Identifying grass fungus involves looking for specific signs and symptoms on the blades, stems and roots of the grass, according to University of California Statewide Integrated Pest Management Program. These signs include leaf spots, yellow leaves, thin or stunted growth, and a powdery white coating on the blades.
The first signs of grass fungus are usually small patches of dead or dying grass, however, these signs can be caused by numerous other problems. Other signs of fungus include rotting roots or damage that takes a specific "frog's eye" pattern, with a ring of dead grass surrounding a circle of still green grass. Almost all grass diseases are caused by pathogenic fungi, according to the UC IPM.
Although most fungi are microscopic, some species of fungus do have visible parts, such as spore masses, sporophytes, mycelium and occasionally mushrooms, states North Carolina State University Department of Plant Pathology. Spore masses are usually seen as fuzzy growths on the surface, while the mycelium is a cottony, spider web-like mass that grows underneath the ground. The sporophytes are usually visible as small black spots on the blades of grass. Most disease-causing grass fungi don't produce mushrooms, with the notable exception of the fairy ring fungi.