Clubroot is a soil-borne disease of cole crops and other brassicas, caused by Plasmodiophora brassicae. It causes roots to enlarge into swollen, misshapen “clubs” that can no longer take up water and nutrients efficiently.

Above ground, plants may look stunted, yellow or wilt badly during hot weather, sometimes recovering overnight at first. The pathogen produces extremely durable resting spores that accumulate in infected roots and can remain viable in soil for many years. Contaminated soil carried on tools, boots, transplants or equipment can spread it to new areas.

How to Fix It

There is no cure for an infected plant. Remove affected plants, including as much of the infected root system as possible, and dispose of them rather than composting them. Clean soil from tools, footwear and equipment before moving to unaffected garden areas.

Avoid growing susceptible brassicas in contaminated soil for several years, although rotation alone will not eliminate clubroot because the resting spores are so persistent. Improve drainage and avoid moving contaminated soil. Where the soil is acidic, raising the pH with lime can reduce disease severity, but it will not eradicate the pathogen.

Choose clubroot-resistant varieties where available. Biological controls have been investigated, including Bacillus and Trichoderma species, but results are variable and they should not be presented as a reliable cure. For the home gardener, resistant varieties, sanitation, soil pH management and preventing spread are the most dependable controls.