effect of planting date and crop density of autumn wheat (triticum aestivum l.) on density and biomass of weeds

weeds in wheat (triticum aestivum l.) fields have always been a big problem in iran and worldwide and must be managed by non-chemical especially cultural methods. a field experiment as factorial based on a randomized complete block design with four replications in a 1000 m2 field in research farm of shirvan college of agriculture was conducted during 2007-2008. treatments included wheat densities of 400, 600 and 800 plants.m-2and planting dates of 1st of nov., 20th of nov., and 1st of dec 2007. the results represented that the presence of rapistrum rogusum, phalaris spp., descurainia sophia, alopecurus myosurides and hordeum murinum dominance. delay in planting of wheat increased relative density of weeds. the lowest relative frequency of weeds was observed in planting date of 1st of november. increase in crop density significantly decreased weed biomass, while it showed little effect on weed density trend. effect of planting date was also significant on weed biomass. the highest weed biomass occurred in the planting date of dec. the 1st. in conclusion, delay in planting of wheat create more chance and space for weed establishment, and therefore planting dense (600 plants.m-2) and early in season of wheat is recommended for lower weed damage.