By Barbara Ziesman, PhD, A.Ag, Provincial Specialist, Plant Disease
Clubroot is a soil-borne disease that can infect and cause significant yield losses in canola, mustard and Camelina. In 2009, Clubroot was declared a pest under The Pest Control Act and is still a relatively new disease in Saskatchewan, but is not new to the Prairies.
Clubroot in canola was first identified in Alberta in 2003 and is now known to occur in more than 2,400 fields throughout Alberta. When established in a field, significant yield losses can occur up to 100% when pathogen levels are high and environmental conditions are favourable. In 2017, clubroot was confirmed in commercial canola fields in Saskatchewan Crop Districts 9A and 9B. Currently, this disease is not widespread in Saskatchewan. As a result, we can prevent the spread of the disease to new areas and to minimize the impact on the canola industry in areas where the disease is already established.
The clubroot pathogen survives in the soil as resting spores that can live for 20 years. The resting spores are small and can be moved any means that soil can be moved. Activities that move large volumes of soil create higher risk. Sanitation can be used to prevent the spread of clubroot by preventing the movement of infected soil into new areas. Sanitation activities can range from wearing plastic boot covers (when walking into a field) to washing and disinfecting all equipment. The highest level of sanitation benefits high risk activities, such as those that involve moving large volumes of soil over large distance or between regions. Complete sanitation is not practical for situations such as during seeding; in these situations doing as little as using a brush to remove as much soil as possible between fields is helpful. Sanitation is not only the responsibility of producers, but also a responsibility of anyone who is working on agricultural land and could move infected soil.
When clubroot is found in a field, the focus should be on keeping pathogen levels low to reduce the impact on yield and minimizing the movement of infected soil. This can be achieved through a combination of crop rotation, clubroot resistant varieties, sanitation and soil conservation activities to minimize soil movement. Following a diverse four-year crop rotation is extremely important for clubroot management. Growing a susceptible crop once every four years will reduce and maintain low spore levels. Clubroot resistant canola varieties are not immune to clubroot but reduce yield losses and significantly reduce the number of spores returned to the soil. It is important that these varieties are used in an extended crop rotation to minimize the selection pressure on the pathogen to overcome resistance. In some Alberta fields, many resistant varieties are no longer effective. Since resistant varieties are one of the most effective clubroot management tools, it is important to maintain their effectiveness for as long as possible.
Early detection is critical for effective disease management. Producers are encouraged to scout susceptible crops (even resistant varieties) regularly. Scouting should involve examining plant roots and be focussed on field entrances, low spots and areas within the field that are showing symptoms of premature ripening or wilting. Clubroot will cause swollen and deformed root tissue (galls) giving the roots a clubbed appearance. At the end of the growing season the infected root tissue will begin to decompose giving the roots a rotten appearance. Soil testing at a laboratory (eg. Discovery Seed Labs) can be used to detect the presence of the clubroot pathogen at levels lower than those required to cause visible symptoms in the field. This is a good method for early clubroot detection and can enable proactive clubroot management before significant yield losses occur.