Adult: The cabbage maggot infests the stems of young cabbage plants and others in the same family. These other favored hosts include broccoli, brussels sprouts, cauliflower, and sometimes Chinese cabbage, collards, kohlrabi, radishes, rutabagas, and turnips. The adult is a 1/4 inch long housefly lookalike; gray, with black stripes on the thorax. The female fly lays her single white eggs at the soil line, and the hatching larvae are small (1/4 to 1/3 inch long) white legless maggots with blunt posteriors. This is the destructive stage.

The maggots make brown tunnels in the subsurface stem and roots as they feed. The affected plants wilt and usually die. These burrowing pests also act as carriers for the fungus that causes black leg, and for bacterial soft spot. The cabbage maggot will produce several generations per year starting in early spring and ending in the fall. They overwinter in the soil as pupae.

Sprouting seedlings can be protected by the use of an agricultural fleece covering (Remay, etc.). If the fly cannot lay eggs there will be no larvae. An impenetrable mulch, or a collar placed around each stem will serve much the same purpose. Make sure the barrier is snug around the stem yet is flexible enough to "grow" with the plant. Other gardeners have used wood ashes (with or without lime added) to surround the plant or use as a dust. The lime can also be used as a drench near the affected plants. The use of diatomaceous earth is another option.

Frequent close inspection of the plants can reveal the presence of the rice-like eggs which can be removed by hand and destroyed. Interplanting with mints, tomatoes, rosemary, or sage is said to repel the pest, and a few types of resistant varieties are available. Predators and parasites include parasitic nematodes, green lacewings, rove beetles, spiders, robber flies, and Chalcid and Trichogramma wasps.