Why does my lawn have brown patches in summer? Causes and fixes
Key takeaways
- The three most common causes of summer brown patches are drought stress, insect damage, and fungal disease.
- A 6-inch screwdriver pushed into the soil tells you whether the lawn is getting enough water.
- Water deeply two to three times per week, about 1 inch total, and mow tall fescue at 2 to 3 inches.
Do not guess: diagnose first
It is easy to blame the heat when brown patches appear. But heat is only one of several suspects. Taun Beddes, a horticulturist with Utah State University Extension, lists the three most common causes of browning lawns as drought stress, insect damage, and fungal disease.
Each one needs a different fix. Watering a grub problem makes it worse. Treating drought with fungicide wastes money.
So the first step is always diagnosis, and Beddes offers a three-step process that any homeowner can run in an afternoon.
This article takes a closer look at why lawns develop brown patches in summer, including the three main causes, how to tell them apart, the watering and mowing habits that prevent them, and how to repair damaged turf.
Cause 1: drought stress
Drought stress is the most common reason lawns brown, according to Beddes. It comes from underwatering, poor sprinkler coverage, broken heads, or clogged filters. The patch pattern often follows sun exposure: the sunniest areas go brown first.
The screwdriver test. Push a long screwdriver or piece of rebar, at least 6 inches long, into the soil a few hours after watering. If it slides in easily to 6 inches or more, the lawn is getting enough water. If it resists, the area is drying out between irrigation cycles.
The watering fix. Most homeowners water too often and not deeply enough. Shallow daily watering keeps roots near the surface, where summer heat dries them fast. Beddes recommends watering deeply but infrequently, typically two to three times per week, and letting the soil dry moderately between cycles. Water should reach at least 6 inches deep.
The University of Georgia Extension puts a number on it: turfgrass needs about 1 inch of water per week, ideally in one or two applications. Water early in the morning so the foliage dries before nightfall. Evening watering leaves leaves wet overnight, which invites disease.
Check the system. If brown patches persist despite watering, walk the irrigation system. Look for broken heads, leaks, and clogged filters. Isolated dry spots that never improve often point to a sprinkler problem, not a weather problem.
Cause 2: insect damage
If the soil is moist but the grass pulls up easily with little root attached, insects are the likely cause. White grubs, billbugs, and sod webworms chew through roots, leaving the turf with nothing to hold onto. Beddes notes these pests are most active from late June through midsummer.
To check, peel back a section of the brown turf. C-shaped white larvae under the surface point to grubs. Birds or skunks digging in specific spots are another clue: they are after the larvae.
Timing matters for treatment. White grubs and billbugs are hard to control once symptoms appear. Preventative treatments go down in late spring or early summer.
Sod webworms, by contrast, can be managed with post-emergence insecticides after they show up.
BobVila's lawn guide lists grubs among the top causes of brown spots, and notes that dull mower blades, thatch, and over-fertilizing can produce similar-looking damage. That is why the tug test matters: roots that lift away with no resistance mean pests, not drought.
Cause 3: fungal disease
If the soil is moist, the grass stays well rooted, but still looks brown or wilted, a fungal disease may be to blame. The best-known summer culprit is brown patch, caused by the fungus Rhizoctonia solani.
Brown patch forms circular patches from a few inches to several feet across during hot, humid weather. The University of Georgia Extension says it strikes when humidity is high and temperatures sit between 75 and 85 degrees Fahrenheit. Brown areas are surrounded by a reddish-brown or purplish halo.
After two to three weeks, the center may turn green again, leaving a doughnut-shaped ring of dead grass.
It attacks most turfgrasses, including bermudagrass, tall fescue, centipedegrass, and zoysiagrass, and no variety is fully immune. Conditions that favor it include excess nitrogen fertilizer, frequent watering, watering late in the day, and high humidity.
Prevention is mostly cultural. Do not over-apply nitrogen. Water early in the morning, deeply and infrequently.
