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Stripe Rust Overwinters In Alberta For The First Time

Stripe rust hit Alberta winter wheat hard last year, after it overwintered there for the first time.

Plant pathologists blame the insulating effect of the deep, persistent snow cover we had last winter for the stripe rust fungus surviving in southern Alberta. The fungus infected the winter wheat and spread into spring wheat, limiting the yield-producing ability of the all-important flag leaf. The disease was the worst south of Highway 3, but it spread to some fields south of Calgary, into nearby areas of Saskatchewan and even as far northeast as Melfort.

Agriculture Canada agronomist Brian Beres has a winter wheat project looking at almost every aspect of winter wheat agronomy at Lethbridge and eight other sites across the Prairies. Among other things, he s looking at the impact of seed treatments and foliar fungicides in the fall.

Beres wasn t looking for control of any particular disease, the goal was to find whether the crop came through the winter in better shape. He tested fungicide seed treatment and foliar fungicide on plump and thin seed and on high and low plant populations. Chemical protection or a high plant population might help a poor-quality seed establish well. On the other hand, large seeds with better vigour might not need chemical protection.

Beres s co-operators are still sending harvest results for him to analyze and tease out findings from this first year of the study. He s already found that at Lethbridge, where winter wheat yields were hammered by stripe rust, they were better in plots sprayed last fall. That s only one year at one site, but Beres will be watching those treatment blocks pretty closely next year. Even if there is a benefit to fall fungicide, it may not translate into an economic advantage.

Beres is also seeing benefits from seed treatment, but not at all sites. It seems there s an advantage to seed treatment in stressed systems, he says. Seed treatment makes a difference where we target for a low plant population with low vigour (thin) seed. And higher seeding rates are definitely better.

Southern Alberta wasn t the only place with stripe rust this year. The Pacific Northwest and Montana had the worst outbreak they d seen since the 1960s. Mary Burrows, plant pathologist at Montana State University explains that this is a new strain of stripe rust, probably developed in California in 2001, that is now reaching our regions. This new high-temperature strain wasn t set back by high (30 C) daytime temperatures, that usually stop stripe rust, but Burrows suggests cool nights within the fungus s favourite range of 10-20 C allowed it to keep growing and spreading. It is a more aggressive strain. It affects more plants, more severely than older strains. It also overcame resistance in Radiant, a previously resistant variety.

A Manitoba Agriculture, Food and Rural Initiatives fact sheet says the disease is not known to overwinter here, but rather it hitches a ride northward on what is known as the Puccinia Pathway from the U.S. in June. As well, the disease favours cool, wet conditions rather than the typical hot, dry summers in this province. However, the wheat varieties grown in Manitoba are generally susceptible.

Burrows in uncertain whether fall spraying of winter wheat is economically justified in Alberta, but she advises watching wheat fields closely. In Montana, spraying to protect the flag leaf of susceptible varieties boosted yields by 40 per cent or more. One farmer sprayed part of an irrigated spring wheat field and harvested 120 bushels compared to 40 bushels in the unsprayed crop.

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Seed treatment makes a difference where we target for a low plant population with low vigour (thin) seed. And higher seeding rates are definitely better.

BRIAN BERES

Agriculture Canada agronomist

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