Two trials were conducted under field conditions during the 1992/93 growing season in Eldorado do Sul, RS, Brazil, in order to evaluate haloxyfop and sethoxydim herbicides for Alexandergrass (Brachiaria plantaginea) control using rates lower than the usual. Haloxyfop rates tested were 120, 90, 60, 30, and 30 + 30 g/ha. Sethoxydim was evaluated under rates of 184, 138, 92, 46, and 46 + 46 g/ha. Herbicides were sprayed 7 and 14 days after soybean seeding date for experiments 1 and 2, when Alexandergrass plants presented 1 to 2 and 3 to 4 leaves, respectively. Herbicide full rates were applied 2 weeks after the reduced ones. It was possible to attain acceptable level of Alexandergrass control only with a few treatments, these being a function of the compound used, and also of time and method of application. Sequencial applications of reduced rates of haloxyfop (30 + 30 g/ha) achieved control levels of 72 and 95%, as averages for experiments 1 and 2, respectively. For experiment 1, soybean yield levels equivalent to hand hoeing were attained only by the full rates of haloxyfop and sethoxydim. In experiment 2, yields equivalent to the hoeing treatment were achíeved by full rates of both products and also by haloxyfop at 90 g/ha and sequencial applications of 30 + 30 g/ha. The research also attest the necessity of complete elimination of Alexandergrass infestation in order to get maximum soybean yield.
Sequencial applica tions; split rates; haloxyfop; sethoxydim; signalgrass interference; Brachiaria plantaginea; Glycine max