Influência do momento da chuva na eficácia do herbicida glifosate, em diferentes concentra??es, no inverno e no ver?o

摘要

Two field assays were carried out aiming to evaluate the rain effects on the glyphosate herbicide activity, applied at different concentrations, under two growing seasons (winter and summer). The experiments were conducted at the FCAV / UNESP Experimental Station, during 2000/01. The winter experiment was installed from June to August of 2000 and the summer one was installed from January to March of 2001. The treatments were glyphosate (0,5; 1,0; 2,0 e 4,0%), used as check treatment. In the field, all the trials were set up in the randomized block experimental design, with four replications. The experimental plots was 3.0 m wide x 3.5 m long in the winter assays. In the summer one, the plots' size was 3.0 m x 4.0 m. The treatments were arranged in factorial designs 5 x 4 factors, with five periods between the herbicide spraying and the rain incidence and four concentrations. The herbicide treatments were applied through a back spraying, with six nozzles DG 11002 spaced by 0.5 m, at 30 p.s.i. constant pressions. The artificial rain was provided by a top irrigation system raining 18 - 19 mm during one hour. The artificial rain reduced the glyphosate action, mainly in the shorter periods. Raising the glyphosate concentration to 2.0% supressed the problems promoted by the rain, one hour after sprayings, under winter conditions. Similar results were observed raising the glyphosate concentration to 1.0%, under summer conditions.