Atrazine selectivity for Panicum maximum cv. Massai under no-till and conventional tillage

Abstract

The objective of this work was to evaluate the effectiveness of atrazine applied in pre-emergence in the control of weeds and its selectivity for forage Panicum maximum cv. Massai in no-till and conventional tillage systems. The experiment was installed in a stripped experimental design, in an 8 x 2 factorial scheme (8 doses of atrazine in 2 planting systems) with three replicates for each treatment. The variables were analyzed and being the presence of phytotoxicity, dry matter accumulation (DM), height of Massai grass plants, and visual evaluation of control effectiveness on weeds. The data were submitted to analysis of variance with the application of the F test, where the control values of 50% of weeds (C50) and a reduction of 50% in the growth of weeds and Massai grass (GR50) were defined. In the no-tillage system the doses for C50 and GR50 of weeds were 944.83 g a.i. ha-1 and 556.39 g a.i. ha-1, respectively. For the conventional planting system, the doses for C50 and GR50 of weeds were 329.52 g a.i. ha-1 and 301.77 g a.i. ha-1, respectively. In both systems, doses below the recommended were able to perform efficient weed control, where the GR50 values of the crop were higher than those of weeds, requiring doses of 1,184.51 g ai ha-1 for no-tillage and 1,632.92 g ia ha-1 for conventional planting.