Delia platura Meigen
Appearance and Life History
The seedcorn maggot is an early season pest of soybean. 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 larva found burrowing into soybean seeds. Full grown maggots are legless, about 1/4 inch (6 mm) long, cylindrical, narrow, and tapered. The maggot lacks a defined head and legs, but has small black mouth hooks at the front of its body.
When mature, the maggot pupates inside a dark brown puparium that resembles a wheat seed. The house fly-like adult emerges in the spring. It is gray to brown and about 1/5 inch (5 mm) long. The fly is attracted to manure that has been spread in a field or other decaying organic matter. The adult lays its eggs on moist soil in these attractive areas. It is believed that the seedcorn maggot spends the winter as a larva inside a puparium in the soil. It pupates in the spring and emerges in April and/or May.
The eggs hatch in a few days and small, white, tapered maggots begin to feed and burrow into seeds. The maggot usually feeds for 2 to 3 weeks before changing into the brown pupal stage in the soil. 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 per year. Later generations are of little to no economic importance to soybean, but the last generation produces the larvae that overwinter in the protective puparium, pupate, and emerge the next spring as soybean fields are prepared and planted.
Soybean 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 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 lightly turned under, may be attractive in the spring to egg-laying flies.
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 in a field. Examine seeds for damage. Record the number of plants, good ungerminated seeds, and hollowed-out or otherwise damaged seeds in each area sampled.
Soybean Insect Control Recommendations: E-series 77-W (PDF)
Since there are no rescue treatments for control of seedcorn maggots, replanting is the only available option. The decision to replant should be based on the remaining healthy plant population, the date, yield expectations, etc. Where planting in wide rows, it may be feasible to replant down the middle of the rows without destroying the healthy plants in the original planting. The result would be the equivalent to narrow row soybean.
The following table may help in making replanting decisions.
If soybean is to be planted in fields that may be attractive to seedcorn maggot flies, see "Damage", a seed treatment labeled for seedcorn maggot is probably warranted.
If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.