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.