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Identify Clubroot

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Pre-Swath and Post-Swath Disease Scouting Video

Learn more about scouting for clubroot and other diseases.

Identification

Fig 1. Early-maturing patches in a fieldThe roots of infected canola plants become malformed due to increased cell division and growth, which leads to the development of galls. Clubroot restrict the flow of water and nutrients within the plant, so that severely infected roots can’t transport adequate water and nutrients to aboveground plant tissues. This can result in wilting, reduced seed production, stunting and possibly premature death of the plant.

Since the clubroot pathogen and primary disease symptoms all occur underground, it is crucial to scout fields throughout the season and pull up roots to look for symptoms (Figure 1). Aboveground symptoms may not always be present or may only be present when pathogen levels are very high. As a result, it is important to always pull plants (carefully, to ensure the root system remains intact) in high clubroot risk areas of the field and look for below ground symptoms.

Clubroot is spread by the movement of soil containing soil-borne resting spores. Soil transport occurs mainly on farm machinery (see Figure 2) and can occur in both canola and non-canola cropping years. The clubroot pathogen can be introduced to a field by soil movement in non-canola years and be present at low levels. Minimizing the movement of soil into and out of the field is the best way to prevent the introductions and spread of clubroot.

Fig 2. Clubroot-infested canola plants wilting

Clubroot surveys in Alberta have found that almost all new infestations begin near the field access, which indicates that contaminated equipment is the predominant spread mechanism. Other areas that are at a higher risk of hosting the disease are low spots which often have excess moisture, water runs, high traffic areas, and exploration activity areas/ areas that are accessed by outside equipment. In addition, Manitoba fields show that areas where pooling water occurs are at a higher risk for infestation. When monitoring for clubroot, it is important to monitor all high clubroot risk areas in the field. If a field is located in an area where clubroot is not yet known to occur, focussing scouting near the field entrances is a good approach as clubroot infested soil will most likely be introduced via equipment in these areas.

Depending on local conditions and timing of infection, clubroot-infected canola may look very similar to canola suffering from other diseases or environmental stresses. Patches of prematurely ripening canola due to clubroot infection (see Figure 1) could be confused with other diseases such as sclerotinia, blackleg or fusarium wilt, or moisture stress (ex. drought or waterlogging) if only viewed from a distance (rather than pulling up and examining the root).

Symptoms in the field will vary depending on the growth stage of the crop when infection occurs, the severity of infection and environmental conditions after the infection takes place. Early infection (at the seedling stage) can later result in wilting, stunting, yellowing and even death of canola plants at the late rosette to early podding stage.

Infection that occurs at later crop stages may not show plant wilting, stunting or yellowing. However, infected plants may ripen prematurely, resulting in shriveled seeds and negatively impacting both yield and quality (ex. oil content). Lack of moisture, high temperatures late in the season and other canola diseases can also produce similar symptoms (hence the importance of examining the plant below ground as well as aboveground).

Fig 3. Always dig up roots when scoutingSince aboveground symptoms of clubroot may be incorrectly attributed to moisture stress or to diseases such as blackleg, fusarium wilt or sclerotinia, proper diagnosis of clubroot should always include digging up plants to check for gall formation on roots (see Figure 3).

Typically, it takes six to eight weeks from initial infection to gall formation, but this depends on when the field receives rain. The best time to scout for clubroot symptoms on roots is late in the season, approximately two weeks before swathing, since root galls should be easy to identify at this time (see Figures 4 to 8).

Another option is to identify patches of concern while swathing and sample afterwards. Since the entire field is traversed during swathing, this will give the most detailed indication of the incidence in the field. If suspicious plants are not sampled until several weeks after swathing, the root galls may have decayed already, and typical whitish galls will no longer be present. Instead, the decayed galls give roots a brown, peaty appearance (See Figures 8 and 9) rather than the healthy white colour associated with normal roots. If clubroot infection is severe, the plants may have very little healthy root tissue which can result in them being easily pulled from the field. In these areas plants may be up rooted during swathing.  If this occurs, it is important to stop and examine the plants in the area from clubroot symptoms.

Fig 4. Early stages of clubroot (small galls)

Fig 5. Early stages of clubroot (small galls)

Fig 6. Moderately infected canola roots  

Fig 7. Decaying clubroot galls

 

Fig 8. Decaying galls appear ‘peaty’ Fig 9. Decayed clubroot galls and whitish stem

Clubroot infects all species of plants in the Crucifer (Brassicaecea) family. Weeds such as Shepherd’s purse, stinkweed, flixweed, wild mustard and many others in this family will carry and increase this disease (see Figure 10).

 

Fig 10. Clubroot hosts: stinkweed and shepherd’s purse
Crucifer species that can be clubroot hosts

Hybridization nodules on canola roots (see Figures 11 and 12), although rare, could be confused with clubroot galls although these appear as small, round nodules located at root nodes. The interior texture of a clubroot gall is spongy or marbled, while hybridization nodules are uniformly dense inside, like healthy roots. Also, hybridization nodules will not decay rapidly to a peaty or saw dust-like appearance as clubroot galls will.

