By Dr. Mark Loux, OSU Extension, State Weed Specialist

On June 3, the US 9th Circuit Court of Appeals issued a decision in a case concerning the use of dicamba on Xtend soybeans.  This decision voided the labels for XtendiMax, Engenia, and FeXapan that allow use on Xtend soybeans.  Tavium was not included in this decision, because it was not approved for use when the case was initially filed.  Several great articles covering this decision can be found here on the OSU Ag Law blog (https://farmoffice.osu.edu/blog).  EPA issued a statement on June 8 providing further guidance about what this decision means for use of dicamba the rest of this season.  The gist of this decision was the following:

“EPA’s order addresses sale, distribution, and use of existing stocks of the three affected dicamba products – XtendiMax with vapor grip technology, Engenia, and FeXapan.

  1. Distribution or sale by any person is generally prohibited except for ensuring proper disposal or return to the registrant.
  2. 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.”

ODA subsequently issued a statement regarding the registration and use of these products in Ohio, stating that any use must happen prior to July 1, 2020.  Partial text from this statement:

“The registration of these  products (XtendiMax, FeXapan, and Engenia) in Ohio expires on June 30, 2020. After careful evaluation of the court’s ruling, US EPA’s Final Cancellation Order, and the Ohio Revised Code and Administrative Code, as of July 1, 2020 these products will no longer be registered or available for use in Ohio unless otherwise ordered by the courts.

While use of already purchased product is permitted in Ohio until June 30, 2020, the Court’s decision and US EPA’s order makes further distribution or sale illegal, except for ensuring proper disposal or return to the registrant. Application of existing stocks inconsistent with the previously approved labeling accompanying the product is prohibited. If you have questions about returning unused products, please reach out to your pesticide dealer’s representative.”

So what is the impact of all of this, and how do we adjust herbicide programs to deal with it?  Some things to consider:

– The majority of the POST applications on Xtend soybeans occurs prior to the end of June anyway, although some certainly do occur in July.  And while XtendiMax, FeXapan, or Engenia cannot be applied after June 30, the previous label restrictions are also still in place – POST application must occur prior to the R1 stage or no later than 45 days after soybean planting, whichever occurs first.  So if the soybeans were planted by May 15, products would have to be applied prior to June 30 anyway, and if planted later, they would have to be applied prior to R1 or before June 30 whichever occurs first.

– It’s important to keep in mind that emergence of most summer annual weeds peaks in early to mid June and then starts to decline, although there can be later flushes of weeds with rainfall events especially.  So except where soybeans are planted late and are still small, applying POST herbicides in mid to late June catches most of the weeds and provides effective control.  We expect the soybean canopy to have developed adequately to suppress weeds emerging after POST application.  Based on our research, this can work even in later-planted soybeans just due to the fact that weed emergence slows down towards the end of June.

– Given how difficult it can be to find suitable weather to apply the dicamba products, we suggest looking for a window to apply and doing so.  As of June 12, we have 18 days left to legally apply, and probably more like 10 days factoring in application stewardship requirements.  Waiting until the last week of June is possibly not a great plan.

– Registration of Tavium, the premix of s-metolachlor and dicamba with VaporGrip, was not affected by this decision and remains a legal option even after June 30.  Tavium can be applied through the V4 soybean stage, or through 45 days after planting, whichever occurs first.

– Without the availability of dicamba to use POST, the Xtend soybean becomes an old school Roundup Ready soybean.  Primary POST option would be a mix of glyphosate with an ALS inhibitor (Classic, FirstRate, etc) or PPO inhibitor (Flexstar and generics, Cobra/Phoenix, Ultra Blazer).  These would also be the options where a second POST application is necessary after June 30.  Not all of these may be viable in July due to soybean growth stage, PHI, or crop rotation restrictions

– Weeds of greatest concern here are marestail, waterhemp, Palmer amaranth, giant ragweed, and also common ragweed in NW Ohio.  These five weeds are mostly glyphosate and ALS resistant in Ohio, and PPO resistance is fairly common in waterhemp and also occurs in some common ragweed and Palmer amaranth populations.  None of these mixtures will be effective for POST marestail control.  Effectiveness on the other weeds will be variable among and within fields across Ohio.  Some giant ragweed populations are still partially controlled by glyphosate, so plant size and glyphosate rate and number of applications makes a difference.  We would expect a complete lack of waterhemp control in some fields.

– Another option would be to replant Xtend soybean fields with another type of soybean that provides for the POST options of 2,4-D choline and/or glufosinate – Enlist, LibertyLink, or LLGT27 – should seed still be available.  This strategy should be used for double crop soybeans also, unless weeds can be handled well enough with the mixtures mentioned above.

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