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Clubroot: how to recognise and treat it

Disease

Clubroot — Photo: Rasbak, CC BY-SA 3.0, Wikimedia Commons

Symptoms

Stunted growth, purplish leaves and wilting in hot weather; wilted plants may recover for a while when it is cooler.
Roots massively swollen and distorted into clubs, with few fine roots left.
Growth and yield are badly reduced, and severely affected plants may die.

Organic treatment

Dig up affected plants with their roots and dispose of them; do not compost them.
On acid soil, apply garden lime (about 500 g per m² the first time, then about 270 g per m² in later years); aim for pH 7.2 or higher — it reduces clubroot but does not eliminate it.
Improve drainage, for example with raised beds.

Chemical treatment

No fungicides are available to home gardeners for clubroot; control relies on liming, drainage and clean plants.

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

Prevention

Buy or accept brassica plants only from a clubroot-free source; the spores survive in soil for up to 20 years.
On infected ground, grow plants to a larger size in pots (at least 9 cm) in clean compost before planting out.
Do not move contaminated soil on tools, wheelbarrows or footwear.
Weed out cabbage-family weeds such as shepherd's purse and wild radish, and choose clubroot-resistant cultivars where available.

Plants it affects

Sources

Figures checked against these sources.