Evaluation of Acetochlor for Control of Multiple-Herbicide-Resistant Waterhemp (Amaranthus tuberculatus (Moq.) J.D. Sauer) in Ontario Crops

Abstract

Twenty-five field trials were conducted in 2021 and 2022 to evaluate multiple-herbicide-resistant waterhemp control with acetochlor. Phaseolus vulgaris dry beans, corn, and soybean were tolerant to acetochlor; tank mixing acetochlor and flumioxazin caused 19% soybean injury. Azuki beans were sensitive to acetochlor at 2X rates. Acetochlor controlled waterhemp 96 and 88% in corn and soybean, respectively; acetochlor tank mixtures controlled waterhemp >95% in corn and >89% in soybean. In corn, acetochlor at low, medium, and high rates controlled waterhemp 81, 85, and 90%, respectively; preemergence or postemergence applications provided better control than preplant. In soybean, acetochlor at low, medium, and high rates controlled waterhemp 63, 70, and 74%, respectively; control was similar among application timings. Of five Group 15 herbicides evaluated, flufenacet and pyroxasulfone provided shortest and longest residual control of waterhemp, respectively. Surveys confirmed MHR waterhemp in three additional counties and confirmed Group 27 and 5-way resistance in Ontario.