Integration of certain crop management practices with chemical weed control could allow a rate reduction of the herbicide to be applied, without significant changes in weed control levels and soybean grain yields. This research aimed to evaluate reduction in the recommended rate of a formulated mixture of fluazifop-p-butyl plus fomesafen, associated with reduction in soybean row width, on alexandergrass (Brachiaria plantaginea) control and crop grain yield. The experiment was conducted at EEA/UFRGS, Eldorado do Sul-RS, during the growing season of 1997/98. Soybean cultivar tested was BR 16, sowed under a no-till system. The treatments consisted of three row widths (20, 40 and 60 cm), and five rates of the herbicide mixture [fluazifop-p-butyl (200 g L-1) + fomesafen (250 g L¹)], applied at the recommended rate of 1.0 L ha-1 (100%) and reduced rates (75, 50, and 25% of the recommended rate) plus a check. Alexandergrass control was visually evaluated at 8 and 17 days after herbicide applications, by obtaining its dry matter weight, as well as the soybean grain yield. The results showed that, for a moderate alexandergrass infestation, soybean row width does not affect weed control when the herbicide is sprayed at the recommended rate. For late herbicide applications, 40 cm row width allows a reduction of herbicide rate up to 50%, without affecting alexandergrass control and a decrease up to 75% of the herbicide rate, without reducing soybean grain yield; reduction of herbicide rate is conditioned to application time and row width used; with reduced row widths application must be performed earlier so that a sufficient amount of the product reaches the weeds.
Glycine max; Brachiaria plantaginea; fomesafen; fluazifop-p-butyl
