Characterization and Management of PPO and Glyphosate Resistant Palmer amaranth

Research was conducted from the fall of 2016 to the fall of 2018 to characterize and manage PPO- and glyphosate-resistant Palmer amaranth (Amaranthus palmeri S. Wats). Studies included a multi-county survey to determine the prevalence of PPO-resistant Palmer amaranth biotypes and the PPX2 mutations that confer PPO resistance, an in-field evaluation of control of PPO-resistant and PPO-susceptible Palmer amaranth populations with herbicide treatments applied at either sunrise or midday, and field studies that evaluated cover crop termination for control of Palmer amaranth in Roundup Ready Xtend® and Liberty Link® soybean systems [(Glycine max (L.) Merr.].Results from this research indicate that PPO-resistant Palmer amaranth infests roughly 80% of west Tennessee fields, at least two herbicides with different, effective sites of action should be applied timely for POST herbicidal control of PPO-resistant Palmer amaranth, and that delaying cover crop termination in both Roundup Ready Xtend® and Liberty Link® soybeans can effectively reduce in-season POST applications and maximize Palmer amaranth control if the correct residual herbicide is included at planting timing.