The battle against waterhemp is complicated mainly because of its extended emergence period (early May until August). Preemergence (PRE) soil residual herbicides serve as a foundation for managing waterhemp, but require follow-up treatments with effective postemergence (POST) products due to late-emerging plants. Group 15 herbicides (HG 15) are commonly used for PRE waterhemp control. However, an increased selection pressure from these herbicides used in corn-soybean rotations has resulted in the evolution of HG 15 resistance in waterhemp populations, recently documented in Illinois. Those populations were resistant to one or more of these products including s-metolachlor, dimethenamid-P, pyroxasulfone, and acetochlor. Waterhemp resistance to HG 15 has not been confirmed yet in Iowa; however, it is important to proactively protect the value of these products for waterhemp control in soybean fields.
Iowa State University
Jha, Prashant, "Performance of Preemergence Herbicides on Waterhemp Control in Soybean" (2020). Integrated Crop Management News. 2622.
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