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 kgha−1)-, flumioxazin (PPL, 0.21 kgha−1)-, and halosulfuron (PPL, 0.054 kgha−1)-based programs with or without S-metolachlor (1.12 kgha−1) fb imazethapyr (0.07 kgha−1); and two sets of sulfentrazone (PPL/PRE)-based programs applied alone (0.21 kgha−1) or as a pre-mixture with carfentrazone (0.11 kgha−1+0.01 kgha−1) with or without S-metolachlor (1.12 kgha−1). The sulfentrazone-based programs included POST applications of imazethapyr fb sethoxydim (0.32 kgha−1) or fluthiacet-methyl (0.0067 kgha−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, sulfentrazone-containing 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.

Field research was conducted in 1983 and 1984 at Scottsbluff, NE, to determine the effect of cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methyl-propanenitrile} applied in corn (Zea mays L. ‘Pioneer 3732’) on fieldbeans (Phaseolus vulgaris L. ‘Valley’) planted 30 days later to replace corn. Cyanazine preplant incorporated at 1.1 kg ai/ha or higher reduced the vigor, stand, and yield of fieldbeans as a replant crop.

The effects of the dimethylamine salt of dicamba (3,6-dichloro-2-methoxybenzoic acid) and the dimethylamine salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid] on fieldbeans (Phaseolus vulgaris L. ‘Great Northern Valley’) were studied in order to assess the potential hazards of using these herbicides in areas adjoining fieldbean production. Dicamba and 2,4-D were applied to fieldbeans at three different rates (1.1, 11.2, and 112.5 g ai/ha) and four different growth stages (preemergence, second trifoliolate leaf, early bloom, and early pod). Application of 2,4-D preemergence or in the second trifoliolate leaf stage of growth did not reduce seed yield, delay maturity, or reduce germination of seed obtained from treated plants. Dicamba or 2,4-D applied at 112.5 g/ha to fieldbeans in the early bloom or early pod stages of growth consistently reduced seed yield, delayed maturity, and reduced germination percentage. Fieldbeans exhibited a greater overall sensitivity to dicamba than to 2,4-D.

Field studies were conducted in 2010 and 2011 at two locations in Michigan to examine the effect of row width and herbicide combination on weed suppression and yield in the new Type II black bean variety ‘Zorro.' Black bean was planted in 38- and 76-cm rows. Six weed control strategies were examined: S-metolachlor + halosulfuron (PRE), S-metolachlor (PRE) followed by (fb) bentazon + fomesafen (POST), halosulfuron (PRE) fb clethodim (+ fomesafen at one site in one year) (POST), imazamox + bentazon (POST), a weed-free control, and a nontreated control. Weed control and crop injury were evaluated throughout the growing season. In addition, weeds were counted by species in late July, and weed biomass was harvested and weighed at the end of the season. Black bean yield was obtained by direct harvest. Narrow rows reduced weed populations in two of the four site–year combinations (referred to hereafter as site–years), reduced weed biomass in three of the four site–years, and often improved control of upright broadleaf weeds. All herbicide combinations generally reduced weed populations and biomass, but control of specific weeds was variable. Crop injury was generally slight and transient. Yield was greater in narrow rows in two of the four site–years. All herbicide combinations increased yield compared with the nontreated control and resulted in similar yields to one another. Yield and weed suppression was often maximized in narrow rows, while herbicide performance varied by year and weed spectrum.