Clubroot is a growing problem in Alberta.
The disease has been reported on occasion from home gardens in central Alberta over the past 30 years, but was confirmed in canola in the St. Albert area near Edmonton, in 2003.
Since then it has been the focus of a number of surveys of canola and cruciferous vegetable crops in Alberta, especially around Edmonton.
Since 2003, the number of canola fields affected has risen dramatically and continues to increase. This has raised the question of whether clubroot is also increasing in cruciferous vegetable crops.
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Robert Spencer, an irrigated and specialty crop specialist with Alberta Agriculture, said clubroot is a fungal disease of cruciferous crops, such as canola and mustards.
Vegetable cole crops such as cabbage, broccoli and cauliflower are also susceptible, as are brussels sprouts, Chinese cabbage, kale, kohlrabi, turnips, rutabaga and radish.
Alberta Agriculture staff surveyed seven commercial vegetable operations in the Edmonton area last summer and collected plant samples from 70 sites for observation. These farms produced a range of cole crops, with the most common being cabbage, broccoli and cauliflower.
One of the operations was found to have a localized clubroot infestation, which significantly reduced yields. Infected plants exhibited typical symptoms, including the formation of large root galls that restrict water and nutrient uptake and stunt plants. Many infected plants did not produce marketable heads.
Other symptoms included yellowing and senescence of older leaves and a slightly blue discolouration.
“The clubroot pathogen can be spread by water, contaminated soil or manure, and infected transplants,” Spencer said. “When the galls produced on roots break down, they release spores into the soil. These spores are very long-lived and can remain viable in the soil for up to 18 years. This disease is most severe in wet, acidic soils in the pH 5.0 to 6.0 range.”
Clubroot is difficult to manage because few effective options are available, and even fewer are cost effective. The three main management options are minimizing disease spread through sanitation, long rotations out of cruciferous crops and liming soils to increase pH.
“Once clubroot has been detected, movement of soil, infected plant material and water must be prevented or minimized,” Spencer said.
“This necessitates rigorous sanitation practices. All equipment or personnel leaving an infected field should be free from potentially contaminated soil. Straw or plant material from an infected field should not be removed and spread elsewhere, and contaminated manure should not be introduced. Soil erosion should be minimized and contaminated irrigation water should be avoided.”
Producers can attempt to reduce disease survival by ensuring good soil drainage or by making pH adjustments by liming the soil to maintain a higher pH, about 7.0. The costs associated with liming can be prohibitive.
“If clubroot is detected, a five to seven year rotation between cruciferous crops is recommended,” Spencer said. “Cruciferous weeds, such as wild mustard, stinkweed, shepherds purse, flixweed, volunteer canola, should be controlled. Additionally, there are some fungicide products registered for application to transplants that may help prevent infection. Only healthy transplants should be used for spring transplanting.”
