Cabbage Maggot
Hylemya brassicae (Weidemann), Anthomyiidae, DIPTERA

DESCRIPTION

Adult - This fly resembles a common house fly although it is somewhat smaller. It is gray with three distinct black stripes on the thorax, a dark stripe along the top of the abdomen, and is 5 to 6 mm long. The eyes are reddish-purple.

Egg - The white, finely ridged egg is about 1 mm long.

Larva - The white, legless maggot has a pointed head and grows to a length of 6 mm.

Pupa - About the size of the adult, the pupa is enclosed in a hard brown puparium.

BIOLOGY

Distribution - Introduced from Europe, the cabbage maggot is most injurious in Canada and the northern U.S. It has been a problem in Illinois and western North Carolina but is rarely serious any further south. In North Carolina cabbage maggots have been reported from practically all mountain counties west of a line from Polk County to Surry County and usually do not occur below 914 meters (3,000 ft) elevation.

Host Plants - The cabbage maggot feeds primarily on crucifers such as cabbage, cauliflower, broccoli, brussels sprouts, collards, kohlrabi, radish, and turnip. Beet, cress, and celery have also been infested.

Damage - Cabbage maggots eat small fibrous roots and tunnel in stems and large fleshy roots. Tunnels where maggots have fed become brown and slimy, and organisms are likely to be introduced at these points. Plants attacked in the plant bed or soon after setting in the field fail to develop normally. Cabbage first takes on a sickly gray-blue color. Other infested crucifers may appear stunted or pale in color. If severe damage has been done, plants may wilt and die during the heat of the day. Infestations are difficult to detect in radishes and turnips because the tunneling of maggots in these large-rooted crops does not cause the foliage to wilt. Damage to these crops can be determined only by pulling some plants early and inspecting them. Cabbage maggots are usually most severe when the weather is cool and wet for a long period of time.

Life History - Cabbage maggots overwinter as pupae 2 to 13 cm deep in the soil. As the soil warms in spring, adult flies emerge from cocoons, feed on the nectar of flowers, and mate. Appearing as early as April, females soon begin depositing eggs in the soil at or near the base of host plants. Three to 7 days later, young maggots emerge from the eggs and move into the soil searching for roots upon which they feed for 3 to 4 weeks before pupating. Pupation may take place within root burrows or out in the soil and usually lasts 2 or 3 weeks. The second generation of adults appears in late June or early July. At least three generations occur annually in North Carolina.

CONTROL

Cultural practices such as late planting, careful selection of seedbed location, and elimination of weedy hosts can help prevent severe infestations. If planting is delayed until the last week of May or first week of June, few flies will be present to deposit eggs. Seedbeds located as far as possible from growing areas and protected from egg-laying flies with a gauze cloth will less likely be infested. The use of transplants grown in North Carolina at elevations below 3,000 feet will eliminate the danger of introducing the maggots on infested transplants. The fall destruction of turnip and cabbage stumps and weeds such as wild mustards will eliminate many larvae or pupae associated with these plants. Proper fertilization, irrigation and good soil practices also lessen maggot damage by improving plant tolerance.

Cabbage maggots often require chemical control. An insecticide can be broadcast and incorporated just prior to planting seed or setting transplants. The application of a drench after setting transplants may also be effective. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.

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