Control of Multiple-Herbicide-Resistant Green Pigweed (Amaranthus powellii) With Preemergence and Postemergence Herbicides in Ontario Corn Production

Green pigweed [Amaranthus powellii S.Wats.] is a prolific annual dicot weed that prominent of crop production in northeastern North America. interference has been documented to reduce corn yields up 54% the absence control strategies. In 2021, green biotype from field near Dresden, Ontario, Canada was determined be resistant MCPA, mecoprop, dichlorprop-p, aminocyclopyrachlor (synthetic auxins), and imazethapyr (acetolactate synthase-(ALS)-inhibitor), further impacting this biotype. Two studies, with herbicides applied preemergence (PRE) or postemergence (POST), were conducted 2020 repeated 2021. The objective research determine most effective PRE POST for multiple-herbicide-resistant (MHR) Ontario production. 18 herbicide treatments evaluated separate studies. Visible injury, visible at specified timepoints after application, density, biomass, yield harvest maturity collected. study, rimsulfuron + mesotrione identified as efficacious treatment providing 88% 8 WAA. atrazine 94% Control all impacted by rainfall following application. MCPA ester controlled 30% WAA; reduced attributed resistance When compared similar some tested. While MHR represents an additional challenge growers, there are would allow it managed