| | Clubroot is a serious disease of cruciferous crops that occurs worldwide. This disease is a major problem in commercial cole crops in Quebec, Ontario and B.C., and has been confirmed in a number of canola and cole crop fields in the Edmonton area. The infestation near Edmonton has spread since the first infested canola field was confirmed in 2003. While clubroot occurs mainly on cole crops such as broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, kale, kohlrabi, radish, rutabaga and turnip, it can also infect black mustard and canola.
"The fungus, Plasmodiophora brassicae Wor., causes large galls to form on roots, which then restrict the transport of water and nutrients to above-ground plant parts," explains Murray Hartman, oilseed specialist with Alberta Agriculture, Food and Rural Development, Lacombe. "Wilting of plants and premature ripening are common symptoms. Prematurely ripened patches of clubroot could be mistaken for a sclerotinia infestation. In canola crops, the seed yield is severely reduced."
The root galls release mobile spores that infect neighboring plants. There is a resting spore stage that is extremely long lived, lasting up to decades. The spores can remain viable throughout this stage even in the absence of hosts. The soil borne spores, and lack of air borne spores, means that soil transport is the main mechanism of disease spread.
Containment strategies:
- Sanitation is essential and producers are encouraged to clean off dirt from all equipment, including tires, before leaving infected fields. Do not remove straw or bale straw from infected fields.
- Minimize soil erosion on infected fields.
- Do not seed canola on infected fields for five to seven years. Also, the following alternate hosts should not be seeded or transplanted: cole crops, red clover, orchardgrass and strawberries.
- Volunteer canola, weeds in the mustard family, dock and hoary cress must be controlled in following crops. Post harvest canola re-growth and winter annuals in the mustard family (stinkweed, shepherd's purse, etc.) should be controlled in the early fall.
- There is evidence that liming acid fields, those with pH less than 6.0 to above pH 7.0, can reduce the disease severity.
"Farmers should check their fields, and have any suspect plants tested," says Hartman. "Farmers are encouraged to contact Alberta's Ag-Info Centre toll free at 1-866-882-7677 for information or assistance."
A color factsheet is posted at: www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex8593
Further information and pictures are posted on the following web sites:
Contact: Murray Hartman (403) 782-8024 |
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