Fact Sheets - Imported Cabbageworm
Pest Management Fact Sheet #5006
James F. Dill, Pest Management Specialist
Clay A. Kirby, Insect Diagnostician
Imported cabbageworms 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 appearance of imported cabbageworm is the 1 1/2 inch white butterfly. Often it emerges from the overwintering pupa. 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 transforms into a 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 are commonly seen throughout the summer.
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.
Bt (Bacillus thuringiensis), an insecticide derived from a bacterium and sold as Dipel, Bactur, Sok-Bt or Thuricide, is management method. Bt is less effective under cooler conditions. Other options include spinosad, insecticidal soap, carbaryl (Sevin) and malathion. Regardless of what is used, the smaller the caterpillars are, the easier they are to kill. Insecticides must be used in late afternoon or early evening to protect bees. This is also the time when the caterpillars feed most actively, making the insecticide most effective.
When Using Pesticides
ALWAYS FOLLOW LABEL DIRECTIONS!
Pest Management Office
491 College Avenue, Orono, ME 04473-1295
1-800-287-0279 (in Maine)
Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.
© 2010, 2013
Published and distributed in furtherance of Acts of Congress of May 8 and June 30, 1914, by the University of Maine Cooperative Extension, the Land Grant University of the state of Maine and the U.S. Department of Agriculture cooperating. Cooperative Extension and other agencies of the U.S.D.A. provide equal opportunities in programs and employment.
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