By: Mark Loux, OSU Extension
Article Updated on June 9, 2020 at 8:15 AM due to EPA statement Monday night.
As most readers are probably aware, last week, the US 9th Circuit Court of Appeals issued a decision in a case concerning the use of dicamba on Xtend soybeans. This decision essentially voided the labels for XtendiMax, Engenia, and FeXapan that allows use on soybeans. Tavium was not included in this decision, because it was not approved for use when the case was initially filed. Last week’s entry in the OSU Ag Law blog covers this decision well and can be found here. EPA issued a statement Monday night, providing further guidance about what this decision means for the use of dicamba for the rest of this season, which can be found here. The critical part of that is as follows:
“Details of the Order
EPA’s order addresses the sale, distribution, and use of existing stocks of the three affected dicamba products – XtendiMax with vapor grip 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.”
The next most immediate question concerns the options for control of glyphosate-resistant weeds in Xtend soybeans, for those growers who have not already purchased their dicamba products, since the EPA info states that no additional sales can occur. Tavium, the premix of s-metolachlor and dicamba with VaporGrip, was not part of this decision and remained an option. Tavium can be applied through the V4 soybean stage, or through 45 days after planting, whichever occurs first. Aside from this option, without the availability of dicamba to use POST, the Xtend soybean becomes just an old school Roundup Ready soybean. Weeds of most significant concern here are marestail, waterhemp, Palmer amaranth, giant ragweed, and also common ragweed in NW Ohio. The 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). However, these five weeds are mostly glyphosate and ALS resistant in Ohio, and PPO resistance is reasonably common in waterhemp and also occurs in some common ragweed and Palmer amaranth populations. None of these mixtures will be effective for marestail control. Effectiveness on the other weeds will be variable among and within fields across Ohio. Some giant ragweed populations are still partially sensitive to glyphosate, so plant size and glyphosate rate and the number of applications make a difference. We would expect a complete lack of waterhemp control in some fields. A third 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.
The Iowa State University ICM blog (June 5) covered the issue of waterhemp control in the absence of dicamba:
“Of the alternatives available, we believe a Group 14 herbicide (acifluorfen, fomesafen, lactofen) has a better chance of controlling waterhemp than glyphosate due to the greater prevalence of glyphosate-resistant waterhemp. Group 14 herbicides should be applied as soon as waterhemp is found in a field, and a Group 15 herbicide (acetochlor, dimethenamid, pyroxasulfone, S-metolachlor) should be included to provide residual control after the POST application. Glyphosate or other appropriate tank-mix partners should be included in the mix to broaden the spectrum of weeds controlled.
Preemergence herbicides appear to be providing effective control in most soybean fields at this time, but the timeliness of application of the Group 14 herbicide will be critical. Spraying waterhemp between 0.5 and 1.5 inches in height is ideal. Follow all recommendations on the Group 14 label to maximize effectiveness, including carrier volume, nozzle type, spray pressure, spray additives, and sprayer speed.”