PHOTO: Becky Wang led a study at the University of Alberta that is the first to assess how soil pH affects the growth of the fungus that causes verticillium stripe in canola.
This is Part 2 of our spring disease forecast. For Part 1 go here.
As canola farmers prepare for the spring planting season, attention turns to a potential issue creeping into the province — verticillium stripe. While this disease isn’t yet widespread in Alberta, its presence in neighbouring provinces and specific areas of southern Alberta is cause for concern.
One of the key factors influencing verticillium stripe is soil pH. Alberta’s soils tend to be more acidic, which has historically helped suppress the disease. In contrast, Manitoba and Saskatchewan, with their more alkaline soils (around a pH of 7 or higher), have seen significant outbreaks. Southern Alberta, particularly around Lethbridge, also has areas of higher soil pH, which could create conditions favourable for the disease.
“I think the pH difference explains why verticillium stripe is becoming a problem in Manitoba and why we’re starting to hear more about it in southern Alberta,” says Becky Wang, a recent graduate from the University of Alberta who has studied the disease extensively.
Like many plant diseases, verticillium stripe thrives in warm, dry conditions. Recent years have seen hotter, drier summers on the Prairies, contributing to outbreaks in affected regions.
“We’ve seen large outbreaks in Manitoba following particularly dry and hot summers,” Wang notes.
Farmers combating other issues, such as clubroot, may inadvertently increase the risk of verticillium stripe by altering their soil’s pH. Lime application, a common practice to mitigate clubroot, raises soil pH, potentially creating a more hospitable environment for verticillium stripe.
“This is a big concern,” Wang explains. “If we raise soil pH to control clubroot, we could inadvertently encourage verticillium stripe.”
One of the most significant challenges is identifying verticillium stripe correctly. It can often be confused with blackleg, another common canola disease.
“People might think they’re dealing with Verticillium stripe, but it’s actually blackleg,” Wang says.
The symptoms of verticillium stripe can look like blackleg, and the two diseases can even interact, exacerbating crop damage. Farmers and agronomists need to be equipped to identify the disease accurately.
