Imported cabbageworm prefer to feed on cabbage, cauliflower, broccoli, Brussels sprouts, turnips, radishes, kale, lettuce and weeds of the mustard family. In fact, this pest is one of the most damaging and destructive enemies of these plants. The caterpillars chew irregular holes in the leaves and usually eat their way into cabbage heads from the bottom. In addition to the feeding damage, the insects’ fecal pellets will stain cauliflower.

Description & Biology

The first sign of imported cabbageworm is the 1 1/2 inch white butterfly. This stage of the insect is seen in early spring since they overwinter as adults. The females fly during daylight hours looking for suitable plants on which to lay their yellowish, elongated eggs, singly, on the underside of leaves.

In 5 to 7 days, the eggs hatch to become velvety green caterpillars which will grow to 1 1/2 inch long. They have a thin yellowish-orange stripe down the middle of the back. It is common for high larval populations in July and August to damage plants so severely that they die or become unmarketable.

When finally grown, the larva form greenish-brown pupa (chrysalis) which can often be found hanging from the bottoms of leaves or other protected areas. Ten days later, the second generation of butterflies emerges, continuing the cycle. There may be a third generation in Maine. Adults may be seen almost anytime during the summer.

Management

Controlling weeds around the garden, especially plants of the mustard family, should help decrease the numbers of this pest. Destroying and removing the remains of plants in the fall, as well as fall tillage, reduces the number of over-wintering pupae. Hand-picking the larvae may be labor intensive but can significantly cut the numbers and keep damage down. Early Globe, Red Acre, and Round Dutch cabbage have shown some resistance to cabbageworm.