Clubroot is a disease that affects crucifers worldwide. In the United States, there have been a number of reports of clubroot on Brassica crops from several states, varying in degree of severity and incidence.
Figure 1. Alberta Clubroot Map: Cumulative clubroot infestations as of December 2013. Map courtesy of S.E. Strelkov, University of Alberta and M. Hartman, Alberta Agriculture and Rural Development.
In Canada, clubroot is primarily established in the vegetable growing regions of British Columbia, Quebec, Ontario, and the Atlantic provinces. It has also been detected in vegetable crops in both Alberta and Manitoba. Identification of clubroot in commercial canola fields in western Canada is a relatively recent occurrence.
In 2003, clubroot was identified in commercial canola near Edmonton, AB. This was the first report of clubroot in a commercial canola field in Canada. Since 2003, clubroot has been found in an increasing number of canola crops in this region. According to information provided by the Alberta Clubroot Management Committee, clubroot has been detected in over 1,000 fields, with incidence levels ranging from below 30% (low) to above 70% (high). The disease distribution in infested fields has generally been patchy but in the 10 to 15% of canola crops with high levels of clubroot infestation, the disease has occurred fairly evenly throughout the field. Alberta named the clubroot pathogen as a declared pest in the Alberta Pests Act in 2007 and released the Alberta Clubroot Management Plan in 2008 (revised in 2010 and 2014).
According to information provided by Manitoba Agriculture, Food and Rural Initiatives, the presence of the pathogen (Plasmodiophora brassicae) responsible for clubroot has been reported in Manitoba on symptomatic cruciferous vegetables. Reports have been very sparse, with the first note dating back to an unconfirmed report on rutabaga in 1925. In the 1980’s, clubroot was found on market garden cruciferous vegetables. More recently, clubroot was found in 2005 on canola. This occurrence was of very low incidence, and the symptoms were of very low severity. In 2011 the clubroot pathogen was again detected in Manitoba from soil samples submitted to the annual canola disease survey in two fields, but concentrations were too low to produce symptoms on brassica test plants in a bioassay. In 2012, the disease survey again found six more positive fields from soil tests, but this year two fields also had clubroot resting spore concentrations high enough to produce galls in the bioassay. Manitoba has not declared clubroot a pest under the Manitoba Pest Act.
According the Saskatchewan Ministry of Agriculture, in 2008, the clubroot pathogen's DNA was first detected in a soil sample collected from one of 30 randomly-selected fields in the clubroot survey. While the pathogen appeared to be present, the clubroot disease itself was absent, since no infected canola plants were identified at that time. But a subsequent bioassay did confirm that the resting spore concentration was sufficient enough to produce clubroot symptoms in plants. In subsequent clubroot surveys in 2009 and 2010, no further evidence of this disease was found.
In 2011, clubroot was identified in canola plants growing in two fields in the rural municipalities of St. Louis and Aberdeen in north central Saskatchewan. Soil tests around these sited confirmed the presence of the clubroot pathogen in the soil. These fields were associated with canola research trials. One more clubroot positive field was identified from the 2012 canola disease survey in the rural municipality of Biggar. This field was randmnoly selected and a soil sample tested positive for the presence of the clubroot pathogen. A subsequent bioassay further confirmed that resting spore concentrations were high enough to produce symptoms in brassica plants.
Clubroot was declared a pest under The Pest Control Act in Saskatchewan in June 2009.