Barley Yellow Dwarf

Symptoms include uneven, blotchy leaf discoloration in various shades of yellow, red, or purple, progressing from leaf tip to base and margin to 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. Stunting also occurs, especially if plants are infected at an early growth stage. Tillering is reduced and maturity is delayed. Severe early infections can kill young plants. An additional symptom of the disease that commonly is visible on oats is blasting (sterility) of florets in the panicle.

Barley yellow dwarf is an aphid-transmitted virus disease of wheat, barley, oat, and other small grains. The virus survives in most common grain aphids (including bird cherry-oat aphid, English grain aphid, rose-grain aphid, corn leaf aphid, and greenbug) and on numerous cereal and grass hosts. The Russian wheat aphid, however, is not a vector of the virus. Aphids acquire the virus by feeding on an infected host plant. Usually 12 to 30 hours of feeding are necessary for acquisition. After acquisition, 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 for transmission to occur. Plants can be infected throughout the season, and epidemics are most likely during cool, moist seasons that favor grass and cereal 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 food produced by the leaves is impeded, thus leading to the expression of the symptoms described above.

Control is through the use of resistant or tolerant barley cultivars (see BARLEY CULTIVAR TABLE), and wheat cultivars with tolerance (see WHEAT CULTIVAR TABLE). Also avoid very early (Sept. to Oct.) or very late (Feb. to Mar.) planting dates. Planting the crops during such times exposes the plants to active aphid populations at a time when plants are most vulnerable (early growth stage).