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What is clubroot?

Clubroot is a soil-borne disease caused by the pathogen Plasmodiophora brassicae. Clubroot affects the roots of cruciferous field crops such as canola, mustard, camelina, oilseed radish and taramira, and cruciferous vegetables such as arugula, broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, kale, kohlrabi, radish, rutabaga and turnip. Cruciferous weeds (such as stinkweed, shepherd's purse and wild mustard) can also serve as hosts.

Root infection of host plants by the clubroot pathogen results in swelling of the root tissue (galls), which reduces the plant’s ability to obtain water and nutrients from the soil, resulting in yield loss. The level of yield loss will be related to the amount of pathogen in the soil, the susceptibility of the host crop and environmental conditions.

Symptoms

Clubroot-infected roots will have swollen root tissues (galls).

Clubroot galls will initially appear white and fleshy. Later in the season they will start to decompose and appear rotten.

Above-ground symptoms of stunting, yellowing and premature ripening may occur. These symptoms may indicate the presence of a clubroot patch, but could also be associated with other diseases or adverse environmental conditions. As a result, it is important to examine plant roots for the presence of clubroot galls.

Clubroot prevention

Clubroot resting spores survive in the soil and can be moved any way that soil can be moved. This includes soil movement on agriculture or industrial equipment, vehicles, tires, shoes, animals, wind or water erosion, or contaminated inputs such as manures. Activities that move large volumes of soil are considered to have a higher risk, as do activities that move soil over large geographic regions and from regions where clubroot is known to be present.

The focus of clubroot prevention is preventing the introduction of clubroot-infected soil. The following practices can be used to prevent clubroot introduction and minimize the spread of clubroot once it has been confirmed in a field and/or region:

• Practise good sanitation to restrict soil movement;
• Knock soil off equipment between fields;
• Minimize traffic to and from fields;
• Practise zero or minimum tillage, which will reduce the movement of clubroot-infected soil through water and wind erosion;
• Create a separate exit as far as possible from the field entrance. Clubroot is often first found at the field entrance, and this area of the field will often have the highest concentration of the pathogen. Exiting the field as far as possible from the field entrance will reduce the amount of pathogen in the soil on equipment leaving the field;
• Notify occupants and landowners who have access to the land if clubroot has been confirmed.and
• Talk openly about biosecurity with all groups working on your land.

Clubroot management

• Restrict movement of potentially contaminated soil on vehicles and equipment;
• Extend your crop rotation; include a break of at least two years, preferably three, between susceptible crops even when clubroot-resistant varieties are used;
• Grow clubroot-resistant varieties;
• Scout canola crops by examining roots for the presence of clubroot galls; focus scouting on field entrances, low areas, and suspicious patches;
• Collect soil and submit it to a laboratory for a DNA-based clubroot test; the test results will provide early detection of the clubroot pathogen and enable early management when pathogen levels are low; and
• See the Clubroot Management and Scouting Tips document for more information.

The key to clubroot management is to keep pathogen levels low to allow continued canola production in the infested fields with minimum impact on yield.