Weed Interference Periods in Sorghum Crop

The aim of this work was to estimate weed control periods and weed coexistence periods in sorghum 'BRS 310' crop. The experiment was carried out in Botucatu, Sao Paulo, Brazil. The experimental design was a randomized complete block with four replications and the treatments consisted of eight control periods, in which the crop was maintained weed-free and of eight coexistence periods, in which the crop was maintained in the presence of the weeds. The periods were 7, 14, 21, 28, 35, 42, 49, and 56 days after sowing (DAS), besides a weed-free control and a control maintained in the presence of weed. To determine the periods of interference, grain yield data, panicle length and dry mass of the aerial part of the sorghum plants obtained were fit to the nonlinear regression model y = a/[1+(x/b)(c)]. Eleven families and 17 species of weeds were identified, with the families Asteraceae and Poaceae presenting the largest number of species. Considering as acceptable a loss of 5% of grain yield, panicle length and dry mass of the aerial part of the sorghum plants, it was possible to determine the period previous to weed interference (PPWI) of 42, 72 and 15 DAS and the total period of prevention of weed interference (TPPWI) of 26, 17 and 12 DAS, respectively. No critical period of weed interference prevention (CPWIP) was observed for the parameters evaluated.