Cowpea is a major specialty crop in the southern US. In recent years, no new herbicide programs have been evaluated for cowpea despite additional herbicide registrations. Studies were conducted from 2014 to 2016 at Fayetteville and Kibler, Arkansas to assess new herbicide programs for cowpea production. The herbicide programs included: three commercial standard programs; fomesafen (PPL, 0.21 kg ha-1)-, flumioxazin (PPL, 0.21kgha-1)-, and halosulfuron (PPL, 0.054 kg ha-1)-based programs with or without S-metolachlor (1.12 kg ha-1) fb imazethapyr (0.07 kg ha-1); and two sets of sulfentrazone (PPL/PRE)-based programs applied alone (0.21 kg ha-1) or as a pre-mixture with carfentrazone (0.11kgha-1 0.01kgha-1) with or without S-metolachlor (1.12 kg ha-1). The sulfentrazone-based programs included POST applications of imazethapyr fb sethoxydim (0.32 kg ha-1) or fluthiacet-methyl (0.0067 kg ha-1) and sethoxydim as necessary. In 2014 and 2015, crop stand loss was minimal and crop injury was generally low (<20%). Weed control from sulfentrazone- and flumioxazin-based programs was excellent (>90%). In 2016, with heavy rainfall around planting time, sulfentrazonecontaining programs reduced cowpea yield 45% to 60%. Flumioxazin-based programs caused >85% injury at Kibler early-season, which lasted until harvest. Heavy rainfall also reduced efficacy of residual herbicides. In general, the sulfentrazone- and flumioxazin-based treatments consistently yielded similar to the weed-free controls. The majority of the programs had <60% weed control in Fayetteville early in the season. POST herbicides improved weed control to >90% in most treatments. Palmer amaranth and annual grass control was generally better in Kibler, with >80% control at harvest. Sulfentrazone is registered for cowpea and is effective on Palmer amaranth, but growers need to be careful about where and when to use it. Flumioxazin should be considered for registration in cowpea once its use pattern and location-specific recommendations are well defined.
Nomenclature: Bentazon; fomesafen; halosulfuron; imazethapyr; sethoxydim; S-metolachlor; sulfentrazone; trifluralin; cowpea, Vigna unguiculata (L.) Walp; Palmer amaranth, Amaranthus palmeri S. Watson.