Comparison of residual activity of pre‐emergence herbicides for control and seed production of multiple herbicide‐resistant Palmer amaranth in food‐grade white corn

Abstract Nebraska is the number‐one producer of food‐grade white corn ( Zea mays L.) in the United States. Food‐grade white corn has not been genetically engineered; therefore, non‐selective herbicides such as glyphosate or glufosinate cannot be used. Multiple herbicide‐resistant (MHR) Palmer amaranth ( Amaranthus palmeri S. Watson) populations have been reported in multiple counties in Nebraska, and their management is a challenge, particularly for white corn producers. The objectives of this study were to evaluate the residual activity of pre‐emergence (PRE) herbicides for acetolactate synthase inhibitor (halosulfuron‐methyl)/atrazine/glyphosate‐resistant Palmer amaranth control, density, biomass, seed production, and grain yield in food‐grade white corn. Field experiments were conducted during summer 2020 and 2021 in a grower's field infested with MHR Palmer amaranth near Carleton, NE. All the PRE herbicides resulted in similar control (>90%) 30 days after PRE application (DAPRE) apart from atrazine (64%). At 45 DAPRE, acetochlor/mesotrione, atrazine/bicyclopyrone/mesotrione/ S ‐metolachlor, and acetochlor/clopyralid/mesotrione controlled 90%–95% Palmer amaranth. Acetochlor/clopyralid/mesotrione and atrazine/bicyclopyrone/mesotrione/ S ‐metolachlor provided 96%–99% MHR Palmer amaranth control and reduced Palmer amaranth density and biomass to 2–4 plants m −2 and 5–12 g m −2 60 DAPRE. The highest corn yields of 12,139 kg ha −1 and 12,093 kg ha −1 in 2020 and 2021, respectively, were obtained with acetochlor/clopyralid/mesotrione. Palmer amaranth seed production was least with acetochlor/clopyralid/mesotrione (32,894 seeds m −2 ). Tested residual PRE herbicides did not show corn injury and were safe to use in food‐grade white corn. It is concluded that acetochlor/clopyralid/mesotrione and atrazine/bicyclopyone/mesotrione/ S ‐metolachlor are the best options for early season control of MHR Palmer amaranth in food‐grade white corn.