WSU Extension


Onions, Garlic : Onion maggot
(revision date: 6/3/2014)

The onion maggot is the larvae of a slender gray fly about 1/4" in length. Female flies lay eggs near the base of host plants including onion, garlic, leek, and shallot. The white larvae tunnel through the underground portions of the stem and into the bulb, where they feed. Soft rots often infect these injuries, causing further damage. Affected plants appear yellow and flabby. Infested seedlings typically die, while larger onion bulbs may be hollowed out by one or more larvae feeding inside. Mildly damaged bulbs usually rot in storage. Mature larvae are dirty white and about 1/3" long. They pupate in the soil, with up to three generations occurring in a season. The maggots overwinter in the soil or in infested onions, emerging in the spring.
Management Options

Non-Chemical Management
  • Rotate crops. Do not replant susceptible crops in the same locations. Do not plant into areas infested the previous year.
  • Cover crops with floating row covers or screen cages to prevent egg-laying by female flies.
  • Clean up plant debris. Destroy or discard culled plants.
Select non-chemical management options as your first choice!

Chemical Management

None recommended

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Caption: Onion maggot and damage
Photo by: E.P. Breakey
Caption: Onion maggot eggs between leaves
Photo by: L.W. Getzin