Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org
Plants most frequently attacked by the cabbage maggot are cauliflower, cabbage, radish and turnip.
Hylemya brassicae (Wiedemann)
The eggs of the cabbage maggot are oval shaped, bone white and about 1 mm long. The eggs are often found on either the plant or soil near where the plant stem emerges from the ground. Larvae are white with no legs, pointed at one end and grow to a length of 6 mm. Pupae are approximately 6 mm long and brown. The cabbage maggot adult has a gray body with 3 black longitudinal stripes on the thorax and one black stripe running along the top of the abdomen and is very similar in appearance to the housefly
The cabbage maggot overwinters as a pupa in the soil. In Pennsylvania, the first summer generation emerges about late May. Newly emerged adults feed on pollen and nectar. Eggs are oviposited singularly on the plant or soil near the soil line. Larvae hatch in approximately a week and begin feeding on small fibrous root systems. The larvae will fed for 2 to 3 weeks and develop most quickly in cool wet conditions. Pupation usually takes place within the larval burrows. Pupation lasts approximately 2 to 3 weeks. Pennsylvania will usually have 2 to 4 generations depending on accumulated degree-days.
The larva of the cabbage maggot damages plants by feeding on the root's system. Young larvae will feed on the fibrous root hairs while older larvae may tunnel into stems and roots. This root feeding and tunneling interferes with proper nutrient uptake in the plant. Additionally, the tunnels provide entry for other opportunistic pathogens.
Often attacked plants appear stunted. Cabbage that has been damaged by the cabbage maggot will often radiate a blue-green color. In contrast, damage to radishes and turnips by the cabbage maggot does not result in wilting foliage, making detection difficult.
Proper cultural controls can reduce populations of the cabbage maggot decreasing the probability of plant injury. Plowing under the crop ruminates after harvest will bury the puparium of many overwintering cabbage maggots. Avoid planting into fields that have recently decaying organic matter such as immediately following the plowing under of animal matter or a cover crop.
Cool wet springs promote conditions that contribute to high populations of cabbage maggot. Fields of cruciferous vegetables should be scouted and closely evaluated for cabbage maggot especially during years with favorable conditions. The first summer generation of the cabbage maggot is the most deleterious to plant health. Young plants are not able to withstand much root feeding from the cabbage maggot before wilting and death occur.
Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.
Authored by: Shelby Fleischer, Professor