Rust never sleeps.
That’s particularly true when it comes to cereal rust disease that can cause yield losses in wheat and barley.
Growers in Western Canada are no strangers to cereal rust diseases, which include stem rust, leaf rust and stripe rust.
Of the three types of rust, stripe rust is the most recent arrival on the Canadian Prairies and is most common across Western Canada.
Reem Aboukhaddour, a research scientist and cereal pathologist with Agriculture Canada in Lethbridge, Alta., said cereal growers should be on the lookout for stripe rust and should be able to recognize its symptoms.
The disease, which just a few years ago occurred predominantly in southern Alberta and British Columbia, is now showing up more frequently in southeastern Saskatchewan and Manitoba, an area traditionally considered to more conducive to stem rust and leaf rust diseases.
In a recent web event hosted by the Alberta Wheat Commission (AWC), Aboukhaddour said new isolates of stripe rust are becoming well-adapted to the eastern Prairies and to warmer and drier growing conditions in general.
As the disease adapts, it is also overcoming genetic resistance that’s contained in the YR genes found in many Canadian wheat varieties.
Since 2000, most known YR resistance genes have been defeated or are in the process of being defeated by new types of virulence, Aboukhaddour said.
“Out of the 18 YR genes, quite a lot of them are defeated right now,” she said.
An estimated 88 percent of the world’s wheat varieties are considered susceptible and global damages caused by the disease are estimated at US$1 billion annually.
Over the past few decades, incidence of older cereal rust disease such as leaf rust and stem rust has diminished in the Canadian Prairies due to a combination of improved genetic resistance in new wheat varieties, more frequent fungicide use and improved management.
During the same period, however, the incidence of stripe rust has been increasing.
Stripe rust, also known as yellow rust, is easy to identify and is not hard to distinguish from leaf rust and stem rust.
Stripe rust can affect wheat or barley and can occur anywhere on an infected plant.
Typically, however, the most common symptom is yellow stripes on the leaves of an infected plant or stripes of light brown pustules.
Stripe rust pustules are usually lighter in colour than the brown or dark brown pustules associated with stem rust or leaf rust.
In Lethbridge, Aboukhaddour’s research team is assessing wheat cultivars for resistance in disease nurseries.
Stripe rust inoculum is applied to test plots at high rates and more than 2,500 wheat genotypes are screened annually.
Researchers are also conducting annual field surveys to monitor the presence of the pathogen in different areas of Western Canada.
Fields surveyed are given ratings — either clean, trace, moderately infected or severely infected — based on prevalence of disease.
In 2020, about 12.5 percent of fields surveyed had severe infection rates, eight percent were moderately infected, 22.5 percent had trace infection levels and 55 percent were rated as clean.
Data from the survey is collected annually and is graphed to show how common disease is, and where it is most prevalent.
“It (the survey) can give you information about how important this disease is in certain regions,” Aboukhaddour said.
She said long-term research aims to determine how stripe rust virulence in Western Canada has changed over the past 30 years or so.
“We know stripe rust virulence has changed in Canada and has increased since 2000,” she said.
“Genetic resistance is a very important tool” in terms of management, she added.
Stripe rust spores are very small and while some spores can overwinter in Canada, spores blown in on winds from the United States are the main source of infection in Western Canada.
The Prairie Crop Disease Monitoring Network located online at prairiecropdisease.blogspot.com/p/cereal-rust-risk-report.html tracks wind trajectories and offers weekly cereal rust risk reports.
Jeremy Boychyn, an agronomy research extension specialist with AWC, said growers should be monitoring wheat fields for signs of stripe rust.
Growers should be asking themselves some basic questions such as, “which variety do I have, what resistance level am I dealing with, am I in an environment where this is going to continue to become an issue, and how quickly do I need to address this?” he said.
In cases of severe infection, yield losses in fields sown with susceptible wheat varieties can exceed 50 percent.
Research in Australia has shown that cultivars rated moderately susceptible (MS), susceptible (S) or very susceptible (VS) could have yield losses ranging from 40 to 80 percent under high disease pressure.
In Western Canada, stripe rust resistance rating for registered wheat varieties can be viewed in provincial seed guides.
“We do know that when (infection) gets to that five percent leaf coverage stage, significant yield impact can happen,” Boychyn said.
Additional information on stripe rust can be viewed at www.alberta.ca/stripe-rust.aspx.