The recent decision by the United States Court of Appeals for the Ninth Circuit to vacate the registrations of XtendiMax, Engenia and FeXapan has generated many questions about herbicide options to control weeds in dicamba-resistant soybean. Tavium, a premixture of dicamba and S-metoachlor, remains in the marketplace and may be applied to dicamba-resisant soybean. Keep in mind all restrictions with respect to application timing on the federal Tavium label (i.e., within 45 days of planting) and the Illinois 24 (c) label (i.e., no applications after June 20 and when actual or forecast air temperature exceeds 85 degrees) still apply. Additionally, Tavium must be applied before soybean exceed the V4 growth stage and Tavium cannot be used in double-crop soybean.
If we assume most postemergence applications in dicamba-resistant soybean will include glyphosate, than any registered foliar-applied soybean herbicide can be tankmixed as long as the tankmix is not prohibited on either product label. Perhaps the most significant challenge will be controlling waterhemp, much of which is resistant to ALS inhibitors, glyphosate and PPO inhibitors. In instances where individual plants are resistant to herbicides from these three groups, there are no other herbicide options in dicamba soybean. Our data suggests 2,4-DB is not an effective option for waterhemp, and while Group 15 herbicides can provide soil-residual control, they provide no foliar control of emerged weeds. Mechanical cultivation, where possible, is another option.
Remember to select appropriate nozzles, additives, volumes, etc., to achieve good spray coverage for any tankmixture applied.