Influence of Application Timing on the Efficacy of Reduced Rate Postemergence Herbicides for Wild Oat (Avena fatua) Control in Spring Barley (Hordeum vulgare)

Abstract

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 respective 1 × and ½ × use rates at either 1, 2, or 3 weeks after crop emergence (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 of the herbicide or rate applied. This response suggests that efficacy is governed not only by wild oat growth stage, but also by weed demographics and environmental considerations. Barley yield and adjusted gross return values were highest at Kalispell when imazamethabenz treatments were applied at 1 WAE, regardless of the level of wild oat control. Adjusted gross return values were similar for the 1 × and ½ × imazamethabenz treatments. Yields and adjusted gross returns with diclofop treatments were more related to the level of wild oat control at Kalispell, with the 1 × diclofop treatments providing the greatest yields and adjusted gross return values. The level of wild oat control at Moccasin had minimal effect on barley yield and adjusted gross returns, with both values being comparable to the nontreated check.