Clubroot Update (with recipe for clubroot management)

September 11, 2019 - Issue 24

Manitoba Agriculture announced this week it has discovered a clubroot pathotype in South Central Manitoba that is able to overcome the first generation clubroot resistance. Outside of Alberta, very few fields have been found to contain novel pathotypes like this, and this is the first finding in Manitoba. See the CCC release.

In Saskatchewan, visible clubroot symptoms have been found in two fields in the northwest part of the province in R.M.s where clubroot symptoms were not previously confirmed.

And in Rocky View County in Alberta, a county where clubroot was confirmed for the first time just last year, a novel pathotype that can overcome first generation resistance is already confirmed.

All of this news means clubroot continues to spread and farmers should continue to scout, even when using CR varieties. Click here for scouting tips and images.

Recipe for clubroot management

When combined, like ingredients in a recipe, the following practices will help growers to limit clubroot damage in canola, allowing for the continued success and profitability of canola production across the Prairies.

  1. Vigilantly scout all canola fields for symptoms, even if growing a CR variety.
  2. Keep a minimum 2-year break between canola crops. This crop rotation is crucial in the stewardship of genetic resistance. With a 2-year break between clubroot hosts, we see a rapid decline in living resting spores.
  3. Seed CR varieties and understand if/when to deploy different sources of CR. Planting CR varieties before the disease arrives and gets established will give you a better chance of keeping the resting spore load at a manageable level and maintaining effective resistance. Rotation of resistance genes could also be important to maintain resistance efficacy. With repeated use of varieties with the same resistant traits under high spore loads, virulent races can multiply and effectiveness of resistant will be seriously compromised. Read about how that happens.
  4. Limit activities that can introduce foreign soil or cause erosion. Minimum tillage and equipment sanitation (as simple as knocking off visible dirt before leaving a field) will greatly reduce the risk of moving infested soil around. Note that wet soil conditions increase the amount of soil that clings to equipment.
  5. Control host weeds. Common weeds that can host clubroot include stinkweed, shepherd’s purse, flixweed, all mustards and volunteer canola. They need to be controlled within three weeks of emergence to prevent a new batch of spores being produced.
  6. Isolate field entrances and hot spots. Use patch management strategies to reduce spore loads, such as grassing the affected area, which will also limit soil movement. Patches that are visibly worse than the remainder of your field often have billions more spores per gram of soil than elsewhere and are often the first place where clubroot resistance breaks down. Removing these hot spots from cultivation for a few extra years significantly reduces spread and risk of resistance breakdown. As part of this, having separate field entrances and exits could reduce the amount of infested soil leaving the field on machinery.

Scout now for clubroot. Symptoms of the disease are most noticeable late in the season, and can still be seen during and after harvest on plant roots. Producers are strongly encouraged to familiarize themselves with clubroot symptoms and start scouting now before the galls degrade. If galls are degrading they will look brown and peaty and may fall off when plants are pulled from the ground. Scout heavy traffic areas (entrances, exploration, gas wells, etc), low areas/water runs and areas where dust/snow tends to drift and settle. It is good practice to pull plants and examine roots whenever you are looking at later-stage canola as the disease could show up anywhere.

Dig deeper:

Canola Watch