Insects and Mites

Seedcorn Maggot

Scientific name: Delia platura (formerly Hylemya platura)
Order: Diptera
Family: Anthomyiidae

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Info

Biological Description
  • Flies: Resemble small houseflies. Dark gray, 1/5" long, wings are held overlapped over their bodies while at rest. Smaller than cabbage and onion maggots, with which they are easily confused.
  • Larvae: Yellowish-white, 1/5" long when fully grown, legless, head end is pointed.
  • Pupae: Reddish-brown, 1/5" long, cylindrical in shape, rounded at both ends.
  • Eggs: White, 1/32" long, and oval in shape.
  • Confused with: Cabbage maggot, onion maggot, bean seed maggot
Economic Importance
  • Seedcorn maggot is a threat to both corn and soybeans.
  • Outbreaks:
    • Seedcorn maggot problems tend to occur more often in cold, wet, spring weather. If a crust forms on the soil, germinating seedlings can become trapped underground with feeding seedcorn maggot larvae.
  • Susceptible crops:
    • Corn
    • Soybeans
    • Vegetable crops (peas, succulent beans, cruciferous crops...)
Life Cycle
  • Seedcorn maggot overwinters in the pupal stage in the soil.
  • Adult flies emerge in the spring with peak emergence in early to mid-May. Swarms of flies are often seen over recently tilled fields. Adults mate within 2-3 days of emergence.
  • Females lay eggs in soils with high organic matter or near seeds and seedlings of susceptible plants. Eggs hatch 2-3 days later.
  • Larval feeding and development lasts about 2.5-3 weeks and occurs entirely below ground.
  • The pupal stage, also below ground, lasts about 1-1.5 weeks. After this time adult flies emerge from the soil.
  • Generations:
    • There are three to four generations per growing season in Wisconsin.
    • Each generation lasts 3-4 weeks
    • The first generation (the eggs laid from the overwintered population) causes the most damage because the larvae are present and feeding at the same time that crops are planted and germinating.
    • Subsequent generations cause little damage because crops are no longer in a vulnerable stage.
Damage/Symptoms
  • Damage is a result of larval feeding on germinating seeds.
  • Cool, wet weather favors seedcorn maggot and delays germination, resulting in a higher risk of seedcorn maggot damage under these conditions compared to warm, dry weather.
  • In soybeans, seedcorn maggot larvae feed on the cotyledons and the below-ground hypocotyl tissue of seedlings. Damage symptoms include:
    • Feeding can kill seedlings before they emerge causing poor germination and gaps in rows.
    • Seedlings that have been fed upon but still emerge may have holes in the first pair of true leaves or no leaves at all ("snakehead" seedlings).
    • Damage to the hypocotyls can leave plants yellow and wilted.
  • In corn, all parts of sprouting corn seeds are attacked by the maggot larvae. Damage symptoms include:
    • Poor germination rates
    • Holes in the leaves
    • Weakened, stunted plants
Scouting Procedure and Economic Threshold
  • Seedcorn maggot damage cannot be detected until it is too late to take control actions.
  • Insecticides can be applied at planting as a protective measure.
  • By monitoring adult populations and calculating degree days, it is possible to determine population peaks and estimate when seedcorn maggot is likely to be in each stage of its life cycle. This information can be used to avoid planting into the larval (feeding) stage and rather into the pupal (non-feeding) stage. To do this, use the following degree-day information:
    • It takes about 270 Celsius degree-days after peak adult flight for seedcorn maggot to complete its egg and larval stages and enter its non-feeding pupal stage.
    • The base temperature for seedcorn maggot is 3.9°C. Information on how to calculate degree-days can be found here.
Integrated Control
  • Natural control: Naturally occurring fungal diseases occasionally will greatly reduce seedcorn maggot numbers, particularly when flies are abundant and relative humidity is high. Predacious ground beetles eat seedcorn maggot eggs, larvae, and pupae, and can be important in reducing maggot numbers.
  • Cultural control: Reducing the amount of decaying organic material at the time of planting will reduce the attractiveness of the field to seedcorn maggot. This can be achieved by tilling in a cover crop that is already dead or by increasing the amount of time between tillage and planting. Additionally, plants can be planted as shallow as possible to speed germination.
  • Chemical Control: For current Wisconsin recommendations, consult University of Wisconsin-Extension Bulletin #A3646, Pest Management in Wisconsin Field Crops.

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