Weed control and corn (Zea mays) tolerance from soil-applied RPA 201772

Field experiments were conducted in 1996, 1997, and 1998 to evaluate weed c ontrol and corn tolerance from soil-applied RPA 201772. Treatments alone an d in tank mixtures with other corn herbicides were applied preemergence (PR E) at two locations with conventional tillage and at early preplant (EPP) a nd PRE application timings in no-tillage corn. RPA 201772 was applied alone and in tank mixtures with one-half the typical field rates of other PRE co rn herbicides. In conventional tillage experiments in 1996, 1997, and at on e location in 1998, all treatments containing RPA 201772 provided > 90% con trol of common lambsquarters, redroot pigweed, common ragweed, and velvetle af. In two no-tillage experiments, common lambsquarters and velvetleaf cont rol was > 90%, regardless of application timing. However, control of redroo t pigweed and common ragweed varied among years and application timings. We ed control was more variable from herbicide treatments applied EPP compared with the PRE application timing. Giant foxtail control in both tillage sys tems was rate, timing, and year dependent. RPA 201772 rates higher than 79 g/ha controlled giant foxtail > 85% at three of five locations. At one loca tion, tank mixtures with RPA 201772 increased giant foxtail control. Corn i njury occurred in one of two conventional tillage locations and at the no-t illage location in both 1996 and 1997. Injury was most commonly observed in coarse-textured soils with low clay and organic matter and was more severe with higher rates of RPA 201772. Increased corn injury was also observed w hen RPA 201772 was combined with acetochlor plus dicloramid or BAYFOE 5043 plus metribuzin. Corn injury from RPA 201772 occurred at application rates above the proposed rate for use on corn. In some cases, severe injury to co rn reduced corn yield. Injury to corn from RPA 201772 was not unique to any tillage system and was site, year, and rate dependent.