Allelopathic Potential of White Top and Syrian Sage on Vegetable Crops

White top [Cardaria draba (L.) Desv.] and Syrian sage (Salvia syriaca L.) are noxious common weeds of field crops and orchards in Jordan. This study was conducted to investigate any allelopathic potential of volatiles, foliage leachates, root exudates, and shoot dried residues of both weed species on cabbage (Brassica oleracea L. var. Capitata cv. Pronzwik), carrot (Daucus carota L. cv. Natus), cucumber (Cucumis sativus L. cv. Beithalpha), squash (Cucurbita pepo L. cv. Byrouti), onion (Allium cepa L. cv. Texas Early Grana), pepper (Capsicum annum L. cv. Red Common), or tomato (Lycopersicon esculentum Mill cv. Special Back) through different laboratory and glasshouse experiments. Volatiles from Syrian sage fresh shoots reduced germination and inhibited seedling growth of most crops, and foliage leachates or root exudates of both weeds were toxic to different crops under laboratory conditions, with most effects on tomato and cabbage. In pot experiments, surface‐placed shoot residues of both weeds significantly delayed seed germination and reduced seedling growth of all crops with carrot, onion, and tomato being the most affected. Decayed residues of white top were also toxic at 32 g kg−1, but lower toxicity was obtained than when fresh materials were used. Foliage leachates or root exudates of both weed species added or released into the soil mixture reduced seedling growth of cabbage and tomato. Results showed that white top and Syrian sage are of great allelopathic potential against different vegetable crops; cabbage, onion, and tomato being the most sensitive crops.