Integrated effect of row spacing and herbicide programs on photosynthetically active radiation, control, and seed production of multiple herbicide‐resistant Palmer amaranth in corn

Abstract Multiple herbicide‐resistant (MHR) Palmer amaranth has been ranked as the most problematic weed in row crop fields in Nebraska. Integration of narrow row spacing with herbicide might augment control of MHR Palmer amaranth. The objectives of this study were to evaluate an integrated effect of row spacing and herbicide programs for MHR Palmer amaranth control, density, seed production, corn injury, photosynthetically active radiation (PAR) interception, and grain yield in glyphosate/glufosinate‐resistant corn. Field experiments were conducted in 2020 and 2021 in a grower's field infested with acetolactate synthase‐inhibitor/atrazine/glyphosate‐resistant Palmer amaranth near Carleton, NE. Herbicide‐by‐row spacing interactions were significant for most variables. Flufenacet/isoxaflutole/thiencarbazone‐methyl followed by (fb) glufosinate, acetochlor/mesotrione applied pre‐emergence (PRE) or fb glufosinate, acetochlor/clopyralid/flumetsulam fb glufosinate, and glufosinate fb dicamba/tembotrione controlled Palmer amaranth ≥90% at 90 days after late post‐emergence (DALPOST) herbicide application. Glufosinate fb dicamba/tembotrione and acetochlor/mesotrione fb glufosinate with 38‐ and 76‐cm row spacing, flufenacet/isoxaflutole/thiencarbazone‐methyl fb glufosinate, and acetochlor/clopyralid/flumetsulam fb glufosinate with 38‐cm row spacing recorded no Palmer amaranth 30 DALPOST. Herbicide programs with narrow row spacing had numerically higher PAR interception compared with 76‐cm row spacing 30 days after early post‐emergence (DAEPOST) and 15 DALPOST. Higher corn yield (13,222–13,596 kg ha −1 ) was obtained with acetochlor/clopyralid/flumetsulam fb glufosinate with 38‐cm row spacing. Palmer amaranth seed production was zero with acetochlor/mesotrione fb glufosinate, and glufosinate fb dicamba/tembotrione; flufenacet/isoxaflutole/thiencarbazone‐methyl fb glufosinate in 76‐cm row spacing; and acetochlor/clopyralid/flumetsulam fb glufosinate in 38‐cm row spacing.