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Abstract
Sunnhemp (Crotalaria juncea L.) is used as a cover crop, but there is little information on its weed suppressive ability. The objective was to determine whether sunnhemp has allelochemical activity to reduce seed germination and seedling growth in weeds, vegetable crops and cover crops. Germination studies were conducted using sunnhemp residues or tissue extracts. The results suggested the possible presence of allelochemicals in the sunnhemp leaves. In the greenhouse, seed germination and seedling growth of the carrot (Daucus carota L.), lettuce (Lactuca sativa L.), and smooth pigweed (Amaranthus hybridus L.), were reduced when grown in soil containing sunnhemp residues. The allelopathic activity was higher in the leaves than in roots or stems. Seeds of various vegetable and cover crops showed inhibited germination when incubated in dishes containing sunnhemp leaf extract, although cereal rye (Secale cereale L.) and wheat (Triticum aestivum L.) were unaffected by the sunnhemp leaf extract.