Cabbage on left is infested with seedcorn maggot Photo: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org

Cabbage on left is infested with seedcorn maggot
Photo: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org

Updated: April 27, 2021

Appearance

  • Eggs: Tiny, elongate, oval, slightly curved, pearly white eggs, usually laid at soil surface singly or in small clusters, near seeds, sprouts, or decaying organic material.
  • Larvae: Yellowish-white maggot with a sharply pointed head and tough skin, about ¼" long at maturity (after completing 3 instars).
  • Pupae: Oval, light reddish-brown to dark brown puparium, in the soil.
  • Adults: Grayish-brown fly, about 1/5" long.
Adult seedcorn maggot fly Pest and Diseases Image Library, Bugwood.org
Adult seedcorn maggot fly
Pest and Diseases Image Library, Bugwood.org

Life cycle/habits

  • Pupae overwinter in the soil. Adult flies emerge in March and April and are attracted to the odor of decay.
  • Flies feed on flowers of many plants, and are most active feeding and laying eggs around mid-day.
  • Flies are attracted to and lay their eggs in sprouting or decaying seeds and plants, organic fertilizers such as fish meal or cottonseed meal, and freshly tilled soil.
  • Hatched larvae burrow about 2-3” into the soil, where 1st instars feed on decaying organic matter, and later instars additionally feed on seeds and seedlings. Larvae pupate in the soil.
  • There are 2 to 4 generations annually in Maryland.

Host plants

  • Corn primarily. Also asparagus, beans, beet, cabbage, cucumbers, melons, onion, potatoes, radish, squash, spinach, turnip.

Signs/symptoms

  • Seeds never germinate, or when you dig up seeds they are damaged or have a white maggot is inside.
  • Most common on warm–season crops with large seeds such as corn, bean, pea, and melon.
  • Seedcorn maggot larva inside an onion
    Whitney Cranshaw, Colorado State University, Bugwood.org

    seedcorn maggot inside onion
  • Seed damaged by seedcorn maggot
    Pest and Diseases Image Library, Bugwood.org

    Seed damaged by seedcorn maggot Pest and Diseases Image Library, Bugwood.org

Monitoring

  • In spring, look for flies clinging to the edge of foliage. Be alert for poor germination rates (seedlings never emerge), and for damaged seedlings.

Prevention/control

  • Avoid planting slow-germinating seeds in cold, wet, highly organic soils. Wait until soil is warm.
  • Pre-germinate corn, pea, and bean seeds indoors in early spring on moist paper towels, prior to planting.
  • Odor of decay (manures, organic fertilizers) attracts flies. Be sure cover crops have decayed (turn under cover crops at least 3 weeks before planting).
  • Plant seeds as shallowly as possible to hasten germination.
  • Replant - later generations are not as damaging.
  • Predators include fungi, ants, and spiders. Ground beetles eat eggs, larvae, and pupae. Braconid wasps are important parasitoids.
  • Floating row covers may be ineffective because pupae overwinter in soil.