Viral Diseases V iruses cause a wide range of symptoms in spring wheat and barley. The symptoms that develop will depend upon the strain of virus, crop variety, and cultural environment. Viruses in small grains are mainly transmitted by feeding aphids and mites that vector the virus. Once the virus enters the healthy plant it begins to replicate itself and moves cell to cell. Small grain virus infections can induce stunting, rosetting, mosaics, chlorotic streaking, yellowing, and necrosis.
Chlorosis ranges from light green to yellow and in some instances white.
Symptoms of virus infection are difficult to distinguish from the signs of malnutrition and adverse weather effects. It is easily confused with a nutritional disorder or the effects of adverse weather. Visible symptoms are contingent upon the time of infection. Infected barley and wheat plants appear as a conspicuous yellow whereas infected oat plants have a reddish hue to their leaves. Barley yellow dwarf virus is carried by the oat birdcherry aphid and infestation coincides with large migrations of aphids.