Barley Stripe Rust in the Pacific Northwest in 1997

Roland F. Line

USDA-ARS, WSU Pullman, WA

A new barley disease, barley stripe rust (Puccinia striformis hordei), has appeared in the Pacific Northwest and could cause wide spread damage to barley in Washington and adjacent states. The disease can cause losses as severe as the losses that occurred in wheat during the early 1960's when there were no resistant cultivars and no other available methods of control. A research program preventing such a disaster was started in 1993 at Washington State University.

Barley stripe rust is one of the many fungal diseases of cereals and grasses that are referred to as rusts. They get their names by the characteristic rust-like, powdery spores that are produced on the foliage of the plants. Stripe rusts appears on young plants as golden-yellow blotches with powdery spores and later as long, narrow golden-yellow stripes on the leaf surface and glume. The stripes generally appear between the leaf veins but can sometimes cover the entire leaf. The spores produced on a leaf are carried by the wind to other leaves on the same plant, to other plants, and to plants in other fields. When the leaves are moist, the spores germinate, infect the leaves, and produce new spores. The cycle can be repeated many times in a growing season. Thus, the disease can start from a few infections and increase to completely cover the plant. The fungus can only infect and grow on living plants. Therefore, the presence of susceptible barley plants throughout the year contributes to the survival and spread of the pathogen.

Barley stripe rust is similar to the well-known wheat stripe rust (Puccinia striformis tritci); however, they are two different pathogens. Wheat stripe rust can attack cultivars of barley as well as wheat, but it has never been observed to cause severe damage to fields of barley in the Pacific Northwest. In contrast, barley stripe rust is known to reduce barley yields by 30 to 100 percent and to greatly reduce the quality of the grain. Barley stripe rust is not known to damage wheat.

Barley stripe rust is a new disease in the United States. It was not known to be present in the United States until 1991. The disease is well known in Europe, and like wheat stripe rust, several races of the barley pathogen occur in that part of the world, as well as in the United States. Barley stripe rust was reported to be present in South America near Bogata, Columbia in 1975. It was postulated that the barley rust was introduced by people traveling from Europe, since the race that was detected in Columbia was the same as a race that was common in Europe. The rust soon spread to other South American countries and eventually to Mexico. It caused wide-spread devastating losses in each of the regions where it occurred. The disease was first detected in Texas in 1991, and since then it has been spreading north and west. It appeared in Oklahoma, New Mexico and Colorado in 1992, and in Arizona in the spring of 1993, where it again caused major yield losses and greatly reduced malting quality. By August 1993, it was detected in southern Idaho and Montana. There were reports of barley stripe rust in California in 1993 that were confirmed during the spring of 1994. Barley stripe rust also appeared in Utah in 1994 and 1995 and caused severe damage. By the spring of 1995, the disease hadappeared in western Washington and Oregon, andby July of the same year, it was detected in eastern Washington. Also by July, the rust developed to severe disease intensities in southwestern Oregon and northern California. In 1996, barleystripe rust was widely destructive in California (causing a total loss of some fields) and was detected in both eastern and western Washington and Oregon. When the weather is favorable for the disease, we expect it to be as destructive as it has been in other regions of the world and as destructive as wheat stripe rusts has been in fields of susceptible cultivars in the Pacific Northwest.

Based on what we know about wheat stripe rust in this region, barley stripe rust in other regions, and controlled temperature tests in the greenhouse, we have determined that the environment in the Pacific Northwest is highly favorable for the disease. Now that barley stripe rust has appeared in in Oregon, Washington, and northern Idaho, it will remain in the region and spread throughout the Pacific Northwest. Field research in the Pacific Northwest was not appropriate until the disease became widespread. Now that the disease is in the region, both field and controlled environmental research will be needed to clearly understand how weather and management contribute to severe epidemics of the rust.

Monitoring the pathogen is important. To forewarn growers and breeders, we must determine the prevalence, distribution, and severity of the disease, identify the races; determine how those races evolve; and determine the vulnerability of cultivars to the races. At this time, barley stripe rusts and wheat stripe rust cannot be differentiated without extensive, detailed tests in the greenhouse. These include testing the cultures of the pathogen on a series of wheat and barley differential cultivars. To add to the difficulties, we determined in 1994 that at least 14 races of the barley stripe rust pathogen exist in North America. Since then, more than twice that number of races have been identified. Therefore, the barley stripe rust pathogen is extremely variable. Until 1994, we did not know how similar or different barley stripe rust and wheat stripe rust are or if they can cross with one another and make races that could be severe on both crops. We have shown that new molecular techniques, such as Random Amplified Polymorphic DNA (RAPD) analyses, can differentiate barley stripe rust from wheat stripe rust, other rusts of wheat and barley, and stripe rust of bluegrass. These techniques as well as studies on pathogen virulence are useful to differentiate the wheat and barley pathogens from one another.

