Delia platura (soybean)
Authors: Buyung Hadi, Jeffrey Bradshaw, Jan Knodel and Ken Ostlie
Seedcorn maggot is the larva of a small fly, Delia platura. This fly is widely distributed in Europe. The first report of seedcorn maggot in the United States was in 1865 from New York. Since then this species has spread over nearly the entire country and into southern Canada. Beside soybean, seedcorn maggot also attack common bean, corn, peas, cabbage, turnip, beets, onion, radish and several other crops.
Full grown seedcorn maggot is 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.
Life Cycle and Seasonal History
Mated female fly deposits eggs in the soil, within soil cracks or under clods. Disturbed soil with decaying organic matter, such as manure or decaying green plant materials, is highly attractive for oviposition. After hatching, the maggots move in the soil, finding and feeding 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 fly in 12-15 days. In the region above latitude 43°North, 4-5 generations are produced per year. In the northern states, seedcorn maggot overwinters as pupae.
Plant Injury and Damage
Feeding by seedcorn maggot may destroy the seeds and thus produce significant reduction in plant stand early in the season. Feeding injuries by seedcorn maggot also open a course for secondary fungal infection causing damping-off and stand loss. When seedcorn maggot feeds on the seedling cotyledon, plant development may be impaired but yield is not significantly altered. Sometimes the maggots feed on the growing tip of the plant, resulting in a plant with two main stem, a condition called 'snakehead' or 'Y-plant'.
The seedcorn maggot is a common pest of soybean, although serious injury is limited to fields that attract oviposition by female fly. Injury is also more likely with cool and wet conditions.
Tillage and incorporation of cover crops may increase the risk of seedcorn maggot infestation since the female flies are attracted to disturbed soil and decaying organic matter to lay their eggs.
Delay of planting time after tillage and cover crops incorporation 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.
Soybean plants can compensate for a relatively high level of stand reduction, cotyledon injury and snakehead plants, but replanting may be a reasonable option in severe stand loss. Seedcorn maggot problems are associated with tillage, thus reduced tillage or no-till fields may not face these problems.
Fields with high risk factors (tillage and high organic matter) may merit insecticidal seed treatment. 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.
Other Online Resources
For information regarding labels of chemical control options, please visit Agrian.com