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Extension scientists discuss new dicamba label

TAGS: Crops
Chad Hayes Sprayer with TTI Nozzles
A sprayer with label-approved nozzles is prepared for a dicamba application.
Mid-South weed scientists weigh in on new EPA regulations regarding over-the-top dicamba use.

With EPA’s announcement of the new registration of dicamba formulations XtendiMax with VaporGrip Technology and Engenia Herbicide, and the extended registration of Tavium Plus VaporGrip Technology, farmers have a little more certainty (at least for now) of what weed management tools will be available to them over the next five years. However, there are some fairly significant changes to the new label, and additional changes to individual states may still be forthcoming. 

We caught up with Extension weed specialists from across the Mid-South to get their take on the new dicamba requirements. 

Cutoff dates 

A big EPA talking point is the simplification of the new dicamba labels. This is most apparent in the category of spray cutoff date. Instead of being based on growth stage or planting date, a national spray cutoff date is now in place — June 30 for soybean and July 30 for cotton. 

“From a practical standpoint, dates are easier for applicators and regulators to track than crop growth stage,” said Larry Steckel, Extension weed specialist with the University of Tennessee. 

Steckel estimates he has responded to hundreds of dicamba drift calls over the past four years —mostly in July and August. 

“As such, the June 30 soybean cutoff could decrease some off-target dicamba issues,” says Steckel, “but the cotton cutoff is really not practical for Tennessee. If a grower is still spraying dicamba in late July, the Palmer amaranth in the field has likely escaped earlier dicamba applications and is dicamba resistant. Liberty should be the go-to for Palmer amaranth management in July.” 

Tom Barber, Extension weed scientist with the University of Arkansas, agrees. 

“We plant soybean from April until mid-July it seems every year, so a growth stage only cutoff would not work well for soybean in Arkansas,” Barber said. “But the cotton cutoff for late July is not practical as we lay our crop by around the first of July each year.” 

Buffer zones 

Downwind in-field buffer zones are now set at 240 feet — more than double the footage required in the previous label. And for counties home to certain endangered species, the downwind buffer goes up to 310 feet, with a 57-foot buffer on all other sides of the field. The goal of the buffer is honorable, but to specialists who spend a lot of time in the fields, the reality is not always practical. 

“If we’re in a county with endangered species, a quick calculation on a square 40-acre field would indicate that an applicator would need to leave at least 36% of the field unsprayed,” says Steckel. “For a typical Mid-South odd-sized field, it could easily be a much larger percentage.” 

“I agree there is a problem in practically abiding by the buffers,” said Kevin Bradley, Extension weed scientist with the University of Missouri. “I also do not believe that these buffers will solve secondary movement that is not physical drift right out of the sprayer, but instead volatility and movement of dicamba through inversions.” 

There is also the issue of weed management inside the in-field buffers, perhaps more important with each passing year as Palmer amaranth resistance to multiple herbicides continues to grow. 

“If Xtend only soybeans are planted, then in some Arkansas counties there will be no option for control of emerged pigweed within the in-field buffer,” Barber said. “If they plant Xtend cotton or XtendFlex soybeans, they can use glufosinate as an option.” 

Applicators that use hooded sprayers can reduce the in-field buffers to 110 feet.  

“We have some growers that use hooded sprayers every year, but I don’t foresee a big run on hooded sprayers in our state just because the in-field buffer is reduced,” Barber said. 

New pH buffer 

A major change to the new label is the requirement of a qualified pH buffering adjuvant to every application of over-the-top dicamba herbicide. This is also known as a Volatility Reduction Agent (VRA). The two products currently approved are BASF’s Sentris Buffering Technology and Bayer’s VaporGrip Xtra Agent.  

The goal of the VRAs is to stabilize the pH of the dicamba spray solution. Dicamba spray mixtures with an acidic pH have been implicated as a potential factor in off-target movement. While the agents have been tested at land-grant universities, the university weed scientists we spoke with had not tested these agents specifically for volatility reduction. Although, in some states, the buffering agents were included in formulations being tested for weed efficacy or crop tolerance. 

“Testing them for weed control is not the same as testing the volatility of the mixture,”  Bradley said. “Seems like we went down this road years ago. 

Said Steckel, “We are currently trying to get some of those agents to conduct our own humidome tests, but at this point, by the time we get our work finished, it will be planting time. That is when the ultimate test will be happening on a very large scale. We will definitely find out then.” 

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