Residues and the root exudates of common cocklebur (Xanthium italicum Moretti) were tested for their allelochemicals influence on the seed imbibition, germination and the early development of six maize (Zea mays L.) hybrids. The negative effects of weed residues were notable starting from seed imbibition. Cv. Giorgio resulted the most sensitive to the water extracts: at the 1% level, germination and root number were significantly reduced by 20 and 65% respectively compared to control. Strong negative effects in the germination corresponding to -34% and -27%, were recorded with cvv. Giorgio and Funo in presence of the root exudates. Data on the leaf area and the plant height confirmed the negative and significant effect of Xanthium residues on maize development, while the results on the effects of root exudates showed only a different behaviour among the hybrids. In summary, results reported in this study showed notable allelochemical effects of X. italicum residues on maize similar to those observed with relatives. The component “genotype” was particularly evident in the experiment with water extracts of residues and root exudates.