Leaf and sheath spot

Diffuse yellow-to-bronze thinning across the lower canopy of bermudagrass putting greens, without the distinct ring pattern sometimes seen with this same pathogen (compare Mini ring). Older leaf sheaths, stolons, and nodes become necrotic under disease pressure; the leaf blades themselves are rarely lesioned directly.

Yellowing or bronzing of turf in diffuse patches, sometimes ranging from about 3 to 24 inches across, most noticeable in the lower canopy. Lower, older leaves may appear bleached or damaged. In severe cases the leaf sheaths, stolons, and nodes become necrotic, though distinct lesions on the leaf blades themselves are uncommon. Symptoms peak from late July through October and can linger into spring.

Diagnosis typically requires lab culturing to confirm Waitea circinata var. zeae, since above-ground signs such as mycelium or sclerotia are not consistently visible in the field.

Leaf and sheath spot is caused by the basidiomycete Waitea circinata var. zeae, long known as Rhizoctonia zeae. Unlike many foliar Rhizoctonia diseases, this pathogen colonizes leaves and sheaths as well as roots and other below-ground tissue, which is part of why fungicide applications must be watered in to reach the infection site. Its complete disease cycle and epidemiology are still not fully understood.

Most active during the heat of summer (July-September) when canopy temperatures reach 83-97 F, with symptoms often becoming most visible as growth slows in late summer and fall. Mechanical damage and low nitrogen fertility amplify symptom expression; the disease can persist at low levels into spring.