The present work was aimed to evaluate the influence of dew simulation on the efficacy of glyphosate on Brachiaria decumbens. For this purpose, two greenhouse assays were accomplished simultaneously. In the first experiment, treatments consisted of the combination of two glyphosate rates (270 and 540 g ha-1), three intervals between the spraying of the herbicide and dew simulation (0.0; 4.0 and 8.0 hours), and five volumes of dew, besides three additional checks, disposed in a factorial scheme (2x3x5)+3, with four replicates. In the second experiment, the treatments were constituted by the combination of simulated dew at five volumes (250, 500, 750, 1000 and 2000 mL m-2) and the spraying of glyphosate, immediately after the simulated dew, at two rates (270 and 540 g ha-1), disposed in factorial scheme (5x2), with four replicates. The rate of 270 g ha-1 of glyphosate did not provide control of B. decumbens, despite either the period of time between the spraying of the herbicide and application of simulated dew or volumes of dew. The increased levels of dew over glyphosate sprayed at 540 g ha-1 interfered with B. decumbens control, being necessary at least eight hours between glyphosate spraying and dew simulation for adequate weed control. Spraying of glyphosate over plants of B. decumbens when the dew was already present resulted in poor weed control at 540 g ha-1 and did not provide any control at 270 g ha-1. Although the simulation of dew interfered with glyphosate efficacy over B. decumbens, weed control seems to be more related to the period of time of dew occurrence after spraying.
environmental conditions; efficacy; herbicide
