Production Blog

JEFFERSON CITY, Mo. (DTN) -- Soybean and cotton growers once again have access to "over-the-top" (OTT) dicamba herbicide products for postemergence weed control. But this season, those products have maximum annual application rates that are half of what was allowed on previous labels, requiring growers to consider when they should spray the herbicide to get the biggest weed-control bang for their dicamba buck.

Previous OTT dicamba labels allowed for up to 2 pounds acid equivalent (a.e.) of the active ingredient to be applied per acre per year. However, the new labels for BASF's Engenia, Bayer's Stryax and Syngenta's Tavium restrict the maximum annual application to 1 pound a.e. per acre per year of dicamba in tolerant soybeans and cotton. The single use maximum application rate of 0.5 pound a.e. of dicamba per acre remained the same.

According to the labels -- and supported in EPA documents and correspondence -- this restriction applies to all dicamba-containing herbicide products, including those formulated for postemergence application and those intended for burndown, early preplant or preharvest.

In a supporting document that EPA published with the labels, the agency emphasized that the max annual application rate applies to all dicamba products and offered a scenario:

"This means that growers planning two OTT dicamba applications at 0.5 lbs a.e. per acre would not be able to use dicamba for preplant burndown weed control," EPA stated in the document. "Conversely, if a grower uses a preplant burndown of dicamba at 0.5 lbs a.e./acre, regardless of product, he or she would be limited to 0.5 lbs a.e./acre of OTT dicamba later in the season."

While this limit of 1 pound a.e. of dicamba per acre per year for all products is stated clearly, there has been some general confusion about the restriction in the weeks since EPA announced the OTT dicamba registrations. It seems that representatives of the agency itself are contributing to the uncertainty.

University of Illinois weed scientist Aaron Hager told DTN that a representative of one state commodity organization relayed to him that a high-ranking official within the EPA Office of Pesticide Programs stated that the 1-pound limit was "specifically for over-the-top applications." A representative for one of the registrants also told DTN that the same EPA official communicated the same misinformation.

In an email shared with DTN, Lindsay Roe, herbicide branch chief within the EPA Office of Pesticide Programs' Registration Division, addressed the dicamba annual maximum.

"The intent is to limit the total amount of all dicamba to 1.0 lb/acre in dicamba-tolerant soybean and dicamba-tolerant cotton fields when Engenia, Stryax, or Tavium is being used, thereby including all dicamba-containing products labeled for use in soybean and cotton," Roe wrote. This is the first time this restriction has been required with use of a dicamba product that is labeled for in-crop use in dicamba-tolerant crops. "If someone makes two in-crop POST applications of Engenia, Clarity (or any other dicamba-containing herbicide) cannot have (been) applied as a spring burndown and cannot then apply as a fall burndown, or preharvest treatment."

While field situations can be unique, and postemergence use of OTT dicamba products might be necessary for certain growers in certain geographies, Hager advised that under the new annual maximum, growers should consider if spring or fall burndown for control of weeds such as marestail could be as important as an in-crop application to soybeans.

"That's the best time to spray dicamba," he said. "In the spring when the temperatures are cooler, you don't have the same volatility. In the fall, there is no more effective herbicide for control of marestail than dicamba."

EPA's "Implementation Resource and Application Day Scenarios for Users of Over-The-Top (OTT) Dicamba Products in Soybean and Cotton" can be found here: https://downloads.regulations.gov/…

Read more from DTN:

-- Production Blog, "Some States Impose Tighter Restrictions on OTT Dicamba Herbicides," https://www.dtnpf.com/…

-- "EPA Green Lights OTT Dicamba Again," https://www.dtnpf.com/…

Jason Jenkins can be reached at jason.jenkins@dtn.com

Follow him on social platform X @JasonJenkinsDTN

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