Clubroot is a serious soil-borne disease of canola and crops in the cabbage family. This disease occurs worldwide and was first identified in Europe in the 13th century. It was detected in Alberta in 2003 around the Edmonton area. Since then, Clubroot has been found in 28 municipalities in Alberta, including Flagstaff County.
Clubroot overwinters in the soil as resting spores. In spring, the roots of host plants stimulate the resting spores of clubroot to germinate and produce zoospores that swim in soil water until they contact the host roots. Infection occurs through root hairs or wounds. Once inside the plant, the pathogen produces secondary zoospores that re-infect the roots of the initial host or nearby plants. The pathogen invades the interior of the host root, altering the normal hormonal balance and leading to the characteristic distorted shapes that give this disease the name "club" root. The infected canola roots will degenerate and will release the resting spores into the soil.
These resting spores have a half life of 3.6 years, but have the ability to survive for up to 20 years. The longevity of the resting spores is a key factor contributing to the seriousness of this disease.
Clubroot symptoms will vary depending on the growth stage that the canola crop is at when infection occurs. Early infection at the seedling stage can result in wilting, stunting, and yellowing of canola plants in the late rosette to early podding stage.
Infection that occurs at the later crop stages may not show plant wilting, stunting, or yellowing. However, infected plants will ripen prematurely and seeds will shrivel. The patches of prematurely ripening canola due to clubroot infection could be confused with other diseases such as sclerotinia, blackleg and fusarium wilt.
PREVENTION AND MANAGEMENT
Resting clubroot spores are most likely to spread via contaminated soil carried from field to field by equipment. Tillage equipment represents the greatest risk of spreading the disease as soil is frequently carried on shovels, discs, and other openers. Clubroot surveys in Alberta have found that almost all new infestations begin near the field access, which indicates that contaminated equipment is the predominant spread mechanism.
Growers, custom operators, and all land users (including oil & gas, recreationalists, etc.) need to be vigilant and diligent in removing potentially contaminated soil from equipment prior to leaving fields, to prevent the introduction of clubroot to clean fields.
BEST MANAGEMENT PRACTICES
1) Use long rotation breaks between canola crops. Although crop rotation will not prevent introduction of clubroot to clean fields, it will restrict disease development within the field and probably avert a severe infestation of clubroot and other diseases such as blackleg. Canola growers in high-risk situations (confirmed clubroot in the area) should follow traditional canola rotation recommendations (one canola crop every four years).
2) Volunteer canola and cruciferous weeds must be controlled on infested fields to prevent more than three weeks of growth to avoid the production of new resting spores.
3) Practice good sanitation to restrict movement of potentially contaminated soil (this will also help reduce the spread of other diseases, insects and weed seeds). The resting spores are most likely to spread via contaminated soil. Moderate to high infestations will leave high spore concentrations in soil on field machinery – thus sanitation is very important in these situations. All producers should follow the practice of cleaning soil and crop debris from field equipment before transport from all fields. Cleaning equipment involves knocking or scraping off soil lumps and sweeping off loose soil.
** For risk adverse producers or with heavy infestations, additional cleaning steps will slightly decrease the risk of spread, but involves considerably more work and expense:
- After removal of soil lumps, wash equipment with a power washer, preferably with hot water or steam.
- Finish by misting equipment with weak disinfectant (1-2% active ingredient bleach solution). Use of a disinfectant without first removing soil is not recommended as soil inactivates most disinfectants.
- Seed an area to grass near the field exit to clean off equipment more effectively.
4) Use direct seeding and other soil conservation practices to reduce erosion. Resting spores can also readily move in soil transported by wind or water erosion. Reducing the amount of tillage on any given field will reduce the spread of the organism within the field and to other fields.
5) Minimize traffic to and from fields.
6) In situations where fields are lightly infested only near the current access, create a new exit at another distant edge of the field if possible.
7) Scout canola fields regularly and carefully. Identify causes of wilting, stunting, yellowing, and premature ripening - do not assume anything.
8) Avoid use of straw, hay, green feed, silage, and manure from infested or suspicious areas. Clubroot spores may survive through the digestive tracts of livestock.
9) Avoid common untreated seed (including canola, cereals, and pulses). Earth-tag on seed from infested fields could introduce resting spores to clean fields. The effect of current seed treatment fungicides on resting spore viability on seed needs research.
Clubroot was declared a pest by the Province of Alberta April, 2007. As a result, Flagstaff County holds the responsibility and must take active measures to prevent the establishment of, or to control or destroy pests in the municipality by following these procedures:
To view the Clubroot Procedure AG 002-2, click here.
Flagstaff County A.S.B. encourages all landowners to implement a management plan that will prevent the spread of Clubroot.
1) Remove soil from equipment prior to moving out of the field.
- Knock off large clumps of soil
- Sweep off loose soil
2) Use 1 in 4 rotation.
3) Use direct seeding or minimum tillage.
4) Scout canola fields regularly.
5) Avoid use of straw, hay, green feed, silage, and manure from infested fields.
Prevention is everyone's responsibility.
We all need to take action to prevent the spread of clubroot.
Producers, Agrologists, Ag Retail Suppliers, Custom Equipment Operators, Oil & Gas Companies, Researchers, and Provincial and Municipal Governments.