Effect of cotton herbicide programs on weed population trajectories and frequency of glyphosate-resistant Palmer amaranth (<i>Amaranthus palmeri</i>)

Abstract The adoption of dicamba-resistant cotton ( Gossypium hirsutum L.) cultivars allows using dicamba to reduce weed populations across growing seasons. However, the overuse this tool risks selecting new herbicide-resistant biotypes. objectives research were determine population trajectories several species and track frequency glyphosate-resistant (GR) Palmer amaranth Amaranthus palmeri S. Watson) over 8 yr in cotton. An experiment was established North Carolina 2011, during first 4 yr, different herbicide programs applied. These included postemergence applications glyphosate, alone or with dicamba, without residual herbicides. During last all received glyphosate plus dicamba. Biennial rotations only preemergence herbicides also included. Sequential applied entire test area for final study. No program entirely successful controlling community. Weed according program, creating possible outcomes; some increased, others decreased, remained stable. Density resistant A. increased glyphosate-only (up 11,739 plants m −2 ) decreased a 96% when implemented. This had strong influence on levels other Goosegrass [ Eleusine indica (L.) Gaertn.] not affected by even its density programs, indicating that resistance but reproductive rates competitive dynamics are critical determining under intensive herbicide-based control programs. Frequency reached maximum 62% after those maintained until end experiment.