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Issue No. 10, Article 5/May 27, 2005

Stripe Rust of Wheat--Watch for It in Illinois

Stripe rust of wheat is appearing in Illinois wheat fields. This disease has been reported at multiple locations in the southern half of Illinois over the past 7 to 10 days and may be spreading northward. The weather has been favorable for the development of stripe rust. Progress should stop if the weather becomes hot and dry, but severity and incidence of the disease may increase if the weather is cool and wet. Stripe rust can spread and reach damaging levels quickly when cool and moist weather occurs.

Stripe rust (also called yellow rust) often appears earlier in the season than leaf rust. These two distinct diseases of wheat, stripe rust and leaf rust, are caused by different rust fungi and can be distinguished by the color and pattern of the pustules on infected leaves. The stripe rust pustules are yellow to orange in color, and they often appear as yellow stripes parallel to veins on infected leaves, whereas the pustules of leaf rust on wheat are darker brown to reddish brown in color and are scattered over the leaves in an arbitrary pattern.

Stripe rust on wheat leaves. Pustules often appear more orange in color. (Photo courtesy of Bob Bowden.)

Stripe rust of wheat appears to have been spreading north and occurring more frequently in Illinois and states to the north of Illinois in the past few years. Although this disease can reach epidemic levels in wheat fields, it has usually been limited in spread and severity in Illinois in part by weather that is typically too warm and/or dry for this disease. Stripe rust develops most rapidly when there is frequent dew or rainfall and temperatures are between 50°F and 60°F, and it slows considerably when temperatures exceed about 60°F to 65°F at night and 70°F to 75°F in the day. The severity can be influenced by wheat variety, temperature, and race of the stripe rust fungus (Puccinia striiformis).

Stripe rust can be managed with fungicides and to some degree with wheat varieties that differ in susceptibility. Fungicides that are labeled for control of stripe rust include Tilt, PropiMax, Quadris, Quilt, Headline, and Stratego. These products have strict application guidelines: some cannot be applied after the ligule of the flag leaf emerges (Feeke's growth stage 8), and some can be applied up to late head emergence (Feeke's growth stage 10.5). If fungicide application becomes warranted because of disease severity, check current labels of fungicides for application guidelines and requirements.--Dean Malvick

Dean Malvick

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