Late postemergence glufosinate‐based programs for glyphosate‐resistant Palmer amaranth control in dicamba/glufosinate/glyphosate‐resistant soybean

Abstract

Glyphosate‐resistant (GR) Palmer amaranth (Amaranthus palmeri S. Watson) is widespread in the Central Great Plains. Introduction of newly developed dicamba/glufosinate/glyphosate (DGG)‐resistant soybean varieties allows postemergence (POST) applications of dicamba and glufosinate for in‐season control of GR Palmer amaranth. Limited information exists on the effectiveness of glufosinate applied late‐POST for tall (70–90 cm) GR Palmer amaranth control in DGG‐resistant soybean. The objectives of this study were to (1) determine the effectiveness of late‐POST glufosinate‐based programs for GR Palmer amaranth control, and (2) determine the impact of those programs on soybeans grain yields. Ten glufosinate‐based programs were tested in a field study at Kansas State University Agricultural Research Center near Hays, Kansas. Results indicated that single (655 or 737 g ha−1) and all sequential (594 followed by [fb] 594, 655 fb 594, and 737 fb 594 g ha−1) applications (7‐days apart) of glufosinate provided 87%–93% control of GR Palmer amaranth 28 days after last POST (DALPOST). Palmer amaranth control with single late‐POST application of glufosinate (594 g ha−1) or glufosinate plus S‐metolachlor did not exceed 84% at 28 DALPOST. Majority of the evaluated programs reduced shoot dry weights of GR Palmer amaranth by 83%–91%. The least control (11%) and shoot dry weight reduction (33%) of GR Palmer amaranth were observed with glyphosate fb glyphosate. Glufosinate‐based programs resulted in soybean grain yield of 626–701 kg ha−1. These results conclude that glufosinate applied late‐POST may provide effective control of tall GR Palmer amaranth in DGG‐resistant soybeans.