The cabbage maggot is a very destructive insect, attacking cabbage, broccoli, cauliflower, brussels sprouts, radishes, rutabagas, turnips, etc., --all cool-season plants. Wilting leaves are usually a sign of maggot damage and indicate that roots need to be checked for maggots.

Description & Biology

Cool weather is necessary for the cabbage maggot’s emergence, which takes place over a 2 to 3 week period. This extended period of emergence, added to the lifespan of the fly, exposes seedlings and transplants to a 30-day egg-laying period. There are 3 to 4 generations per year.

The insect overwinters as an egg-shaped pupa buried in the soil. Flies emerge and mate during May. The females deposit their eggs at the base of plants. In 3 to 9 days, the white tapered, legless maggots (larvae) emerge from their eggs. The maggots move to the root zone where they feed, sometimes damaging or destroying the root system. Larvae feed for 20 to 30 days, until they are mature or fully grown (1/4 to 1/3 inch long) and ready to pupate. Adult flies emerge in 10 to 14 days. The flies resemble houseflies, but are 1/4 inch long with black stripes on the thorax.

Because of the variation in time of adult emergence in the spring and the variation in length of developmental stages, it is possible for maggots to be present much of the growing season. However, high temperatures and disease suppress populations in July and August. The cooler temperatures of September and October favor development. At that time, the maggots damage fall-maturing plants such as rutabagas, turnips and Brussels sprouts, as well as other late cole or crucifer crops.

Management

It is important to remove roots, root crops and other host plants, and destroy them in the fall. Destroying wild host plants, especially the mustards at any time will help.

Chemical controls for this pest are limited. Rotenone placed around the plant stem at 5 to 7 day intervals may help.