Barley Yellow Dwarf

Symptoms include uneven, blotchy leaf discoloration in various shades of yellow, red, or purple, progressing from the leaf tip to the base and from the margin to the midrib. The most striking symptoms occur on older leaves; the youngest leaves usually are not affected. Wheat and barley leaves usually turn yellow, while oat leaves are more red. Plants can also become stunted, especially if they are infected at an early growth stage. Tillering is reduced and maturity is delayed. Severe early infections can kill young plants. In oats, blasting (sterility) of florets in the panicle is common.

Barley yellow dwarf is an aphid-transmitted virus disease of wheat, barley, oats, triticale, and other small grains. The virus is vectored by most common grain aphids, including bird cherry-oat aphid, English grain aphid, rose-grain aphid, corn leaf aphid, and greenbug (see aphid information in Invertebrate Management section). The Russian wheat aphid, however, is not a vector of the virus. Numerous small grains and grasses are hosts of this virus.

Aphids acquire the virus by feeding on an infected host plant. Usually, 12 to 30 hours of feeding are necessary for aphids to acquire the virus. A latent period of 1 to 4 days must pass before the aphid is able to transmit the virus to another host plant during feeding. Usually, at least 4 hours of feeding are required to transmit the virus. Plants can be infected throughout the season, and epidemics are most likely during cool, moist seasons that favor grass and small grain growth as well as aphid multiplication and migration.

The virus interferes with the growth of infected plants, slowing the development of foliage and roots and sometimes preventing heading or killing the host. The virus multiplies within the phloem tissues of the plant; phloem cells are killed and downward movement of sugar produced by the leaves is impeded, leading to the symptoms described above.

Cultural Control

Plant resistant or tolerant barley cultivars and tolerant wheat cultivars (see barley and wheat cultivar information). Avoid early (September to October) or late (February to March) planting dates, which expose plants to active aphids when plants are most vulnerable (early growth stage).