The allelopathic effects of aqueous extracts of plant residues from zea mays (root and tassel) and cajanus cajan (leaves and stem) were examined on the two weeds, euphorbia heteropyhlla l. and bidens pilosa l. the results obtained showed that the aqueous extracts retarded the germination and the initial growth of both weeds. the effects were concentration dependent as the degree of retardation increased with increase in the concentrations of the extracts. the retardation of germination of e. heterophylla seeds was more pronounced in seeds treated with extracts from c. cajan leaf. The % germination decreased from 18% in the 5g concentration to 10% in 25g/200mL concentration at 144hrs experimental time. Similarly, the retardation of germination of B. pilosa seeds was more pronounced in C. cajan stem extract treated seeds. The % germination decreased from 52% in the 5g concentration to 20% in 25g/200mL concentration at 144hrs experimental time. The radicles of the two weeds were also retarded by the extracts. The retardation of radical lengths of E. heterophylla and B. pilosa seedlings were more pronounced in Cajanus cajan stem extract treated seeds as no radicle emerged until 72hrs experiment time. The radicle length of E. heterophylla seedling at 144hrs experiment was 0.93cm in the 5g concentration which reduced to 0.29cm in 25g/ 200mL extract concentration. The radicle length of B. pilosa seedling at 144hrs experimental time was 1.25cm in 5g concentration which decreased to 0.59cm in 25g/ 200mL concentration. The plumule lengths of the two weeds were also retarded by the extracts. The plumule length of E. heterophylla seeds were mostly retarded by extract from C. cajan stems. Plumule length in the 5g concentration was 0.53cm which decreased to 0.06cm in the 25g extract concentration. .B. pilosa seedlings were retarded mostly by extracts from C. cajan leaves. Plumule length was 1.20cm in the 5g extract concentration which decreased to 1.03cm in 25g/200mL extract conc