NPIPM:Barley yellow dwarf
Authors: Byamukama, E. and Smith, M.
Causal Organism
Barley yellow dwarf (BYD) is caused by several strains of either Cereal yellow dwarf (CYDV) or Barley yellow dwarf virus (BYDV). There are several aphid species which transmit these viruses, and the efficiency of transmission depends upon the aphid species/viral strain combination. The most common virus strains that cause BYD in the Great Plains Region are: Barley yellow dwarf virus-PAV (BYDV-PAV), BYDV-MAV, and BYDV-SGV. These viruses are transmitted most efficiently by bird cherry oat aphid (Rhopalosiphum padi), English grain aphid (Sitobion avenae), and greenbug (Schizaphis graminum) respectively. Green bug, however, does not occur with high frequency in the Great Plains.
Symptoms and Signs
Symptoms of BYD can vary based on the strain of virus present, the cultivar, environmental conditions, and the growth stage at which plants become infected. Typical BYD symptoms include yellow, purplish-red discoloration of leaves, usually the flag leaf. Depending on the time of infection, the symptomatic flag leaf may start to die from the leaf tip. Other common symptoms include upright and stiff leaves, serrated leaf borders, reduced tillering and flowering, small grain heads, and inability to fill the grain. If plants are infected very early in the season, severe stunting may occur, and this is when yield is most likely to be significantly impacted.
Disease Impacts
BYD can cause estimated yield loss of about 5% on average but BYD epidemics at an individual field can be as great as 40%. The extent of yield loss is influenced by the level of susceptibility of the cultivar planted, time of infection, weather conditions, and strain of the virus.
Life Cycle and Epidemiology
Barley yellow dwarf virus is vectored by different aphid species as stated above. The virus is not seed borne, therefore the only means of virus spread is through the vectors, the aphids. The aphids acquire the BYDV as they feed on infected plants and transmit it to healthy plants as the feed within a field or when they are emigrating from other fields and hosts. BYDV can survive between crop cycles in volunteer wheat, barley, oats and several grass weed hosts, or in winter sown cereals.
Management Approaches
There are no fully resistant wheat cultivars, but there are cultivars available that have some tolerance. Delaying planting of the winter wheat crop can help evade early colonization and transmission. Insecticides have had some success when applied in limiting secondary spread, but the challenge remains in predicting aphid influx and by the time aphids reach noticeable levels in the field to trigger spraying, some transmission of virus has likely already occurred. Insecticide seed treatment can be used to manage early arriving aphids from outside the field, especially in early planted winter wheat.
Other Online Resources
Wegulo, S. Barley yellow dwarf. http://cropwatch.unl.edu/plantdisease/wheat/barley-yellow-dwarf .
Marshall, J and Rashed, A. Barley yellow dwarf in Idaho Cereal Crops. http://www.cals.uidaho.edu/edComm/pdf/CIS/CIS1210.pdf
