Vegetable Program
Insect Management

Cabbage Maggot

Delia radicum, Cabbage root maggot

Flies over-winter as pupae near roots of fall Brassica crops. Adult flies become active one or two weeks after Forsythia starts to bloom or when yellow rocket (winter cress, Barbarea vulgaris) starts to bloom. Cabbage root maggot flies are delicate, hump-backed gray-brown flies, about 5- 7 mm long. Eggs are laid in soil and maggots feed on roots. Plants wilt, turn yellow or purple, and die. Control should begin in early spring when adult flies are active. Look at the base of the plant for small (1/32"), white, bullet-shaped eggs. Once one egg is found, often many will appear within a few days. Apply a soil drench 2 to 3 days after finding an average of one egg/plant. The direct spray method is effective only if it is applied as a narrow band with enough water to penetrate the root zone -- over the row for direct seeded Brassicas or directed to the base of the plant for transplanted crops. A wider spray band reduces the concentration of the insecticide over the row and, therefore, decreases its effectiveness.

Cabbage maggot eggs are very sensitive to high soil temperatures (above 95°F), and will die if they are exposed to these temperatures for several days in a row. Generally these soil temperatures are reached by late May/early June, unless there has been excessive rain, which has a dramatic cooling effect on the soil. This means that under high soil temperatures there is no need to spray for this pest. There are 3-4 generations per year. A late summer flight (late August, early September) may damage fall crops.

Incorporate and disk Brassica crops after harvest to expose and kill pupae, especially in the fall. Rotate spring crops to fields that were not planted with fall Brassicas. Protect spring crops with spunbonded row covers. Place cover over the crop at the time of seeding or transplanting and
seal the edges with soil. Use only on rotated fields. Delayed planting, until after soil temperatures are high enough to kill eggs, avoids damage.

More details and photos on cabbage maggot life cycle, monitoring, and management.

For current information on production methods (including varieties, spacing, seeding, and fertility), weed, disease, and insect management of cabbage, broccoli, cauliflower and other Brassica crops, please visit the New England Vegetable Management Guide website.