The following clubroot prevention strategies have been adapted from Alberta Agriculture and Rural Development’s Agri-Facts: Clubroot Disease of Canola and Mustard, March 2011.
1. Use long rotations — do not grow canola more frequently than once every four years in the same field. Although this practice will not prevent the introduction of clubroot to clean fields, it will restrict clubroot and other canola disease development within the field and probably avert a severe infestation.
2. Planting clubroot-resistant varieties on fields with no history of the disease can be useful when clubroot is present nearby. This strategy relies on using the genetic resistance to greatly reduce disease development or establishment if clubroot is inadvertently introduced to the field.
3. Practice good sanitation to restrict the movement of possibly contaminated material (this approach will help reduce the spread of other diseases, weeds and insects too). The resting spores are most likely to spread via contaminated soil and infected canola plant parts. Farmers should follow the practice of cleaning soil and crop debris from field equipment before entering or leaving all fields. The equipment cleaning procedure involves knocking or scraping off soil lumps and sweeping off loose soil.
For risk-averse producers, the following additional cleaning steps may provide some extra benefit, but involve considerably more work and expense:
- after removing soil lumps, wash off equipment with a power washer, preferably with hot water or steam; and,
- finish by misting equipment with weak disinfectant (one to two per cent household bleach solution)
4. Use direct seeding and other soil conservation practices to reduce erosion. Resting spores move readily in soil transported by wind or water erosion and overland flow.
5. Scout canola fields regularly and carefully. Identify causes of wilting, stunting, yellowing and premature ripening — do not assume anything! (The Canola Council of Canada has posted a video with more information about identifying clubroot online at www.clubroot.ca).
6. Avoid the use of straw bales and manure from infested or suspicious areas. Clubroot spores are reported to survive through the digestive tracts of livestock.
7. Avoid common untreated seed (including canola, cereals and pulses). Earth-tag on seed from infested fields could introduce resting spores to clean fields. Certain seed treatment fungicides may control spores on contaminated seed, but this observation needs further research to confirm.
If you already have clubroot
Once you have the clubroot in your fields, control is considerably more difficult than prevention, but the following control strategies are encouraged.
Commercial varieties with clubroot resistance are currently available from most seed companies, and are reported to provide high levels of clubroot control in clubroot-infested fields. However, because the source of resistance in most varieties is currently provided by a single gene, that clubroot resistance is not expected to be durable (meaning it will break down over time). Therefore, farmers should not rely solely on clubroot resistance to manage this disease once it is established in a field.
Extended rotations can extend the usefulness of genetic resistance. In slightly infested fields, susceptible crops — including canola, mustard, kale, and cole crops — should not be grown for at least four years and at least seven years in severely infested fields. Because the clubroot spores are suspected to survive up to 20 years, these long rotations are necessary to reduce the levels of viable spores.
Within other crops in rotation, ensure that susceptible weeds such as stinkweed, wild mustard, shepherd’s purse and volunteer canola are controlled. Otherwise, these weeds will act as a bridge to continue to maintain and increase the levels of spores in the soil.
Keep contaminated soil and infected crop debris from being transported from infested fields by sanitizing equipment and personnel and practicing soil conservation measures. When infested fields are wet, try to avoid field work wherever practical because more mud will stick to equipment.
Reduced tillage or direct seeding will also help in fighting a clubroot infestation by reducing movement of contaminated soil within a field and between fields.
Other potential control strategies such as fungicides and liming to raise soil pH have been tried but are currently uneconomic or too inconsistent to be used in canola.
Although clubroot is a serious disease in canola, there are a number of prevention and control strategies that are effective in reducing its spread and severity. A vigorous scouting strategy is invaluable in finding the disease in your fields.
Be “outstanding in your fields” to make sure clubroot and other factors don’t take a big chunk out of your canola profits. †