Clubroot Incidence Rising in Alberta

EDMONTON - Oct 11/06 - SNS -- Alberta Agriculture reports there has a solid increase in the scope and severity of clubroot infections in canola and other susceptible crops since 2003.

Since first found in a canola field in St. Albert area in 2003, it has been the focus of a number of surveys of both canola and cruciferous vegetables crops across Alberta and especially in and around the Edmonton area.

"Clubroot is a fungal disease (Plasmodiophora brassicae Wor.) of cruciferous crops, such as canola and mustards," says Robert Spencer, irrigated and specialty crop specialist, with Alberta Agriculture, Food and Rural Development’s Ag-Info Centre, Stettler. "Vegetable cole crops such as cabbage, broccoli and cauliflower are also susceptible to this disease, as are Brussels sprouts, Chinese cabbage, kale, kohlrabi, turnips, rutabaga and radish."

In the summer of 2006, Alberta Agriculture staff surveyed seven commercial vegetable operations in the Edmonton area and collected plant samples from 70 sites within these operations for observation. These farms produced a wide range of cole crops, with the most common ones being cabbage, broccoli and cauliflower.

Of the seven operations surveyed, one was found to have a localized clubroot infestation, which contributed to a significant yield loss due to the high levels of disease present. 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 discoloration and temporary wilting of younger parts during the day with possible recovery at night.

"The clubroot pathogen can be spread by water, contaminated soil or manure, and infected transplants," says Spencer. "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."

Management of clubroot is difficult because few effective options are available, and even fewer are cost-effective. The three main management options are minimizing disease spread (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," says Spencer. "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," adds Spencer. "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."

The potential for clubroot to have an adverse effect on Alberta canola and cruciferous vegetable production is significant and producers should make every effort to prevent the introduction and/or spread of the disease on their farms.