Identifying verticillium. Or is it blackleg, sclerotinia or grey stem?

September 7, 2017 - Issue 24

We don’t know how common verticillium is in canola across the Prairies. We don’t know how severe it can get or how much yield loss it can cause. And we don’t know how best to manage the disease in a field where high yield loss is discovered.

Verticillium species can cause yield loss in other crops in Canada and they are known to cause yield loss in Brassica napus crops in Europe. But we don’t have a good handle on the Canadian canola situation following the first confirmation of verticillium symptoms on canola in Canada (Manitoba) in 2015.

Before investing in verticillium research for canola, it would help to turn these “don’t knows” into “knows”. To do that, Canola Watch is calling on agronomists to look for plants with verticillium-like symptoms and to send these plants in for disease identification. (Note, labs can identify verticillium, but most cannot identify the specific species.)

Verticillium whitened stem. Credit: Justine Cornelsen


Verticillium peeling stem with black spots inside. Credit: Justine Cornelsen

Verticillium symptoms

Verticillium is one disease that can be more obvious and easier to identify after swathing or straight combining. As the plant dies, look for: (1) Streaking on the outside of stems. (2) Specks of verticillium microsclerotia under the stem’s skin. As cut stems start to dry, these microsclerotia will be widespread on infected plants. Use a hand lens to look for them. (3) Peeling of the outer skin.

Verticillium needs moisture to get into the plant from its soil-borne spores, but infection then accelerates in dry conditions. With a dry August in 2017, conditions would seem to favour infection.

Labs that will provide disease identification:
Manitoba: Crop Diagnostic Centre, Manitoba Agriculture, 201-545 University Crescent, Winnipeg, MB R3T 5S6, Phone: 204-945-7707
Saskatchewan: Crop Protection Laboratory (346 McDonald Street, Regina, SK S4N 6P6
Alberta: Alberta farmers and agronomists who suspect verticillium should contact Alberta Agriculture’s Michael Harding (for those south of Red Deer) or Jie Feng (for those north of Red Deer). Their emails are michael.harding@gov.ab.ca and jie.feng@gov.ab.ca.

If confirmed, check nearby fields next year for incidence (the percentage of plants with symptoms) and severity (how bad the symptoms appear).

Verticillium or blackleg?

Specks of black underneath the outer layer are likely verticillium. Specks of black on the outer layer are likely blackleg.

Verticillium or sclerotinia stem rot?

Verticillium can leave stems white and shredded-looking, which are symptoms commonly associated with sclerotinia stem rot. Dry stems that shred apart easily are probably sclerotinia stem rot. Verticillium stems will have peeling skin, but tend not to be as brittle. Verticillium will also have specks of black under the peel. Black sclerotia bodies inside the stem are a clear indicator of sclerotinia stem rot, but these are not always present in sclerotinia cases.

Verticillium or grey stem?

Symptoms of grey stem are most likely to show up after swathing, while the striping symptoms of verticillium may be apparent earlier in the season. The fruiting bodies associated with the symptoms of grey stem will usually be present on the outside of the stem. If the outer layer of the stem is breaking away, it is likely verticillium.

Further reading:

Canola Encyclopedia chapter on verticillium
CCC Disease Scouting Guide

Canola Watch