EFFECTS OF TILLAGE AND APPLICATION METHOD ON CLOMAZONE, IMAZAQUIN, AND IMAZETHAPYR PERSISTENCE

Effects of tillage and herbicide application method on the persistence and residual activity of clomazone, imazaquin, and imazethapyr were investigated in a 2-yr field study. Herbicides were applied preemergence and preplant incorporated to conventional- and reduced-tillage soybeans in 1987 and 1988. Herbicide dissipation was monitored using chromatographic and bioassay techniques. In 1987, dissipation rates for clomazone, imazaquin, and imazethapyr were similar, regardless of tillage system or application method. In 1988, all three herbicides applied preplant incorporated dissipated more slowly than in preemergence treatments. Corn planted in rotation in 1989 displayed greater levels of injury in the incorporated treatments for all three herbicides. Although herbicide concentrations were similar 322 d following application in both tillage treatments in 1989, corn injury was greater with imazaquin and imazethapyr and less with clomazone in the reduced-tillage plots than in the conventional-tillage treatments.