Control of Brachiaria decumbens Stapf with urea added to the glyphosate spray solution

Abstract

The addition of nitrogen sources to herbicide spray solutions has been related to improvements in phytosanitary treatments. This study aimed at evaluating the control of Brachiaria decumbens with urea added to the glyphosate spray solution. Treatments consisted of a combination of glyphosate (0.0 g ha^-1, 360.0 g ha^-1, 720.0 g ha^-1 and 1,080.0 g ha^-1 of the a.i.) and urea doses (0.0 g L^-1, 7.5 g L^-1, 15.0 g L^-1 and 25.0 g L^-1 of the spray solution), and a control with no application, in a randomized blocks design, in a 4x4 factorial scheme, with three replications. Applications were carried out with the aid of a CO₂ constant pressure sprayer, equipped with a bar for two flat jet nozzles, operating at the pressure of 300.0 kPa. Densities and coverage percentages of plants leaves, provided by the jet nozzles drops, were evaluated, as well as the instantaneous gas exchanges, at 12 a.m., at 2, 4, 6 and 11 days after application (DAA), by using a portable infrared gas analyzer. Visual evaluations of control percentage were carried out at 7, 14, 21 and 28 DAA. No difference was observed in the density and coverage of leaves, for the different urea concentrations. The addition of urea to the glyphosate spray solution improved the B. decumbens control, regardless the herbicide dose, up to the 25.0 g L^-1 spray solution concentration. The gas exchange of B. decumbens was lower after 6 DAA, in treatments with higher concentrations of urea in the herbicide spray solution, resulting in a higher control level for these treatments.