Beginner

Scientific Name
Delia platura

Identification

• Small (< 5 mm, ¼ in.), white maggots
  
• Feed on the swollen, ungerminated seed of vegetable crops
  
• Poor stand establishment is often a symptom of infestation

Often Confused With
Wireworm feeding injury
3-leaf dieback

Period of Activity
Maggots are usually a problem during cool, wet springs when germination is delayed. The first generation of adult flies lay their eggs from April until the middle of June. There are several generations per year in Ontario; the first generation is generally the most damaging.

Scouting Notes
Begin walking fields at the spike to 4-leaf stage; look for wilted plants and/or gaps in the plant stand where the seedlings have failed to emerge. Dig around the seed trench to look for the cause of the damage. Seedcorn maggots are often found in the seed. They will also tunnel up the stem of newly emerged seedlings and transplants. Record the percentage of the field impacted by root insect damage. Do a plant population count to determine if re-seeding is necessary.

Thresholds
None established. Fields with a plant population of less than 11,000 plants per acre may require re-planting.

Advanced

Scientific Name
Delia platura

Identification
The translucent white maggots are small (< 5 mm or ¼ in.), legless and oblong-shaped with a pointed anterior. The adult seedcorn maggot is a small (5 mm, ¼ in.) grey-black fly.

These small white maggots feed on the swollen, ungerminated seed of vegetable crops. Poor stand establishment is often a symptom of infestation. Maggots may also attack young seedlings, shortly after emergence.

Often Confused With
Wireworm feeding injury
3-leaf dieback

Biology
Seed Corn maggots over winter as pupae in the soil. The adults emerge in early spring. Females often deposit their eggs on fresh manure applications or decomposing crop residue. Larvae hatch in 7- 10 days and remain in the field for 1- 3 weeks feeding on residue, seeds and young seedlings. Larvae may be active at soil temperatures as low as 10°C (50°F). There are 3- 6 generations per year. Once the plants grow past the seedling stage, they are no longer susceptible to seedcorn maggot injury.

Period of Activity
Maggots are usually a problem in direct-seeded crops during cool, wet springs when germination is delayed. The first generation of adult flies lay their eggs from April until the middle of June. There are several generations per year in Ontario; the first generation is generally the most damaging.

Scouting Notes
Begin walking fields at the spike to 4-leaf stage; look for wilted plants and/or gaps in the plant stand where the seedlings have failed to emerge. Dig around the seed trench to look for the cause of the damage. Seedcorn maggots are often found in the seed. They will also tunnel up the stem of newly emerged seedlings and transplants. Record the percentage of the field impacted by root insect damage. Do a plant population count to determine if re-seeding is necessary.

Thresholds
None established. Fields with a plant population less than 11,000 plants per acre may require re-planting.

Management Notes

• Plant only once the soil has reached an appropriate soil temperature based on the type of sweet corn grown. Supersweet (sh2) varieties will not germinate at soil temperatures lower than 18°C (64°F). Sugar enhanced (se) varieties require temperatures greater than 16°C (61°F). Under cool soil conditions, plant only normal (su) varieties.
  
• Avoid heavy manure applications in the 3- 4 weeks before planting.
• Kill or plough down green manure or cover crops at least 3- 4 weeks ahead of planting.
  
• Insecticide seed-treatments will usually control seed corn maggot. However, slow germination may reduce the efficacy of the seed treatment.