Prairie growers on alert for fast spreading disease

A winter wheat field near Burdett, Alta., is the proverbial canary in the coalmine for stripe rust.

The large field, up to 40 percent infected with the disease, showed the potential for infection in other winter wheat fields, as well as possible spread to susceptible varieties of spring wheat.

“It’s definitely showing up in a lot of the (winter wheat) fields we’re looking at now,” said Agriculture Canada plant pathologist Denis Gaudet.

“It’s showing up at low levels in a number of different areas of southern Alberta so we’re sort of on the watch for it.”

Saskatchewan has had only one report of stripe rust so far this crop season. It was found in winter wheat in the Wolseley area and has put crop experts in that province on alert.

“We know that we had the disease last summer at higher levels than we were used to seeing,” said plant disease specialist Faye Dokken Bouchard of Saskatchewan Agriculture.

However, she said wind trajectories forecast by Environment Canada indicate only a moderate risk of stripe rust spores spreading from the U.S. Pacific Northwest.

In the case of the Burdett field, however, Gaudet said it appears stripe rust overwintered.

The leaf disease also overwintered in 2010-11, which led to severe infestation and yield losses in winter and spring wheat last year.

Stripe rust usually arrives in Canada later in the growing season via spores borne on winds from the United States. By then, it is too late to do major crop damage but the spore cloud spreads the disease and creates a risk that stripe rust will overwinter.

Gaudet encouraged wheat producers to scout their crops every two or three days for signs of stripe rust, which is characterized by orange-yellow stripes of pustules that grow in lines parallel to the leaf veins.

Stripe rust flourishes in cool, wet conditions, which have been common across the Prairies this spring. A hot, dry spell could eliminate the threat. Even if discovered, Gaudet urged producers to carefully consider whether spraying with fungicide is warranted.

“What we would like to see is only spraying if it becomes necessary to control stripe rust, because at trace levels, stripe rust is not going to do any damage at all.”

Winter wheat is now in the heading stage in southern Alberta, and the crop cannot be sprayed after flowering. However, Gaudet said there is danger the disease could spread to spring wheat crops.

“There is a potential there for real problems because obviously that rust can move from a more mature winter wheat to a very early development stage spring wheat.”

The most popular varieties of spring wheat are resistant to stripe rust, he added, so producers should not be compelled to spray if they’ve planted one of those types.

Stripe rust, like many pathogens, can change rapidly, and researchers are hard-pressed to keep up with it. A high-temperature strain evolved 10 years ago, and it is now causing problems in Kansas and Nebraska. Thirty-six different strains have been identified in Canada.

Dokken Bouchard said stripe rust is easy to identify, though it can sometimes resemble leaf spotting diseases. If the spores come off when leaf pustules are rubbed with a finger, it’s stripe rust.

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