The name sharp eyespot describes the symptom which is a conspicuous lesion on the lower leaf sheath and culm. The centers of these eyespots are pale to straw-colored and often studded with dark mycelium. The margins are dark brown. Small black compact masses of hardened mycelium, known as sclerotia, may develop in the space between the culm and leaf sheath. As plants mature, infected tillers die prematurely, producing white heads with shriveled kernels.
Diseased tillers are also prone to lodging.
The Fungus Rhizoctonia cerealis produces no spores, but lives on crop residues and in the soil as mycelium and as small resistant structures called sclerotia. This fungus differentiates into hardened mycelial masses or sclerotia, on host plants and in culture. The sclerotia, which are very small and irregular in shape, germinate to form mycelia. Rhizoctonia cerealis is the name given to the asexual state of this fungus, characterized by white to brown mycelium, the presence of sclerotia and the absence of spores. This fungus has been found to have a sexual stage, known as Ceratobasidium, but the Ceratobasidium stage is not important in the disease cycle.