white rot diseased onion bulbs

White rot (Stromatinia cepivora) on onions. Ed Kurtz, Bugwood.org

Updated: October 11, 2021

Stunting, yellowing, and dieback of foliage of onions, garlic or moldy bulbs

The first symptoms of stunting, yellowing, and dieback of foliage of onions, garlic, and other family members can be a symptom of a  very destructive fungal disease called white rot.  When bulbs are pulled out of the soil they are either coated with a white to gray colored fuzz or with a crusty covering that is embedded with thousands of tiny black sclerotia (reproductive structures). The sclerotia can live in the soil for years without the benefit of host plants.

yellowing and wilting garlic foliage
White rot infested garlic bed causes premature yellowing of garlic foliage
Bruce Watt, University of Maine, Bugwood.org
white rot infested garlic bulbs
White mycelium and tiny black sclerotia (that allow the fungus to remain dormant for years) are signs of white rot.
closeup of white rot infected garlic bulb
Garlic bulb infected with white rot

Management

  1. Always buy certified disease-free vegetative planting stock (garlic, onion sets, etc.) and seedlings.
  2. Never plant garlic purchased from a grocery store. It may be a symptomless carrier of the disease.
  3. Remove and dispose of infected plants. Do not attempt to compost these plants.
  4. Work in a lot of compost to infected beds and don't plant allium family members for 4-5 years.