UPDATE EB1839

Barley Stripe

Barley Stripe Rust is a barley disease new to the . The pathogen, Puccinia striiformis f. sp. hordei, is closely related to the Stripe Rust . Symptoms of the two diseases are very similar. The fungus produces stripes of rust pustules between the veins of the leaves (Figure 1). Pustules also may form on the heads. In susceptible cultivars the entire leaf blade may become covered with the rust. In barley, the pustules may be more yellow than orange; the disease is sometimes referred to as yellow rust.

Figure 1. Stripes of rust pustules on barley leaves.

Barley Stripe Rust has occurred in Europe for many years. The first incidence in the Americas was recorded in Colombia in 1975. From Colombia, the disease spread south into Chile and Argentina and then north into the United States (Figure 2). The disease was found in Texas in 1991, from Texas to Montana and

southern in 1993, in California in 1994, and in Oregon and Washington in 1995. The disease now occurs throughout the western United States. In 1996, the disease spread rapidly through barley fields in the central portion of Washington, where it caused some crop loss.

Figure 2. Spread of Barley Stripe Rust from Europe to Central, South, and now North America.

Life Cycle The Barley Stripe Rust fungus spreads by summer spores known as urediniospores. These spores form the orange, powdery material on the leaves. The spores blow in the wind from to plant and from field to field. The rust spores need about 8 hours of moisture on the host plant leaves to germinate and infect the host. Without dew or rain, new infections cannot take place, flag leaves remain healthy, and crop loss does not occur. The rust must reside within a living host. To survive the winter, spores from last year's crop must find a suitable host in which to overwinter (see Host Range). Late in the summer, the black spore stage develops as linear black pustules on the leaf. These spores serve no purpose, since no known alternate host for the pathogen exists.

Host Range The major commercial spring barley varieties are susceptible to this disease. Some resistance may occur in winter barley varieties (see Resistant Varieties). Certain races of the rust also will survive on wild barley varieties such as jubatum (foxtail barley), wheat, and volunteer . The latter two are very poor hosts for the fungus, but some races of the Barley Stripe Rust fungus do survive on wheat. For

many years, in Europe, the Barley Stripe Rust fungus was known as Race 24 of Wheat Stripe Rust, identified by its ability to attack specific wheat and barley varieties referred to as differential varieties. Researchers have identified 31 races of the Barley Stripe Rust pathogen, Puccinia striiformis f. sp. hordei. Probably at least 10 more races will be described when the 1996 data are completely analyzed.

Resistant Varieties None of the commercially available spring barley varieties in Washington is considered resistant to the disease. The winter barley 'Kold' is resistant, and 'Hundred' may show reduced infection. Although some barley is resistant to one or more races, none is resistant to all. This type of resistance to races is known as race- specific or seedling resistance. Even when breeders can incorporate race-specific resistance into new varieties, it often lasts only a few years. A more durable type of resistance is adult plant resistance­the type of disease resistance we depend on in wheat.

Adult plant resistance may be present in some barley varieties and breeding lines. Researchers are investigating which varieties have resistance, and how much. Local researchers could not start working on this problem until the disease was present in Washington. They did not want to be responsible for accidentally bringing the disease to Washington any sooner than it would arrive naturally.

Conditions for an Epidemic Warm, wet winters with mild temperatures or plenty of snow cover favor survival of the rust fungus as mycelium in the leaves of winter barley, volunteer barley, and other hosts. Cold, dry winters destroy the infected leaves, reducing the amount of rust available to spread the disease in the spring. Spring weather often is more important in determining the amount of disease the crop may suffer. Warm and dry conditions are unfavorable for disease; cool and wet conditions favor disease. Also, early increase of the disease means more severe damage to the crop.

Planning for Barley Since no resistant spring variety is available, growers must decide to plant something else or be ready to use fungicides if necessary. Both are economic risks to weigh carefully. Developing a risk management plan before planting the crop is a great idea. Doing so in advance can relieve some of the stress about making those decisions if the disease shows up at a time when other critical decisions demand attention.

Disease Control Plant spring barley as early as possible to help reduce the number of initial infections and to give the barley plant a head start on the pathogen. Baytan seed treatment can delay the onset of an epidemic by preventing early buildup of the disease on seedlings. Check the label for rates and ask your dealer about costs. Consider seed treatments in areas where Barley Stripe Rust was detected last year. Also consider seed treatments if the disease is present in the region on winter barley, volunteer barley such as Steptoe, or susceptible grasses. Seed treatment generally is cheaper than later foliar applications, which usually are made by airplane. However, windblown spores could still attack the crop later in the season, making another application of fungicide necessary.

Tilt can be used to protect the crop after you find the disease in the planting, and crop loss is imminent. However, you cannot use it after flag leaf emergence. Always read and follow label instructions before applying any pesticide.

Scouting If you grow barley, inspect it regularly for the rust. Look for rust pustules on lower leaves first, but remember to check often. Stripe rust can build up rapidly if conditions are cool and wet. Plan an extra inspection just before flag leaf emergence. Apply fungicides if stripe rust severity is greater than 5% at the late tillering stage. Protecting the flag leaf can preserve much of your yield.

By Edward B. Adams, Ph.D., Washington State University Cooperative Extension plant pathologist, WSU Spokane; and Roland F. Line, Ph.D., USDA-ARS plant pathologist, WSU Pullman.

College of Agriculture and Home Economics

© Copyright 1997 by Washington State University. WSU Cooperative Extension bulletins contain material written and produced for public distribution. You may reprint written material, provided you do not use it to endorse a commercial product.

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Use pesticides with care. Apply them only to , animals, or sites listed on the label. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.

Issued by Washington State University Cooperative Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Cooperative Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, color, gender, national origin, religion, age, disability, and sexual orientation. Evidence of noncompliance may be reported through your local Cooperative Extension office. Trade names have been used to simplify information; no endorsement is intended. Published October 1997. Subject codes 240, 356 C

EB1839

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