Herbicide resistant hairy fleabane biotypes may have lower competitive ability compared with herbicide-susceptible biotypes in coexistence with soybean. The objectives of this work were to evaluate the soybean competitive ability with glyphosate resistant and susceptible hairy fleabane biotypes. Three experiments were conducted in a greenhouse in a completely randomized design, with four replications. The treatments of the first experiment were conducted in additive series and the others were conducted in replacement series, with a density of 315plantsm-2 . The variables assessed were height, leaf area, height, dry matter, total phenols, lipid peroxidation and electrolyte leakage. Competitive analysis was performed by application of diagrams and interpretations of competitiveness indices. The glyphosate resistant and susceptible hairy fleabane biotypes have greater competitive ability than the cultivar CD226RR, while both hairy fleabane biotypes have similar ability to compete with the crop. Interspecific competition causes more damage to the soybean crop, whereas intraespecific competition causes more injuries to hairy fleabane biotypes. Changes on the crop secondary metabolism are due to competition from hairy fleabane plants.
Glycine max; competition; hairy fleabane; replacement series
