Clubroot in the County
2018 Positive Clubroot Locations
All information below is sourced from the Government of Alberta Clubroot Management Plan
What is it?
Clubroot is a serious soil-borne disease of canola, mustard and other crops in the cabbage family. Cole crop vegetables, for example, broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, kale, kohlrabi, radish, rutabaga and turnip, are susceptible to clubroot, as are many cruciferous weeds, for example, wild mustard, stinkweed and shepherd’s purse.
What does it look like?
As the name of this disease suggests, roots of infected plants may exhibit a club-like appearance; however, overall symptoms will vary depending on the growth stage of the crop when it becomes infected. Infection at the seedling stage can result in wilting, stunting and yellowing symptoms by the late rosette to early podding stage, while premature ripening or death can be observed in canola or mustard plants nearing maturity. Plants infected at later growth stages may not show wilting, stunting or yellowing, but may still ripen prematurely, and seeds may shrivel, thus reducing yield and quality (oil content).
Can any other diseases or disorders be confused with clubroot?
Above ground symptoms of clubroot may be confused with drought, nutrient deficiencies or other diseases, so suspect plants should be carefully dug from the soil to check for typical clubroot galls on the roots. Swellings of unknown origin called hybridization nodules are occasionally seen on canola roots and can be confused with young clubroot galls. These nodules are more spherical and firmer than clubroot galls and do not decay when mature as clubroot galls do. Exposure to phenoxy herbicides can also result in swellings on lower stems and roots of canola, mustard and cole crop vegetable plants, but these malformations usually lack the large size and lobed appearance of typical clubroot galls.
What causes it?
Clubroot is caused by a microscopic, soil-borne plant pathogen called Plasmodiophora brassicae. The clubroot pathogen is classified as a Protist, a group of organisms with characteristics of plants, fungi and protozoans. The life cycle of the clubroot pathogen is illustrated in the Alberta Agriculture and Rural Development factsheet Clubroot Disease of Canola and Mustard, Agdex 140/638-1, available online.
Why is it of concern?
Most varieties of canola, mustard and cole crop vegetables currently being grown in Alberta are highly susceptible to clubroot. This disease is capable of significantly reducing yield and quality, and may destroy a crop if infestation levels are high. Swedish researchers found that infestations in canola fields nearing 100 per cent affected plants caused about 50 to 80 per cent yield loss, while infestations of 10 to 20 per cent led to 5 to 10 per cent yield loss. These results are similar to sclerotinia stem rot infection in canola, where a general rule of thumb is that estimated yield loss is half of the percentage of infected stems. A few cases of total crop loss, that is, not worth combining, have been reported in central Alberta.
How long can it persist in the soil?
The resting spores of P. brassicae are extremely long lived and may survive in soil for up to 20 years according to Swedish research. Similar persistance is being reported in Alberta. Resting spore longevity is a key factor contributing to the seriousness of the clubroot disease, especially under short crop rotations. Clubroot is not a phytosanitary issue affecting international trade of canola or mustard.
How can it be spread?
In Alberta, clubroot is being spread mainly through soil infested with resting spores. Infested soil can be carried from field to field by farm machinery, especially tillage equipment, and can also be moved by wind and water erosion. Seed of various crops, as well as hay and straw, can also become contaminated with resting spores via dust or earth tag when they are grown in clubroot-infested fields.