Weed Management Programs in Glufosinate-Resistant Soybean (Glycine max)1

Field trials were conducted at two sites in both 1997 and 1998 to evaluate soybean response and weed control with glufosinate alone or combined with quizalofop, lactofen, imazethapyr, flumiclorac, or bentazon plus acifluorfen in narrow-row, glufosinate-resistant soybean. Soybean injury ranged from 0 to 21% at 2 wk after treatment (WAT) and from 0 to 5% by 4 WAT. Glufosinate alone at 0.29 and 0.4 kg ai/ha controlled velvetleaf, common waterhemp, common ragweed, morningglory species, and giant foxtail greater than 85% in all studies. Mixtures containing glufosinate and other herbicides controlled these species greater than 81% but did not improve control over glufosinate alone. Estimates of weed biomass closely reflected visual control evaluations. However, giant foxtail biomass was higher for mixtures of glufosinate plus lactofen, flumiclorac, or bentazon and acifluorfen, indicating possible antagonism of glufosinate activity. At both locations, soybean yields were similar among most treatments, but that of the glufosinate plus lactofen treatment was lower when compared with other treatments. Additional trials evaluated soybean response and weed control with a preemergence herbicide followed by glufosinate postemergence (POST), glufosinate applied once or twice POST, and mixtures of glufosinate plus imazethapyr or flumiclorac POST in wide-row soybean. Glufosinate applied twice controlled common waterhemp, morningglory species, prickly sida, common cocklebur, and giant foxtail up to 39% greater than did glufosinate applied once. The addition of imazethapyr, but not flumiclorac, to glufosinate improved weed control when compared with glufosinate alone.Nomenclature: Acifluorfen; bentazon; flumiclorac; glufosinate; imazethapyr; lactofen; quizalofop; common cocklebur, Xanthium strumarium L. #3 XANST; common ragweed, Ambrosia artemisiifolia L. # AMBEL; common waterhemp, Amaranthus rudis Sauer # AMATA; giant foxtail, Setaria faberi Herrm. # SETFA; morningglory species, Ipomoea spp. # IPOSS; prickly sida, Sida spinosa L. # SIDSP; velvetleaf, Abutilon theophrasti Medik. # ABUTH; soybean, Glycine max (L.) Merr. ‘Asgrow 2704 LL’.Additional index words: Herbicide mixtures, herbicide-resistant crop, soybean injury.Abbreviations: COC, crop oil concentrate; EPOST, early postemergence; LPOST, late postemergence; MPOST, midpostemergence; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.