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Extension > Agriculture > Crops > Soybean Production > Insects & mites > Seedcorn maggot in Minnesota soybean

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Seedcorn maggot in Minnesota soybean

Robert Koch, Extension entomologist and Suzanne Wold–Burkness, Research assistant
2015

Seedcorn maggot adult

Photo: Pest and Diseases Image Library, Bugwood.org

Figure 1. Seedcorn maggot adult.

Name

Seedcorn maggot (Delia platura)

Identification

Adults (Figure 1)

Eggs

Eggs are elongated and white and not usually seen.

Larvae

Larvae are white–colored with a brown head, and less than ¼–inch long.

Pupae

Pupae are brown, cylindrically shaped, and less than ¼–inch long.

Natural history

seedcorn maggot cotyledon

Photo: T. Hillyer, Iowa Crop Consultant

Figure 2. Seedcorn maggots in a soybean cotyledon.

Seedcorn maggot overwinters as a pupa in the soil. In the early spring, adult flies emerge and mate. Female flies lay eggs within cracks in the soil, or under soil clods.

Disturbed soil with decaying organic matter, such as manure or green plant material (cover crop or weeds), is highly attractive to female flies for egg laying. Eggs can hatch within 2–4 days and maggots move to and feed on seed and germinating plants (Figure 2). Fully developed larvae pupate in the soil, about 3–6 inches deep, and emerge as flies 12–14 days later. There are 4–5 generations per year.

Impacts

seedcorn maggot snap bean

Photo: E.C. Burkness, U of MN

Figure 3. Seedcorn maggot damage on snap bean, which led to secondary infection.

Seedcorn maggot feeding can result in direct loss by destroying the seed and causing stand loss.

Maggots will also feed on developing cotyledons, which can destroy the growing tips, resulting in "snakehead" plants. These then may die or become "Y–plants," where branching develops at surviving nodes.

Yield from "Y–plants" may be reduced if competing with neighboring healthy plants.

Feeding by seedcorn maggot can also lead to secondary infection by fungi and can cause damping off (Figure 3).

Management

Thee are no rescue treatments for seedcorn maggot. Once seedcorn maggot injury is noticed, it is too late to use any control methods. All management decisions need to be made prior to planting and should be based on the risk of economic infestation.

Risk for economic infestation by seedcorn maggot is greater in:

Cultural control

Chemical control

Rescue treatments are not available for this pest. Preventative use of seed–applied or in–furrow insecticides may be considered for fields with high risk for economic infestation by seedcorn maggot (see above for risk factors). Follow instructions on insecticide label.

Estimation of stand loss and replant decisions

Fields should be inspected for stand loss during seedling growth stages. Soybean is a resilient crop, able to tolerate relatively high levels of stand loss. However, when significant stand loss occurs, replanting may be required, but this option should be considered carefully. Information is available on how to estimate plant stand and guide replant decisions in soybean (U of M Extension soybean replant guide). This emphasizes the importance of knowing the field history, previous infestations, and current degree days.

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