As stripe rust advances across the Canadian prairies, researchers report it can drastically affect cereals by causing defoliation and shriveled kernels.
Stripe rust, or yellow rust, is primarily a disease of cool climates and has been found in southern Alberta and British Columbia for years. Recently, it has increased in central Alberta in wheat, barley and triticale.
It has also been frequently observed in western Saskatchewan and occasionally in the eastern Prairies, causing substantial losses in some wheat fields.
The stripe rust information has been compiled in a report by Agriculture Canada, Alberta Agriculture and the University of Alberta.
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One of the most common cereal disease inquiries received by the
Alberta Agriculture call centre deals with stripe rust identification and management advice.
In a 1988 study, researchers determined that wheat yields in the Lethbridge area were as much as 75 percent lower due to stripe rust.
More recent research showed a 45 percent yield reduction in Lacombe. In 2004 and 2005, disease severity reached 100 percent in wheat research plots at Lacombe, Olds and Trochu.
Stripe rust spores need several hours of moisture on plant leaves to germinate and infect the host.
After penetration, the fungus grows in parallel with the leaf veins, causing a yellow striped appearance that extends the entire length of the leaf blade.
The stem can also be infected, causing similar symptoms.
Symptoms appear about one week after infection, with the production of spores occurring between eight days and two weeks after infection.
The yellow stripes consist of rust pustules that contain numerous spores that are ready to be dispersed for further infections.
Grain yield reduction is caused by the loss of green leaf area used for photosynthesis, plus water loss through evaporation due to the destruction of the leaf epidermal layer.
Mycelial infection may occur in the early spring, but the spores germinate optimally at temperatures between 5 and 15 C.
Disease development is most rapid in intermittent rain when the temperature is between 10 and 15 C.
While spores carried from the
Pacific Northwest are considered the major source of stripe rust inoculum, fungus overwintering in winter wheat in southern Alberta has been known to cause stripe rust epidemics on soft white spring wheat.
Yield losses can be reduced or prevented by timely fungicide application. It is important to plan an inspection just before flag leaf emergence. The early appearance and increase of disease means more severe damage to the crop.
Experience in Australia showed that spraying should be done before stripe rust reaches five percent of leaf area on the flag leaf.
Once this infection level is reached, stripe rust becomes very difficult to control.
Recent field evaluations for stripe rust reaction in New Zealand, Washington, and Creston, B.C., showed that many wheat cultivars commonly grown in Western Canada – are moderately resistant to stripe. AC Barrie was highly susceptible.
Although winter temperatures in central Alberta may be too low for the fungus to survive locally, weather conditions during recent summers appear to have been more favorable for stripe rust development.
This is supported by the observation that although stripe rust was not often detected in the field until the middle of July to early August, severity often reached 100 percent on susceptible cultivars that may sustain substantial yield losses.
