Brownpatch, a fungal disease caused by Rhizoctonia solani, presents
a serious threat to most turfgrasses each fall. With the onset of slightly
cooler temperatures and wet conditions each fall, brownpatch presents a
challenge to the professional turf manager.
Conditions most favorable for brownpatch development include (1) the presence of active fungi, (2) vigorous growth of a susceptible grass, (3) daytime temperature ranges between 75° and 85°F, (4) the presence of free moisture on the foliage, and (5) night temperatures below 68°F.
Symptoms. On warm season turfgrasses, the disease is characterized by at least two different types of symptoms. The most common symptom is a circular pattern of brown grass with a yellowish colored ring ("smoke ring") of wilted grass at the perimeter of the diseased area. The leaves can be easily pulled from the stolons within the "smoke ring" because the fungus destroys the tissue at the base of the leaf sheath. Symptoms first appear as small circular patches of water-soaked, dark grass that soon wilt and turn light brown. Stolons often remain green. As the disease develops, the circular patches enlarge, "smoke rings" become more apparent and new green leaves may emerge in the center of the circular areas.
Disease development occurs most rapidly when air temperatures are between 75° and 85° and free moisture is present. Those conditions occur most often and for longer duration in the fall. High levels of nitrogen may also increase the severity of the disease. Fungal activity generally stops when air temperatures reach 90°F.
On cool season grasses, the disease first appears as dark green, water-soaked circular patches that range from a few inches to several feet in diameter. The affected leaves wilt and turn light brown, but remain upright. A dark, grayish-black ring (smoke ring) of wilted grass often is present around the perimeter of the diseased areas in the early morning.
Control. When environmental conditions are favorable brownpatch is likely to develop on susceptible turfgrasses. The severity of the disease can be somewhat controlled by avoiding heavy applications of nitrogen during spring and fall, by watering early in the morning to remove dew and allow the grass to dry quickly and, where possible, by removing grass clippings during periods of disease activity. A number of fungicides are recommended for brownpatch control. The fungicides are most effective when used on a preventative basis as compared to their use after the disease has become well established.