By: Brett Rumpel, BSc (Agr.), Crop Lab and Field Technician, Alireza Akhavan, PhD, AAg, Provincial Specialist-Plant Disease, Carter Peru, BSc, PAg, Integrated Pest Management Agrologist and Cory Jacob, PAg, Provincial Specialist – Oilseed Crops, Crops and Irrigation Branch, Regina
First discovered in Manitoba in 2014, verticillium stripe (Verticillium longisporum) can infect canola and other brassica crops. In 2021, Saskatchewan officially reported the first confirmed report of verticillium stripe with typical symptoms in the province, which may pose a new threat to brassica crops. Like clubroot, verticillium is a soil-borne pathogen; symptoms of verticillium include leaf chlorosis, early ripening, stunting, necrosis and stem shredding.
Diagnosing verticillium may be difficult for those who are not sure what they are looking for. Symptoms may appear similar to sclerotinia on the exterior of the plant, or blackleg when looking at a stem base cross-section. The exterior of a canola plant infected with verticillium can show signs of bleaching. Once the pathogen has progressed, plant tissue becomes necrotic, stems become fragile and the epidermis may peel causing a shredded appearance.
Internally, a cross-section of a canola plant infected with verticillium will have black to grey discolouration, usually peppered throughout. This could be easily confused with blackleg, but, it is important to note that a cross-section of a stem infected with blackleg will have solid black sections that are accumulated in the infected area, not peppered throughout.
The most indicative factor of verticillium is the small microsclerotia found beneath the epidermis. Scouting for verticillium is best done during harvest. When the crop is fully ripe, the stem peels back and tiny dark pepper-like microsclerotia will become visible. Microsclerotia may remain on stubble or fall to the soil. These hard structures can survive in the soil for many years and can move similarly to the clubroot pathogen.
As there are currently no fungicides registered to control verticillium stripe and no resistant varieties, prevention is the best form of management. Prevention of verticillium is highly beneficial as these same practices to reduce the spread of verticillium stripe will also reduce the risk of spreading clubroot (Plasmodiophora brassicae). Longer crop rotations (three-year break between canola crops), sanitizing and removing soil from equipment and minimizing the overall amount of soil movement, all help reduce the risk of spreading verticillium.
The Saskatchewan Ministry of Agriculture initiated a verticillium-specific survey in 2022, targeting areas in eastern Saskatchewan to assess the prevalence and incidence of the disease and help evaluate the risk this disease poses to canola production in Saskatchewan. Multiple research studies were also supported by SaskCanola to study different aspects of this less explored disease including its impact on yield.