Imazethapyr, Alone or with Other Herbicides for Weed Control During Alfalfa (Medicago sativa) Establishment

Abstract

During the establishment of alfalfa, POST applications of imazethapyr at 50 g/ha, following PPI applications of trifluralin at 1,100 g/ha, consistently provided ≥ 80% control of wild oat, volunteer canola, and shepherd's-purse with no crop injury. POST applications of the same rate of imazethapyr without PPI applications of trifluralin provided similar volunteer canola and shepherd's-purse control, but ≥ 80% wild oat control was achieved only 25% of the time. Imazethapyr, alone or following trifluralin, did not control common groundsel. Broadleaf weed control from imazethapyr at 50 g/ha tank mixed with fluazifop-P at 125 g/ha or sethoxydim at 200 g/ha was not reduced compared to imazethapyr alone. However, the probability of controlling wild oat by ≥ 90% was reduced from 83% to 0 when the same rate of imazethapyr was tank mixed with fluazifop-P, compared to fluazifop-P alone. Tank mixtures of imazethapyr at 50 g/ha and sethoxydim controlled wild oat only slightly less than sethoxydim alone. First cut and total herbage yields, obtained 1 yr after alfalfa establishment, increased where treatments effectively controlled broadleaf weeds and wild oat, compared to check plots. Second cut herbage and seed yields, also obtained 1 yr after alfalfa establishment, were not affected by any of the treatments.