By Eric Jones and Philip Rozeboom et.al
The cutoff date to apply dicamba (i.e., Engenia and Xtendimax) postemergence to dicamba-tolerant soybeans is June 20, 2024 in South Dakota. The weather has delayed the planting of soybean, and the clock is ticking to spray dicamba. The best option would be to apply the herbicide early postemergence. While the weeds will be small and likely effectively managed, a sequential application may be needed to control later emerging weeds. Adding an herbicide with soil residual activity will extend the effectiveness of the early postemergence. Be sure to consult the herbicide label to ensure the tank mix is approved. Additional herbicides that are approved tank mix partners should be applied with dicamba as commonly recommended.
If soybean planting is still delayed, dicamba can be applied preemergence. However, the length of residual activity is much shorter than other preemergence herbicides and the herbicide will be washed through the soil profile after a rain event. If the forecast shows dry conditions after planting, then dicamba may be a viable option. Adding another common preemergence herbicide (i.e., S-metolachlor [Dual Magnum] or flumioxazin [Valor]), can hedge yourself against the weather conditions and likely increase the spectrum of weed control. A complete list of herbicides that can be applied pre- and postemergence can be found in the latest South Dakota Pest Management Guide: Soybean; however, consult the labels for approved herbicide tank mix partners. There are two websites that also provide this information for Engenia and Xtendimax.
Before spraying dicamba (or any other pesticide) check the weather conditions. Temperature should be below 85 F, wind speed between 5 and 10 miles per hour, and no temperature inversion present. The Mesonet at SDState is a great place to check weather conditions near your farm. What should you do if you cannot get dicamba sprayed before June 20? Do not spray dicamba! While you have purchased dicamba to use in your soybeans, applying dicamba now is illegal and can bear great repercussions if caught doing such. Applying dicamba after the cutoff date is not worth the risk when there are other viable options. More information on weed management without dicamba can be found in the article, Dicamba Label Vacated: What are the implications for weed control in soybean?.
Lastly, while the cutoff date does make weed management even more difficult, this should be a reminder that an effective weed management plan should not focus solely on one tactic or herbicide. While having a solid plan developed before planting is a great practice, being amendable should also be a part of the plan. Every growing season is different and things like rain and wind are out of our control. Integrating on-chemical tactics such as crop rotation and row spacing will aid in managing weeds but can also provide agronomic benefits as well. The best non-chemical tactics are the ones that are easily adaptable to current production practices.
Source : sdstate.edu