Tithonia rotundifolia which belong to the family Asteraceae has become an invasive weed in Nigeria as it is displacing traditional weedy species. The allelopathic effects of the extracts prepared from this weed on the growth and biomass accumulation of Vigna unguiculata and Zea mays were investigated. These plants were subjected to different concentrations (25%, 50%, 75% and 100%) of the extract while water served as control. The growth parameters were determined according to standard methods. The data obtained were subjected to Analysis of Variance (ANOVA) followed by Duncan's Multiple Range Test (DMRT) to determine significant (P< 0.05) effects. Result showed that the extracts of the donor plant inhibited the shoot height, root length, leaf area, fresh and dry weights of the test crops (Vigna unguiculata and Zea mays). The phytotoxic effect of the extract was dose dependent. There was inhibition of growth and biomass of the receptor plants which was an indication that the extracts contain some allelochemicals which were responsible for the phytotoxic inhibition observed in this study. Therefore, these plants should be grown on field free of T. rotundifolia.

Keywords : Allelopathic, Allelochemicals, Phytotoxic, Tithonia Rotundifolia, Extracts,