Clubroot Distribution in Manitoba 

The map shows positive clubroot findings by Rural Municipality (RM), discovered through visual field symptoms and/or presence of clubroot spores in soil through laboratory testing for DNA.  Testing completed from 2009 to September 2019 is still considered limited.  Positive findings have been at low concentrations, usually below 5,000 spores/gram soil and throughout the province. As more fields are sampled, the map will be updated.
RMs have been highlighted to show the highest concentration of clubroot spores found.  This does not mean all fields in the specific RM have these concentrations. As clubroot spore concentrations can be highly variable within a field, the RM classification indicates only the maximum spore concentration found in any field in the RM.  Further explanation on the concentration categories are as follows: 
RED = Symptoms Observed - Clubroot symptoms have been observed in fields in this RM.  Management to prevent continued build-up or spread of this pest should be implemented on farms.
ORANGE = 10,001 to 80,000 spores/gram soil -  Clubroot spores have been found in fields in this RM at concentrations approaching levels known to cause field symptoms. Without management, concentrations may increase to where symptoms are visible in the field within one crop cycle.
YELLOW = 1,001 to 10,000 spores/gram soil - Clubroot spores have been found in this RM at low to intermediate levels. With proper management, spore concentrations can decline over time.
GREEN = 0 to 1,000 spores/gram soil - Clubroot spores have not been detected, or detected at very low levels. At this concentration, clubroot is not a major concern, but fields should be monitored over time. Re-testing is recommended within the next five years to determine if concentrations are increasing.
It is generally reported that 100,000 spores/gram of soil are required to see symptoms under field conditions, but under favourable conditions, lower concentration can cause field symptoms of clubroot.
Annual surveys for clubroot started in 2009, testing 80 - 100 fields annually. Since 2015, soil sampling and laboratory testing increased, as part of expanded efforts to better understand clubroot distribution in Manitoba. From the cumulative survey efforts, as of September 13, 2019 - 296 individual fields were found positive for clubroot through soil analysis and 35 fields were confirmed to have symptoms. 

Alternative Clubroot Distribution Map

This alternative depiction of clubroot distribution situation in Manitoba is based on the same data as the map above. How do the two maps differ? Primarily in the number of categories. Another difference is that the alternative map identifies how many fields within a Rural Municipality have had documented symptomatic cases (galls on canola roots), rather than the number of clubroot spores detected in the soil. Thus far, none of the RM's in Manitoba has had 10 or more fields identified. 
This map is intended for those who farm and/or advise growers on either side of the Manitoba-Saskatchewan border. The Ministry of Agriculture in Saskatchewan posted a new map early in 2020. Eventually, it will be possible for the release of a map that covers the whole prairie region, including Manitoba, Saskatchewan, Alberta, and the BC Peace River region.
For now both maps are posted since canola growers in Manitoba have been accustomed to the green-through-red scale. Vigilance and awareness of the clubroot risk in all geographic regions is vital.

2021 Alternative Clubroot Distribution map

Biosecurity Implications

As less than 10% of farms in Manitoba have been sampled, it is recommended that all fields be tested to determine if clubroot spores are present, regardless of RM classification.
Clubroot is a soil-borne pest that can move from field to field on both agricultural and non-agricultural equipment. Specific biosecurity activities to minimize the spread of clubroot will differ by the known levels of clubroot DNA found within the field.  Manitoba Agriculture has a series of suggestions for all industries operating on agricultural land to minimize the potential of spread on the Crop Biosecurity page.  Soil testing for clubroot spores can be conducted at a number of labs across western Canada.
Data from Manitoba Agricultural Services Corporation (MASC) annual harvested production numbers shows the distribution of canola in Manitoba.  The map indicates the percentage of insured arable acres in a Rural Municipality that were canola in a given year. 
For example, if an RM is producing canola on 30 to 39.9% of the acres in that RM, the average crop rotation length is assumed to be about 3 years.  This means on average, canola is grown on the same ground 1 in every 3 years, with a 2-year gap between successive canola crops.  This is the recommended minimum crop rotation for growing canola on the same field. 
Over time, certain municipalities are shown to be producing canola on a large percentage of the cropped acres in that RM.  Since canola is a preferred host for Plasmodiophora brassicae, the clubroot pathogen, the widespread presence and frequency of canola in rotation of a susceptible host crop poses a higher risk for clubroot spore increase and infection in those areas.  The presence of a clubroot-susceptible host is not the only factor determining risk for development a clubroot infection.  Soil pH, soil texture, as well as landscape features and farming practices all play a role in movement of clubroot spores across the prairies.
The canola distribution map does not correlate exactly to where clubroot has been discovered in Manitoba.  It is a possibility that clubroot may be more difficult to detect or have gone underreported in parts of northwestern Manitoba, due to the greater number of canola acres or lower clubroot spore loads in the soil.
For more information on clubroot, please contact the Manitoba Agriculture Crops Branch at (204)745-5663 and visit Clubroot of Canola:The Facts or