Description: Velvet-green larvae are 1-1/4 inches long at maturity. The chrysalis is light green, tan or yellowish and about one inch long. The adult is a white butterfly with black spots on the wings. Spherical eggs are yellow to cream in color.
Life Cycle: Adult butterflies emerge in spring and begin laying eggs on the underside of leaves of host plants. The resulting caterpillars reach maturity within 10-14 days and feed on hosts of broccoli and cabbage typically. Chrysalises attach to the food source with silken threads. There can be multiple generations of cabbage worms each year.
Damage: No damage is caused by the adults but the larvae feed on their host plant and can defoliate entire plants sometimes preventing the formation of heads. Boring into the heads can also cause them to be inedible due to their presence along with the fecal pellets.
Control: Monitor plants for signs of cabbage worms regularly. White butterflies near cole crops are an indicator of cabbage worms. Larvae are camouflaged against plant leaves so look for irregular-shaped holes and dark green fecal pellets on the plant or ground nearby.
Prevent cabbage worms by removing debris after the growing season to reduce overwintering habitats. Use row covers to prevent butterflies from laying eggs. Choose cultivars that mature faster to shorten the season. Remove larvae by hand. Bt (Bacillus thuringiensis) is effective on young caterpillars as are Spinosad, neem and pyrethrum. Always follow label instructions and practice safe application. A spreader sticker will increase efficacy due to the slick leaves of the host plants.
