Large patch

Large circular patches (0.3–3 m+) that are yellow-to-orange at the advancing margin, often with reddish-brown rotted leaf sheaths at the base.

Symptoms of large patch include circular patches of dead or dying grass, with an outer ring that appears reddish-brown, and the patches often occur in the same spot annually.

Hyphae at the sheath/stem base, not much mycelium

R. solani, is a pathogenic fungus that causes large patch disease in warm-season grasses. The fungus belongs to anastomosis group 2-2 LP, which is characterized by a dark brown, pigmented network of mycelium. The mycelium produced by R. solani does not have clamp connections but has constricted hyphae near the right angle branches. R. solani is a soilborne fungus that infects the roots, crowns, and lower leaf sheaths of the grass plants. The fungus can survive in the soil for long periods of time as sclerotia or thick-walled mycelia.

Large patch is most severe in poorly drained soils and is most likely to occur during cool, wet weather in the spring and fall. The disease is favored by temperatures between 68-77F and high relative humidity above 90%. Additionally, when there is abundant precipitation or irrigation, the risk of infection increases, leading to the formation of large patches quickly.