Sequential Herbicide Applications in Stale Seedbed Soybean (Glycine max)

Abstract

Field experiments were established in 1991 and 1992 on silty clay and sandy loam soils to evaluate various split rates of early PPI and PRE (to soybean) selective herbicides with and without paraquat for sicklepod and pitted morningglory control in stale seedbed soybean. Metribuzin at 360 g ai/ha plus 60 g ai/ha chlorimuron tank-mixed with 700 g ai/ha paraquat controlled sicklepod and pitted morningglory 83 and 91%, respectively, 4 wk after planting. Without paraquat, sicklepod and pitted morningglory control was only 65% and 67%, respectively. Imazaquin at 140 g/ha PRE tank-mixed with paraquat controlled sicklepod 78% and pitted morningglory 92%. Without paraquat, control was 38% and 84%, respectively. Early PPI applications of metribuzin plus chlorimuron or imazaquin at the full rate alone or followed by paraquat at planting resulted in poor control. With sequential treatments (PPI followed by PRE) the addition of paraquat at planting did not usually improve control, and either imazaquin or metribuzin plus chlorimuron provided equivalent control when compared with the full rate of either herbicide applied PRE. Season-long weed control was not obtained with any treatment in any experiment, and the crop was not harvestable.