Palmer Amaranth (Amaranthus palmeri) Control with Preplant Herbicide Programs Containing Dicamba, Isoxaflutole, and 2,4‐D

Abstract

Glyphosate‐resistant (GR) Palmer amaranth (Amaranthus palmeri S. Wats.) prevalence in Midwest soybean [Glycine max (L.) Merr.] production has increased in recent years. New soybean herbicide‐resistant traits will be important management tools for herbicide‐resistant weeds. The objectives of this research were to evaluate preemergence (PRE) herbicide treatments that contain dicamba, isoxaflutole, metribuzin, S‐metolachlor, and 2,4‐D for GR Palmer amaranth control. Herbicide programs that contained isoxaflutole provided 58 to 95% control compared with 41 to 85% control by 2,4‐D or dicamba. Control of GR Palmer amaranth with mixtures containing dicamba ranged from 71 to 85% compared with 41 to 53% control with mixtures of 2,4‐D. Treatments containing one herbicide mode of action (MOA) failed to provide more than 57 and 50% GR Palmer amaranth control at 21 and 42 days after the preemergence treatment (DAPT), respectively. A mixture that contained three herbicide MOA (metribuzin plus S‐metolachlor mixed with dicamba, isoxaflutole, or 2,4‐D) controlled GR Palmer amaranth 83 to 86% compared with a treatment with a single MOA that provided 31 to 50% control. Coapplication of metribuzin with dicamba, isoxaflutole, or 2,4‐D resulted in 67 to 72% control, while mixtures of S‐metolachlor with dicamba, isoxaflutole, or 2,4‐D provided 63 to 91% GR Palmer amaranth control. In most instances mixtures with two MOA resulted in GR Palmer amaranth control that was similar to mixtures with three MOA at 42 DAPT.