Seedcorn Maggot
Larva-When fully grown, the larva is yellowish white. About 6 mm long, it is sharply pointed at the front, legless, and tough skinned.
Pupa -The capsulelike puparium is dark brown and about 5 mm long.
Host Plants -The seed attacked by the seedcorn maggot usually fails to germinate. If it does sprout, the plant is weak and sickly. Injury is usually most severe during wet, cold seasons and on land rich in organic matter.
Damage -Wilting leaves on individual twigs or drooping girdled tips usually indicate infestation by this borer.
Life History -The seedcorn maggot does no harm to dogwood trees, but it is a frequently reported guest of dogwood and other ornamental plants. Only the adult is found on dogwood. It is infected by a fungus (Entomophthora), which apparently causes the fly to light on and cling to protruding twigs. It usually dies in the afternoon as its abdomen swells with internal fungal strands. Early the next morning when humidity is high, the fungal spores are released into the air to infect other flies. The dead flies shrivel and eventually fall from the twigs.
Most of the life cycle is spent in the maggot stage in the soil of various field crops. Flies emerge in May to deposit their eggs on seed, on plantlets, or on soil with an abundance of decaying vegetable matter. Upon hatching, the maggots burrow into the seed, often destroying the germ. They develop into pupae inside brown puparia in the soil and emerge as adults 12 to 15 days later. As many as three to five generations occur each year.
On dogwoods and other ornamental shrubs, no control of the adults is necessary since infected adult flies indicate a natural mortality factor at work.
For control of the maggots in field crops, shallow planting in a well-prepared seedbed, sufficiently late for quick germination of the seed, is probably the best means of preventing injury. Land where manure is heavy or where a cover crop is turned under should be plowed early in the fall, if possible, to make it less attractive to the egg laying flies the following spring. Prompt resetting or replanting of the damaged crops will usually give a good stand.