Verticillium wilt, caused by Verticillium longisporum, was detected in canola in Manitoba last summer. While verticillium wilt is common in northern Europe — it’s the number one disease in oilseed crops in Sweden — this was the first case of the disease in an oilseed crop in North America.
What is verticillium wilt?
Verticillium longisporum is a disease in canola that overwinters in the soil as microsclerotia. Microsclerotia are small masses of fungal cells that are hard and compact. They can survive in the soil for 10 to 15 years, but will decline over time.
Once they’re stimulated by the roots of host plants, microsclerotia will germinate. The fungus then infects the plant via its root system. As the plant matures, the fungus spreads upwards through the xylem tissue.
What are the symptoms?
Symptoms of verticillium wilt in canola usually appear at the end of the season just when the plant begins to ripen. Although it will still appear green, once infected, the stem of the plant will have a vertical yellow or brown band extending up its side.
As the plant continues to mature, it will be possible to peel back the stem’s epidermis, revealing black microsclerotia below the surface.
The microsclerotia appear as black pepper-like spots, visible with the naked eye. When examined under a microscope, the same microsclerotia will also be visible in the inner pith tissue.
Should canola growers be worried?
Michael Harding, plant pathologist with Alberta Agriculture and Rural Development says verticillium wilt presents a significant threat to canola production on the Prairies. “The disease is very difficult to manage because there are no resistant varieties,” Harding says, “and it survives in soil for long periods of time.”
Because infected soil can travel, it’s difficult to predict how far or fast the disease will move. “From what we know so far, it’s very localized in distribution,” says Harding. “If it is contained at its current location, it may never make its way west. However, we just don’t know how far or how fast it will move.”
“However,” adds Ralph Lange of Alberta Innovates, “dispersal should be slower than an air or seed-borne disease, say more like clubroot than fusarium.”
What can growers do?
Scouting is important when it comes to managing for verticillium wilt. The best time to scout in canola is at swathing, although the disease can be identified in the field where it will continue to develop after harvest as well.
There are no foliar or seed treatment fungicides available to growers to control verticillium wilt. This makes management all the more important. Harding recommends that growers avoid long rotations of susceptible crops, no more than three years. This will allow the pathogen to naturally decline in the field.
Strict sanitization of tools and equipment is also recommended, as are enhanced biosecurity measures, including controlling off-farm traffic, monitoring seed, farm and fertilizer sources and developing an on-farm biosecurity plan.
To learn more about verticillium wilt, check out Manitoba Agriculture, Food and Rural Development’s fact sheet on the subject.