HERBICIDE SYSTEMS IN STALE SEEDBED SOYBEAN (GLYCINE-MAX) PRODUCTION

Field experiments were conducted using a stale seedbed production system to determine the effect of herbicide application time on preplant, preplant incorporated (PPI), and at-planting treatments on weed control and soybean yield. Herbicides were applied on the surface preplant (PPL) or PPI at 6 to 7, 4 to 5, and 2 to 3 wk before planting and just prior to planting. The differences in weed control and soybean yield among years were due to rainfall patterns 2 wk after herbicide application and during the growing season. Preplant treatments applied 2 to 5 wk before planting generally controlled common cocklebur and pitted morningglory better than preplant treatments applied 6 to 7 wk before planting due to persistence of herbicide activity or treatments at planting due to a greater chance of obtaining adequate rainfall for herbicide activation, more uniform seedbed at planting, and larger weeds at application. Metribuzin plus chlorimuron was less suited than imazaquin as a preplant treatment when applied more than 2 weeks before planting.