How to collect soil samples for clubroot

Timing. Soil sample the fall after canola harvest or the spring immediately following. This gives galls time to break down and release spores. If sampling this fall, target fields that are going into canola next year…not fields that were in canola this year.

Sanitize. Use a fresh two per cent bleach solution or “Spray Nine” to disinfect tools.

Sampling tool. Use a tool that can measure the top two to four inches of soil (Ex. dutch auger).

Sample in high-risk area. Sample field entrances, high-traffic area, low spots, waterways and low pH areas. Submit separate samples for each location. Find out more about provincial clubroot soil test programs.

How to sample. Collect two to three cups of soil from each high-risk area. Clubroot spore-load tests should be plotted points, not composite samples from the field. Place in a paper bag labeling with date and location sampled. Sanitize tools between sampling sites to avoid false positives and to avoid spreading spores to other locations.

Test options. PCR will detect the presence or absence of clubroot spores. qPCR will give an approximation of spores per gram of soil. Labs that offer clubroot tests.

Important tip: Don’t pull from the same soil collected for nutrient analysis. Soil nutrient tests are generally gathered from average-producing areas within each field and are often composites of cores from various locations and deeper depths than you would want this.

Disclaimer: Due to the patchy distribution of clubroot spores, results are not indicative of the spore presence and/or concentration throughout the field. False negatives in the field are possible by missing an infested patch.

Dig deeper

• Labs that test soil for clubroot DNA
• Clubroot testing programs – SaskCanola, Manitoba Canola Growers, Alberta Canola
• Clubroot risk management recipe in the Management section here.
• The provincial agriculture departments for Alberta, Manitoba and Saskatchewan produced two helpful factsheets: (1) Clubroot soil sampling on the Prairies. (2) Interpreting a clubroot soil test result.
• Video on clubroot soil sampling
• Discovery Seed Labs video
• Saskatchewan clubroot soil test brochure