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Seedcorn Maggot

Delia platura Meigen

Appearance and Life History

The seedcorn maggot is an early season pest of corn. It may be more of a problem during damp, cool seasons and in manured or reduced tillage fields with decaying residue.

The seedcorn maggot is a pale, yellowish-white maggot found burrowing into corn seeds. Full grown maggots are legless, about 1/4 inch (6 mm) long, cylindrical, narrow and tapered. Maggots lack heads and legs, but have small black mouth hooks in front.

The seedcorn maggot spends the winter as a larva inside a "wheat seed-like" puparium in the soil. When mature, the maggot pupates inside this dark brown structure. First generation adults emerge in April and May, mate, and lay eggs on moist soil high in organic matter, or near decaying vegetation. The adult, which resembles a small house fly, is a gray to brown fly about 1/5 inch (5 mm) long that can be easily seen flying over freshly worked soil or where manure has been previously spread.

Seedcorn maggot eggs hatch in a few days after being laid and small, white, tapered maggots begin to feed on and burrow into seeds. The maggots usually feed for 2 to 3 weeks before changing into the brown pupal stage in the soil. Pupae do not damage plants or seeds. Adults emerge from the pupal case in about 7 to 14 days, mate, and begin a new cycle. The entire life cycle may require no more than 21 days, resulting in 3 or more generations each year. Later generations are of little to no economic importance to corn.

Damage

Corn seeds attacked by seedcorn maggots may never emerge, thus reduced stands may be noted. The maggots burrow into the seed, often destroying the germ. The seeds fail to germinate and plants do not emerge from the soil leaving large gaps in the stand. When infested seeds do germinate, the seedlings are weak and may die. Any condition that delays germination may increase damage from this pest. Maggot damage, unlike wireworm damage, usually covers most of a field (an exception might be in a field where manure was not spread throughout the field or levels of crop residue vary). Land that is heavily manured, or where a cover crop is turned under, may be attractive to egg-laying flies in the spring.

Sampling Method

Examine soil by digging in areas where plants have failed to emerge. Check ungerminated seed for injury and presence of maggots. Dig up 2 linear row-feet (0.6 m) in each of 5 areas. Examine seeds for damage. Record the number of plants, good (sound) ungerminated seeds, and hollowed-out or otherwise damaged seeds in each area sampled.

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

Since there are no rescue treatments for control of seedcorn maggot, replanting is the only available management option. The decision to replant should be based on the remaining healthy plant population, the date, yield expectation, etc. If replanting before June, a seed treatment and/or soil insecticide may be advisable. IPM As temperature and humidity rises during the summer, seed corn maggot adults are often attacked by fungal pathogens. The infected flies are found dead and in large numbers clinging to crops, weeds, etc.

The following chart may help in replant decision making. For example, corn planted on April 25 but with only 16,000 plants per acre because of seedcorn maggot damage, is at 86% optimum yield. Replanting on May 21 and obtaining a population of 25,000 plants per acre should increase your optimum yield to approximately 95%. Although this 9% increase in potential yield appears good, one must consider factors such as seed and machinery/labor costs, hybrid maturity, and extended weather forecasts before replanting decisions are made.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.