Control of glyphosate‐ and mesotrione‐resistant Palmer amaranth in glyphosate‐ and glufosinate‐resistant corn

Abstract Increasing reports of herbicide‐resistant Palmer amaranth (Amaranthus palmeri S. Watson) pose a serious management concern for Kansas corn (Zea mays L.) producers. The objectives of this study were to evaluate various herbicide programs, including preemergence (PRE) alone, PRE followed by (fb) early postemergence (EPOST), and PRE fb late POST (LPOST) for control of glyphosate‐ and mesotrione‐resistant (GMR) Palmer amaranth in glyphosate‐ and glufosinate‐resistant corn, and their effect on crop injury, yield, and net economic return. Field experiments were conducted in 2018 and 2019 in grower fields with natural infestations of GMR Palmer amaranth near Seward in Stafford County, KS. Preemergence programs, including dicamba + thiencarbazone‐methyl + atrazine and dicamba + [atrazine, bicyclopyrone, mesotrione, S‐metolachlor (ABMS)] or dicamba + ABMS in mixtures with atrazine, mesotrione, S‐metolachlor, and metribuzin provided 89–93% control of GMR Palmer amaranth 3 wk after PRE. Preemergence fb EPOST programs provided 87–96% control of GMR Palmer amaranth at 2 wk after EPOST through 7 wk after LPOST. In comparison, PRE‐only programs provided 62–82% and PRE fb LPOST programs provided 75–86% control. The various herbicide programs resulted in greater corn grain yield ranging from 9,207 to 10,508 kg ha–1 compared with 6,056 kg ha–1 in the nontreated control. The highest net return ($1,300 ha–1) was achieved from dicamba + ABMS + atrazine applied PRE fb EPOST application of ABMS + atrazine. These results suggest that effective PRE fb EPOST herbicide programs consisting of multiple sites of actions are available and provide effective control of GMR Palmer amaranth in glyphosate‐ and glufosinate‐resistant corn.