The objective of this work was to evaluate the growth of barnyard grass biotypes resistant and susceptible to the herbicide quinclorac, under competition between plants of the same and opposite biotypes. Plants of both biotypes were grown in different proportions in the experimental units. The treatments were arranged in a factorial scheme 2 x 6, with four replications in a completely randomized block design. Forty-five days after emergence, the leaf area and dry mass of the shoots were determined, sorted out into leaves and shoots. Growth rate (TC), specific leaf area (AFE), leaf area index (IAF), leaf weight rate (RPF) and leaf area rate (RAF) were calculated. The variables dry mass, growth rate, leaf area index, leaf weight rate and leaf area rate did not differ between the biotypes, independently of the treatment evaluated. However, the susceptible biotype was superior to the resistant one in relation to the specific leaf area, both isolated or in community. It was concluded that only discrete differences occur between biotypes resistant and susceptible to the herbicide quinclorac in relation to growth potential under competition.
Echinochloa sp.; resistance; herbicide