Introduction, frequency and density of weed in corn fields of Qazvin province

Weed s are the most important factors that decrease yield of crops. Weed species of fieldcorn of Qazvin collected and identified on 2005, then their density and frequency weredetermined. The results of this study showed that 31 species belong to 17 genera disturbed in Qazvin corn field. The most frequent weed species were Amaranthus blitoides L., Amaranthus retroflexus L., %; Portulaca oleracea L and Setaria viridis L. respectively The life forms of Terophyta and Hemichryptophyta are the best frequent life form of Qazvin province. The most of species had Irano –Touranian distribution.