To evaluate the chemical control and the influence of weed population occurring in the sugarcane culture (3rd ratoon), variety NA56-79, with different vinasse dosages, an experiment was installed at Santa Lúcia Sugar and Alcohol Mill, in Araras-SP. The soil was distrophic Red Yellow Latossol, loam texture, Haplorthox. No rainfall level occurred during the 10 days following herbicide application . The experiment was installed in 10/08/83, being the soil dry at the moment of vinasse application, which was through tank truck, with pump discharge without pressure. Herbicides were applied with knapsac at constant pressure CO2 , using Teejet 110.04 nozzle, at an outflow of 370 1/ha. Experimental design was constituted by randomized blocks with split plots and 3 replications. Treatments were 0, 50, 100 and 150 m3/ha vinasse and mineral fertilization. Subtreatments were constituted by the herbicides alachlor at 2.40 kg a.i/ha; diuron at 1.60 kg a.i/ha; ametrin at 2.40 a.i/ha and tebuthiuron at 0.96 kg a.i/ha. Infestation of crabgrass (Digitaria horizontalis Willd) was highter in the areas which received only mineral fertilization, however, in the treatments receiving increasing vinasse dosages, crabgrass population was higher with the increase of doses. The most efficient control was provided by tebuthiuron, having alachlor caused a marked control when applied with 150 m3 /ha of vinasse. This was also observed with diuron and less markedly with ametrin. The purple nutsedge (Cyperus rotundus L.) had a less intense infestation in the treatments receiving 100 m3 /ha vinasse, increasing its population with lower doses. The best control was achieved was with alchlor and less satisfactory with tebuthiuron. Purslane (Portulaca oleracea L.) wire weed (Sida rhombifolia L.) and red tassel flower (Emilia sonchifolia D.C.) had their populations altered by the interaction of vinasse and the herbicide dosages. Therefore, by this assay it was concluded that the different vinasse dosages influenced the populations of crabgrass, purple nutsedge, purslane, wire weed and red tassel flower. Besides, mainly in the doses of 100 and 150 m3 /ha, it has an influence on the herbicides, specially on alachlor and diuron, under the conditions this experiment was carried out.
Weeds; chemical control; sugarcane; vinasse