Brown Patch Lawn Disease: How to Identify, Treat, and Prevent It

Brown patch is a fungal disease caused by Rhizoctonia solani that attacks grass under warm, humid conditions. It appears as circular brown rings 6 inches to several feet in diameter, typically expanding after nights above 70°F when foliage is wet. Most cases respond to fungicide application and irrigation correction, but preventive treatment in late May costs significantly less than curative treatment after visible infection has spread.

What Brown Patch Looks Like #

The diagnostic pattern is a circular or roughly circular ring of brown, blighted grass. The ring often has a darker grayish-green border at its outer edge, newly infected tissue that has not yet fully browned.

In early stages, affected grass looks matted and water-soaked at the base of the blades, typically visible in the morning before dew evaporates. Blades turn tan or light brown from the tip downward, while the lower stem and crown may remain green initially.

Brown patch spreads outward from the original infection point. A ring that was 12 inches across on Monday can be 3 feet across by Friday under disease-favorable conditions. Multiple rings merge across a lawn during sustained warm, humid weather.

What Causes Brown Patch #

Brown patch requires three conditions to develop: warm temperatures, high humidity, and wet foliage overnight.

Temperature. The Rhizoctonia fungus activates when nighttime temperatures hold above 70°F for several consecutive nights. In Phoenix, Las Vegas, and Dallas, summer nights frequently stay above this threshold from June through August.

Moisture on the leaf surface. The fungus requires high humidity at the blade level. This is why Tampa and Atlanta see significantly more brown patch than drier markets. Evening irrigation is the primary controllable driver. Wet foliage overnight creates ideal conditions even when ambient humidity is moderate.

Stressed turf. Rhizoctonia moves through weakened grass faster than healthy grass. Over-fertilized lawns with excess nitrogen, over-watered lawns with shallow root systems, and scalped or compacted lawns are all more vulnerable.

Which Grasses Are Most Vulnerable #

All common lawn grasses can develop brown patch, but vulnerability varies by species and market conditions.

Most vulnerable: St. Augustine, particularly in Tampa, Jacksonville, and Orlando. Tall fescue in shaded areas of Atlanta and in transitional climates where summer heat combines with humid nights.

Moderately vulnerable: Bermuda under heavy disease pressure. Zoysia under sustained favorable conditions, though lower risk than either of the above.

Less vulnerable: Kentucky bluegrass, which is more likely to go dormant than develop active brown patch.

St. Augustine’s vulnerability stems from its broad, dense blade structure, which holds moisture longer, and its sensitivity to crown damage. Tall fescue’s risk in Atlanta stems from the combination of summer heat stress and humid nights, which weaken the grass and create ideal fungal conditions.

Brown Patch vs. Similar Lawn Problems #

Brown patch is often confused with drought stress, dollar spot, and other fungal diseases. The table below covers the key differences.

Symptom	Brown Patch	Drought Stress	Dollar Spot
Pattern	Circular rings, 6 inches to several feet	Irregular, tracks irrigation zones	Silver-dollar sized spots scattered widely
Blade appearance	Tan from tip down, matted at base	Browning throughout, no matting	Bleached tan spots on individual blades
Spread speed	Rapid (days) in humid heat	Gradual over weeks	Moderate
Most visible	Morning with dew present	Any time of day	Morning with dew present
Primary cause	Rhizoctonia fungus	Water deficit	Sclerotinia fungus

Brown patch rings that are circular and expanding after warm nights are a reliable field diagnosis. Drought stress browning tracks the geometry of irrigation zones and does not form rings.

How to Treat Brown Patch #

Step 1: Correct irrigation timing immediately. Move all irrigation to the 5-9 am window. Evening watering sustains the conditions the fungus needs to keep spreading. This is the most important intervention before any chemical application.

Step 2: Reduce irrigation frequency during active infection. Allow the top 2-3 inches of soil to dry slightly between cycles. The goal is to reduce leaf surface moisture without stressing the root zone. Do not eliminate irrigation entirely on warm-season grasses in summer.

