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Quick guide to insects and diseases of onions

Quick facts

This page highlights non-chemical practices to prevent or manage common insect and disease problems of onions. 

For more detailed information follow the links in each section.

Click on an image to enlarge it.

Cutworms

Aluminum foil around bean plant stem during transplanting to prevent cutworm infection
Beans stems infected by cutworm
  • Remove weeds and plant residue.
  • Till garden before planting.
  • Place cardboard collars or aluminum foil around plant stems when planting transplants.

More information on cutworms.

 

Onion maggot

White row cover covering the young plants
Green onion with a tunnel near its roots
  • Avoid using animal manure or green manure in spring.
  • When possible, delay planting onions until after June 1.
  • Remove and destroy host plants in fall.
  • Cover plants with a row cover (light weight fabric) in spring.
  • Don't plant onions in the same area in consecutive years.

More information on onion maggot.

Purple blotch

Brown, sunken spots on onion leaf
Yellow, wilting onion leaves
  • Yellow storage onions are more resistant than Spanish onions.
  • Use drip irrigation.
  • Don't leave culls near field.
  • After harvest, remove and destroy or bury any infected leaves.
  • Don't plant onions, leeks or shallots in the same field for 3-4 years.

Fusarium basal rot

Rotten, mushy inside of an onion cut in half
White, powdery deposit at the base of an onion
  • Plant varieties with tolerance or resistance to disease.
  • Plant in well drained soil or use raised beds to improve drainage.
  • Don't plant onions, shallots, garlic or chives in the same field for 4 years.

Michelle Grabowski, Extension educator and Jeff Hahn, Extension entomologist

Reviewed in 2019

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