barley yellow dwarf virus

 Pathogen

Barley yellow dwarf virus (BYDV), a representative of the Luteoviruses, is a group of 5 nearly related viruses. Embrace of BYDV differs serologically and in virulence, host limit and vector particularity. Virus particles are spherical. More than 20 aphid species transmit BYDV. The most significant are the oat bird-cherry aphid, the corn leaf aphid, the English grain bee and the green dereliction. Aphids achieve BYDV by feeding infected plants and transmitting the virus in subsequent feedings.

Disease Symptoms

Symptoms of barley yellow dwarf are highly changeable and can be distracted with those of wheat streak mosaic, nutrient deficiency, root and crown infection, and environmental stress. Barley yellow dwarf is tentatively diagnosed from the presence of the aphid vector and the occurrence of yellow, stunted plants singly or grouped in small patches among normal plants. Yellow, red, or purplish discolouration of the leaves from the tip down to the midrib is common. In wheat, symptoms begin to become evident at the jointing growth stage. Barley yellow dwarf wheat does not form a distinct mosaic pattern like streak mosaic or soil-borne mosaic. Pale yellowing of older leaf tips is common. During cooler temperatures, the tips can sometimes turn reddish-purple. In years of high aphid activity, patches of BYDV-infected plants can be quite large in some cases.

Favourable Weather Conditions

Barley yellow dwarf results from passive migrations of the winged form of the aphid vectors in cool (50° to 68° F), moist seasons. Aphid flights can be localized or can cover several miles with wind assistance. Disease symptoms usually occur about 2 weeks after infection, and symptom expression is favoured by bright, sunny weather. During late summer, aphids migrate to early planted winter wheat, usually stopping during fall.

Administration

Seed days

Delaying the sowing of wheat until aphids are reduced reduces the risk of the yellowing of barley. Optimal dates for planting winter wheat seed are established in the various growing regions of Nebraska. These can be obtained from your local extension office. Avoid sowing wheat before the date recommended for your area.

Genetic Resistance

An important strategy for controlling BYDV is to plant resistant or tolerant varieties. High levels of resistance or tolerance are not found in wheat; however, commercial cultivars vary in susceptibility to barley yellow dwarf. A good strategy is to plant various varieties to reduce the chance that one variety will be heavily affected by the disease. (See UNL's Wheat Variety Selection Tool.)

Cultural Practices

Traditional methods of barley yellow dwarf include controlling grass weeds, including volunteer grains, in and around wheat production fields. Small grains should not be planted mid-summer as cover or companion crops in wheat-producing areas. These methods will reduce the virus and vector reservoirs in wheat-growing areas.

Chemical / Pest Control

Fungicides do not affect barley yellow dwarf and should not be used to control this disease. Seed treatment of imidacloprid (Gaucho and other products) or thiamethoxam (Cruiser) can reduce aphids in the fall and reduce primary infection. However, insecticide treatment to control aphids may not be cost-effective due to the transient nature of aphid infestations. Control of foliar aphids in the fall can reduce the incidence of barley yellow blight but may not be effective if the aphid escapes treatments or migrates from unirrigated areas.