the objectives of this work were to evaluate the possibility of reducing herbicide rates in flooded rice, using flooding as a tool to avoid weed emergence; to evaluate echinochloa spp. control, culture establishment and growth and the effect of herbicides applied in pre-emergence on the physiological attributes of the rice culture. the experiment was conducted in a randomized block design with split-split plots, four floodings, two herbicides and three rates, with four replications. the plots were the floodings (a) 5, 10, 15 and 20 days after herbicide application and the split plots were the herbicides (h) bispyribac-sodium and bispyribac-sodium + clomazone, and the split-split plots the herbicide rates (d), 32, 40 and 48 g ha-1 of bispyribac-sodium alone and in mixture with 300 g ha-1 of clomazone. bispyribac-sodium was efficient in controlling echinochloa spp. plants up to the stage of three leaves, when flooding occurred in the field until 5 days after application, and/or until rice tillering started when mixed with clomazone. it is possible to work with rates of bispyribac-sodium alone below the recommended dosage if flooding starts immediately after application. when using the bispyribac-sodium and clomazone mixture, it is possible to start the flooding when the tillering process begins.