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How to manage weeds without dicamba on dicamba-tolerant soybeans

Other options exist, but farmers need to reset weed control expectations, say North Dakota State University specialists.

On June 3, the United States Court of Appeals for the Ninth Circuit issued its decision that effectively vacated the registrations of the dicamba-containing products XtendiMax, Engenia and FeXapan. 

Since this ruling, Extension weed specialists like Aaron Hager at the University of Illinois have received many questions about the fate of these products already in the commercial channel. During a recent conversation Hager had with officials at the Illinois Department of Agriculture, officials presented their interpretation of the court ruling as follows:

It is the current interpretation of the Illinois Department of Agriculture that the dicamba-containing products XtendiMax, Engenia, and FeXapan are no longer registered products and are not to be distributed, sold, or used, effective upon the decision of the United States Court of Appeals for the Ninth Circuit.

The registration of Tavium Plus VaporGrip Technology – marketed by Syngenta – and all other dicamba-containing products are not affected by this ruling.


So What Are Your Options?
Much depends on which weeds are present in your field. Tavium is still legal to apply. Here are some non-dicamba options that Joe Ikley, North Dakota State University (NDSU) Extension weed specialist, and Tom Peters, NDSU Extension sugar beet agronomist, have been telling North Dakota farmers about to control some of that state’s problematic weeds that will likely show up in Xtend soybean fields. Bear in mind, your state and fields may differ from these recommendations. 
 
Waterhemp. It is safe to assume that any waterhemp is resistant to ALS-inhibiting (Group 2) herbicides, say Ikley and Peters. Glyphosate-resistance is also present on most acres, though not all plants will be resistant. Glyphosate is most effective on waterhemp up to two leaves when applied at labeled rates with adjuvants. The best remaining options would be PPO-inhibiting (Group 14) herbicides. Flexstar (fomesafen), Cobra, or Ultra Blazer could all be used on small waterhemp. The addition of oil adjuvants will be important for weed control. Flexstar cannot be applied after June 20 west of Highway 281 in North Dakota. 
 
Common lambsquarters. Glyphosate (Group 9) has historically provided variable control of common lambsquarters in North Dakota, they say. Harmony (thifensulfuron, Group 2) will be one of the best options left for the Xtend acres.
 
Kochia. Glyphosate is the best option for those who do not have glyphosate-resistant kochia. For the acres with glyphosate-resistance, Flexstar is one of the few remaining options and must be applied to small plants. Flexstar will work best by maximizing spray coverage and using full rates of oil adjuvants. 
 
Common ragweed. Glyphosate, FirstRate (Group 2), and Flexstar are the best remaining options for common ragweed control, say Ikley and Peters. Several North Dakota populations resistant to glyphosate and FirstRate exist, so do not expect control with either product on those populations.
 
Horseweed/marestail. The safe assumption for horseweed is that it is glyphosate-resistant. This leaves FirstRate as the best remaining option. However, some North Dakota marestail populations also resist FirstRate. Unfortunately, North Dakota farmers are left with no effective postemergence options in Xtend soybean for horseweed populations that resist both glyphosate and FirstRate.  
 
Remember Best Practices
Ikley and Peters say it is important to remember best practices for applying these alternate options. For instance, Group 14 herbicides (like Flexstar) are contact herbicides that work better with higher carrier volumes and smaller droplets. Flexstar can also have carryover issues for rotational crops like corn and sugar beets. 

Basagran is another herbicide option that can help control these weeds. However, reset weed control expectations to target weeds smaller than 1 inch, they say. Many weeds may already be larger than 1 inch, so expect inconsistent control, they say. 

Now is also a good time to reinforce the use of tank-mixing Group 15 herbicides with postemergence applications for waterhemp control. The Group 15 herbicides will not control any emerged plants, but will help control later emerging waterhemp, say Ikley and Peters. 
 

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