Large Patch

Rhizoctonia solani AG 2-2 LP

Warm-Season Grasses Severe Fungus

Symptoms

Large, irregular to circular patches of orange-brown turf that can reach 20+ feet in diameter. The orange-brown color at patch margins is diagnostic. Most active during spring green-up and fall dormancy.

Circular to irregular patches from 3 to 25+ feet in diameter
Distinctive orange to reddish-brown color of affected leaf blades — especially at the patch margin
Patches may have a "sunken" appearance relative to healthy turf
Crown and stolon tissue can be infected, slowing recovery
Patches often appear in the same locations year after year, slowly expanding
Smoke ring may be visible in early morning on active margins

Signs

White to tan mycelium may be visible at the base of infected leaf sheaths under moist conditions
A faint "smoke ring" of dark, water-soaked grass may appear at the advancing margin of active patches in early morning
No distinct macroscopic fruiting bodies — R. solani AG 2-2 LP does not produce easily visible spore structures in the field
Infected crown and stolon tissue appears brown and water-soaked when split

Biology

R. solani AG 2-2 LP survives in thatch and soil as sclerotia and mycelium. The pathogen is most active during transitional temperatures (50–75°F) when warm-season grasses are entering or breaking dormancy and are physiologically stressed. Excessive fall nitrogen dramatically increases disease severity.

Favorable Conditions

Temperature range: 50–75°F (transitional seasons)

Soil temperatures between 50–75°F during green-up and dormancy transition
Excessive nitrogen in late summer or fall
Prolonged leaf wetness and high humidity
High-cut turf with thick thatch
Poorly drained soils

Cultural Practices

Eliminate nitrogen applications after August 1 in most climates — most critical cultural practice
Reduce thatch through core aeration and vertical mowing
Improve drainage to reduce prolonged surface wetness
Avoid evening irrigation in spring and fall
Raise mowing height to reduce stress
Apply preventive fungicides at the appropriate soil temperature trigger

Related Reports

No published reports yet for this disease.

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