Larvae eat large, ragged holes in leaves and heads of cabbage family plants, soiling leaves with dark green droppings.
Adults emerge from overwintering pupae in early spring to lay eggs. Larvae feed for 2 to 3 weeks, then pupate in debris on soil surface; adults emerge in 1 to 2 weeks. Three to five overlapping generations per year; all ages of larvae present all season.
Scout for and destroy eggs. Encourage parasitic wasps by planting small-flowered annuals in and near your garden. Cover plants with floating row cover; handpick larvae in light infestations. Apply garlic or hot pepper spray weekly, starting when butterflies appear. As a last resort, spray with BTK or spinosad when you find small cabbageworms on foliage.
Photo: Clemson University, USDA Cooperative Extension Slide Series, Bugwood.org