Seedcorn Maggot - Vegetables | University of Maryland Extension

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

Updated: February 20, 2023

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.

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.

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

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

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

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.