| ||What is stripe rust?
Stripe rust is a disease of cereals caused by the fungus Puccinia striiformis. This disease can result in yield losses of 10 to 70 per cent in susceptible varieties and a total yield loss has been reported when severe epidemics occur. Like other leaf and stem diseases, yield losses are roughly proportional to the plant area infected. Yield losses are generally most severe when the infection occurs prior to heading. Historically stripe rust has not been of economic significance in western Canada but incidences of the disease have been increasing over the past few growing seasons.
Why has stripe rust become a problem recently?
Although stripe rust is not a new disease, it was limited to cooler climates (e.g. Pacific Northwest region of the USA), and so was previously not a disease of concern for wheat breeding programs on the Canadian prairies. However, new races of the fungus appear to have evolved that are adapted to the moderate summer temperatures on the prairies. As for all rust diseases, stripe rust spores do not typically over-winter this far north, instead arriving on wind currents from rust-infested cereal regions in the United States. However, the stripe rust fungus has been overwintering in the prairie region in recent years, which is why the disease has been observed earlier in the growing season. Warmer winters may have led to a greater potential for overwintering in the prairie region. Widespread production of susceptible varieties and delayed seeding of wheat for swath grazing may have also exacerbated stripe rust levels.
How do I identify stripe rust in my fields and what fields are most at risk?
With the exception of soft white spring wheat, current varieties in western Canada have not been selected for resistance to stripe rust. However, there are varying levels of resistance to stripe rust in current varieties. More extensive rating for stripe rust reaction has recently been initiated and ratings are included in variety selection charts. Refer to the Alberta Seed Guide for stripe rust ratings.
If you are growing a susceptible variety, it is important to scout. Know the visual symptoms of stripe rust and monitor fields in the morning when new spores are a distinct yellow colour. Stripe rust can be identified as small orange-yellow colored pustules forming in vertical lines that run parallel to wheat leaf veins. Spore development is favoured by cool (7 -20 C) environmental conditions. At higher temperatures, development of the fungus slows. This web document from North Dakota State University has excellent pictures for rust identification, even though some of the information in the text is not relevant to Alberta: Stripe rust ID.
Stripe rust attacks all the above-ground parts of the wheat plant. On young plants the pustules occur in blotches covering large areas of affected leaves. On older plants (after the jointing stage of growth) the powdery masses
(pustules) of yellow-orange spores are arranged in parallel lines, giving affected leaves a characteristic striped appearance. Infection of leaf sheaths and stems can also occur, but spore production on these parts is less than on leaves. Stripe rust can also attack the heads. The rust fungus infects the glumes and awns at flowering. This results in an accumulation of spores in the florets and on the surface of the developing grain. However, stripe rust is not seed-borne. Later in the season, the yellow summer spores in the pustules are replaced by dark brown winter spores that are considered to play no role in infection.
Stripe rust should not be confused with leaf rust or stem rust, which have reddish brown spores or septoria tritici blotch, which is characterized by grey leaf blotches that are speckled with small black fruiting bodies of the fungus.
Stripe rust can be confirmed by collecting plants suspected of being affected and placing them in a bucket with their base in water in a cool sheltered position. If stripe rust is present the rust pustules will produce a fresh crop of spores overnight.
How do I decide if I need to take control measures and what can I use?
Seed treatment can delay the onset of the disease on seedlings. However, windblown spores could still attack the crop later in the season, making a foliar of fungicide application necessary.
Experience in Australia showed that spraying should be done before stripe rust covers 5% of leaf area on the flag leaf. Once this infection level is reached, stripe rust becomes very difficult to control. The period of infection to release of spores is as short as 8 days, which can result in multiple generations per growing season.
What agronomic practices can I use in the future to limit the impact stripe rust has on my farm?
Crop management in terms of a combination of crop choice, timing of seeding, and weed/volunteer wheat management may provide effective control of stripe rust. Early planting of spring crops to be used for swath grazing or green feed will allow them to ripen before major amounts of stripe rust inoculum typically become available in late July and August. The use of resistant or tolerant varieties is a good method to reduce the impact. If you are using susceptible varieties then scout fields frequently.
More information on Stripe Rust management, environmental conditions and disease development can be found at: "Stripe Rust management, environmental conditions and disease development."
Stripe rust of winter wheat has also been observed in central Alberta. Investigation has been initiated to determine if severity of stripe rust on spring crops are associated with adjacent winter crops.
Additional links for identification:
Prairie Soils & Crops Journal
Stripe Rust in Washington State
Stripe Rust in California
Stripe Rust photo
Prepared by Jim Broatch, Ag-Info Centre, Alberta Agriculture and Forestry