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White mould (Sclerotinia): how to recognise and treat it

Disease

White mould (Sclerotinia) — Photo: Schlaghecken Josef, CC BY-SA 4.0, Wikimedia Commons

Symptoms

A soft, wet rot on stems, often near soil level; plants suddenly turn yellow, wilt and collapse.
Masses of fluffy white, cotton-like mould on the affected parts, especially in cool, damp weather.
Later, hard black seed-like bodies (sclerotia) 0.5–1 cm across in the mould and inside hollow stems.
Roots, heads, pods and fruit can rot too, also in storage.

Organic treatment

Remove and destroy affected plants promptly, before the sclerotia drop into the soil; do not compost them — home heaps do not get hot enough to kill sclerotia.
Work infested beds last and clean tools, pots and boots afterwards, so you do not carry sclerotia to clean ground.
Where the disease keeps returning, work a biological product with spores of the fungus Coniothyrium minitans into the soil; it attacks and destroys sclerotia.

Chemical treatment

No fungicide is available to home gardeners (UK, US extension advice); fungicides only prevent infection and do not cure it — rely on hygiene and rotation.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Prevention

Rotate with non-hosts such as sweet corn and cereals for at least 5 years; sclerotia survive in soil for years.
Space and prune plants for air flow, avoid overhead watering and water before noon so plants dry by night.
Mulch early in the season to stop spores splashing up, and control weeds that also host the fungus.
Clear all crop residues at the end of the season; use healthy seed and transplants and do not save seed from infected plants.

Plants it affects

Sources

Figures checked against these sources.