Stripe Rust

Washington State University Bulletin

SP0004 -- 1993

Diseases of Washington Crops.

Otis C. Maloy and Debra Ann Inglis

 

Small Grains Home * Wheat Diseases * Barley Diseases

Cause

Hosts

Symptoms and Signs

Disease Cycle

Control

1997 PNW Pesticide

Recommendations

Other Interesting Stripe Rust sites

Stripe rust (yellow rust or glume rust) has occurred (unpublished) in Washington since the early 1900s; it became a major disease on wheat in the late 1950s. The epidemic resulted from several factors which coincided. A susceptible cultivar, 'Omar,' was widely grown, and a series of open, mild winters aided the survival of the rust on infected plant tissue. Unusually cool, wet springs enhanced early season spread. Also, 'Omar' wheat planted as a ground cover in the orchards of the Dalles was suspected to provide inoculum to areas farther north. Development of the resistant cultivar, 'Gaines,' was an important factor in stopping the epidemic. Stripe rust is the most damaging of three cereal rusts occurring in Washington. It can develop at lower temperatures than the other rusts (Figure 5) and, therefore, can increase earlier in the spring and act upon the host for a longer period of time.

Cause
Stripe rust is caused by Puccinia striiformis (synonym P. glumarum). A number of pathogenic races occur and continue to form as new cultivars are released. The fungus, a basidiomycete, produces round, yellow-orange urediospores that have thick, spiny walls and 6 to 12 scattered germ pores. Telia develop but have no apparent function.

Hosts
In the United States, wheat is the only host of consequence, but barley and some perennial grasses may also become infected. The aecial host is not known.

Symptoms and Signs
As is the case with most rust diseases, symptom development parallels developmental stages of the causal fungus. The first sign is the appearance of small, yellow, elongated uredial pustules in rows on the leaf (Photo 9). These rows resemble sewing machine stitches. When the pustules mature, they break open to release a yellow-orange mass of urediospores. In many varieties, the pustules develop in long, narrow, yellow stripes on leaves, leaf sheaths and heads. Once infected plants mature or become stressed, the tissue becomes brown and dry, and plants have a scorched, drouthy appearance.

Disease Cycle
Urediospores perpetuate the fungus on green host tissue, such as volunteer wheat or susceptible wheat growing in other fields. Urediospores lose their viability rapidly at temperatures above 59F. Germination is best between 41 and 59F, with limits at 32 and 68F. Infection may occur through the winter, since the mycelium remains viable to 23F. The disease develops most rapidly between 50 and 59 F when intermittent rain or dew occurs. Many disease cycles may take place in one season, since the time between infection and sporulation under optimal conditions is about 8 days. Cool, wet falls; mild, open winters; and long, cool, wet springs favor stripe rust.

Control
Chemical. Certain systemic fungicides can interrupt epidemic outbreaks. Timing is a critical and elusive consideration. Early application may stop an outbreak if cool, wet weather does not follow. If you apply fungicides too early, enough late infection may occur to cause serious losses. Because of the fungicide cost, it may be worthwhile to consider a split application. A second spray would add only the application cost; moreover, if the second application is not needed, you save both material and application costs.

A predictive model has been developed to forecast occurrence of stripe rust and need for fungicidal sprays. This model is based on the fact that mild winters and springs favor stripe rust development. It uses a base temperature of 7C (44.6F), the optimum temperature for urediospore germination and infection of the wheat plant.

Calculate degree days by subtracting 7 from the temperature for each day. Given a temperature of 10C there would be three positive degrees for that day; at 4C count three negative degrees. Accumulate negative values for the coldest period (December 1 through January 31) and positive values for the spring period (April 1 through June 30). If negative degree days total less than 500, or if positive degree days total less than 440, there is a high probability of severe rust. In other words, the milder the winter and spring season, the greater the chance of rust. Use this method with other considerations, such as cultivar planted, relative susceptibility, date of seeding, and presence of rust in the fall.

Resistance. Use of resistant cultivars has become the major means of controlling stripe rust. Most of the resistance develops in the mature or adult plant (MS or MR in Table 4). Cultivars with this resistance are still susceptible in the seedling stages. Cool weather during the growing season can delay development of adult plant resistance.

In some wheats, resistance is of a specific type which is effective at all stages of plant growth (R in Table 4), barring development of a race of rust that can attack that resistance type. However, when a pathogenic race develops that can overcome the specific resistance, all cultivars bearing the same gene for resistance are vulnerable. To circumvent this possibility, wheat breeders use multilines, which are physical mixtures of disease resistant genotypes. If a race arises that can attack one of the components of the multiline, the genotype can be replaced in future plantings by one that is resistant.

Table 4. Resistance to stripe rust and leaf rust in Leaf rust selected Washington wheat varieties. a Adapted from the 1985 ratings of the Washington State Crop Improvement Association.

Winter Wheat

Spring Wheat

S = Susceptible;seedlings, adult plants, and heads susceptible.

MS = Moderately susceptibel; seedlings and head susceptible. Adult plants moderately resistant.

MR = Moderately Resistant; seedlings and heads susceptible. Adult plants resistant.

R = Resistant; seedlings, head and adult plants resistant.

References
Coakley, S.M., R.F. Line, and L.R. McDaniel. 1988. Predicting stripe rust severity on winter wheat using an improved method for analyzing meteorological and rust data. Phytopathology 78:543-550.

Qayoum, A., and R.F. Line. 1985. High-temperature adult-plant resistance to stripe rust of wheat. Phytopathology 75:1121-1125.

Other Interesting Stripe Rust sites:
UC Pest Management Guidelines, STRIPE RUST -- Descriptions and pictures.

Alberta Agriculture, Food and Rural Development. Descriptions and pictures of all the cereal rusts.