Dollar Spot — Sclerotinia homoeocarpa
Dollar spot is characterized by round, bleached-out or straw-colored spots, ranging from the size of a quarter to the size of a silver dollar. Spots appear as sunken areas in the turf, especially low mown turfgrass (0.5 inches or less). Fluffy white mycelia can be seen when fungus is actively growing during morning periods of heavy dew. Symptoms on individual grass blades appear as bleached-out or tan lesions that are often accompanied by reddish brown bands present at the outer edge of the leaf lesion (except on annual bluegrass).
Dollar spot occurs when daytime temperatures are between 59-88° F (15-31° C) and disease development is favored by warm, humid weather followed by cool nights that produce heavy dews.
Leaf Spot — Bipolaris sorokiniana
Symptoms first appear as small dark purple to black colored spots on the leaf blade. As the spots enlarge, the centers often turn light tan. In warmer temperatures (> 85° F), the entire blade often appears dry and straw colored. The disease is mostly confined to the leaf blades during the cool weather, but can infect leaf sheaths, crowns and roots during hot, humid weather.
Leaf spot is a warm-weather disease, but the pathogen overwinters as dormant mycelium in infected plants and dead grass debris. Leaf spot can become evident when temperatures reach 70° F (21.1° C). The disease is most severe when temperatures are above 90° F and humidity is high.
Red Thread — Laetisaria fuciformis
Red thread is a disease of slow growing turf. Red thread is easily recognized by the red to coral-pink fungal strands (stromata) produced on leaf blades and sheaths. When turf is wet, the fungal stroma looks gelatinous and fleshy. As the grass dries, the stroma also dries and becomes thin and thread-like. Infected turf often appears to be suffering from lack of water, often times symptoms resemble dollar spot. Under close examination of the grass blades reveals red to coral-pink stromata. Under conditions of high humidity, pink cottony flocks of arthroconidia can be seen in the patches.
Red thread occurs is favored by high humidity at temperatures between 60°-90° F (15.5° and 32° C). Cool, drizzly days of spring and fall are ideal for the development, and the disease spreads from plant to plant by growth of the stromata. These can be spread by wind, and mechanical equipment.
Rust — Puccinia striiformis
Rust diseases are characterized by yellow to dark brown urediospore infestations that, from a distance, make turf stands appear orange or yellow. These rust-colored urediospores protrude through the plants epidermis causing spots that elongate parallel to the leaf or stem axis. When rust is severe, areas of infected turf appear thin, weak and are have a red, brown, or yellow tint. Heavily infected plants may wither or die from excessive loss of moisture from rusted leaves.