 

Fig 11. Hybridization nodules on canola root

Fig 12. Hybridization nodules on canola root

Photo courtesy of Rob Dunn Photo courtesy of Alvin Eyolfson, Battle River Research Group

Testing

Soil and plant testing for clubroot is conducted by commercial laboratories, but fields should be scouted and identification of other potential problems considered first.

Soil and plant samples can be tested for the presence of clubroot DNA via PCR (Polymerase Chain Reaction) methodology. The labs in Canada that currently provide this service are listed below:

  • 20/20 Seed Labs
    507 11th Ave
    Nisku, AB T9E 7N5
    (780) 955-3435
     
  • Exova
    7217 Roper Road NW
    Edmonton, AB T6B 3J4
    (780) 438-5522
     
  • SGS BioVision
    #310 - 280 Portage Close
    Sherwood Park, AB T8H 2R6
    1-800-952-5407
     
  • Discovery Seed Labs
    450 Melville Street
    Saskatoon, SK S7J 4M2
    (306) 249-4484
     
  • Quantum Genetix
    Site 501, Comp 11
    RR 5 Station Main
    Saskatoon, SK S7K 3J8
    (306) 956-2071
     
  • Pest Surveillance Initiative (PSI)
    5A 1325 Markham Road
    Winnipeg, MB R3T 4J6
    (204) 813-2171
     
  • A&L Canada Laboratories Inc.
    2136 Jetstream Road
    London, ON N5V 3P5
    (519) 457-2575 


For soil sampling
: Obtain approximately two to three cups of soil for this test. This should be a composite sample taken in a “W” pattern near the major approach or entrance to the field, in the plot area or other high clubroot risk areas in the field. Sample soil from the top 5 to 10 cm (A horizon), excluding as much surface organic matter as possible.

For plant sampling: Obtain roots from suspected plants and place in a zip-lock bag. These can be fresh or dry roots. If fresh roots are collected, it is important to ship or send samples quickly to avoid rotting of the plant tissue. If available, root tissue samples are preferable to soil samples to test for the presence of the clubroot pathogen.

The PCR test is a reliable method for molecular detection of the clubroot pathogen and will give either a positive or negative result for the presence of clubroot in the sample. However, there is currently no mechanism in place to correlate this test result to the potential for infection in the field or the expected level of yield loss. Research is underway in this area.

If a sample tests positive for the presence of the clubroot pathogen, use caution when extrapolating the results obtained for a particular sample to an entire field.

When sending soil or plant samples to a laboratory for testing, it is important to ensure that they are packages securely to prevent cross-contamination between samples and/or escape of the clubroot infested tissue or soil during transport. 

In Alberta:

Producers finding suspicious roots can contact and send samples to one of four commercial labs (20/20 Seed Labs, SGS Biovision, Discovery Seed Labs or Exova Edmonton) for testing.

In Manitoba:

For visual diagnosis, submit suspicious samples to the Manitoba Crop Diagnostic Centre. Send a complete sample (the entire fresh plant in a plastic bag) along with the proper form, with as much information filled out as possible, to the Crop Diagnostic Centre. General guidelines for submitting a sample can be found at:

Submitting Samples for Diagnosis to the Crop Diagnostic Centre (PDF)

This submission form is available directly from the Diagnostic Centre, through Manitoba Agriculture, Food and Rural Initiatives offices, or can be accessed at the following link.

Diagnostics Form for Crops, Insects and Weeds (PDF)

There is currently no charge for crop related samples. For more information or to submit a sample:

Crop Diagnostic Centre, Crops Knowledge Centre
Agricultural Services Complex
201 – 545 University Crescent
Winnipeg, Manitoba
R3T 5S6
(204) 945-7707

For PCR diagnosis, farmers finding suspicious roots can also contact and send samples to one of three commercial labs (20/20 Seed Labs, SGS Biovision or Pest Surveillance Initiative) for testing.

In Saskatchewan:

For visual diagnosis of plants, submit suspicious samples to the Crop Protection Laboratory. To submit, send a complete sample (the entire plant, preferably more than one) along with the proper form with as much information filled out as possible to the Crop Protection Laboratory. This form is available directly from the laboratory, through Saskatchewan Agriculture, or can be found online. Note: when downloading and using the Internet version of the form, four copies of the fully completed form are required, along with the sample, for submission to the laboratory. For more information or to submit a complete sample:

Crop Protection Laboratory
346 McDonald Street
Regina, Saskatchewan
S4N 6P6
(306) 787-8130

For PCR diagnosis, farmers finding suspicious roots can contact and send samples to one of the commercial labs listed above. 

References

Information adapted from Agri-Facts, Clubroot Disease of Canola and Mustard, Alberta Agriculture and Rural Development, May 2007 Revision.

Information also provided by the Clubroot Steering Group (the CCC chairs)

Date modified: April 23, 2019