Bioassay experiments were conducted to determine the phytotoxicity of methanol and ethyl acetate extracts of hairy vetch and cowpea residues on the germination and radicle elongation of three vegetable crops and three weed species. The species tested included common chickweed, redroot pigweed, wild carrot, tomato, corn, and cucumber. The extracts of both species were dissolved in methanol to yield seven concentrations ranging from 0 to 8 g/L. Germination was significantly reduced by methanol and ethyl acetate extracts of hairy vetch extracts except for corn and tomato. Common chickweed and wild carrot were the only species that showed consistent reduction in germination with the methanol and ethyl acetate cowpea extracts. The radicle growth of most species, with the exception of corn and cucumber, was reduced by the extracts of both cover crops. Corn and cucumber radicle elongation was stimulated at low concentrations of the extracts; however, these observations were not significantly different among treatments. This study demonstrated that methanol and ethyl acetate extracts of hairy vetch and cowpea contained allelopathic compounds and that their phytotoxicity is likely species specific. Future studies should focus on the identification and isolation of the allelochemical(s) found in the methanol and ethyl acetate extracts of the hairy vetch and cowpea residues.
Nomenclature: Hairy vetch, Vicia villosa Roth; cowpea, Vigna unguiculata (L.) Walp; common chickweed, Stellaria media (L.) Vill. STEME; redroot pigweed, Amaranthus retroflexus L. AMARE; wild carrot, Daucus carota L. DAUCA; corn, Zea mays L; cucumber, Cucumis sativus L; tomato, Lycopersicon esculentum Mill.