Problem: Yellow Patch
Rhizoctonia cerealis, the fungus that causes yellow patch, is especially destructive to Kentucky bluegrass, annual bluegrass, and creeping bentgrass. Tall fescue, perennial ryegrass, bermudagrass, and zoysiagrass are less severely affected. An attack of the fungus disease yellows these grasses for several weeks, but they usually recover. Wet weather between 40°F and 60°F favors yellow patch. Temperatures below 40°F or above 75°F can eliminate symptoms. Yellow patch can easily be mistaken for necrotic ring spot.
Regular mowing, thorough irrigation, and careful use of fertilizer help prevent yellow patch. Most fungicides are ineffective against the disease. In severe cases, plant seeds of a resistant strain of Kentucky bluegrass in affected areas. Ask your supplier for a strain suited to your region.