This study aimed to identify the herbicidal effects of sorghum extract to control the weed Amaranthus viridis L. and to determine the appropriate phenological stage of sorghum for extract collection. The experiment was done in greenhouse covered with transparent plastic, with 50 % shade to reduce solar radiation. Polyethylene containers were filled with 12 kg substrate (Soil, sand and manure in 3:1:0.5 ratio). The treatments were replicated thrice in completely randomized design. The sorghum extract was obtained at 3-phenological stages (E1, E3 and E6) and a control (witout extract) and 4-extract concentrations (0 %, 25 %, 50 % and 100 %). Using high-precision manual sprayer, 20 ml extract/plant was sprayed in 3-applications at 33,39 and 43 days after emergence (DAE) of A. viridis L., when the plants had enough leaves to receive the extract. The sorghum extract obtained at the phenological stages corresponding to the vegetative periods E1 and E3 greatly inhibited the growth of Amaranthus viridis L., thus, it was recommended to harvest sorghum leaves at these stages for extract preparation. The 25 %, 50 % and 100 % extract concentrations decreased the shoot and root growth of A. viridis L.. However, the highest growth inhibition occurred at the undiluted 100 % concentration, making it the most promising concentration for Amaranthus viridis L. control.
Santos et al. (Thu,) studied this question.