below to stay up-to-date regarding state approvals of XtendiMax, as well as other site-specific information: bit.ly/XtendimaxApprovals