Understanding control of glyphosate-resistant (GR) Palmer amaranth with multiple herbicide sites of action, including synthetic auxins, is crucial for growers to minimize GR Palmer amaranth interference with crops. Field studies in 2013 and 2014 and a greenhouse study in 2014 were conducted in Stoneville, MS, to evaluate POST control of GR Palmer amaranth with 2,4-D alone and in mixtures with glyphosate and/or glufosinate. In the greenhouse study, control of 5- and 10-cm GR Palmer amaranth was 87% with 2,4-D at 0.84 kg ae ha ^–1. Dry weight reduction of GR Palmer amaranth was ≥81% with 2,4-D at 0.84 kg ha ^–1. In field studies, mixtures of glufosinate at 0.59 kg ai ha ^–1 and 2,4-D at 0.56 or 1.12 kg ae ha ^–1 controlled 5- to 10-cm GR Palmer amaranth 87% at 28 d after treatment (DAT). Averaged across glyphosate treatments, glufosinate applied alone applied to 5- to 10-cm GR Palmer amaranth reduced dry weight at 28 DAT to 20 g m ^{– 2} from 82 g m ^{– 2} and was comparable with that following 2,4-D applied alone at 1.12 kg ae ha ^–1 and mixtures of glufosinate plus 2,4-D at 0.56 and 1.12 kg ae ha ^–1. Mixtures of 2,4-D plus glufosinate provided ≥92% control of 15- to 20-cm GR Palmer amaranth at 28 DAT. When applied to 15- to 20-cm plants, mixtures of 2,4-D plus glufosinate reduced GR Palmer amaranth density to ≤5 plants m ^{– 2} compared with 65 plants m ^{– 2}Â where no 2,4-D or glufosinate was applied. Glufosinate and 2,4-D are viable control options for 5- to 10-cm or 15- to 20-cm GR Palmer amaranth. However, 2,4-D did not improve GR Palmer amaranth control when added to any herbicide mixture except glyphosate and glufosinate applied to 15- to 20-cm plants at the 28 DAT evaluation.

Nomenclature: 2,4-D; glyphosate; glufosinate; Palmer amaranth Amaranthus palmeri (S.) Watson AMAPA