Mow slightly higher during heat waves to reduce stress. Remove excess thatch: more than half an inch retains moisture and favors disease. Sharp mower blades matter too, since torn grass tips brown faster and open wounds invite infection.
Other causes worth checking
Dog urine. Urine burns small round spots into the lawn. The fix is quick action: soak the area with plenty of fresh water to dilute the salts, then reseed if the grass is dead. Reseeding works best after scratching up the dead grass and covering the seed with fresh soil.
Fertilizer burn. Too much fertilizer, or uneven spreading, produces streaks or patches that appear soon after application. Always follow the label rate. Lawns that get heavy use need three to four applications per season, while light-use lawns may need only spring and fall feeding, according to Beddes.
Mowing too short. Scalping exposes roots and heats the soil. Beddes recommends mowing at 3 to 4 inches to encourage deep rooting. The University of Georgia gives specific heights: bermudagrass 1 to 1.5 inches, zoysiagrass 1 to 2 inches, and tall fescue 2 to 3 inches, with taller cuts performing better in summer heat.
Thatch and compaction. Thatch is the layer of stems and roots at the soil surface. More than half an inch blocks water and air. Heavy foot traffic compacts the soil with a similar effect. Core aeration in spring fixes both on clay soils.
Homeowners fixing one outdoor problem often spot another. While you are out diagnosing the lawn, check garden beds too. Our guide to keeping squirrels out of garden beds covers the barriers that actually hold up.
Repairing brown patches
Once you know the cause, repair follows a simple pattern. Fix the cause first: adjust watering, treat pests, or correct the mowing height. A lawn still under stress will not take new seed.
For small dead areas, scratch up the dead grass, spread grass seed, and cover it with a thin layer of fresh soil. Keep the seedbed moist until the seedlings are up. Kentucky bluegrass and bermudagrass can also spread by runners to fill small gaps on their own.
For fungal damage, a change in weather often stops the spread, and healthy turf recovers on its own. Beddes and the Georgia Extension both recommend cultural fixes first and reserve fungicides for cases where practices cannot correct the problem. When in doubt, bring a 4-by-4-inch turf sample, half dead and half alive from the edge of a patch, to a local Extension office for diagnosis.
Frequently asked questions
Will a brown lawn turn green again?
Often, yes. Grass that is dormant from drought usually greens up when water returns and temperatures cool. Grass killed by grubs or disease will not recover on its own and needs reseeding.
The tug test tells you which you have: dormant grass stays rooted, dead grass lifts away.
How much should I water my lawn in summer?
About 1 inch per week, in one or two deep applications, is the standard guidance from university extensions. Lawns in extreme heat may need slightly more. Research cited by BobVila notes that lawn irrigation accounts for nearly one-third of all residential water use, so watering deeply and rarely also saves water.
Can mowing fix brown patches?
Mowing correctly prevents them. Never remove more than one-third of the grass height in a single cut, keep blades sharp, and mow higher in summer. For tall fescue, 2 to 3 inches in summer performs best.
Mowing alone will not cure grubs or fungus, though.
Is brown patch disease dangerous to pets or kids?
Brown patch is a turfgrass fungus, not a human or pet pathogen. It damages the lawn's appearance and health. Standard lawn hygiene, keeping children and pets off freshly treated areas per product labels, applies if you use any fungicide.
A prevention routine that works
The lawns that stay green through summer share the same habits. Water deeply two to three times per week, early in the morning, to about 1 inch total. Mow high with sharp blades.
Fertilize on a soil-test schedule, not by guesswork. Aerate compacted soil in spring.
Run the screwdriver test once a month through the hot season. It takes a minute and catches drought stress before it becomes a brown patch. Catch the cause early, and most summer lawn problems stay small enough to fix in an afternoon.
Related lawn and garden care: hardening off seedlings step by step for transplants that survive their first summer.
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