Stripe rust on the horizon for winter wheat

Keep an eye on the weather. Precipitation may bring you more than just moist soil

Stripe rust is moving up the Pacific Northwest, so western Canadian producers might see infections in winter wheat this spring, says Randy Kutcher, associate professor at the University of Saskatchewan.

Last year, there was a lot of stripe rust throughout the continent, but it was too dry on the Prairies to become a major concern for winter wheat producers. “We didn’t have rain in Saskatoon until the end of July,” says Kutcher.

Stripe rust — a cousin of stem rust and leaf rust — thrives in cool, moist conditions. Most inoculum spreads northward from the U.S. to the prairie provinces, although Canadian researchers are investigating the possibility that stripe rust is overwintering in Alberta and, to a lesser extent, Saskatchewan.

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This year, because of the prevalence of stripe rust in several northern U.S. states, inoculum may travel on spring winds into the prairie provinces as early as April.

If the weather grows moist, producers should be on the alert. But if temperatures stay dry and warm, there may be nothing to worry about.

“There are three things that make a disease: a susceptible crop, a pathogen and the right weather,” says Kutcher. “Weather conditions are the ultimate factor — if it stays warm and dry, and they’re predicting El Niño will hang on, that will limit the amount of disease here.”

Kutcher has completed three years’ worth of work on a varietal resistance and fungicide timing study for spring wheat. His team’s winter wheat project, which looks at varietal resistance, is in year one. He says spraying should depend on when the spores arrive.

“Winter wheat producers should be considering spraying at flowering (anthesis) time or even earlier if the situation warrants it,” he says.

Variety resistance

Denis Gaudet, a research scientist with Agriculture and Agri-Food Canada’s Lethbridge Research Station, has led stripe rust surveys over the last several years in Alberta.

He says his team generally heads out to the field in late fall and mid-April, or as soon as the spring growth is underway.

“It’s been a fairly mild winter, and we certainly saw lots of stripe rust around last fall on the winter wheat, so it could overwinter this year,” he says.

If stripe rust does overwinter in the Prairies, or blows in early, frequent and thorough scouting will be key for early management. When scouting, producers should check new leaves for pustules arranged in longitudinal rows along the leaf veins.

Gaudet says spraying too early might be ineffective, as the crop may become re-infected later in the season — or, depending on the weather, stripe rust may not become an issue at all.

“The important thing to remember there is that you only need to protect the flag leaf and the penultimate leaf with fungicide,” he says.

But Gaudet says spraying early isn’t necessarily the best strategy for Prairie winter wheat producers. “Last year, we had an overwintering event in southern Alberta, but because of the dry conditions that we had from late May on until mid-July, we didn’t get any serious stripe rust development,” he says. “It was a case where if you’d gone out and sprayed you would have wasted your money.”

He recommends producers closely monitor winter wheat spring growth and keep an eye on the weather before making any spraying decisions.

But by far the most effective management strategy is the use of resistant varieties. Robert Graf, a winter wheat breeder with AAFC, says producers growing winter wheat varieties that are considered “intermediate” have some protection but should keep a close eye on their fields.

“I would suggest that anything that is rated resistant (R) or moderately resistant (MR) has a good level of resistance,” he says.

Varieties that have a resistant or moderately resistant rating are AAC Gatzeway, CDC Chase, Emerson, Moats and AAC Wildfire. In the general purpose class, varieties that are rated moderately resistant are Peregrine, Pintail, Sunrise and Swainson.

AAC Wildfire is a newly released variety currently in the multiplication stage. Graf says it looks very good for stripe rust resistance, as do AAC Gateway, Emerson and Moats.

For producers who planted non-resistant (susceptible) varieties in the fall, management recommendations boil down to careful scouting. “Scout by the end of May, or as soon as it starts to green up, and use a fungicide only if necessary,” says Kutcher.

Gaudet adds that while stripe rust starts in winter wheat, the disease moves readily into spring wheat, which covers the largest acreage in Western Canada. Decisions to select resistant spring wheat varieties can still be made.

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Julienne Isaacs

Julienne Isaacs is a Winnipeg-based freelance writer and editor. Contact her at [email protected]

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