Yellow Dwarf

Washington State University Bulletin

SP0004--1993

Diseases of Washington Crops

Otis C. Maloy and Debra Ann Inglis

Small Grains Home

Cause

Hosts

Symptoms and Signs

Disease Cycle

Control

1997 PNW Pesticide

Recommendations

Other interesting Barley Yellow Dwarf sites

Barley yellow dwarf, also called yellow dwarf and red leaf of oat, is a virus disease that frequently occurs in small grains in Washington, and occasionally causes significant yield reductions. Disease incidence often is high in irrigated areas that support aphid populations during summer and where wheat is seeded early. Use of the enzyme-linked immunosorbent assay (ELISA), a serological test, has facilitated disease detection and diagnosis.

Cause
A virus transmitted only by aphids, not mechanically or by seed, causes barley yellow dwarf. As many as 20 different aphid species reportedly transmit the virus, but in Washington, only five-the bird cherry-oat aphid, the corn leaf aphid, the English grain aphid, the greenbug, and the rose-grass aphid- are important. The Russian wheat aphid is reported to be a non-vector.

The virus is persistent and circulative in its aphid vector but does not pass through the ovaries into eggs. Isolates of the virus have been grouped according to serological and pathological relationships: Group I-MAV, PAV and SGV; Group II-RPV and RMV. Virus isolates are named according to vector specificity, that is, PAV = Padi-avenae (bird cherry-oat and English grain aphids) specific. In eastern Washington, the bird cherry-oat aphid is considered the most abundant and effective vector of the nonspecific Barley yellow dwarf virus strain (PAV).

Hosts
Most cereals and many grasses are hosts of barley yellow dwarf virus. Corn is a symptomless host (at least the symptoms on corn are not conspicuous). At least 20 grass and cereal genera tested have carried Washington isolates of the virus.

Symptoms and Signs
Symptoms of barley yellow dwarf vary with hosts and are greatly influenced by environment. The disease usually appears as patches of stunted plants in the field. The leaves of affected plants are stifffly erect, in comparison with the gracefully drooping leaves of healthy plants; leaf tips are drawn out to a longer point than normal. Leaf color may vary in wheat from yellow to red or purple; this apparently depends on the cultivar. In barley the leaves have a bright golden yellow color (Photo 16); in oats, the leaves are red or purple. Discoloration often is mottled, appearing more intense at the leaf tip, then extending along the leaf margin to give a "chevron effect."

Temperature, nitrogen fertility and light influence leaf symptoms. Higher temperatures result in more pronounced symptoms; more nitrogen produces more color; and higher light intensity supports intense color development. Mottling may occur during intermittent, sunny weather. Time of infection also influences symptom expression. Early infections result in stunted plants, reduced tillering, blasted florets, shriveled grain, and serious losses. Late infections usually result in only flag leaf discoloration and small yield reduction (Figure 6).

Disease Cycle
Aphids acquire the virus by feeding from some source-wheat or barley (planted or volunteer), wild grasses, corn, etc.-and move to wheat, barley or oats. Feeding periods of 12-30 hours are most efficient for virus acquisition. Evidence indicates that corn constitutes a major reservoir of both the virus and its aphid vectors, particularly the bird cherry-oat aphid. Surveys in central Washington have shown that in some years more than half of the corn fields contain barley yellow dwarf virus. As the corn matures, aphids that have acquired the virus from corn move in search of green hosts, often early-seeded winter wheat.

Barley yellow dwarf is most severe in cool (50- 64F), moist seasons because of continued plant growth and aphid activity. The disease frequently does the most damage in early- seeded winter wheat or barley, or in late-seeded spring grains when aphids are still active and plant tissues are young and succulent.

Control
Chemical. In some areas (irrigated areas with lighter soils), applying granular systemic insecticides at planting may help reduce early infection. Opinions vary on the merits of this method, since aphids may transmit the virus before they succumb to the insecticide. However, some argue that the treatment will prevent or retard aphid buildup and secondary spread of the virus.

Cultural. Late seeding of fall grain [after September 15 most years (Table 7)] or early seeding of spring grains reduces barley yellow dwarf damage, because plants can emerge and grow through the highly vulnerable seedling stage while temperatures are too low for aphid activity.

Resistance. No resistant wheat or barley cultivars are currently adapted or accepted by Northwest growers. Nevertheless, resistance offers the best possibility for long-term control of this virus disease.

Disease Incidence

Table 7. The relationship of planting date to barley yeallo dwarf incidence in eastern Washington. From Wyatt, S.D., LJ. Seybert, and G. Mink. 1988 Plant disease 72:110-113.

*Plants infected/plants tested.

References
Bruehl, G.W. 1961. Barley yellow dwarf. American Phytopathological Society Monograph No. 1.

Rochow, W.F., J.S. Hu, R.L. Forster, and H.T. Hsu. 1987. Parallel identification of five luteoviruses that cause barley yellow dwarf. Plant Disease 71 :272-275.

Wyatt, S.D., L.J. Seybert, and G. Mink. 1988. Status of the barley yellow dwarf problem of winter wheat in eastern Washington. Plant Disease 72:110-113.

Other Interesting Barley Yellow Dwarf sites:
Alberta Agriculture, Food and Rural Development -- Barley Yellow Dwarf Virus, Red Leaf of Oats -- description and pictures.

University of California Statewide Integrated Pest Management Project -- description and links to pictures.