Two experiments were carried out under greenhouse conditions to evaluate the efficacy of the metribuzin herbicide associated to Pennisetum americanum mulch in the control of the weeds Ipomoea grandifolia and Sida rhombifolia. The treatments in the first experiment were constituted by different metribuzin application positions, over and under the straw, under different humidity conditions. In the second experiment, different periods of metribuzin permanence on the mulch before the occurrence of the first rain were observed on 0, 7, 14, 21 and 28 days after herbicide application on the mulch. The vases were filled up with soil and the weeds were sowed superficially and covered with P. americanum (8 t ha-1) mulch. The experimental design was randomized with four repetitions. The metribuzin dose used was 480 g ha-1 (a.i.). The control was evaluated visually, by percentile note scale and by counting the plants and evaluating plant dry mass. In the first experiment, an excellent control of the two species studied in the different positions of the tested herbicide was observed, except for I. grandifolia applied on the humidity mulch. The herbicide promoted an efficient control in post-emergence and pre-emergence, even when absorbed by direct contact with the mulch. In the second experiment, an excellent I. grandifolia control was observed in the periods without rain until 7 days after application (>96%), being unsatisfactory in the other periods. S. rhombifolia showed an excellent control during the periods up to 14 days without rain, presenting a satisfactory control even up to a 21 day period. The 28-day period did not present a satisfactory control.
weed; mulch; Pennisetum americanum; metribuzin
