Onion White Rot
Disease · Commonly affects: Onions, Garlic, Leeks, Shallots, Spring onions, Chives, Ornamental alliums
Onion white rot is a serious soil-borne fungal disease of onions, garlic, leeks and their relatives. It can persist in contaminated ground for many years, making it a long-term problem on allotments. Infection is most damaging in cool conditions, when plants yellow, wilt and collapse despite apparently adequate watering.
How to identify it
Affected plants become stunted, with yellowing leaves that wilt and die back from the tips. Lift a sick plant and inspect the roots and bulb base. White, fluffy fungal growth coats the tissue, followed by many tiny black resting bodies called sclerotia, usually about 0.5-1 mm wide. Roots rot away and bulbs become soft. The symptoms may occur in patches or along a row, rather than being evenly spread across the bed.
Damage
The disease destroys roots and bulb bases, so plants cannot take up water or nutrients. Seedlings may die, while larger onions, garlic and leeks stop swelling and rot before harvest. Infected bulbs do not store well. Most importantly, sclerotia remain dormant in soil for many years, allowing the disease to recur whenever alliums are planted there.
Prevention
Inspect sets, seedlings and garlic cloves before planting, using only healthy material from reliable sources. Keep tools, boots and harvested produce free of clinging soil before moving between beds. Do not share plants or soil from an affected plot. Rotate alliums as widely as your site permits, but remember that rotation alone may not remove a long-lived infestation. Grow onions and garlic in clean containers or raised beds filled with fresh compost if a bed is known to be contaminated.
How to manage it
Lift and remove affected plants as soon as they are found, taking surrounding soil as carefully as practical without spreading it elsewhere. Bag and dispose of plants and bulbs; do not compost them at home. Mark the affected area and avoid onions, garlic, leeks, shallots and spring onions there for many years. Clean tools and footwear before using another bed. Use containers or a separate clean bed for future allium crops, and monitor neighbouring plants closely.
Onion White Rot: frequently asked questions
How do I identify onion white rot?
Affected plants become stunted, with yellowing leaves that wilt and die back from the tips.
How do I prevent onion white rot?
Inspect sets, seedlings and garlic cloves before planting, using only healthy material from reliable sources.
How do I get rid of onion white rot?
Lift and remove affected plants as soon as they are found, taking surrounding soil as carefully as practical without spreading it elsewhere.
General guidance for UK home gardens and allotments, focused on prevention and non-chemical control. For a confirmed diagnosis, the RHS or a local garden centre can help. Page updated 19 Sep 2026.