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If you're growing cabbage, broccoli, cauliflower, or Brussels sprouts, keep your eyes peeled for any small white butterflies that seem overly interested in your plants. These pretty little butterflies could be the first sign of an impending infestation of imported cabbage worms.

In addition to the head crops already mentioned, cabbage worms may also infest leafy crops such as collards, kale, mustard greens, and turnip greens, and also root crops such as radish, turnip, and rutabaga.

These sluggish green caterpillars not only riddle the plant leaves with irregular-shaped holes, they also eat their way into the cabbage heads (or edible parts of other plants), leaving holes and an unpleasant excrement. Left unchecked, cabbage worms can ruin your garden's yield.

(Related pests include the cabbage looper and the Diamondback moth larvae, but this article focuses exclusively on the cabbage worm.)

IDENTIFICATION

The cabbage butterfly is about one-and-a-half inches long, and white with a black tip on the front wings, and a black spot on both the front and back wings.

Elongated yellowish eggs are found individually on the undersides of leaves.

The cabbage worm is velvety green with a faint yellow stripe on its back and faint yellow spots on its sides. It grows to a little over an inch long.

The pupa is slightly less than an inch long, green and angular with sharp, tan-colored edges, vaguely resembling a stubby caterpillar.

HABIT

The imported cabbage worm survives the winter in its pupal state, dangling by a fine thread from leaves, branches or any other convenient surface. The adult butterfly emerges in the early spring, laying its eggs singly on the underside of the host plant's leaves.

The egg hatches in about a week, and the larva feeds for about two weeks before pupating. The adult butterfly emerges in a week or two. Because the life cycle is about five weeks, three to six generations appear each year depending on the climate. The heaviest infestations will be in July and August.

PREVENTION

Eliminating left over foliage after harvesting your crop can help eradicate any remaining eggs, larvae or pupae and reduce potential infestation the following year. Populations can also be reduced by identifying and destroying pupa found in any adjoining spaces before the butterflies emerge in the spring.

Before planting, investigate varieties that have specific resistance to cabbage worms. Covering plants with plastic or netting can prevent the butterfly from laying eggs on susceptible plants.

CONTROL

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