Horseweed (<i>Conyza canadensis</i>) Control in No-Tillage Soybeans (<i>Glycine max</i>) with Preplant and Preemergence Herbicides

Abstract

Research was conducted in 1987 and 1988 to identify effective horseweed control strategies in no-tillage soybean production. Paraquat at 560 g ai ha -1 plus metolachlor at 2200 g ai ha -1 , linuron at 840 g ai ha -1 , and nonionic surfactant at 0.25% (v/v) applied preemergence provided less than 61% horseweed control. Glyphosate at 840 g ai ha -1 , 2,4-D ester at 560 g ai ha -1 , HOE-39866 at 840 g ai ha -1 , or BAS-514 at 70 g ai ha -1 applied early preplant controlled more than 96% when followed by the above preemergence herbicide combination. Substituting either glyphosate at 840 g ha -1 or HOE-39866 at 840 g ha -1 for paraquat in the preemergence application program significantly increased control. Adding BAS-514 at 70 g ha -1 to preemergence treatments containing paraquat significantly improved control. The substitution of metribuzin, metribuzin plus chlorimuron (10:1 ratio), or linuron plus chlorimuron (16:1 ratio) for linuron resulted in greater control and soybean yield. Sequential applications controlled horseweed equal to or better than a single preemergence application at the same total rate.