Early-Season Weed Control Using Herbicides with Adjuvants in Direct-Seeded Onion

Early-season weed competition may cause substantial yield losses in onion. Oxyfluorfen and bromoxynil are POST herbicide options for weed control once onion has developed two leaves, which often takes 4 to 6 wk. Multiple applications of oxyfluorfen at 35 and 18 g ai ha−1and bromoxynil at 35 and 18 g ae ha−1with adjuvants were evaluated for onion safety and weed control under controlled greenhouse conditions. Oxyfluorfen at 35 g ha−1plus organosilicone surfactant caused 42% onion injury at 12 d after three sequential applications. Onion treated with bromoxynil at 18 g ha−1plus high surfactant oil concentrate had lower fresh weight (0.7 g) compared to methylated seed oil (MSO) (1.2 g) or petroleum oil concentrate (POC) (1.3 g) at the same bromoxynil rate. The addition of nonionic surfactant to bromoxynil, averaged across bromoxynil rates, provided 17 and 39% control of redroot pigweed and common lambsquarters, respectively. Redroot pigweed control with oxyfluorfen at 35 or 18 g ha−1plus any tested adjuvant was excellent (≥ 93%). Results suggested the use of POC or MSO with either oxyfluorfen or bromoxynil for subsequent field trials because of similar common lambsquarters and redroot pigweed control and onion safety.