EPA’s dicamba cancellation order: What does this mean for Michigan farmers?

Options for weed control in Roundup Ready 2 Xtend soybean.

Photo by Christy Sprague, MSU

On June 3, 2020, the Ninth Circuit Federal Court of Appeals ordered the immediate vacatur of the United States Environmental Protection Agency’s (EPA) conditional registrations of three dicamba products: XtendiMax with Vaporgrip Technology (Bayer Crop Science), Engenia (BASF) and FeXapan (Corteva Agriscience). These three dicamba products were brought to market for preemergence and postemergence use in Roundup Ready 2 Xtend soybean. EPA responded to this ruling by issuing a cancellation order of these three products to be effective as of the time of the court order on June 3, 2020.

On June 8, 2020, EPA issued a news release offering clarity on what the cancellation of the registrations of XtendiMax, Engenia and FeXapan would mean for the distribution and use of these products for the rest of the growing season. Below are the summarized details of the order from EPA’s news release.

Details of the order

EPA’s order addresses sale, distribution and use of existing stocks of the three affected dicamba products: XtendiMax with Vaporgrip Technology, Engenia and FeXapan.

  • Distribution or sale by any person is generally prohibited except for ensuring proper disposal or return to the registrant.
  • Growers and commercial applicators may use existing stocks that were in their possession on June 3, 2020, the effective date of the Court decision. Such use must be consistent with the product’s previously approved label and may not continue after July 31, 2020.

How does this order affect weed control in Roundup Ready Xtend soybean?

What this order means is if a farmer (private applicator) or commercial applicator has existing stocks as of June 3, 2020, of any of these products—XtendiMax, Engenia or FeXapan—they may apply them as long as they follow the instructions on the previously approved labels.

In addition to the label, there is a factsheet in Michigan State University Extension’s 2020 Weed Control Guide for Field Crops on page 105 outlining “Guidelines and Precautions for Dicamba Use in Roundup Ready 2 Xtend soybean.” The use of these products may not continue after July 31, 2020.

What are my options if I can’t use XtendiMax, Engenia or FeXapan in Roundup Ready 2 Xtend soybean?

There was one dicamba-based product registered for use in Roundup Ready 2 Xtend soybean that was not impacted by the Ninth Circuit Courts ruling. This product was Tavium (Syngenta), which is a premixture of dicamba plus s-metolachlor (Dual Magnum). Currently, Tavium can still be purchased and used in Roundup Ready 2 Xtend soybean. Tavium has very similar use restrictions as XtendiMax, Engenia and FeXapan, with the exception that it can only be applied postemergence through the V4 growth stage of Roundup Ready 2 Xtend soybean or within 45 days after planting.

Using non-dicamba-based herbicides

One of the advantages for using dicamba in Roundup Ready 2 Xtend soybean was to help manage glyphosate- and other herbicide-resistant weeds. If dicamba cannot be applied, here are some options that are available to farmers to help manage glyphosate- and multiple-resistant weeds in a Roundup Ready 2 Xtend soybean system. Regardless of the presence of glyphosate-resistant weed, glyphosate will still be the backbone of a postemergence (POST) weed control program.

Horseweed (marestail)

Postemergence control of horseweed can be extremely difficult in soybean since a majority of the horseweed populations in Michigan are glyphosate-resistant (Group 9). Without the use of dicamba in Xtend soybean, the only other options for control are the Group 2 (ALS-inhibiting) herbicides of FirstRate and Classic. Unfortunately, a large percentage of Michigan horseweed populations are also resistant to the Group 2 herbicides, leaving no postemergence options for control.

For more information on options for control, consult the “Herbicide-resistant horseweed (marestail) in Michigan” factsheet.

Waterhemp and Palmer amaranth

There are a few options for POST control of waterhemp or Palmer amaranth if they are present in Roundup Ready 2 Xtend soybean and dicamba cannot be used. These options are the Group 14 herbicides, which include Flexstar (fomesafen), Cobra (lactofen) or Ultra Blazer (acifluorfen). In addition to these products, the premixtures of Prefix (fomesafen plus s-metolachlor) or Warrant Ultra (fomesafen) can also be used.

There are a few key points in using these herbicides. Try to make applications when waterhemp and Palmer amaranth are small (less than 3 inches). Using additives (COC or MSO) will help improve control, and make sure to use the maximum use rates for the weed size and crop stage. Remember, if you are using any of the fomesafen products, crop rotation restrictions need to be considered; four months for wheat, 10 months for corn and 18 months for sugarbeet.

One other thing to keep in mind, in Michigan we do have a few fields where Group 14 in addition to glyphosate (Group 9)-resistance has been identified. Under these circumstances, the herbicides listed above will not provide control.

For more information on management of these weed species, consult the factsheet, “Multiple herbicide-resistant Palmer amaranth and waterhemp: Keys to successful management.”

Common ragweed and giant ragweed

Similar to the options listed for POST control of waterhemp and Palmer amaranth, the Group 14 herbicides are our best options for controlling glyphosate- and ALS (Group 2)-resistant ragweed species. While there are a few fields identified in Michigan with Group 14 resistant ragweed species, these herbicides are still our best options for control of non-Group 14 resistant ragweed species.

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