By Rory Cranston
Regional Crops Specialist, Outlook
Clubroot was first identified in canola in Western Canada in 2003 in a commercial field near Edmonton. Since then it has been detected in over 1,000 fields in Alberta, four fields in Saskatchewan and it has most recently been confirmed in two fields in Manitoba. With this recent detection, this potentially devastating disease is back in the spotlight
Clubroot is a soil-borne disease caused by the microbe, Plasmodiophora brassicae. It affects the roots of all cruciferous crops such as canola, mustard, camelina, cabbages, cauliflower as well as some cruciferous weeds like stinkweed, shepherds purse and wild mustard. Clubroot spreads by soil transportation. An infected root will break down in the soil and release the resting spores of the disease into the soil. This now infected soil can then be transported by agricultural machinery, livestock, erosion, vehicle tires and foot traffic to another field beginning an infection there.
The disease invades the roots of a host crop and alters the hormone balance in the crop. This leads to increased cell division and growth which cause the roots to develop large galls. The deformed roots have reduced surface area and this will impede with the plant’s ability to absorb water and nutrients from the soil. This can cause severe stunting, wilting, yellowing, and premature ripening. Infection at the seedling stage in a canola crop can result in an almost total yield loss.
The best way to deal with clubroot is prevention. Clubroot can survive a long time as resting spores in soils. Once it’s in a field, it’s there for good. There are many steps that can be taken to prevent or slow clubroot spread.
Clubroot is primarily spread by soil stuck on machinery; therefore cleaning of equipment and minimization of in and out traffic is very important to prevention. Using a scraper, wire brush or compressed air to remove loose soil from equipment can remove 90 per cent of possibly infected soil from equipment. If clubroot has not been identified near your fields often, this is all the cleaning that will be needed. Using a pressure washer can remove stuck on dirt. If clubroot is a concern in your area, disinfecting equipment may be required before leaving fields. To disinfect your equipment, use a one per cent bleach solution and a three gallon backpack sprayer. Spray all openers, tires and wheels. To be effective, all areas should remain wet for 15 to 20 minutes.
Follow proper crop rotation. Do not plant a susceptible crop more than once in every four years. A good crop rotation will not prevent clubroot infection but it will slow development and effects of the disease.
Control volunteer canola and susceptible weeds. These can act as alternate hosts for clubroot and increase the disease inoculum in years that there is not a host crop. Poor weed control will reduce the effectiveness of rotations as a management tool.
There are some clubroot resistant varieties available to canola producers. These varieties can reduce the plant infection and disease severity on a clubroot infested field. Extend rotation and alternate between different clubroot resistant varieties. This will prevent the risk of clubroot adapting to a resistance gene.
For more information contact your local regional office or the Agriculture Knowledge Centre at 1-866-457-2377.