Oklahoma Lawn Diseases: Identification & Treatment

Brown Patch (Rhizoctonia)

Primary target: Fescue and other cool-season grasses

Circular brown patches ranging from a few inches to several feet in diameter. Active infections show a darker "smoke ring" at the expanding edge, especially visible in the early morning.

When it strikes: Hot, humid weather (daytime 80–90°F, nighttime above 60°F) with prolonged leaf wetness. Most common June through September.

Treatment: Water in early morning only. Reduce nitrogen during hot weather. Improve air circulation. Fungicides containing azoxystrobin or propiconazole can treat active infections.

Dollar Spot (Clarireedia)

Primary target: Bermuda grass and Zoysia (can affect Fescue too)

Small, silver-dollar-sized tan spots that can merge into larger irregular patches. Individual blades show bleached lesions with reddish-brown borders. May see white, cobweb-like fungal growth in early morning dew.

When it strikes: Moderate temperatures (60–80°F) with high humidity. Often appears in spring and fall. Low nitrogen levels make grass more susceptible.

Treatment: Maintain adequate nitrogen levels. Water deeply but infrequently. Remove dew in the morning by mowing or dragging a hose. Fungicides effective if needed.

Take-All Root Rot (Gaeumannomyces)

Primary target: St. Augustine grass and Bermuda grass

Irregular yellow or light-green patches that don't respond to fertilizer or water. Roots are short, dark, and rotted. Grass pulls up easily because roots are dead.

When it strikes: Spring and fall during mild, wet weather. Alkaline soil pH (common in Oklahoma) makes it worse.

Treatment: Improve drainage. Apply sulfur to lower soil pH. Avoid excessive nitrogen. Focus on prevention and building overall lawn health.

Spring Dead Spot

Primary target: Bermuda grass

Circular dead patches that appear in spring when Bermuda greens up. Patches are completely dead, not just slow to green. Often recur in the same spots year after year, sometimes getting larger.

When it strikes: The fungus infects roots in fall and winter. Damage becomes visible in spring. Cold, wet winters followed by late spring freezes worsen the problem.

Treatment: Reduce thatch. Improve drainage. Avoid excessive nitrogen in late summer. Fungicide in fall (before dormancy) can help. Affected areas usually fill in by mid-summer.

Fairy Ring

Primary target: All grass types

Circular or arc-shaped rings of dark green grass, dead grass, or mushrooms. Rings expand outward each year. Caused by fungi feeding on decaying organic matter in the soil.

When it strikes: Usually after wet weather in spring through fall. Often found in lawns with buried organic debris (old tree roots, construction lumber).

Treatment: Difficult to control. Core aeration helps water penetrate. Remove mushrooms when they appear. Fungicides have limited effectiveness. Patience is often the best approach — rings eventually exhaust their food source.

Water Correctly

Early morning only. Deep and infrequent. Most diseases need wet conditions to spread and thrive.

Don't Over-Fertilize

Excess nitrogen promotes lush growth that is more susceptible to disease infection.

Improve Air Circulation

Trim overhanging branches and shrubs that block airflow around your lawn.

Mow Properly

Use sharp blades, correct height, and follow the 1/3 rule to reduce grass stress.

Aerate Annually

Reduces thatch and compaction, improving overall lawn health and disease resistance.