Any conditions that retard seed germination may result in seedling disease. Only partly filled seed will be found in the infected spikelets. The disease is not common when small grains are rotated with corn because the fungus grows on corn residue. This disease begins with dark gray, pale gray, or bluish gray lesions. Later, the lesions assume a water-soaked appearance.
Lesions are oval to oblong.
Most of the symptoms appear on the leaf blade and sheath. Helminthosporium leaf spot is the most common leaf spot of oats in North Carolina and is sometimes found on wheat, barley, and rye. Symptoms vary depending on the host and the particular Helminthosporium species causing the disease. The outer edges of the spots merge from brown to yellow or red and frequently spread over the greater part of an infected blade. Sometimes the disease does not produce well-defined spots but causes a leaf to look withered as if it has been injured by adverse weather.