In laboratory choice and no-choice tests, an aqueous extract of tansy,Tanacetum vulgareL. (Compositae), reduced feeding on cabbage leaf disks by imported cabbageworms,Artogeia(=Pieris)rapae(L.). Imported cabbageworms reared on cabbage leaves treated with tansy extract took longer to develop to pupation, and pupae weighed less than insects reared on control leaves. In oviposition choice tests, imported cabbageworms laid three times as many eggs on control (water-sprayed) cabbage plants as on tansy-treated plants. Diamondback moths,Plutella xylostella(L.), laid more than twice as many eggs on control as on tansy-treated plants. In both spring and fall cabbage field trials, 1 and 5% tansy treatments reduced insect numbers significantly on at least some dates. Insect damage ratings at harvest were significantly lower for tansy-treated plants than for plants treated with either water or water plus surfactant, although higher than damage ratings forBacillus thuringiensis-treated plants. The surfactant used with the tansy treatments, 1% (vol/vol) Triton B-1956 (now Latron B-1956), reduced cabbage head weights substantially in water plus surfactant control treatments compared with the water-only treatment.