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White Rot

Disease

White rot is a destructive fungal disease that attacks the root systems of allium crops like garlic, onions, and leeks. It is a serious concern because the fungus persists in the soil for many years, making it difficult to grow susceptible plants in the same area again.

Symptoms by part

Roots

The roots decay and turn into a soft, mushy mass, often accompanied by a white, fluffy fungal growth that eventually develops tiny, black, seed like structures called sclerotia.

Causes

  • Cool, moist soil conditions that favor fungal growth.
  • Planting in soil already contaminated with the fungus.
  • Moving infested soil or plant debris to new areas on tools or footwear.

Could be confused with

  • Onion Maggot · Onion maggots cause wilting and yellowing, but you will find small white larvae inside the bulb rather than white fungal threads on the roots.
  • Fusarium Basal Rot · Fusarium causes a reddish brown decay of the roots and bulb base without the characteristic white, fluffy fungal growth or black sclerotia.

Treatment

  1. Carefully dig up and remove the entire affected plant, including all roots and surrounding soil, to prevent the spread of sclerotia.
  2. Place all infected plant material and the immediate root zone soil into a sealed bag and dispose of it in the trash, never in a compost pile.
  3. Clean all gardening tools that touched the infected area with a stiff brush and water to remove any clinging soil particles.

Without chemicals

  • Practice strict crop rotation by avoiding alliums in the affected area for at least 8 to 10 years.
  • Ensure excellent soil drainage to prevent the moisture levels that the fungus thrives in.
  • Remove and destroy any volunteer alliums that sprout in the infested area.

Preventing it

  • Only plant certified disease free bulbs or sets.
  • Avoid moving soil from one part of the garden to another.
  • Clean your boots and tools thoroughly after working in areas where alliums are grown.
  • Improve soil structure with organic matter to encourage beneficial soil microbes that may compete with the fungus.

Season

The warm growing season, though it is most active when soil temperatures are cool to moderate.

Spread risk

High

Severity

High

When to act

Act immediately upon seeing the first signs of wilting or yellowing foliage, as the fungus spreads rapidly through the soil. If a large portion of your crop is affected, remove the plants and do not replant alliums in that spot for many years.

Think it's White Rot?

This guide covers the general picture. Pocket Botanist looks at your actual plant from a photo and tells you what's really going on, how serious it is, and what to try first. Identification and a health check are free.

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Questions people ask

Can I compost plants that died from white rot?
No, you should never compost them. The fungus produces long lived structures that will survive standard composting temperatures and spread the disease throughout your garden when you use the compost.
How long does white rot stay in the soil?
The fungus can remain dormant in the soil for 8 to 10 years or even longer, waiting for a host plant to be planted nearby.

Plants it affects

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This guide was generated with AI and is general information, not horticultural advice. Read about how we build these guides.