Response of New Cultivars to Early Postemergence Chlorimuron Applications1

Field studies were conducted in Alabama and Georgia in 2002 and 2003 to determine whether the peanut cultivar that replaced the cultivar Florunner can tolerate earlier applications of the herbicide chlorimuron than what is registered. The application timing restriction of chlorimuron on peanut had been established in the late 1980s with Florunner. In a factorial treatment arrangement, the cultivars AT201, Georgia Green, Viragard, C99R, and Florunner were treated with chlorimuron at 8.75 g ai/ha at 5, 7, 9, or 11 wk after planting. Only the later two application timings are covered by the current registration. Across all 4 yr-location replications, yield was influenced by the main effect of peanut cultivar. C99R was consistently the highest yielding cultivar. Chlorimuron had no effect on yield, regardless of application timing when compared to the nontreated entries in three of the four repetitions (i.e. Plains 2002, Plains 2003, and Headland 2002). Cultivar-based chlorimuron tolerance differences were detected only at Headland in 2003. For this location, chlorimuron applied at 5 wk after planting reduced yield across all cultivars, while application at 7, 9, and 11 WAP had no effect on yield. Results indicate that chlorimuron possesses a yield-reducing risk only when the crop has been stressed by other factors. Assuming that the crop has been stressed, the potential of yield reduction can be avoided only by observing the currently registered application timing. No clear indication was obtained that one cultivar was more tolerant to chlorimuron than another cultivar.