Phytosociological survey of weeds in grain sorghum in the function of chemical management.
The objective of this work was to identify the weeds present at the end of the crop cycle of sorghum after chemical control. The experiment was conducted in a randomized complete block design with 23 treatments and three replicates. The treatments were glyphosate + 2,4-D (1500 + 1000 g ha-1), isolated at 28, 21 and 7 days before sowing; and/or atrazine + paraquat (1000 + 300 g ha-1) on the day of sowing, and/or atrazine (1000 g ha-1) isolated or sequential in early and late post-emergence; an additional treatment with atrazine + glyphosate (1000 + 1500 g ha-1) on the day of sowing, and two controls (weeded and no weed). The phytosociological study was carried out in the pre-harvest of sorghum. Weeds were identified and quantified using the square inventory method (0.25 m2); and the parameters frequency, density and abundance (absolute and relative), and the importance value index (IVI) were Analyzed. The desiccation at 28 days before sowing, associated to the application on the day of planting with contact and residual herbicides, plus initial and late post-emergence applications reduced the frequency, density and abundance of the species.