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. Infection sites can appear as stunted yellow single plants or as groups or clusters of yellow plants among healthy plants. This disease can be confused with aryloxyphenoxypropionate, benzonitrile, imidazolinone, and sulfonylurea herbicides. See photos 42 and 43.