Diagnosing Verticillium Stripe in Canola Stubble

By Allie Noble, BSc, AAg, Crops Extension Specialist, Regional Services Branch, Prince Albert

Scouting for disease after taking this year's crop off may not be the first thought after parking the combine, but in the case of verticillium stripe it can be an optimal time to determine its presence. Verticillium stripe is a soil borne disease caused by Verticillium longisporum. The pathogen was first discovered in Canada in Manitoba during the 2014 growing season and has since spread across the prairies. It was previously reported in Europe and was assessed to cause yield losses from 10 to 15 per cent. The University of Alberta started a project to assess yield loss potential in canola production on the prairies. The upcoming results will be valuable in understanding impacts of the disease and what type of management strategies will be needed for producers.

As we wait to learn more about potential yield losses caused by this disease, determining the extent of the spread across Saskatchewan will allow us to better understand other general pathogenicity characteristics of this organism. Verticillium stripe was likely not detected for a few years in many fields due to the timing of obvious disease symptoms occurring late in the season, when harvest efforts are in full swing or are completed. Most often, disease scouting in canola fields occurs around swathing time when growers are looking for symptoms of other diseases like blackleg, clubroot and sclerotinia. Earlier in the season, while the crop is still green, there can sometimes be a visible stripe down the main stem with half green tissue and half yellowing tissue that is dying down because of verticillium stripe infection. This can make identifying the disease tricky – however, later in the season you can find more obvious disease symptoms in canola stubble including:

• Shredding of the stem and peeling back of the epidermis – look for peeling of the outer layer of the stem on stubble. Stem shredding can also be a symptom of sclerotinia, but you won’t find the peppery microsclerotia underneath the peeling epidermis in case of sclerotinia stem rot.
• Microsclerotia under the shredding epidermis – on infected stems, if you peel back the shredding epidermis you can spot tiny peppery looking microsclerotia that have formed along the stem. These will be extremely small (almost a powder consistency) and may require a hand lens to see. These are much smaller in size than pycnidia that can be visible from a blackleg infection.
• Discoloured stem cross section – once a plant is infected with Verticillium, the pathogen will move upwards in the xylem. This can be visible in the vascular tissue of the stem when a cross section is cut and greying or blackening can be seen. Blackleg also causes symptoms in a cross section, but those are darker and show up as pie shaped pieces versus greying across the whole stem.

If you find some of these symptoms in your field, what should be done? Ensure it is verticillium stripe. To get confirmation from suspected verticillium stripe samples, this year SaskCanola has a program offering free testing for Saskatchewan producers. If you find symptoms in your field and would like assistance, reach out to a local crops extension specialist or call the Agriculture Knowledge Centre at 1‑866‑457-2377 for more information.