The research was carried out with the objective of determining the critical periods of weed interference in the culture of the common bean (Phaseolus vulgaris L.) cultivated in no tillage system in Rolim de Moura-RO. Two trials were conducted simultaneously where in the first the culture remained free of the competition with weeds since the emergency until the 7; 14; 21; 28; 35; 42; 49 and 64 days, and in the second the culture remained in competition with the weed community since the emergency until the relevant periods cited in the first assay. The experimental design was a randomized complete block, with four replications. The D. horizontalis reached high relative frequency, dominance and relative density of up to 95.3%. The Z. mays despite having low density and relative frequency accumulated a great relative dominance by high biomass accumulation. The yield of bean was affected by living with the weeds. Assuming loss of 5% in the yield of grain of the common bean by interference with the weed community, the period preceding the interference was four days, the total period to prevent interference was 18 days after emergence and the critical period for preventing interference was between 4 and the 18 days after emergence. In this period until 18 days after emergence coexistence of beans and weed cause a reduction in crop yield by competing for resources from the environment, where there was a need to control.
Weeds community; Competition; No tillage