Imported cabbageworm (Pieris rapae) — white butterflies with black tips and one or two black spots — feed and lay eggs on plants in the mustard family, including broccoli, cauliflower and kale. Seven days after being laid on the underside of the plant’s leaves, the yellow, ribbed eggs hatch into larva — green caterpillars. Larva feed on plants, leaving leaves damaged with large holes. To stop the pests from wreaking havoc, starting treatment with insecticidal soaps or products containing Bacillus thuringiensis (Bt) as early as possible is important.
Mix 2 tablespoons of a vegetable oil-based liquid soap with 1 gallon of water or select an insecticide that contains Bt. Put the insecticidal soap mixture in a spray bottle.
Spray the insecticidal soap on the pests in the early morning when the plants are dewy, or in the late afternoon or after sunset when the temperatures are mild. Coat the tops and undersides of the plant, soaking all the growing points of the plants where the pests lay eggs and hide.
Continue spraying the plants several times a week for three weeks or every two or three days for two weeks to treat severe infestations. Remove all infested plant material after harvest to limit overwintering sites.
- Test spraying a leaf before beginning treatment will help indicate if the insecticidal soap will damage the plant.
- Row covers or netting over the plants will deter egg laying by the butterflies.
- Early-grown cabbage is substantially less susceptible to infestations than late-grown cabbage.
- Insecticidal soap is not toxic to people or pets, but it is not safe to inhale or put in your eyes.
- Using a soap with additives or perfumes may harm plants.
Beth Porter has been a writer since 2008, with strong experience in early childhood education, gardening, home living and crafts. Porter is presently attending college, pursuing a Bachelor of Arts in early childhood education at the University of Cincinnati.