Resistant cultivars are the preferred control. There is already a significant effort in searching for resistance to barley stripe rust. Barley germplasm is being evaluated in South America, Mexico, Texas, Colorado, Oregon, and Washington for resistance to the disease. We have identified sources of resistance and are conducting studies to determined what genes provide resistance. The current barley cultivars grown in the United States are susceptible, and it will take a few years to incorporate some types of rust resistance into locally adapted cultivars. Also, new races may circumvent some typesof rust resistance. We know little about the types of resistance to barley stripe and how durable the resistance may be. There appears to be types such as the high-temperature, adult plant resistance that is so effective in wheat. Therefore, various types of resistance must be identified and germplasm must be evaluated more thoroughly in order to be used to develop locally adapted, resistant cultivars.

Fungicides have been useful for the control of the wheat rusts and have potential for control of barley stripe rust. They might be used when resistance is ineffective or in combination with certain types of resistance. However, the use of fungicides must be economical and non-hazardous to the environment. Therefore, seed treatments and foliar fungicides must be evaluated under various integrated management systems to determine what fungicides are effective and how they may be used.

Some barley cultivars are also susceptible to stem rust. Stem rust is characterized by red pustules on stems and leaves. Stem rust was severe in 1993 in fields that were planted late because it appears later in the growing season. The cool, wet weather of 1993 was highly favorable for stem rust. Resistant cultivars and foliar sprays are possible controls for stem rust.

What can we do to prevent a barley stripe rust epidemic?

Monitor your crop. The disease will continue to exist in Washington and other states in the PNW. The fall and winter weather was favorable for stripe rust. Cool wet spring weather will provide conditions that are even more favorable for the disease. The same weather conditions are favorable for wheat stripe rust and barley stripe rust; therefore, one clue that barley stripe rusts might be present is the presence of wheat stripe rust on early winter wheat. . The barley stripe rust may not develop until late in the spring, when damage is less severe. Being forewarned is half of the battle against the disease. Timely control is important. Fields should be examined frequently throughout the growing season. The rust will probably appear first on the lowest leaves of the biggest plants of winter barley and volunteer barley that survived the winter. It should appear first in southern Washington and adjacent barley growing areas of Oregon. First, look on the lowest leaves for small golden-yellow blotches with powdery spores. Later as the plants grow, look for small golden-yellow stripes. Contact your county agent, and verify that it is stripe rust. Barley and wheat stripe rust look alike. If it is stripe rust, send a sample of several diseased leaves to Roland F. Line, USDA - ARS Plant Pathologist, PO Box 646430, WSU, Pullman, WA 99164-6430 or call (509) 335-3755 to determine if it is barley stripe rust or wheat stripe rust on barley. Continue to monitor the field. If it begins to spread and becomes more severe, it is probably barley stripe rust.

Plant early in the spring. Early planting should enable the barley crop to get a head start on the disease. Stripe rust development at late stages of growth will cause less damage. The amount of rust that survives the winter is important because if little rusts survives, the disease will not develop until late in the season. Even though early planting is preferable, sometimes very late plantings may escape the disease if the months of June and July are very dry, but yield of the very late plantings will usually be lower.

Consider treatment of the barley seed with Baytan. Baytan controls early stripe rust development but will not control the disease throughout the season. Also, Baytan is more expensive than the other seed treatments. Be sure to use Baytan at the rate indicated on the label. Higher rates may delay emergence when seed is planted deep.

Consider using foliar fungicides if the disease starts to spread and increase rapidly. Foliar sprays are not necessary unless severe rusts is expected. Best control should be before the rust develops on the upper leaves. Tilt (manufactured by Ciba) is the only systemic fungicide registered for control of barley stripe rust. Tilt cannot be used beyond the late jointing stage. New fungicides may be available later in the growing season. Determine the economical benefits before using the foliar fungicide.