Control of acetolactate synthase-inhibiting herbicide-resistant Palmer amaranth (Amaranthus palmeri) with sequential applications of dimethenamid-Pin dry edible bean

Abstract

AbstractBiotypes of Palmer amaranth that are resistant to acetolactate synthase (ALS) inhibitor are becoming widespread in western Nebraska. There are limited effective postemergence (POST) herbicides labeled for ALS-inhibitor-resistant Palmer amaranth control in dry edible bean. The objective of this study was to evaluate the efficacy of dimethenamid-Pin a sequential preemergence (PRE) fb followed by (fb) POST program at two POST application timings, the first and third trifoliate stages (V1 and V3, respectively), for controlling ALS-inhibitor-resistant Palmer amaranth in dry edible bean. A field study was conducted in 2019, 2020, and 2021 in Scottsbluff, NE. PRE-alone applications of pendimethalin + dimethenamid-Pprovided inconsistent Palmer amaranth control. Dimethenamid-Papplied POST following a PRE application of pendimethalin + dimethenamid-Pprovided effective (>90%) Palmer amaranth control at 4 wk after V3 only at the V1 application timing in 2019. In 2020 and 2021 dimethenamid-Papplied POST at V1 and V3 following a PRE application of pendimethalin + dimethenamid-Pprovided 99% and 98% Palmer amaranth control at 4 wk after V3, and 98% and 94% Palmer amaranth control at harvest, respectively. Palmer amaranth biomass was reduced by 95% to 99% and by 96% to 98% compared with the -nontreated control when dimethenamid-Pwas applied POST at V1 and V3, respectively, following a PRE application of pendimethalin + dimethenamid-Pin 2020 and 2021. Application of a mixture of dimethenamid-Pwith imazamox + bentazon POST provided similar results to those of the fomesafen-containing treatments and dimethenamid-Palone POST. Dimethenamid-Papplied POST following a PRE application of pendimethalin + dimethenamid-Presulted in similar yield as the fomesafen-containing treatments. If fomesafen is not an option due to the crop rotation interval restriction, using dimethenamid-Pin a sequential PRE fb POST program is the only effective alternative to control ALS-inhibitor–resistant Palmer amaranth in Nebraska. The use of dimethenamid-Pin a sequential PRE fb POST program, alone or mixed with foliar-active herbicides should be considered by dry edible bean growers who are dealing with ALS-inhibitor-resistant Palmer amaranth.