A harvest survey found the disease club root in more than a dozen widely separated canola fields around Edmonton this year.
“It is there at low levels,” said Murray Hartman of Alberta Agriculture.
Club root is a fungus that infects plants in the cole family, such as cabbage, turnips and rutabaga. Canola is also in the family.
Although the disease is a problem in vegetable crops in Ontario and British Columbia, it had not been observed in prairie canola crops.
That changed this summer when it was confirmed in several fields in the St. Albert area near Edmonton.
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The discovery prompted Hartman to survey 70 Edmonton-area fields. He found the fungus in 12 fields owned by four different farmers. He also found it on an Alberta Agriculture research farm.
“So it is not isolated to one field or one little area. But on the other hand, there were 58 canola fields where we didn’t detect it, so it is certainly not widespread through the area,” Hartman told a canola industry conference here last week.
The fungus is called Plasmodiophora brassicae Wor. It causes galls to form on the plant’s roots, which in bad cases can grow to the size of golf balls.
They restrict water and nutrients from getting to the rest of the plant, stunting growth, causing wilt and reducing yield.
Another symptom is creamy white stems.
“They are not as white as sclerotinia, but I can really understand how a producer could look at his field and see these preripening areas with kind of white stems and say it is sclerotinia,” Hartman said.
The disease is a problem in oilseed rape in northern Europe, he said, and the experience there may illustrate potential yield loss.
There, a 100 percent infection can reduce yield by 50-80 percent. At an infection level of 10-20 percent, damage of five-10 percent is common.
There are no resistant canola varieties, but there is resistance in some other cole crops and it might be possible to breed it into canola if it becomes a problem.
Fungicides are used on high value crops such as cabbage, but the same application method would be uneconomical for canola. A potential solution is to band the fungicide under the canola seed so the roots grow down into it, but that would need study, Hartman said.
It’s not clear yet that club root will be a major canola disease, but there are reasons for concern.
It likes acidic soils and a large portion of Alberta’s canola belt fits that description.
Spores produced by the root galls are not air borne and so do not spread like blackleg.
However, the spores can persist in the soil for many years.
If it ever became established, it would be a hard disease to shake, he said.
“Swedish research found that when a field was infested with club root, it took 17 years for it to go down to a non detectable level in a bio-assay. And it had a 31/2 year half life.
“So think about. Even if we went to a one-in-four year rotation we will only decrease the spores by about a half.”
In other places in the world where it is a problem, cole crop rotations of five to seven years are recommended.
Next year, Hartman plans to survey a wider area for the fungus.
Containment strategies:
- Sanitation – Clean dirt from all equipment before leaving infected fields. Do not remove straw or bale straw from infected fields.
- Rotation – Do not seed canola or alternate hosts on infected fields for five to seven years.
- Weed control – Volunteer canola, weeds in the mustard family, dock and hoary cress must be controlled post-harvest in following crops.
- There is evidence that liming acid fields, those with a pH less than six, to above pH seven can reduce the disease severity.
