Doctoral Dissertations

Date of Award

12-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

Larry Steckel

Committee Members

Bobby Haygood, Angela McClure, Thomas Mueller, Scott Senseman, Scott Stewart

Abstract

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.

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