Imported cabbageworm
Click for larger image Imported cabbageworm adult is a white butterfly (Lepidoptera) that feeds on nectar and lay eggs on plants in the mustard family, including cabbage, cauliflower, broccoli, kale, etc.

The presence of white butterflies fluttering around the garden signals the start of a possible infestation of imported cabbageworm. The adult cabbage butterfly, Pieris rapae, is white with black tips and one or two black spots on the forewings. The larva (the cabbageworm) is a bright green caterpillar clothed in fine, short hairs that give it a velvety appearance. The imported cabbageworm will attack all growth stages in cole crops.

Symptoms and Diagnosis

When the adult butterflies are observed fluttering around the garden, the larvae and the damage they do will soon be obvious. All stages of growth in cole crops can be attacked by the larvae, but they are often observed on the underside of developing leaves. The outer leaves may become riddled with large ragged holes from the larvae's feeding. If leaves are parted, masses of greenish-brown excrement can be found at the base of the leaves. The larval feces often contaminate edible portions of the plant.

Life Cycle

The imported cabbageworm overwinters as a pupa attached to plant debris. The adult butterfly emerges the following spring and flies about the garden area during daylight hours. The elongated, yellow, ribbed eggs (shaped somewhat like a football) are laid on the underside of the foliage. The eggs hatch in 7 days. The emerging caterpillars are velvety green. Theyfeed on all cole crops for about 15 days. After this, they pupate, and new adults emerge in about 10 days. There are 2 or 3 generations of imported cabbageworm each year.

Integrated Pest Management Strategies

1. Handpick the cabbageworms off of the underside of the leaves while plants are young. This procedure is effective when plants are young or if only a few larvae are present.

2. Use row covers. Position row covers or netting over plants to prevent egg laying by the butterflies. Start controls before the white cabbage butterflies are seen fluttering around the yard.

3. Fall sanitation. Clean up and remove infested plant material after harvest to eliminate overwintering sites of the pupae.

4. Use Btk spray or dust. Dust plants with Bacillus thuringiensis kurstaki (Btk). Begin treating the plants when white butterflies are first noticed and the cabbageworms are still small. It may take several days before the insects die after feeding on Btk, but feeding will usually stop shortly after the plants are treated.

5. Chemical controls. Spray with insecticidal soapcarbaryl (Sevin), malathion, cyfluthrin, or permethrin when plants and larvae are young and damage is increasing. The larvae are more easily killed when young and this will minimize the amount of insecticide needed for control. Carbaryl (Sevin), the active ingredient in Sevin, is very toxic to honey bees; do not use near flowering plants.

Organic Strategies

Strategies 1, 2, and 3 are strictly organic approaches. For an organic approach to Strategies 4 and 5, consult the Organic Materials Review Institute (OMRI™) for appropriate Bacillus thuringiensis kurstaki (Btk) and insecticidal soap products.

More images:

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The adult imported cabbageworm (Lepidoptera) is a butterfly called the cabbage white. The male (on the left) has only one black dot on the wings; the female (on the right) has two.
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Larva of the imported cabbageworm (Lepidoptera) on kale (Brassica oleracea)
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Cabbage white butterflies (male on the left; female on the right); these are the adult stage of the imported cabbageworm (Lepidoptera).
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Imported cabbageworm larvae (Lepidoptera) on underside of kale leaf (Brassica oleracea)
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Two cabbageworms (Lepidoptera) on upper leaf surface of kale (Brassica oleracea). Note, dark pellets of feces on the right at the base of the leaf.
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These velvety looking green caterpillars on a kale leaf (Brassica oleracea) are imported cabbageworms (Lepidoptera)
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You are what you eat. Look closely. These imported cabbageworms (Lepidoptera) blend in so well with the kale (Brassica) they're eating that they can be hard to see.
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Cabbage white butterfly, the adult form of the imported cabbageworm (Lepidoptera)
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Cocoons of Cotesia glomerata, a Braconid wasp (Hymenoptera) that parasitizes imported cabbage worms, a.k.a., cabbage white butterflies (Lepidoptera)