Leaf blotches that are yellow, orange, or red develop until entire leaves are discolored. 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. This disease is spread by several species of aphids, which are active under 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 than late-planted oats because they are older during the period of greatest aphid activity. Average planting date for oats in Iowa is April 20, but planting before April 15 is recommended. This year, only 4 percent of the oats were planted as of April 15. The later planting this year will result in a greater risk for losses from crown rust and yellow dwarf. Some oat cultivars also have resistance to crown rust and yellow dwarf, and it is advisable to plant these cultivars in Iowa because both diseases are potentially severe each year.