INFLUENCE OF APPLICATION TIMING ON THE EFFICACY OF REDUCED RATE POSTEMERGENCE HERBICIDES FOR WILD OAT (AVENA-FATUA) CONTROL IN SPRING BARLEY (HORDEUM-VULGARE)

Field experiments were conducted during 1992 and 1993 at Kalispell and Moccasin, MT, to determine the influence of application timing on the efficacy of reduced rate postemergence applications of imazamethabenz and diclofop in spring barley. Herbicides were applied at their respe ctive 1 X and 1/2 X use rates at either 1, 2, or 3 weeks after crop em ergence (WAE). While excellent wild oat control was sometimes achieved with reduced rates, there was no consistent relationship between wild oat growth stage and the level of control at either site regardless o f the herbicide or rate applied. This response suggests that efficacy is governed not only by wild oat growth stage, but also by weed demogr aphics and environmental considerations. Barley yield and adjusted gro ss return values were highest at Kalispell when imazamethabenz treatme nts were applied at 1 WAE, regardless of the level of wild oat control . Adjusted gross return values were similar for the 1 X and 1/2 X imaz amethabenz treatments. Yields and adjusted gross returns with diclofop treatments were more related to the level of wild oat control at Kali spell, with the 1 X diclofop treatments providing the greatest yields and adjusted gross return values. The level of wild oat control at Moc casin had minimal effect on barley yield and adjusted gross returns, w ith both values being comparable to the nontreated check.