Leaf blotches that are yellow, orange, or red develop until entire leaves are covered. Plants along the edges of fields are usually affected first. Severely affected plants produce little or no grain. The virus can infect all cereal grains, corn, and grass weeds. The aphids that spread yellow dwarf viruses are more active during warm conditions in the late spring and summer.
Plants infected in the seedling stage are the most severely damaged.
Early-planted oats typically suffer less yield loss because they are older during the period of the greatest aphid activity. On winter wheat, planting date has the opposite effect on yellow dwarf severity. Earlier-planted crops have more problems because aphids are still active during the seedling stage of the crop. Winter wheat planted after the Hessian fly-free date usually escapes fall infection by the virus. These crops can still be infected in the spring, but the impact of spring infection on winter wheat is usually minimal.