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

Green pigweed [Amaranthus powellii S. Wats.] is a competitive, annual, broadleaf weed that can significantly reduce soybean yield due to rapid early growth and biomass production. As consequence of green pigweed’s high competitiveness with crops, the species generally managed use herbicides; this may, however, lead selection resistance. A biotype resistance MCPA, mecoprop, dichlorprop-p, aminocyclopyrachlor (synthetic auxins), imazethapyr (acetolactate synthase-(ALS)-inhibitor) was recently confirmed in Ontario, Canada. Research conducted identify alternative effective preemergence (PRE) postemergence (POST) herbicides for control multiple-herbicide-resistant (MHR) Ontario Four field trials, two PRE POST were near Dresden, 2019 2020. Visible injury, control, density, aboveground biomass, evaluated following application 19 herbicide treatments 12 separate studies. At 8 wk after (WAA), pyroxasulfone/flumioxazin applied controlled 95% most soil-applied herbicide. In study, glyphosate herbicide, controlling 94% at WAA. Imazethapyr, or did not as it also resistant ALS-inhibitors. Control other ALS-inhibiting well PPO-inhibiting variable, further research needed determine reason variable these herbicides.