Cabbage Maggot

Cabbage Maggot Adult
Adult Cabbage Maggot (© Trevor and Dilys Pendleton (www.eakringbirds.com))

Cabbage Maggot Damage on Broccoli (Shimat Villanassery Joseph, University of California)
Cabbage Maggot Damage on Broccoli (Shimat Villanassery Joseph, University of California)

Description

Adult: These dark gray flies are about half the size of the common house fly. 
Egg: Small white, oval-shaped; eggs are typically laid on the soil near the stem of the host plant. 
Larva: Small, white, legless maggot have a blunt tailend and pointed head. 
Pupa: They are about 6 mm long and brown.

Life History

Cabbage maggot pupae overwinter in crop debris and soil. Adults emerge in early May, and mated females lay eggs in the soil at the base of host plants. Small maggots hatch in 4-10 days and immediately burrow into the stem of the host plant. After about 3 weeks, mature larvae leave the stems and pupate in the soil close to the soil surface. About 2 weeks later, adult flies emerge and lay eggs for another generation. Larvae from this generation feed on roots or stems and develop into the overwintering pupae.

Damage

Cabbage maggot larvae feed on the roots of cole crops, and can tunnel through tap roots. Tunnels provide an entry for decay, fungi, and bacteria. Damaged plants show wilting, reduced growth, and lighter green plant parts. Cabbage maggot prefers cauliflower, Brussels sprouts, radish, cabbage, broccoli, collards, kohlrabi, and turnip. Cress, beet, and celery can also be infected. Cauliflower and Brussels sprouts can be more susceptible than hybrid cultivars of broccoli. Seedlings and young plants are most vulnerable, while healthy plants can tolerate moderate infestations. 

Monitoring

After susceptible crops emerge, watch for wilting, reduced growth, and signs of chlorosis (yellowing). If cabbage maggots are suspected, pull up affected plants and check the roots and soil to confirm maggot presence. If tunnels are found in roots but no maggots are present, then maggots have already exited roots to pupate in the soil. This timing is too late for an effective insecticide treatment.


Management

Cultural

  • Rotate crops. Plant susceptible hosts as far away as possible from where they were planted the previous year.
  • Use a set of drag chains when direct-seeding susceptible crops. Drag chains can help eliminate moisture where seeds have just been planted. Adult flies may be more attracted to moist areas for egglaying.
  • Be aware of cabbage maggots in cool, wet spring weather. These conditions are more favorable for cabbage maggot development.
  • Plant seeds into raised soil beds. Promote soil drying and warming and discourage egg-laying by cabbage maggots.
  • Immediately after harvest, destroy or disc under crop residues. Maggots are able to survive for an extended time in crop residues.
  • When several rows of seedlings are infested, remove them and replant.

Chemical

Fumigate or treat infested soil before planting. In areas where cabbage maggot causes economic injury, treat with a band of insecticide at the plant’s base at the time of planting or transplanting. 

Biological

Carabid beetles, rove beetles, and parasitic wasps may help suppress cabbage maggots. However, biological controls alone generally do not keep cabbage maggot populations below economically damaging levels, especially once a population has established.