| ||What is Clubroot?
Clubroot is a serious soil-borne disease of crucifer crops in many parts of the world. The crucifer family includes vegetable crops like cabbage, broccoli, and cauliflower as well as field crops such as canola and mustard. In British Columbia, Quebec and Ontario, clubroot is a major concern for commercial vegetable producers. Clubroot is especially problematic because the pathogen persists in soil for many years, and cannot be controlled with crop protection products currently registered in Canada. Clubroot has the potential to be a significant threat to canola production in parts of Alberta.
How much yield loss will clubroot cause?
Research with canola indicates infestations approaching 100% led to 50% yield losses, while 10 to 20% infestations led to 5-10% yield losses. As a rough estimate, the % yield loss from clubroot is about half the % of infected plants.
Does Alberta currently have a clubroot problem?
In 2003, the first case of clubroot in western Canadian canola was found in a field near St Albert. Surveys of neighboring fields suggested that the problem was not isolated to one field or one producer. Surveys conducted since 2003 have confirmed clubroot throughout much of central Alberta and two counties in southern Alberta. Survey results indicate that clubroot poses a serious threat to canola production in Alberta.
Where is clubroot likely to be a problem?
Computer simulations based on disease and environmental factors suggested that the Edmonton region was the only part of Alberta likely to have significant clubroot problems. Field surveys since then, however, have found clubroot fanning out in all directions from the Edmonton region, and also two counties in southern Alberta.
See this map of confirmed clubroot infested counties, and their severities, in Alberta.
What do symptoms look like in canola?
The causal agent, Plasmodiophora brassicae Woronin, infects roots causing irregular club-like galls that restrict the flow of water and nutrients to leaves, stems and pods. Visible symptoms on the plant include wilting, stunted growth, yellowing, premature ripening, and shriveled seed. Plants infected early in the growing season may appear heat or drought stressed. Crops that have finished flowering may have symptoms that from a distance resemble sclerotinia stem rot or possibly fusarium wilt. In most cases however, clubroot can be diagnosed with close examination of the root system.
Clubroot Disease of Canola and Mustard has good pictures of infected roots.
What is being done about the problem?
The threat of clubroot to Alberta canola growers is being addressed through regulations and research. Clubroot was added as a declared pest to the Agricultural Pests Act in April 2007. Alberta Agriculture and Forestry is responsible for this Act, however, enforcement is the responsibility of the local municipality. Agricultural Fieldmen (or appointed pest inspectors) have the power to enter land at a reasonable hour, without permission to inspect for pests and collect samples. The owner or occupant of land has the responsibility of taking measures to prevent the establishment of any pest on land, property and livestock and to control or destroy all pests in the land or property.
Control measures for clubroot are specified in the Alberta Clubroot Management Plan. It is important to understand that these control measures represent an acceptable minimum standard that is to be applied in all municipalities across the province. Municipalities, however, can adopt more stringent standards within their own jurisdictions.
Are there canola varieties that are resistant to Clubroot?
Clubroot resistant canola varieties are available. Although clubroot resistance is a great tool available to canola growers, producers should maintain realistic long-term expectations for how this tool fits into their overall pest management program. Disease resistance tends to break down with time as pathogens adapt to modified hosts, and this occurs with clubroot resistance as well. Clubroot resistant canola planted on land that is heavily infested with clubroot loses its resistance very quickly. A one in four year rotation of clubroot resistant canola in conjunction with good equipment sanitation practices should keep the pathogen at manageable levels. This will ensure that genetic resistance is maintained as long as possible and that canola will remain a viable part of the production system. It must be understood that every time a resistant variety is grown is one less time that the same genetics can be used successfully in the future.
What strategies can be used to manage clubroot?
Since there is no real cure for clubroot, prevention is the best management strategy - an ounce of prevention is worth a pound of cure.
- A long rotation between canola crops (1 in 4 years) is the single most important preventative strategy. Fields that have clubroot problems have a history of short (often 1 in 2 years) canola rotations. Lengthening out the canola rotation may reduce profitability in the short-term but the long term gains will be substantial if the longer rotation prevents clubroot.
- Equipment sanitation. Clean dirt from equipment, including tires, when moving between fields.
- Avoid hay or straw purchases from regions where clubroot is known to occur or if infestation is suspected. Straw and hay could be carrying soil and the pathogen. Once land is infected with clubroot, management strategies are more difficult and/or expensive.
- Canola should not be seeded on infected land for 5-7 years. Research indicates that the pathogen can survive in soil for up to 17 years so a 5-7 year break from canola will not eliminate the problem, but keep the problem manageable.
- The extended rotation away from canola must also include diligent control of plant species susceptible to clubroot including volunteer canola, weeds in the mustard family, dock, hoary cress, orchardgrass, red clover, red-top, and perennial ryegrass.
- Minimize soil erosion with zero or minimal tillage. Since clubroot is a soil borne disease, the pathogen will move with wind or water-eroded soil.
Who to contact for additional information
Murray Hartman and the Alberta Ag-Info Centre (toll free 310- 3276) can provide additional information on Clubroot of canola.
Links to Additional Information:
Alberta Clubroot Management Plan
Best Management Practices for Disinfecting Farm Machinery
Canola Council of Canada maintains clubroot information on Clubroot.ca
Prepared by Ag-Info Centre, Alberta Agriculture & Forestry