Field experiments were conducted in 2016 and 2017 to evaluate the effects of seeding rate and herbicide programs on weed control and pinto bean yield under irrigation. The experiments comprised a 5 × 5 factorial randomized complete block design with five replications. The weed control treatments comprised a nontreated control, hand-weeded control, EPTC + ethalfluralin PRE, EPTC + ethalfluralin PRE followed by (fb) dimethenamid-P POST at V1, and EPTC + ethalfluralin PRE fb bentazon/imazamox POST. There were five seeding rates ranging from 247,000 to 494,000 seeds ha–1 planted in 19-cm rows. Weed biomass was reduced by 6 kg ha–1 with every additional 1,000 seeds ha–1. EPTC plus ethalfluralin fb either dimethenamid-P or bentazon plus imazamox reduced weed biomass by at least 29% compared to the nontreated control. There was a significant effect of weed control treatment on pinto bean yield (P = 0.0004). However, there was no significant seeding rate (P = 0.42) or seeding rate–by–weed control interaction effect on pinto bean yield (P = 0.38). Pinto bean yield ranged from 3,080 kg ha–1 in the nontreated control to 4,740 kg ha–1 hand-weeded treatment. Increased seeding rate in narrow rows is a cultural practice that can improve weed control in pinto bean but may not necessarily increase yield.

Spurred anoda is an increasing weed problem in Colorado pinto bean production. This research was designed to evaluate reduced rates of bentazon and imazethapyr applied at various times for spurred anoda control and profitability. In 1993, spurred anoda control with early applications of either bentazon or imazethapyr was superior to late applications. Bentazon provided better spurred anoda control than imazethapyr in June. Spurred anoda control in 1993 was better than in 1994 due to late-emerging weeds and herbicide treatments not providing residual control. In 1994, bentazon controlled spurred anoda better than imazethapyr 1 and 3 wk after late POST, but no treatment provided commercially acceptable full-season control. The number of treatments with gross margins greater than the untreated check increased as pinto bean prices increased, but ranking of gross margin did not change due to pinto bean prices.