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A deeper dive into EPA’s dicamba re-registration

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Greg Kruger, weed science extension specialist at the University of Nebraska-Lincoln, kneels in a soybean field that recently received a treatment of dicamba. He continues to conduct research on dicamba drift and boom heights.
University of Nebraska weed scientist shares how the latest action from EPA on dicamba is good for growers.

Many growers are finishing up the 2020 harvest and already looking to purchase their seeds for 2021. As many genetics have moved to include dicamba resistant varieties, the news Oct. 27 by the Environmental Protection Agency to offer a five-year re-registration for dicamba use for over-the-top applications offers another important tool for growers in managing weeds.

EPA approved new registrations for two “over-the-top” (OTT) dicamba products—XtendiMax with VaporGrip Technology and Engenia Herbicide—and extended the registration for an additional OTT dicamba product, Tavium Plus VaporGrip Technology. These registrations are only for use on dicamba-tolerant (DT) cotton and soybeans and will expire in 2025.

Greg Kruger, a weed science extension specialist at the University of Nebraska-Lincoln, said the timing of the announcement is good for growers as many are making decisions on what to plant next year. “This decision allows them to have confidence that if they buy a dicamba-resistant trait, the tool will be there to use.”

Grower confidence was clearly shaken in the summer of 2020 when a court issued an immediate vacatur of three dicamba pesticide registrations. Growers and commercial applicators were allowed to use existing stocks that were in their possession as of June 3 consistent with the approved label until July 31. EPA then set out to create an improved data profile in this latest re-registration as it worked to update label requirements for the chemistry used by widely by growers. In 2018, approximately 41% of U.S. soybean acreage was planted with dicamba-tolerant (DT) seed and almost 70% of U.S. cotton acreage was planted with DT seed in 2019.

Kruger has spent a considerable amount of time with growers, chemical companies and even the EPA to help better understand how dicamba operates. At the research level, he has worked with pesticide registrants to generate the data sets to defend the registration decisions made by EPA. His ongoing research on off-target movement and the impact of boom heights is already being considered in the registration of a second generation dicamba product.

Kruger shares it is important for producers to understand the label changes. “Every applicator needs to have enough fear to handle the product responsibly.”

He added that at some level it is incumbent on professionals in the industry, as well as the companies and university specialists, to make sure growers are properly educated on how to comply with the very specific label for dicamba application.

“You can’t dump a very specific label and expect them to get it all right,” Kruger said of the growers and applicators using dicamba. “I believe there’s a huge gap in education and training. Responsibility has to be conveyed to applicators that in order to continue to have these tools available, we have to take the label seriously and follow that label.”

Moving forward, in addition to properly following the label, Kruger always suggests direct conversations between farmers to rectify any problems with potential drift. Although it is important to discuss any potential drift with state departments of agriculture, Kruger always recommends calling your neighbor first. “It’s a tough conversation to have, but if you start there, a lot of times things can be worked out.”

In 2016, EPA began receiving reports of crop injury alleged to be caused by off-target movement from the use of dicamba. Because the registrations for OTT use had not yet been issued, EPA concluded these 2016 incidents were related to misuse of previously registered, more volatile dicamba pesticide products on DT cotton and DT soybeans. In 2017, over 2,700 official cases of crop damage were reported to state departments of agriculture, estimated to be over 3.6 million acres of soybeans.

Kruger said in 2017, the first year dicamba was approved for OTT for soybeans and cotton, he would challenge that glyphosate experienced more drift issues than dicamba, however, low levels of dicamba drift create a visual response even if yields didn’t suffer.

Cut-off dates

The mandatory application cut-off dates - June 30 for soybeans and July 30 for cotton - on the product labels reduces the probability of dicamba application on days more favorable for dicamba volatilization. EPA stated the June 30 and July 30 dates were informed by data on the effect of temperature on volatility. EPA utilized historical incident information and meteorological data to conduct its analysis.

EPA compared the maximum temperature data on the day of each reported incident and determined that over 94% and 82% of the incidents occurred at temperatures above 75 degrees F and 80 degrees F, respectively. EPA then reviewed historical meteorological data to determine the proportion of total days less than 75 degrees F and 80 degrees F.

Based on this analysis, the soybean cut-off of June 30th would mean that application temperatures will be below 80 degrees F between 12% (Texas) to 89% (Minnesota) of the time, and below 75 degrees F between 3.2% (Texas) to 72% (Minnesota) of the time. The cotton cut-off of July 30th would mean that application temperatures will be below 80 degrees F, between 8% (Florida) to 66% (Virginia) of the time, and below 75 degrees F between 0.3% (Florida) and 36% (Virginia) of the time.

Kruger noted the cut-offs could limit use for many places that double crop soybeans or often experience later planting dates for soybeans.

Hooded sprayers

EPA also determined the use of hooded sprayers has the potential to reduce spray drift and therefore change what other control measures are necessary to achieve the same results. A hooded sprayer is an example of a drift reduction technology that can cover the entire spray boom and shields pesticide droplets from the wind from the height of release to the canopy reducing the potential for pesticide drift. EPA received data on tests of the RedBall 642E particular hooded sprayer which demonstrated a substantial reduction in spray drift.

A limited number of field studies on bare soil and soybean crops were conducted and the data received indicate dicamba drift would be limited to approximately 20 ft from the point of application, EPA stated. These data show great reductions in the possible movement off-field when using this particular hooded sprayer, but based on the limited information provided to EPA, the Agency determined that a 5X safety factor would address the uncertainties with this limited set of data. “Therefore, the use of this hooded sprayer would allow the 240-foot in-field spray drift buffer to be reduced to 110 feet and still be protective of non-listed plant species with a high level of confidence,” EPA said in its final rule.

EPA’s trials did not evaluate the use of other types of sprayers (alternative hooded broadcast, hooded in-row and layby sprayers) nor did they evaluate the use of a hooded sprayer over cotton crops. As a result, the reductions in buffer distance permitted when using hooded sprayers is limited to this one sprayer for use on soybean crops. Additional brands or models of hooded sprayers can qualify for the reduced downwind buffers for soybeans if they meet the performance standard established by testing according to EPA’s approved protocol in comparison to the currently assessed hooded sprayer, the agency said.

Kruger said this could be important for some states, especially those with smaller fields. Requiring a downwind buffer of 240 feet and 310 feet in areas where listed species are located could be very difficult to manage in places with smaller field tracks. “A small fragmented field with a 310-foot buffer could take out half of the field’s ability to use the product,” Kruger said.

Additional leeway for states

The 2020 registration labels also provide new flexibilities for growers and states. For example, there are opportunities for growers to reduce the downwind spray buffer for soybeans through use of certain approved hooded sprayers as an alternative control method. If a state wishes to expand the federal OTT uses of dicamba to better meet special local needs, the EPA said it will work with them to support their goals.  

Kruger said he would expect some states to look to expand the label, while others could further restrict the national label. Because the national label allows for the one hooded sprayer to reduce buffer zones, Kruger said this is an example of the creative things that some states may look to in encouraging a safe application, and also make it as usable as possible.



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