Brassica Pest - Seedcorn Maggot
Cabbage infested with seedcorn maggot (left); note the yellow leaves and stunted growth.
Adult: Seedcorn maggot adults are about 0.2 inches (5 mm) long with gray to brown bodies and are similar in appearance to the onion maggot.
Egg: White elongated; deposited in soils rich in organic and decaying matter and on seeds and seedlings.
Larva: Maggots are legless, tapered, about 0.25 inches (6 mm) long, and yellowish-white in color. Head-ends are wedge shaped with small black mouth hooks in front.
Pupa: Oval shaped, dark brown, about the size of a grain of wheat, and found in the soil.
Adult flies emerge in April and May and begin mating within 2 to 3 days. Females lay eggs in or on soils and/ or on seeds. Eggs hatch in 2 to 4 days at which point the larvae burrow into seeds and feed on emerging cotyledons and plant roots. Mature larvae pupate in the soil and remain in this stage approximately 7 to 14 days. Seedcorn maggots overwinter as pupae. A complete generation takes about 3 to 4 weeks and about 2 to 3 generations occur per year.
Maggots prefer feeding in soils rich in organic and decaying matter (such as manure). They burrow into the seeds and roots of many vegetable crops, destroy the seed germ, and may cause rot in plant tissue. Damaged seeds are unable to provide adequate food resources to support initial plant growth. Seeds and plants attacked by seedcorn maggots may not emerge causing reduced stands. Seedcorn maggots cause damage by feeding on roots and tunneling into taproots of susceptible plants. The lower leaves of infested plants often become chlorotic (yellow) and severe damage results in halted plant growth.
Seedcorn maggots are polyphagous (feed on several vegetable host plants), and prefer soybeans and corn. Other susceptible plants include brassicas, beans, peas, cucumber, melon, onion, potato, and others.
- Use the cultural control methods listed above in the cabbage maggot management section
- Direct seed when conditions are ideal for rapid seed germination. Longer germination time results in higher infestation risks.
- Early season infestations can be avoided by planting susceptible hosts later in the season.
Birds, ants, and spiders have been observed attacking adults and fungal diseases can infect larvae. However, these natural enemies are not considered a significant form of control.
Apply a preventive seed treatment for optimal control.
Image 1, Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org