By: Barb Ziesman A.Ag, Provincial Specialist, Plant Disease
Clubroot of canola is an important and relatively new disease in Saskatchewan. Monitoring for clubroot has been ongoing in Saskatchewan for many years and, since 2008, has involved examining plant roots for symptoms of clubroot and collecting soil from the field entrance to detect the clubroot pathogen at low levels. The clubroot pathogen was first detected in a single field without the presence of visible symptoms in 2008. In 2011, visible clubroot symptoms were first identified at two private research sites in the province.
Since then, visible symptoms of clubroot have been confirmed in 43 commercial Saskatchewan canola fields. These findings include:
- Clubroot fields identified through the Ministry’s 2017 and extensive 2018 clubroot survey; and
- Clubroot-infested fields reported to the Ministry by producers and agrologists outside of the survey in 2017 and 2018.
The increased number of clubroot-infested fields in Saskatchewan indicates that the risk and distribution of clubroot in the province is greater than previously thought. The good news is that clubroot has still been confirmed in only a small number of canola fields in the province. This indicates that we still have an opportunity to implement proactive prevention and management strategies to minimize the impact of clubroot in canola.
The Saskatchewan clubroot distribution map
The Saskatchewan clubroot distribution map illustrates the distribution of clubroot and the clubroot pathogen in the province and can be used as an estimation of regional clubroot risk. The map is cumulative and includes all findings of clubroot and detections of the clubroot pathogen from 2008 to 2018. All detections of clubroot and the clubroot pathogen are included in this map, as the clubroot pathogen is long lived and cannot be eradicated. As a result, areas where clubroot and/or the clubroot pathogen were first identified in Saskatchewan are considered to still have an increased risk and are therefore included in this map illustrating cumulative findings. In addition to illustrating the distribution of fields with visible clubroot symptoms, the map provides information on the number of fields in each rural municipality (RM) confirmed to have clubroot visible symptoms.
The information in this map is organized into four main categories that are illustrated by four different colours.
- Blue: In these RMs, the clubroot pathogen was detected at low levels in soil samples from at least one field in the RM. When only the clubroot pathogen is detected it means that the pathogen is present at levels lower than those required to cause disease symptoms under field conditions. When this occurs, producers are encouraged to implement proactive management strategies to keep the pathogen levels low to prevent symptom development and potential yield losses.
- Yellow: Visible symptoms of clubroot were identified in one to nine fields in the RM.
- Orange: Visible symptoms of clubroot were identified in 10 or more fields in the RM.
- Grey: The grey area on the map outlines the area of the province that was included in the 2018 extensive clubroot survey. The grey colour indicates that the RM was surveyed but neither clubroot visible symptoms nor the clubroot pathogen were detected.
Using the map to guide clubroot management
When using the clubroot distribution map to assess your clubroot risk, it is important to remember that the map should only be used as a guide to estimate regional risk. Producers are encouraged to monitor their own fields and consider the following questions when looking at the clubroot distribution map:
- Have visible symptoms of clubroot been found in your RM?
- Has the clubroot pathogen been detected in your RM?
- Have either clubroot or the clubroot pathogen been detected in your crop district or in close proximity to your RM?
If you answered yes to any of these questions, you should consider your farm to have an increased risk of clubroot. In response to this increased risk, you are encouraged to begin implementing proactive clubroot management and prevention strategies on your farm. At a minimum, a proactive clubroot management plan should include extended (minimum of a three-year) crop rotation, the use of only clubroot-resistant varieties, and strategies focused on preventing soil movement. These strategies will prevent clubroot spread and will also keep pathogen levels low to minimize the impact of clubroot on canola yields and protect the effectiveness of clubroot-resistant canola varieties. It is important not to use clubroot-resistant varieties in short rotations, as this will place significant selection pressure on the pathogen to overcome the resistance in the clubroot-resistant variety. Extended crop rotations will reduce this selection pressure by allowing time for the pathogen population decrease between susceptible host crops.
In Saskatchewan, we are encouraging all producers in the northern agricultural region to start thinking about clubroot. The earlier we detect and start managing the disease, the easier it will be to manage and minimize yield losses due to clubroot. If you farm in the northern agricultural region, please consider using a clubroot-resistant canola variety and extend your crop rotation to allow a two-year break (three-year rotation) between canola crops.
In addition to the distribution of the clubroot pathogen and clubroot-infested fields, we have learned a lot about clubroot through the 2018 clubroot survey and additional reports. For more information on what the survey results mean, the pH and the spore levels of the clubroot-infested fields, see “Learnings from the 2018 clubroot survey.”