Field studies were conducted to evaluate soybean injury and yield reduction from foliar applications of mesotrione. Mesotrione was applied at 1.1, 3.2, 11, 35, and 105 g ai/ha to ‘BT 386C’ soybeans at the V1 stage of growth. All rates of mesotrione resulted in visual injury to soybean at 7 and 14 d after treatment (DAT). Overall soybean injury from mesotrione was greatest at 14 DAT, with 25 to 78% injury observed. By 28 DAT, soybean injury was 31 and 66% from mesotrione at 35 and 105 g/ha, respectively, and less than 10% from mesotrione at 1.1, 3.2, and 11 g/ha. Soybean yield was reduced 11 and 22% by mesotrione at 35 and 105 g/ha, respectively. No reduction in soybean yield was observed from mesotrione at rates up to 11 g/ha. Regression analysis indicated that soybean injury from mesotrione at 28 DAT was the best predictor of yield loss (r2 = 0.77), compared with injury evaluations at 7, 14, and 56 DAT. Greenhouse studies were conducted to determine whether soybean injury from mesotrione was affected by soybean growth stage and variety. Soybean varieties BT 386C, ‘Asgrow 4602RR’, ‘Pioneer 94B01’, and ‘LS 930375’ were more sensitive to mesotrione at the VC growth stage than at the V1 and V2 stages. At the V2 stage, Asgrow 4602RR was three to five times more sensitive to mesotrione than the other three varieties.
Nomenclature: Mesotrione; soybean, Glycine max L. (Merr.) ‘Asgrow 4602RR’, ‘BT 386C’, ‘LS 930375’, ‘Pioneer 94B01’.
Additional index words: Herbicide drift, tank contamination.
Abbreviations: DAT, days after treatment; POST, postemergence.
