Onion White Rot
Risk near you, next 48h
See whether your local forecast favours this disease right now.
When it strikes
Remove affected material now
Take out the affected leaves, shoots or whole plants before the next wet spell, bag them as you cut, and wash your hands and tools before touching healthy plants.
Soil and crop debris
It waits in the ground or in last season's debris, so removing the plant does not clear the bed. Rotation and debris removal are the working controls.
It carries over to next season in soil, debris or seed — which is why rotation matters here, not just treatment.
Keep out of the compost
This survives a garden heap. Bag it for municipal green waste, which is composted industrially at temperatures a garden heap cannot reach, or burn it where that is permitted.
When and where to look
Scout the planting while temperatures hold between 10°C and 24°C, with humidity above 80%.
Rule these out first
Same category, and at least one host crop in common — so they are genuinely confusable in the same part of the garden.
The signs that lead here
Full problem lists for these crops
About
White rot (Sclerotium cepivorum) is the most serious disease of onions, garlic and leeks anywhere they are grown. Its resting bodies survive in soil for twenty years or more without a host, so once a bed is infected it is effectively finished for alliums for a generation.
Symptoms
Leaves yellow and die back from the tips while the plant is still growing, and the whole plant lifts out easily. The base of the bulb is covered in a dense white, fluffy mat studded with poppy-seed-sized black sclerotia.
Organic Treatment
Lift and bag infected plants whole, roots and surrounding soil included — never shake the soil off in the bed and never compost them. Grow alliums in fresh compost in containers or raised beds instead of the contaminated ground.
Chemical Treatment
No fungicide is available to gardeners that controls established white rot. Commercial growers use tebuconazole seed treatments, which delay rather than prevent the disease and are not a garden solution.
Prevention
This is a hygiene disease: clean soil off boots, tools and machinery between plots, buy sets and seed from reputable sources, and never move soil from an infected area. Long rotations help only marginally, because the sclerotia outlast any realistic rotation.
Crops at risk
Related problems
Onion White Rot risk by location
Each location has a month-by-month profile computed from the weather archive: how many hours a year actually meet this disease’s thresholds.