By Barb Ziesman AAg, Provincial Specialist, Plant Disease
Clubroot is an important disease of canola in Western Canada. The history of clubroot in canola starts in 2003 when it was confirmed in 12 canola fields located near central Alberta. Since then, the disease has been confirmed to occur in 3,044 fields in Alberta, 33 fields in Manitoba, and, so far, 43 fields in Saskatchewan.
Clubroot is a disease that can be best managed when detected early. Provincial monitoring programs provide useful information that can help producers determine the clubroot risk in their area and help guide the use of proactive clubroot management strategies. Different provinces monitor for clubroot in slightly different ways, which means that the resulting clubroot distribution maps will also be different. In all cases, these maps provide a good indication of the known clubroot distribution and can be used as an indication of regional risk. When looking at these distribution maps, it is important to understand how they are developed and what they really mean. The surveillance approach and information included in each of the provincial clubroot distribution maps are outlined below.
In Alberta, canola fields are surveyed annually for the presence of visible clubroot symptoms. This information is used to monitor the spread of clubroot in the province and used to guide regulation at the municipal level.
Alberta’s clubroot distribution map illustrates the distribution of the disease across the province and the cumulative numbers of infestations over time. The map uses four colour categories that indicate the number of canola fields that have been confirmed to have clubroot symptoms in each municipality (County). The four categories are as follows:
- Green: no clubroot has been found (includes counties where clubroot surveillance has occurred).
- Yellow: One to nine fields with clubroot symptoms.
- Blue: 10 to 49 fields with clubroot symptoms.
- Red: More than 49 fields with clubroot symptoms.
In Manitoba, the provincial government monitors the distribution of both the clubroot disease and the clubroot pathogen. The distribution of clubroot is determined by surveying fields for visible clubroot symptoms using a similar method as in Alberta. In addition to assessing plants for visible symptoms, the level of the clubroot pathogen is determined through DNA-based soil testing. The Manitoba clubroot distribution map is cumulative and includes information from ongoing provincial surveys and reports of clubroot infestations by producers and Agrologists to Manitoba Agriculture since 2009.
The Manitoba clubroot distribution map differs from the Alberta map in that it provides information on the distribution of the clubroot pathogen but does not contain information on the number of fields that have been confirmed to have symptoms of the disease. The information is illustrated in the map and categorized into four colours as follows:
- Green: Zero to 1,000 spores per gram of soil. In Rural Municipalities (RMs) that are coloured green, the clubroot pathogen was not detected or was detected at very low levels.
- Yellow: 1,001 to 10,000 spores per gram of soil.
- Orange: 10,001 to 80,000 spores per gram of soil.
- Red: More than 80,000 spores per gram of soil AND symptoms observed. In these RMs, visible symptoms of clubroot have been confirmed in at least one field.
Generally speaking, the higher the level of the pathogen in the soil, the greater the risk for symptom development and corresponding yield loss. When the clubroot pathogen is detected early, proactive management strategies can be implemented to keep pathogen levels low and minimize the impact of the disease.
When an RM is coloured according to one of the four categories listed above, it means that at least one field within the RM has pathogen levels or visible symptoms that fit with the corresponding category. The colour is associated with the highest level of clubroot risk in that RM. Though this map does not provide information on the abundance of clubroot-infested fields in each RM, it does give a good indication of the risk of clubroot development in each RM across the province.
In Saskatchewan, clubroot surveillance is conducted in a similar way to Manitoba. In each surveyed field, the presence of visible clubroot symptoms is assessed by examining the roots of canola plants. From each field, soil samples are also collected for DNA-based testing to detect the clubroot pathogen at low levels.
In Saskatchewan, when clubroot has been confirmed, that means visible symptoms of the clubroot have been detected in the field. When the clubroot pathogen alone has been detected in a field, that means the risk of disease development exists and those fields should be managed in a proactive manner to keep pathogen levels low to minimize symptom development and resulting yield loss.
The number of fields confirmed to have clubroot, as well as the distribution of the clubroot pathogen, is illustrated in the Saskatchewan Clubroot Distribution map. This map includes all findings of clubroot and the clubroot pathogen from 2008 to 2018, including provincial survey results and clubroot findings reported to the Ministry by producers and agrologists. This information is classified into four categories:
- Blue: The clubroot pathogen was detected but no visible clubroot symptoms were present.
- Yellow: One to nine fields with visible symptoms of clubroot.
- Orange: More than 10 fields with visible symptoms of clubroot.
- Grey: Extensive clubroot surveillance area. RMs in this category were included in the 2018 clubroot grid survey but neither clubroot nor the clubroot pathogen were detected in surveyed fields.
This map illustrates the areas that have been confirmed to have clubroot or the presence of the clubroot pathogen. When looking at this map, it is important to use it as an indicator of regional risk. Just because clubroot has not been detected in an RM does not mean it is not present. As a result, producers are encouraged to monitor their own fields and continue to assess their clubroot risk. If a farm is located in close proximity to an area where clubroot is known to occur, the risk of clubroot development is considered to be high and clubroot prevention and management strategies should be implemented proactively.
For more information on the Saskatchewan clubroot survey and distribution map, as well as what they mean for your farm, see the article “Understanding the Saskatchewan Clubroot Distribution map.”