Update on Rust Diseases in Wheat
|Figure 1. Stem rust on stems of an experimental line in a Uniform Eastern Soft Red Winter Wheat Nursery at Havelock Farm, Lincoln on June 19.||Figure 2. Stem rust on a flag leaf of an experimental line in a Uniform Eastern Soft Red Winter Wheat Nursery at Havelock Farm, Lincoln on June 19.|
|Figure 3. (right) Stem rust on triticale at Havelock Farm, Lincoln on June 19.|
July 2, 2008
|Figure 4. Stem rust on barley stems at UNL's Agricultural Research and Development Center near Mead, July 1.|
|Figure 5. Stripe rust and a few leaf rust pustules on a wheat flag leaf at the High Plains Ag Lab near Sidney, June 24.|
|Figure 6. Leaf rust on a wheat flag leaf.|
Natural infections of stem rust were found at UNL's Agronomy Research Farm in Lincoln on June 19. The heaviest infections were found in the Uniform Eastern Soft Red Winter Wheat Nursery. Susceptible entries were severely infected (Figures 1 and 2). Infections were also found on triticale (Figure 3).
At UNL's Agricultural Research and Development Center (ARDC) near Mead, stem rust spread from inoculated wheat plots to barley plots (Figure 4).
Stem rust is one of the most destructive diseases of wheat. Under conditions favorable for disease development (wet weather and warm temperatures) the disease can destroy an entire susceptible crop in less than a month. Some grasses and certain cultivars of barley, rye, and triticale also are susceptible to stem rust. The last major epidemic of wheat stem rust in Nebraska was in 1986.
Most of the commercial cultivars grown in Nebraska, including the newly released Husker Genetics Overland, have good resistance to stem rust. However, because the stem rust fungus is capable of mutating into new races which can overcome the existing resistance, wheat producers should scout for the disease every year, especially given the natural infections observed this year.
A trace amount of stripe rust (Figure 5) was found on June 24 at the High Plains Ag Lab near Sidney. Stripe rust has occurred sporadically in Nebraska over the last eight years. This year the disease has been observed late in the growing season and at such a low level that it is not expected to cause yield loss.
Leaf rust (Figure 6) is widespread throughout the state, but at much lower levels than last year. It is not expected to significantly impact wheat yields.
Distinguishing Between Rust Diseases
The three wheat rust diseases that occur in Nebraska can be distinguished by their symptoms.
- Stripe rust appears as yellow-orange pustules arranged between leaf veins in stripes (Figure 5). Because of the color of its pustules, stripe rust is also known as yellow rust.
- Leaf rust pustules (Figure 6) are orange-brown and are scattered randomly on leaves; they do not occur on stems.
- Stem rust pustules are dark red and are also randomly scattered. They are longer than wide and are much larger than leaf rust pustules. They occur on leaves and stems where they raise and rupture the epidermis, making them rough to touch. They turn black as plants mature, hence stem rust is sometimes also called black stem rust.
Managing Wheat Rusts
Wheat rusts are effectively managed by planting resistant cultivars and applying fungicides in a timely manner. All fungicides routinely applied to wheat in Nebraska are effective in preventing or controlling rust diseases.
Extension Plant Pathologist
P. Stephen Baenziger
Eugene W. Price Professor of Agronomy and Horticulture