Studies were conducted in Oklahoma and Arkansas to evaluate the tolerance of nine advanced cowpea breeding lines and one cultivar treated PRE with halosulfuron at 1× (0.054 kg ha⁻¹) and 2× ( 0.107 kg ha⁻¹) rates. The breeding lines, developed by the University of Arkansas, included 01-103, 01-111, 01-117, 01-140, 01-174, 01-180, 01-181, 01-184, and 01-198. ‘Early Scarlet’ was also included as the standard commercial cultivar. Halosulfuron did not reduce the emergence of the breeding lines and Early Scarlet in Oklahoma, but reduced cowpea emergence 14% at the 2× rate in Arkansas. All breeding lines and Early Scarlet had similar emergence capacity in both locations. Higher injury (crop stunting, up to 59% at the 2× rate) and reduction in flowering (up to 83% points at the 1× rate) were observed in Arkansas, but not in Oklahoma. Averaged over herbicide rate, yield was higher and did not differ among cultivars in Arkansas (0.89 to 1.18 Mg ha⁻¹) versus Oklahoma (0.36 to 0.82 Mg ha⁻¹). The highest yield in Oklahoma was obtained from 01-174, 01-103, and 01-117. Despite the observed phytotoxicity symptoms, halosulfuron did not reduce cowpea yield. Halosulfuron is safe to use with these breeding lines and cultivar, at the 0.054 kg ha⁻¹ rate, but may delay cowpea maturity almost 1 wk in soils of close to neutral pH or higher.

Nomenclature: Halosulfuron-methyl; cowpea, Vigna unguiculata L. Walp.