Brown Patches in Your Lawn: 3 Causes and How to Tell Them Apart
Kelly Smith Trimble brings practical gardening knowledge and experience explaining how plants grow and thrive. Her interests include vegetable growing, seasonal garden care, and the everyday decisions that help gardeners make the most of their outdoor spaces.
Quick answer
Brown patches usually come from drought dormancy, fungal disease like brown patch, or white grub root damage. Each cause leaves different clues you can spot. Check the patch shape and the time of year. See if the grass pulls free from the soil easily. Looking at these clues before you treat saves time and money.
The Three Most Common Reasons for Brown Patches
Brown patches in a lawn almost always trace back to one of three things: the grass going dormant from heat or drought, a fungal disease, or white grubs chewing through the roots underground. Fungal disease is most often brown patch or large patch. All three can look similar from a distance, but a few simple close-up checks tell you which one you have.
Dormancy: Brown Grass Is Not Always Dead
One of the most common misconceptions in lawn care is that brown grass is dead grass. It usually isn’t. Both cool-season and warm-season grasses go dormant when conditions get tough, and they turn brown in the process.
Cool-season grasses grow best in spring and fall. Common types include Kentucky bluegrass, tall fescue, fine fescue, and perennial ryegrass. During a summer heat wave or dry spell, they slow down and can turn brown. According to NC State Extension, Kentucky bluegrass can turn brown in a two- to four-week summer drought and still recover well without watering. Tall fescue can also survive short dry spells, though a drought lasting more than three weeks may cause some loss.
Warm-season grasses follow a different pattern. Common types include bermudagrass, zoysiagrass, centipedegrass, and St. Augustinegrass. They go dormant after the first heavy frost in fall, turn brown, and stay that way until they green up the following spring. That winter brown color is completely normal. If you are not sure about your grass type, cool-season or warm-season, that difference shapes every decision about timing and treatment.
What to check: If the browning follows a dry stretch or a frost, and the grass blades are intact (not rotted or spotted), dormancy is the most likely explanation. Avoid fertilizing dormant grass — it stresses the plant further without helping recovery.
Fungal Disease: Circular Patches With Specific Clues
Brown patch and large patch are caused by different strains of the same fungal pathogen, according to Clemson Extension. The pathogen is called Rhizoctonia solani. Brown patch affects cool-season grasses, and large patch affects warm-season grasses. These are among the most common and damaging turf diseases in the United States.
What the patches look like
Fungal patches are typically circular and range from a few inches to several feet across. Sometimes the center of the patch recovers while the fungus moves outward, creating a doughnut shape. On cool-season grasses like tall fescue, you may see a smoky brown ring at the active edge of the patch, especially in the early morning. On warm-season grasses, the leaf sheaths near the soil surface rot rather than showing spots on the blades. If you tug gently on the discolored grass at the patch edge, the blades pull free easily. That easy pull is a diagnostic sign of large patch disease.
When it happens
Brown patch on cool-season grasses typically starts in late spring and continues through summer. Large patch on warm-season grasses is most active in fall and again in spring during green-up, though symptoms are often most visible in spring. The disease spreads fast when leaves stay wet — more than 10 hours of continuous leaf wetness is especially favorable for it.
Cultural steps that reduce fungal disease
- Water in the morning so leaf blades dry out during the day, not overnight.
- Aim for about 1 inch of water per week (roughly 623 gallons per 1,000 sq ft), watering deeply rather than lightly and often.
- Avoid excess nitrogen on cool-season grasses in late spring and summer, and on warm-season grasses in mid-to-late fall or early spring before full green-up. Lush, fast-growing grass is more vulnerable to fungal attack.
- Mow at the right height. Clemson Extension notes that mowing too low or too high both increase disease severity — too low stresses the plant, too high slows leaf drying. For tall fescue, stay between 2.5 and 3.5 inches. For centipedegrass, 1.5 to 2 inches. See recommended mowing heights by grass species for other types.
- Core aerate to reduce compaction and improve drainage. Lawn aeration also helps reduce thatch, which traps moisture near the crown.
- Get a soil test and follow its recommendations. Disease can get worse when soil pH drops below 6.0. Centipedegrass is an exception — it prefers more acidic soil.
Fungicides are available for brown and large patch, but they can be hard to rely on in home lawns. If you use one, rotate between active ingredients to reduce resistance risk. Always follow the product label — label directions are legally binding under US federal law. Brand recommendations from extension publications reflect local conditions and local rules about which products are allowed. Check your local extension office for current guidance.