Step 3: Apply a curative fungicide. Fungicides containing azoxystrobin, propiconazole, or thiophanate-methyl are the standard curative options for Rhizoctonia. Apply at label rates. A single application slows the spread but rarely eliminates active infection. Most curative protocols require two applications, 14-21 days apart.

Step 4: Hold fertilization during active infection. Nitrogen fertilization accelerates leaf growth and feeds the fungal spread. Resume fertilization only after the infection is visibly controlled and new growth looks normal.

Step 5: Monitor and re-treat if spread continues. An active brown patch in warm, humid conditions can outpace a single fungicide application. If rings continue expanding after 7-10 days, a second application is warranted.

How to Prevent Brown Patch #

Curative fungicide treatment for an established lawn costs $150- $ 400 per application, depending on lawn size and market. Preventive fungicide applied once in late May or early June costs the same or less and covers the full high-risk window.

Prevention checklist:

For St. Augustine in Tampa and tall fescue in Atlanta, preventive fungicide is not optional on properties with active rental tenants. A single summer outbreak that spreads before treatment generates tenant calls, potential HOA citations, and a recovery window that extends through the year’s most difficult growing conditions.

Brown Patch by Market #

Tampa and Jacksonville #

Tampa sees more brown patch outbreaks than any other Breasy market. St. Augustine is the primary grass type; the rainy season runs from June through September; and nighttime temperatures remain above 70°F for four consecutive months. Daily rainfall, warm nights, and a disease-susceptible grass type create the highest risk of fungal disease in our footprint.

Preventive fungicide in late May is standard protocol for active Tampa accounts. Irrigation timing checks run before the rainy season starts. Properties that skipped preventive treatment typically see their first outbreak by mid-July.

Atlanta #

Atlanta brown patch risk is concentrated in shaded tall fescue areas. Bermuda in full sun handles the heat without significant disease pressure, but tall fescue under tree canopy in July and August becomes vulnerable, where reduced air circulation traps humidity at the leaf surface.

Properties with shaded fescue areas in Atlanta should add a preventive fungicide to their summer maintenance contract, along with the mowing schedule adjustment.

Dallas #

Dallas sees brown patch pressure during humid stretches following storm cycles in July and August. Bermuda is moderately resistant, but Zoysia on Dallas properties can develop brown patch after consecutive days of heat above 95°F combined with post-storm humidity. Monitor for circular rings in the 7-10 days following significant weather events.

Building Brown Patch Prevention Into Your Maintenance Contract #

The most common reason brown patch becomes an expensive problem across a rental portfolio is that it is treated as a reactive event rather than a seasonal risk.

Include preventive fungicide in the standing maintenance contract for the Tampa and Atlanta accounts. Specify late May application timing. Require documentation of irrigation timing to confirm that controllers are running morning cycles before June 1.

Our lawn care service includes same-day completion photos on every visit, showing surface turf changes before they become tenant calls. Property managers who have handled a single reactive brown patch season typically want preventive protocols in every subsequent year’s contract.

Frequently Asked Questions #

What does brown patch look like on a lawn? #

Brown patch appears as circular or irregular rings of blighted, brown grass ranging from 6 inches to several feet in diameter. Rings often have a darker grayish-green border at the outer edge, representing newly infected tissue. Blades turn tan from the tip downward and appear matted in the morning before the dew evaporates.

What causes brown patch in lawns? #

Brown patch is caused by the fungus Rhizoctonia solani. It requires nighttime temperatures above 70°F, high humidity or wet foliage, and a susceptible host grass. Evening irrigation that leaves foliage wet overnight is the most controllable factor in most rental property cases.

How do I treat brown patch? #

Correct irrigation to 5-9am immediately, slightly reduce cycle frequency during active infection, and apply a curative fungicide containing azoxystrobin or propiconazole at label rates. Hold nitrogen fertilization until the infection is controlled. Most cases require two fungicide applications 14-21 days apart.

Can brown patch kill my lawn? #

Brown patch damages turf but rarely kills an entire lawn. Warm-season grasses typically recover within 3-6 weeks after infection is controlled. Tall fescue in heavily infected areas may need fall overseeding to restore full density. Delayed treatment over multiple weeks extends the recovery window and total repair cost.