How to combat clubroot in your crops (June 2013)

Clubroot can be a tricky disease to identify. The above-ground symptoms can mimic drought, nutrient deficiencies or other diseases, so suspect plants need to be carefully dug from the soil to check for typical clubroot galls on the roots. Other causes of root galling in canola can include hybridization nodules and injury from phenoxy herbicides, so suspect plants should be sent to a lab for confirmation. Most of the varieties of canola, mustard and cole crop vegetables currently being grown in Alberta are highly susceptible to clubroot.

Root galls are usually visible on plants that are 6-8 weeks of age, when canola and mustard are usually at the bolting to early flowering stage, so this is a good time for producers and agronomists to start scouting for the disease. Crops can be examined throughout the remainder of the season, but tall stands can be very difficult to walk through. After crops are swathed and combined, clubroot galls can be looked for in stubble fields, which are much easier to walk through; however, plants should be dug up rather than pulled because mature galls may break off and remain behind in the soil.

So what should producers do if they suspect clubroot in their fields this season?

• First confirm the disease diagnosis. To avoid misdiagnosing a suspect plant by relying on visual symptoms alone, symptomatic plants should be submitted to a provincial plant health lab or to a private lab that offers a clubroot testing service. Consult the Canola Council of Canada’s website (www.clubroot.ca) for a list of plant diagnostic labs in western Canada.
• Confirmed cases of clubroot should be reported to a local municipal authority, such as an agricultural fieldman, or to the provincial agriculture department using the Alberta Pest Surveillance System toll-free number (310-2777). In Alberta, clubroot is a declared pest under the Agricultural Pests Act and the owner or occupant of land where this disease has been found has the responsibility to take measures to prevent its establishment and spread. Recommendations for the prevention and control of clubroot can be found in the Alberta Clubroot Management Plan (http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex11519).
• Practice good sanitation to restrict the movement of potentially contaminated soil and plant material between fields. This approach will help reduce the spread of other diseases, weeds and insects too. Clubroot resting spores are most likely to spread via contaminated soil and infected canola plant parts adhering to farm equipment, machinery and vehicles that have worked in infested fields. Consult the “Managing Clubroot: Equipment Sanitation Guide” on the Canola Council’s website (www.clubroot.ca) for practical tips on sanitizing various kinds of equipment. The website also sets out recommended protocols for entering clubroot-infested fields or those of unknown status.
• To recap, careful scouting of canola crops and the use of best management practices (BMPs) are the key to preventing or controlling clubroot. Growers should consider the following key management strategies:

1. Assess your risk and prevent clubroot from arriving on farm (equipment sanitization).
2. Identify clubroot early (crop scouting).
3. Develop a comprehensive clubroot management plan, including the use of clubroot-resistant varieties, longer and logical crop rotations, and the sanitization of vehicles, machinery and equipment used in infested fields. These BMPs serve both to prevent the introduction of clubroot and to deal with the disease if and when it arrives on a farm.
4. Work with your local municipality. Ag Service Board Fieldmen in Alberta are designated inspectors under the Agricultural Pests Act and can provide growers with advice on recognizing and managing clubroot in susceptible crops. They may also know where clubroot has been found in their respective jurisdictions and will have the responsibility to enforce municipal clubroot regulations.