Technical Abstract: Conservation systems using cover crops offer many benefits, including enhanced weed suppression. Researchers have shown that some cover crops leach allelopathic chemicals that contribute to weed growth inhibition. Twelve cover crops were evaluated for allelopathic potential in two experiments using an extract-agar technique. Five weeks after planting, plants were clipped at the soil surface and cut into 15 mm pieces, which were soaked in distilled water for 24 h. After 24 h, filtered extracts, along with a distilled water control, were mixed with autoclaved agar and poured into petri dishes. After solidification, five pre-germinated radish seeds with radicals less than 2 mm in length were placed on each petri dish. Radish radicle lengths at 48 h were recorded. Significant differences were found among cover crops in both experiments. All cover crop extracts inhibited radicle elongation significantly more than distilled water, supporting previous research which noted allelopathic effects in cover crops.