Cause The soilborne fungus, Rhizoctonia cerealis, can infect barley, wheat, and rye. It overwinters as sclerotia in soil or debris as well as persists as mycelium in litter. Long rotations in susceptible grasses can increase pathogen to severe levels. Cool, moist conditions at the plant's base favor infection. Well-drained soils enhance subsequent pathogen growth and disease development. Later, sclerotia develop, perpetuating the pathogen population.
Symptoms Light brown to straw-color, elliptical (lens shape) to round lesions develop on the leaf sheath. Lesions may be up to a half-inch long and are surrounded by a dark brown, sharply delineated border. A characteristic hole is left when affected tissues rot away. Lesions resemble those of eyespot (see Wheat-Eyespot) but sharp eyespot lesions are more clearly delineated, develop later, and are found higher up on the plant, around 1 foot above ground, compared to lesions produced by eyespot (also known as strawbreaker foot rot). Whitish mycelium is often present beneath the culm lesion and this is where whitish to dark-brown, irregularly-shaped sclerotia develop during the summer. White heads (premature ripening) and lodging are apparent when disease is severe.
- Rotate with a legume or other nonhost.
- Delay fall planting of winter barley.
Chemical control Fungicide sprays are effective if sharp eyespot is known to be severe in the area.
Reference Mathre, D.E. 1997. Compendium of Barley Diseases, 2nd ed. St. Paul, MN: APS Press.