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Adjacent and Neighboring Dicamba Applications: How Far is That?

In Illinois, knowing how far a dicamba application can occur next to a sensitive crop is important, but elusive.

Editor’s note: Labels of dicamba products for dicamba-tolerant soybeans do not state how close applicators may safely apply dicamba next to sensitive crops. Below, Aaron Hager, University of Illinois Extension weed specialist, gives his insight as to what this means for Illinois chemical applicators.

An article posted last November outlined several changes made by the Environmental Protection Agency to XtendiMax, Engenia, and FeXapan labels. The intent of these label amendments is to reduce sensitive plant species exposure to dicamba primarily through physical movement (i.e., drift during the application or particle movement during temperature inversions) and via dicamba residues dislodged from application equipment.  

Illinois applicators who have completed the required dicamba training being conducted by registrant personnel likely heard repeatedly that preventing off-target movement during the application is solely and completely the responsibility of the applicator.  

Cloudy, Not Clear

Less clear, though, is how far from the treated field off-target extends. The following statements can be found on the current labels of XtendiMax/FeXapan and Engenia, respectively:

  • “Do not apply this product when the wind is blowing toward adjacent nondicamba-tolerant susceptible crops; this includes nondicamba-tolerant soybean and cotton.”
  • “Do not apply when wind is blowing in the direction of neighboring sensitive crops.”

The labels clearly specify that applications may be made only when wind speed is between 3 and 10 mph, meaning there always will be a downwind side or sides. However, neither product label defines “adjacent” or “neighboring” with respect to distance from the treated field.  

In instances where no downwind areas can be included in a buffer (cornfield, paved road, building, etc.), there always will be some sensitive crop at some distance downwind.  

  • Is a sensitive soybean crop adjacent or neighboring if it is less than 10 feet from the treated field?  
  • What about 100 feet from the treated field?  
  • What if the sensitive soybean field is 1 mile from the treated field?  

“Adjacent” and “neighboring” can be defined by a dictionary, but no dictionary can provide the distance(s) considered adjacent or neighboring for these products. Registrants of dicamba-containing products labeled for use in dicamba-resistant soybean varieties indicate they do not intend to include distances that define adjacent and neighboring on the labels. Rather, manufacturers intend to leave the decision to spray or not to spray at the discretion of the applicator.  

Inspectors Will have Final Say

However, inspectors with the Illinois Department of Agriculture (IDOA) ultimately will have the final determination of distance to adjacent and neighboring sensitive crops during investigations. If an inspector’s interpretation of adjacent or neighboring is different from the applicator’s interpretation, penalties and fines against the applicator could result.

A request was made of the IDOA to define how agency personnel will interpret adjacent and neighboring with respect to distance. The following paragraph, reproduced in its entirety and with permission, is the response from IDOA:

“Every situation is unique and numerous factors must be considered when evaluating whether an application is appropriate. The Department interprets this label provision (“adjacent” or “neighboring”) to go beyond “side by side,” but we do not have a specific distance limitation. Users are instructed to “survey the application site for neighboring nontarget susceptible crops.

"Based on this survey, they make their spray/no spray decision. It is not just a simple 1-mile, 2-mile, 3-mile measurement because every situation, including local topography, weather conditions, etc., is unique.”

So, how will an applicator determine whether or not an application should be made when the wind is blowing toward a dicamba-sensitive crop that is 5, 10, or 5,280 feet adjacent or neighboring the field to be treated? The answer remains critically important but rather elusive.

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