Performance of Preemergence Herbicides on Waterhemp Control in Soybean

Abstract

<p>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.</p>