Gardening: Clubroot disease a concern for gardeners

Do you know where your potatoes are coming from?

Depending on where you get your seed potatoes, garlic bulbs, lily plants/bulbs, perennials or even soil grown shrubs and trees, you may be getting more than you bargained for. You may be infecting your garden with a disease that is on the rise in Saskatchewan: clubroot.

Clubroot is caused by a microscopic pathogen, Plasmodiophora brassicae, which lives in the soil. You may have heard about clubroot in relation to reduced yields and vigour in canola fields. However, club root affects all plants in the Brassicaceae family (cabbage family), including: broccoli, cauliflower, Brussels sprouts, cabbage, canola, mustard and cruciferous weeds such as wild mustard, stinkweed and shepherd’s purse. In the last 15 years, Plasmodiophora brassicae has become more and more prevalent in Saskatchewan soils.

Clubroot was first reported in western Canada in a few home gardens in the Edmonton area in the mid-1970s. Broccoli, cabbage and cauliflower plants were exhibiting symptoms. The disease first became an economic issue in 2001 when a crop of Chinese cabbage was damaged near Edmonton. In 2003, clubroot was detected, for the first time, in a canola field northwest of Edmonton.

A recent report released by the Saskatchewan government indicates that visible symptoms of clubroot were reported in 43 commercial canola fields in Saskatchewan in 2017-18; most fields are located in northern Saskatchewan.

The symptoms of clubroot vary, depending on the stage of growth at the time the plant is infected. In early seedling stages, infected plants will be wilting, stunted, prematurely set flowers (broccoli) or fail to form quality sized heads (cabbage and cauliflower). Eventually the stunted, yellowing plants succumb to a premature death.

Above ground clubroot symptoms are often confused with drought or nutrient deficiencies but the actual reason for these symptoms is due to galls on the roots. Club root galls are usually more lobed and larger than normal nodules on the roots:  these galls inhibit the plant’s ability to absorb water and nutrients. The disease is favoured by warm, moist soils.

Because clubroot is a soil borne disease, resting spores of the disease found in the soil can be spread from field to field via contaminated soil on agricultural equipment, vehicles, construction equipment, rototillers, gardening tools, potatoes, bulbs (lily, garlic, onions and others) or even shrubs, trees or perennials that have been dug up in infected soil.

Secondary contamination can occur via wind, soil with water and soil on plant material such as bales, organic mulch or infected compost. Resting spores can survive an animal’s digestive system and can live in the soil for up to 20 years.  Because clubroot can be an economically devastating disease for farmers and market gardeners, it is very important to eliminate the movement of soil from infected to non-infected areas.

Once clubroot spores have infected an area, it is very difficult to eliminate the spores: the goal is to prevent contamination in the first place. To minimize the spread of clubroot, source garden/landscape plants from clubroot-free areas. Remove soil from garden tools, rototillers and plants when moving from one area of soil to another. Practise a minimum three-year rotation, with brassica plants being planted in the same area only once every three years. Control weeds belonging to the Brassica family in the garden (ex. wild mustard, shepherd’s purse, stray canola).

If clubroot is suspected and you want a professional diagnosis, air-dry root samples in double paper bags OR freeze the samples in a double Ziploc bag (samples must remain frozen if this option is chosen). Send the samples to the Ministry of Agriculture’s Crop Protection Laboratory at 346 McDonald Street, Regina SK, S4N 6P6, telephone 306-787-8130 for diagnosis. You may mail, courier or drop off samples in person. There is a $50 fee for visual inspection.

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