Onion Maggot

Delia antiqua

1 host plant

Last updated

Quick Reference

Order
Diptera
Type
fly (root maggot)
Host Plants
1
Peak Activity
First flight April-May; second July; third August-September.
What Damage Looks Like

Larvae feed on developing bulbs and roots, tunneling into the basal plate and lower stem. First-generation damage in spring causes wilting and death of seedlings; later generations damage developing and mature bulbs, opening them to secondary bacterial rots. Heavily infested fields show patches of stunted, yellowed, or collapsed plants. Damaged bulbs are unmarketable and store poorly." # Source: PNW Insect Management Handbook

Cultural Controls

  • Practice crop rotation; do not plant alliums in the same ground two consecutive years.
  • Use floating row cover from emergence through harvest to exclude egg-laying adults.
  • Remove and destroy culls, volunteer onions, and harvest debris; these support overwintering populations.
  • Avoid heavy nitrogen fertilization which stimulates lush growth attractive to flies.
  • Plant onion sets and transplants only into well-prepared, free-draining soil; weakened plants are preferred egg-laying sites.

Host Plants (1)

Sources & References

Primary: PNW Insect Management Handbook

  • WSU HortSense — Onion pests
Data Maturity
Structured Multiple sources. Expert review underway.