Pest profile

Seedcorn Maggot

Delia platura · Diptera: Anthomyiidae[2]

When beans, corn or other seeds fail to come up in a cool, wet spring, seedcorn maggots feeding on the germinating seeds are a likely cause.[1]

Adult seedcorn maggot fly, a small dark gray fly resembling a house fly, perched on a fingertip
Adult seedcorn maggot fly, a small dark gray fly resembling a house fly, perched on a fingertip. (c) Zachary Dankowicz, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Larvae are small, legless white maggots, under about 1/3 inch when grown, pointed at the head end and blunt at the rear.[1]
  • Adults are dark gray flies about half the size of a house fly.[1]
  • Pupae are brown and egg shaped, found in roots or nearby soil.[1]

Look-alikes

Look-alikeHow to tell them apart
House flySeedcorn maggot adults look like house flies but are only about half their size.[1]

Where it lives

In most California growing areas the maggots are active all year, with several generations.[1]

US map: public records from 11 states since 1990 (GBIF).

Biology and life cycle

Females lay small white eggs in stems at the soil line or in soil cracks next to plants.[1]

Eggs hatch in a few days, and the maggots burrow into roots or germinating seeds.[1]

After one to several weeks of feeding they pupate in roots or the surrounding soil.[1]

Damage and signs

  • Maggots kill germinating seeds and very small seedlings.[1]
  • Once seedlings have a few leaves, economic damage is unlikely.[1]

Health risk

The maggots attack seeds and seedlings; UC IPM describes no risk to people.[1]

Control

Prevention

Cool, wet weather favors them, so plant when conditions promote fast germination, or use transplants or pregerminated seed.[1]

Keep them out

Cover seedbeds with fabric or cover individual plants so flies can't lay eggs nearby.[1]

Sanitation

Avoid heavy manure applications, since females prefer to lay eggs in rich soil, and work weeds in at least two weeks before planting.[1]

Common questions

Why didn't my bean seeds come up?
In cool, wet weather, seedcorn maggots may have killed the germinating seeds; prevention is the best approach.[1]
Do I need to treat established plants?
Usually not. Once seedlings have a few leaves, the maggots are unlikely to do economic damage.[1]

Sources

  1. University of California Statewide IPM Program, “Seedcorn Maggot (Pests in Gardens and Landscapes).” ipm.ucanr.edu/PMG/GARDEN/VEGES/PESTS/seedcornmaggot.html (accessed 2026-10-06)
  2. iNaturalist, “Delia platura taxon page (order and family).” www.inaturalist.org/taxa/243756 (accessed 2026-10-06)

Updated 2026-10-14. Built from sourced records. Spot an error? Tell us.