Bentgrass, annual bluegrass, and bermudagrass are damaged more than coarser bluegrass, fine-leaved fescue, and ryegrass. Creeping bentgrass is particularly susceptible when cut at golf-green height and grown under a high level of maintenance. In addition, tall fescue lawns in the southern region of the state may be attacked and scorched.
Brown patch appears in two forms. On close cut bentgrass, the patches are 2 to 3 feet wide, roughly circular, and light brown. When moist, a dark purplish to grayish black ring ("smoke ring") of wilted and blighted grass blades may mark the advancing margin. This ring appears because the leaves are dying so rapidly that they seem to be dying in unison. The smoke ring disappears as the grass dries. Usually, only the leaf blades are killed. After several mowings, new but thinned-out grass appears in the affected areas. Algae often invade diseased patches and dry to form a hard crust. On high-cut lawn grass, the roughly circular, irregular patches are light brown, matted down, and up to about 2 feet wide. The patches sometimes develop green centers and may resemble the "frogeyes" of summer patch and necrotic ringspot. Diseased patches of grass, however, often appear to be sunken. The appearance of the smoke ring borders is rare in this type of turf.
Usually only the leaf blades are killed. However, in severe and repeating epidemics, particularly in the southern third of Illinois, the turf may be thinned or killed due to crown, rhizome, stolon, and root decay. Enzyme-linked immunosorbent assay (ELISA) kits are available to quickly and accurately identify this pathogen in the field.
Brown patch is also known as Rhizoctonia blight, Rhizoctonia leaf and sheath blight, and large brown patch of zoysiagrass. It is common in dense, highly fertilized turfgrass, during extended periods of hot, moist, overcast weather when the temperature at night is above 68 F and the leaf surfaces are covered with water.
Avoid excess nitrogen and improve air movement to the area by trimming trees and shrubs. Remove dew and guttation fluids from the leaf surfaces in the early morning by mowing, brushing the grass with a long limber pole, or by dragging a mat, hose, or rope across the turf. Preventive applications of fungicides may be needed in extreme cases, especially for bentgrass cut at golf-green height and for which a history of disease exists. If you have had brown patch in a turf, apply the first spray when the night temperature is expected to remain at 66-70 F, the daytime temperature is 82 F or above, and the air is near the saturation point for 8 hours or longer. Repeat applications are needed at 5- to 14-day intervals during hot, humid weather.