White Grub Damage: When the Grass Lifts Like a Rug
White grubs are the larvae of scarab beetles. Larvae are the young, worm-like stage of an insect. Common types in the southeastern US include Japanese beetles, masked chafers, May and June beetles, and green June beetles. They feed on grass roots underground. A heavy infestation can cut through enough roots that the turf dies in irregular patches.
Signs that point to grubs
- The damaged turf wilts quickly and turns yellow or brown.
- The soil beneath feels spongy.
- You can peel back the sod like a loose carpet because the roots are gone.
- You may notice skunks, raccoons, or armadillos digging in the lawn — they’re hunting grubs.
How to check
Cut three sides of a 12-inch square with a shovel, pry the flap back, and inspect the root zone and the top 1–3 inches of soil. Count the grubs. According to Clemson Extension, healthy turfgrass that is not under stress can generally tolerate 5–7 grubs per square foot. Stressed turf may show damage at lower numbers. Sample several spots across the lawn, since grubs tend to concentrate in certain areas.
Drought conditions and hot weather can make grub damage look worse than the grub count alone would suggest, because the weakened root system can’t compensate for heat stress.
If you confirm a grub problem, you have two main product types to choose from. Preventative products are applied in spring. Curative products are applied in summer when grubs are small and near the surface. These two types work differently, so picking the right one for your timing matters. Granular products must be watered in right after application. Read and follow all label directions — rates and timing vary by product and active ingredient.
Comparing the Three Causes at a Glance
| Cause | Patch shape | Key clue | Typical timing |
|---|---|---|---|
| Drought dormancy | Irregular, follows dry or sunny areas | Blades intact; follows dry spell or frost | Summer heat or after first frost |
| Fungal brown/large patch | Roughly circular, few inches to several feet | Smoky ring at edge; blades pull free on warm-season grass | Late spring–summer (cool-season); fall–spring (warm-season) |
| White grub damage | Irregular; sod lifts easily | Spongy soil; grubs visible in root zone | Late summer–fall most severe |
The Shared Principle: Healthy Turf Resists All Three
Whether the problem is drought stress, fungal disease, or grubs, a well-managed lawn handles it better. Water deeply and infrequently rather than a little every day. Mow at the correct height for your grass type, fertilize at the right time and rate, and keep thatch and compaction in check through core aeration. A soil test is the most reliable way to know if pH or nutrient levels are making your lawn more vulnerable. Apply lime or fertilizer only based on what the test shows, not a general schedule.
The one thing to avoid: treating for the wrong cause. Applying a fungicide when grubs are the problem, or watering more when the grass is already sitting in excess moisture, makes things worse. Take five minutes to check the patch up close before deciding on a next step.
Frequently asked questions
Can brown patch fungus spread to the rest of my lawn during mowing?
Yes, it can. Clemson Extension recommends removing clippings when weather is warm and moist. Let morning dew dry before you mow. Mow diseased areas last to reduce the chance of spreading the fungus to healthy turf on the same pass.
Should I water my lawn more if it turns brown in summer?
It depends on the grass type. Kentucky bluegrass recovers well from a two- to four-week summer drought without extra watering, and too much water can increase disease problems. Tall fescue may need irrigation if drought goes beyond three weeks. Find out your grass type before adding more water.
How many grubs per square foot actually require treatment?
According to Clemson Extension, healthy turfgrass not under stress can generally tolerate 5–7 grubs per square foot. Stressed turf may show damage at lower counts. For Japanese beetles specifically, 6–8 grubs per square foot is suggested as a safer treatment threshold for healthy turf.
Does mowing height affect how likely brown patch disease is to develop?
Yes. Clemson Extension states that mowing too low stresses the plant and increases disease severity. Mowing too high slows leaf drying and keeps the canopy wet longer. Both conditions favor fungal spread. Staying within the recommended height range for your grass type is one of the simplest preventive steps.
Will warm-season grass that turns brown in fall come back in spring?
In most cases, yes. Warm-season grasses like bermudagrass, zoysiagrass, and centipedegrass go dormant after the first heavy frost and turn brown. They green up again the following spring. This is normal dormancy, not death, as long as the crowns were healthy going into winter.
Sources
- Brown Patch & Large Patch Diseases of Lawns · Home & Garden Information Center (hgic.clemson.edu)
- Carolina Lawns: A Guide to Maintaining Quality Turf in the Landscape | NC State Extension Publications · content.ces.ncsu.edu
- White Grub Management in Turfgrass · Home & Garden Information Center (hgic.clemson.edu)
Prepared from these references and checked against them. References retrieved October 11, 2026.
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