Why Are My Brassica Roots Swollen and Distorted?

If your broccoli or cauliflower plants are wilting in warm weather despite adequate moisture, and pulling one up reveals grotesquely swollen, club-shaped or distorted roots, you are looking at clubroot — one of the most serious diseases in the brassica family. It is a soil-borne water mould that infects brassica roots and can persist in the soil for twenty years or more. There is no cure, but it can be managed.

What clubroot does to the plant

The clubroot pathogen (Plasmodiophora brassicae) infects root cells and causes them to multiply abnormally, producing the swollen galls that give the disease its name. These galls prevent the roots from absorbing water and nutrients efficiently, which is why infected plants wilt in heat even when the surrounding soil is moist. Above ground, plants may be stunted, pale and slow-growing with leaves that yellow progressively. Heads that do form are often small and poor quality.

Confirming the diagnosis

Pull a suspect plant and examine the roots. Healthy brassica roots are slender and relatively uniform. Clubroot-infected roots have irregular, rounded swellings that may be fused together. The swellings are firm at first but become soft and rotting as they break down. A foul smell is common. If the swellings are small and separate rather than fused into large galls, check also for cabbage root fly damage, which causes different but similarly alarming root distortion.

Managing an infected plot

There is no chemical cure for clubroot in the home garden. Remove infected plants immediately and bag them for the bin — never compost them, as this spreads the spores. Lime the soil generously to raise the pH to 7.5 or above; clubroot is much less virulent in alkaline soils. Avoid growing any brassica (including cabbage, kale, turnip, radish and wallflower) in the affected area for at least seven years. Growing brassicas in containers filled with fresh compost is a practical way to continue growing them while the soil rests.

Preventing future infection

Clubroot spreads through contaminated soil on tools, boots and transplants. Always buy certified disease-free transplants or raise your own from seed in clean compost. Disinfect tools between plots. Maintain soil pH at 7 or above — test annually and lime if needed. Several clubroot-resistant brassica varieties are now available and worth using in any garden with a history of the disease.