Yield Reports On Dicamba Injured Soybeans


   The question going into this fall is how much yield loss have the dicamba injured soybeans sustained? As with every concern with this dicamba drift mess, the answers are hard to get and then the results are often a mixed bag.
   Based mostly on last year’s dicamba drift reports. I first estimated that with continued good growing conditions the soybeans just drifted on once in late May and through most of June would have minimal if any yield loss. Fortunatly, that appears to be the case in many fields.
   There have been a few reports of yield loss in the 5 to 10 percent range for fields that were drifted on when soybeans were in the early reproductive period in late June or early July. The reported yield loss has been considerably higher for fields drifted on multiple times. These of course are estimates. It is very hard to get a precise figure as often there are no areas in these fields that did not suffer dicamba injury to check against.
   Most recently we have received a few reports of LL or RR soybeans damaged by dicamba that are not maturing properly. They are staying green and often have malformed pods (often described as “Jay-Hooked”) or a noticeable lack of pods from mid-way up to the top of the plant. This has typically been on later planted soybeans that were apparently exposed to dicamba at a very susceptible soybean growth stage/stages. Combines have not run in these fields yet so time will tell.
   In these cases where the soybeans remain green, an application of Gramoxone as a harvest aid will likely be needed to aid harvest.
   Overall, soybean yields in the state will be very good again this year. We have been very fortunate with the weather helping mitigate all the dicamba drift damage on the soybeans in 2016 and 2017. All the data I have seen is that dicamba injury magnifies drought stress. We may not be so fortunate next year. ∆
   DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee
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