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What to Expect With Dicamba Technology

Dicamba use will require enhanced stewardship.

The EPA recently approved a new, low-volatile dicamba formulation (Xtendimax with VaporGrip Technology) for dicamba-resistant soybeans. While an additional chemical tool will provide another option for managing herbicide-resistant weeds, there are concerns with off-target drift. Widespread injury associated with off-target movement could cause greater restrictions or a loss of these technologies along with additional restrictions on alternative products.

“Without question, there are instances and scenarios in which dicamba will improve control of certain weed species, but dicamba will not bring back the good ol’ days of post-only weed-control programs in soybean,” says University of Illinois Extension weed specialist Aaron Hager. 

Current expectations of what this technology can accomplish tend to be a bit more optimistic than what the technology actually will be able to deliver, says Hager. It’s important to keep in mind where it fits, the realities, and the concerns of the technology.

“All herbicides have risks, especially when used over large areas of the landscape,” say Iowa State University Extension weed scientist Bob Hartzler and Extension weed specialist Mike Owen in a university integrated crop-management article. “Synthetic auxin herbicides (Group 4) can cause significant plant injury at fractions of normal use rates, resulting in a higher risk of off-target injury than with most herbicides.” 

The new dicamba formulations that are either approved or pending approval have lower vapor pressures than earlier dicamba formulations. The lower vapor pressure reduces, but does not eliminate, the potential for off-target movement via volatilization, say Hartzler and Owen.

Applicators must become familiar with—and follow—the application practices specified on the new product labels. Several of the restrictions involve significant changes in typical application procedures. The widespread injury to soybeans, horticultural crops, and other sensitive plants that occurred during 2016 in Missouri and other states due to illegal applications of dicamba on RR2 Xtend soybean illustrates the risks when the proper stewardship is not practiced, say Hartzler and Owen.

The label restrictions will help reduce risks associated with particle drift. It’s important to follow the label regarding the following:

  • Nozzle type
  • PSI
  • Boom height
  • Buffer zones

Another concern for potential crop injury from dicamba is from residue being left in the sprayer when the applicator moves from an RR2 Xtend soybean field to nondicamba-resistant soybean fields.

Hager is concerned with the confusion about particle drift and volatilization. 

“While the newly labeled formulation is reportedly less likely to volatilize after application, there is absolutely nothing unique about the formulation that will reduce physical drift during application,” says Hager. “Off-target movement of dicamba is of particular concern due to the number of sensitive dicot species grown in Illinois. The new formulation of dicamba is no more likely to drift than any other herbicide formulation, but the symptoms that indicate drift did occur can be induced at extremely low concentrations of dicamba. Several years ago, we were able to induce soybean leaves to cup with as little as 1/10,000 pint of dicamba,” he says.

Hager says the reports suggest that the use of older, more volatile dicamba formulations was largely responsible for the widespread off-target injury that occurred in areas of the mid-South during 2016, but volatility is generally a minor component of off-target movement when compared with actual physical drift during application.

 

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