The most frequently asked question at Dakotafest was: How will soybean fields affected by dicamba drift or sprayer contamination yield? It would be nice if there was a formula that could be used to determine that answer but unfortunately, that is wishful thinking. There are some things however, that can be considered that may be useful in answering the question.
First, examine the growing point of the soybean plant. Continued development of new leaves is a positive sign. Historically, when dicamba injury was noted on soybean before June 15 and if the growing point remained healthy, it was very likely that no yield reduction would be noted. If the growing point was damaged, a yield reduction was likely. Throughout most of the fields I have scouted this year, the growing point is still intact.
Many dicamba applications occurred this year after June 15. No credible information exists on the potential yield reduction to soybean when dicamba injury happens after June 15. Dicamba injury also can delay soybean maturity which can place the crop at risk if an early frost occurs.
Past research conducted at SDSU, in the late 1970s, by Auch looked at the yield impact of dicamba injury to soybean. In many cases soybean yield was decreased. In other situations, a yield increase was recorded from dicamba-damaged soybean. However, soybean response to dicamba injury was highly rate-specific and environmentally dependent. Trying to predict soybean yield response to observed short-term plant injury symptoms caused by dicamba injury is nearly impossible. Consider documenting areas of the field that appear to have low, medium, and high foliar injury symptoms. Today’s yield monitor technology will show a possible answer to the question of yield impact.