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University of Minnesota Extension

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.


  • 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

  • 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

  • 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

  • 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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