SIMULATED DRIFT OF DICAMBA AND 2,4-D ON SOYBEANS: EFFECTS OF APPLICATION DOSE AND TIME

The use of soybean varieties resistant to the herbicides dicamba and 2,4-D may lead to drifts towards areas grown with non-resistant varieties. The aim of this study was to evaluate the effects of dicamba and 2,4-D underdoses applied at the phenological stages V-4 and R-2 of soybeans. Two experiments were conducted with dicamba or 2,4-D in a randomized block design with four replications. The 4 x 2 + 1 factorial scheme was composed of four doses (0.028, 0.28, 2.8, and 28 g ae ha(-1)) of dicamba or 2,4-D applied at two phenological stages (V-4 and R-2) + a control treatment (without herbicide application). Dicamba underdoses caused damage to soybean crop affecting its vegetative growth and yield; the injuries caused by 2,4-D were neither enough to damage crop nor affect yield components. Dicamba underdoses applied at V-4 caused injuries of up to 41%, while in R-2 they reached 70%. Plant height decreased by up to 61% when treated with dicamba. Soybean yield was reduced by 29 and 76% when the simulated drift occurred at V-4 and R-2, respectively, and at a dose of 28 g ae ha(-1) of dicamba. For the tested underdoses, only 2,4-D had no effect in soybean crop yield.