A field experiment was conducted at the research farm of the University of Tehran to evaluate the effect of cover crops and herbicide (nicosulfuron) dosage on corn (Zea mays L.) productivity. Cover crops suppressed weed biomass and density during the fallow period; however, there was no significant effect on weed biomass or weed density in the subsequent corn crop. A mixture of cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth.) was the most weed-suppressive cover in the fallow period. Nicosulfuron applied at different amounts suppressed weed biomass and density in corn when compared with weedy plots. Application of 40 g ai ha−1 of nicosulfuron was as effective on weed control as the recommended application. Cover crops did not affect corn growth; however, corn yield improved with herbicide application.