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Rain-Splashed Herbicide Injury (06/13/19)

I have received several phone calls this week about PPO-inhibiting (Group 14) herbicide injury on soybean, dry bean, and pulse crops.

I have received several phone calls this week about PPO-inhibiting (Group 14) herbicide injury on soybean, dry bean, and pulse crops. These calls have originated from the northeastern part of the state and all have three things in common: these fields received some rainfall this past weekend; this is the first activating rain since the herbicides were applied preemergence; and the crops had previously emerged with no obvious herbicide injury. This is a different set of circumstances than I wrote about two weeks ago for the Crop and Pest Report. My previous article focused on applying sulfentrazone (Spartan/Authority, generics), flumioxazin (Valor, generics) or saflufenacil (Sharpen products) to emerged soybean. In the injury cases fielded this week, herbicides have sat on the soil surface without any rainfall to incorporate them into the soil. Once fields received a heavy rainfall, the herbicide that is still on the soil surface can be splashed up onto emerged crop leaves and stems. The injury symptoms observed are the typical necrotic/”burned” lesions on leaves and stems that are associated with herbicides with this mode of action. Injury from splashed herbicides tend to be spotted wherever herbicide droplets deposit onto plant surfaces.

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After confirmation of herbicide damage, the next questions are: “Will it grow out of it?” or “Do I need to replant?” The answer to those questions is a strong maybe, and fields should be evaluated individually. In most fields, plants should respond favorably enough that yield loss should not occur and replanting in the middle of June would not be warranted. However, some of these fields also have the confounding factor of wind damage from June 7th’s hot, dry winds. In general, replanting should only be considered when there is severe injury to the growing points of the crop, or if stand loss is severe enough to warrant a replant. While herbicide injury cases can be hard to stomach, it is important to remember that this is a very important herbicide mode of action for broadleaf weed control in our broadleaf crops, and these herbicides remain important tools to help mitigate herbicide resistance weed issues. Moving forward, we will gain more benefits in weed control than the negative results in crop injury that we are seeing in many fields this year.

 

Joe Ikley

Extension Weed Specialist

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