Brown patch is a fungal lawn disease that creates circular patches of dead grass. It thrives in overly wet lawns, so it’s most prevalent during warm, humid weather when nighttime temperatures exceed 60 °F and grass routinely stays wet for 10-12 hours or longer.
In this guide, we’ll talk about how to identify brown patch symptoms, the causes, and susceptible grass types. Once you’ve confirmed what’s invading your grass, check out our guide on “How to Get Rid of Brown Patch Fungus” to rescue your lawn.
Signs and symptoms
If you wake up to white, cotton-like webbing across your grass, making your lawn look like spiders have invaded your lawn, you’ve likely got brown patch fungus. This fungal growth, called mycelium, shows up on humid mornings and signals it’s time to act fast because this lawn disease spreads quickly.
Early warning signs
A telltale sign of brown patch is small, dark, or translucent spots on grass blades. Look for tan lesions with dark brown borders on grass blades where the fungus is actively attacking your turf. Gray-green wilted areas often appear before turning brown.
Advanced symptoms of fungal growth are circular patches ranging from 6 inches to several feet wide. These areas turn brown, tan, or yellow as the grass dies, with the blades staying upright rather than matting down.
Quick test: Pull on brown grass. Brown patch-infected grass breaks at the crown, while drought-stressed grass stays firmly rooted.
Causes of brown patch disease
Brown patch develops when:
- High nighttime temperatures are above 60 degrees Fahrenheit, but significant damage occurs when warm nights persist after hot, particularly humid days.
- Too much moisture from poor drainage keeps the grass soggy, shade prevents the morning dew from drying quickly, or watering too late in the day keeps the grass wet all night. Check out our guide to Lawn Drainage Solutions to stop water buildup.
- A lawn gets too much nitrogen fertilizer, has low phosphorus and potassium levels, or a thick layer of thatch.
Daniel Banting, vice president of Operations at Native Pest Management, warns about a critical mistake: “Nitrogen is like adding gasoline to the fire and will cause the brown patch to quickly spread. Also, make sure that you, your landscapers, or pest company do not apply any fertilizer containing nitrogen when brown patch is present.”
My tip: Keep an eye on areas like under trees, around sprinkler heads, or north-facing areas that get less direct sunlight, staying damp longer. Spots like these are a fungi paradise.
Regional patterns of brown patch
Brown patch strikes across the United States is predictable, with most regions seeing peak activity from May through September. Your location determines when you’re most likely to see brown patch fungus pop up.
Regional timing patterns:
- Southeast (FL, GA, SC, NC, AL): Peaks from June – August
- Mid-Atlantic (VA, MD, DE, NJ): June through early September
- Midwest (OH, IN, IL, MO, IA): Most active June – August
- Northeast (NY, PA, MA, CT): Primarily July – August
- Southwest (TX, AZ, NM, OK, southern CA): Spring (April – May) and fall (September – October) in irrigated lawns.
- Pacific Northwest (WA, OR, northern CA): Rare, but possible July-August during heatwaves.
Banting emphasizes seasonal vigilance: “Water and cold weather are breeding grounds for brown patch. Many times, you can’t prevent brown patch, and it appears in the same areas each year. One of the best things you can do is have a regular lawn service with a licensed pest company to provide regular iron and nutrients to keep the lawn healthy.”
Grass types susceptible to brown patch
Brown patch plays favorites when it comes to turfgrass. Cool-season grasses (CS) tend to suffer the most damage, while some warm-season grass (WS) varieties exhibit better resistance.
Highly susceptible grasses:
- Perennial ryegrass (CS): Most vulnerable of all turfgrasses
- Tall fescue (CS): Older varieties can suffer severe damage
- Annual bluegrass (CS): Brown patch often kills rather than damages this grass.
Moderately susceptible grasses:
- Kentucky bluegrass (CS): Is damaged but can self-heal if the fungus is treated.
- Fine fescue (CS): Types like hard, chewings, and creeping red handle the disease fairly well.
- Bermudagrass (WS): Can get brown patch, but bounces back fast during warm weather.
Least susceptible grasses:
- St. Augustinegrass (WS): Rarely affected, but can get “large patch”, a similar disease.
- Centipedegrass (WS): Shown to have good resistance to this fungus.
- Buffalograss (WS): A naturally resistant native grass.
FAQ: Brown patch
Very fast. Brown patch can expand 2–3 inches per day during warm, humid nights. A small 6-inch patch can grow to several feet within a week if left untreated. The disease spreads more rapidly when the grass remains wet for extended periods.
While both create brown areas, brown patch forms distinct circles, sometimes with a weird purplish edge, that continue to spread. Often found in damp areas, the grass pulls out easily and needs treatment to clear up. Over-fertilized areas often show worse damage.
Drought damage causes irregular patches in areas that get full sun, with no rings or borders. The grass stays in place when pulled but it is dry, crunchy, and you can see your footprints in the lawn. Recovers quickly with water and doesn’t spread to neighboring areas.
Battling back brown patch
Now that you know what brown patch looks like and why it attacks your lawn, you’re ready to defend your turf. Watch for telltale circular patches with purplish edges when it’s hot and humid. Keep your lawn healthy with proper watering, good drainage, and balanced fertilization, and brown patch doesn’t stand a chance.
If you can’t seem to win against brown patch or you’d rather spend your weekends relaxing rather than mowing your lawn, then let Lawn Love connect you with a local lawn care pro from simple lawn mowing to lawn disease and pest control, we’ve got you covered.
Main Photo: A ring of brown patch in an otherwise green lawn. Scot Nelson | Flickr | CC0 1.0
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