NPIPM:Seedcorn maggot on corn
Authors: Buyung Hadi, R. Jeff Whitworth, Holly Davis, and J.P. Michaud
Seedcorn maggot is the larva of a small fly, Delia platura. The first report of seedcorn maggot in the US was in 1865 from New York. Since then this species has spread over nearly the entire country and into southern Canada. Beside corn, seedcorn maggot also attacks common bean, soybean, peas, cabbage, turnip, beets, onion, radish and several other crops.
Identification
Fully-grown seedcorn maggots are yellowish white in color, about 0.25 in (6.4 mm) long, legless with tough skin. The fly of seedcorn maggot is grayish brown in color about 0.2 in (5.1 mm) long. The adult fly appears slender with longer legs than house flies. The adult flies of seedcorn maggot hold their wings above the abdomen when resting, giving the flies an oval appearance from above.
Life Cycle and Seasonal History
Mated female flies deposit eggs in the soil, within soil cracks or under clods. Recently plowed soil with a high content of organic matter, such as manure or decaying green plant materials, is highly attractive for oviposition. After hatching, the maggots move in the soil and feed on germinating seeds. Seedcorn maggots can successfully survive on decaying organic matter. Fully developed larva pupate inside brown puparium within the soil and emerge as adult flies in 12-15 days. In the region above latitude 43°North, 4-5 generations are produced per year. Seedcorn maggot survives the winter as pupae in the soil.
Plant Injury and Damage
Seedcorn maggot feed on the seeds, either reducing vigor of the resulting seedlings or completely kill the seeds. High levels of seedcorn maggots may produce significant plant stand reductions early in the season.
Management Approaches
Cultural Methods
Planting on freshly tilled fields and in fields where the cover crops are still decaying may increase the risk of seedcorn maggot infestations since the female flies are attracted to disturbed soil and decaying organic matter to lay their eggs. Delaying planting after tillage and incorporating cover crops may suppress injury due to seedcorn maggot feeding. The female fly deposits eggs upon tillage and 3.5 weeks after tillage the maggots start to enter non-feeding pupal stages. Thus, planting seeds this late may serve to avoid feeding by the maggots. Cool and wet conditions may prolong the duration of larval development and feeding. Such conditions must be taken into account in planning for planting.
Chemical Control
Fields with high risk factors (tillage and high organic matter) may merit insecticidal seed treatment. Insecticidal seed treatments and soil insecticides are effective to control seedcorn maggot. However, the decision of treating the seed is taken before the actual infestation of seedcorn maggot can be ascertained in the field, thus it always carry a risk (financial and environmental) of treating a non-existent problem.
