effect of density and relative time of emergence of jimsonweed (datura stramonium l.) on yield and yield components of chitti been (phaseolus vulgaris l.)

jimsonweed (datura stramonium l.) is an important weed in bean fields in iran. in order to investigate the effect of density and relative time of emergence of jimsonweed on yield and yield components of chitti bean, a field study based on factorial experiment was conducted at farm bean research national station in khomein in 2006. treatments were chosen to provide four different weed densities (4,8,12 and 16 plant m-1) and three time of weed emergence (with crop emergence, in first trifoliate leaf stage and third trifoliate leaf stage of bean) with a weed free treatment as control. results showed that the effect of jimsonweed interference on bean yield and yield components was significant. the yield of bean was more affected by relative time of jimson weed emergence than its density and decreased 52%, 47% and 23% in 1st, 2nd and 3rd time of weed emergence respectively in highest level of density. the number of pod per plant and 100-seed weight of bean were the most important yield components which be decreased by jimsonweed competition, but the number of seeds per pod was not affected. the effect of interaction between experimental factors was significant on bean yield. the effect of jimsonweed density on bean yield decreased when the relative time of weed emergence increased, so effect of weed density on bean yield in 3rd time of emergence was not significant. the results demonstrated the high sensitivity of bean yield to early competition of jimson weed even at low densities.