Brown Patch

Rhizoctonia solani AG 2-2

Cool-Season Grasses Severe Fungus

Symptoms

Circular, brown patches ranging from a few inches to several feet in diameter. A smoke-ring of gray mycelium may border active patches in early morning.

Circular patches of blighted turf, tan to brown, ranging from 6 inches to 3+ feet in diameter
A "smoke ring" of dark, water-soaked grass borders the active lesion in early morning
Individual leaf lesions are tan with a brown margin and yellow halo
Crown and roots generally remain alive — recovery occurs when temperatures moderate
On tall fescue, patches can be very large and irregular

Signs

Gray to brown "smoke ring" of mycelium visible at the outer margin of active patches in early morning — disappears as dew dries
Basidia and basidiospores not typically visible without magnification
Sclerotia (small, dark resting structures) may be found in thatch of heavily infested areas

Biology

R. solani survives as sclerotia and mycelium in thatch and soil. Spores spread via water, equipment, and foot traffic. Disease develops rapidly when night temperatures exceed 70°F during periods of high humidity. Crown tissue often survives, allowing recovery in cooler weather.

Favorable Conditions

Temperature range: 70–90°F (21–32°C) nights above 70°F

Night temperatures above 70°F with daytime highs above 85°F
Prolonged leaf wetness from rain, dew, or irrigation
High humidity and poor air circulation
Excessive nitrogen fertilization in summer
Lush, succulent growth

Cultural Practices

Avoid high nitrogen fertilization in late spring/summer — use slow-release sources
Water deeply and infrequently in early morning
Improve air circulation through selective pruning of surrounding vegetation
Raise mowing height during heat stress periods
Avoid evening irrigation
Core aerate to reduce compaction and improve drainage

Related Reports

No published reports yet for this disease.

Reports will appear here as they are peer-reviewed and published.