Brown Patches in Your Lawn? How to Tell What's Causing Them

A lawn that was green last month and now has brown patches is frustrating, especially because the patches look alike from the porch. The short answer: brown patches usually come from grubs, fungus, drought or heat stress, dog urine, mower scalping, or fertilizer burn — and the patch shape, whether the grass pulls up easily, and recent yard events will usually point you to the right cause before you spend money on the wrong fix.

Start with the pattern, not a product

Walk the lawn and look closely. The pattern is your best clue, and it costs nothing.

• Round or irregular patches growing outward: often fungus or grubs.
• Patches in the same spots every year, or along a dog route: often dog urine or wear.
• A wide area browned all at once after a hot, dry stretch: usually drought or heat stress.
• Brown stripes, or a section browned right after mowing or fertilizing: often scalping or fertilizer burn.
• Patches in low spots or damp, shady corners: often fungus, since damp grass stays wet longer.

Also note the edges. Fungus patches often have a darker ring or a faint gray or pink tint in the morning dew. Drought-stressed grass looks dull and bluish-gray before it turns brown, and footprints linger after you walk across it. Dog spots tend to be small and sharply defined, sometimes with extra-green grass around a dead center — urine nitrogen burns the middle and feeds the edge.

Grubs: the tug test

Grubs are beetle larvae that feed on grass roots just below the surface. Grub damage often looks patchy and wilted even when watered, and usually shows up in late summer, when grubs feed actively.

Try the tug test: grab brown grass and pull gently. If it lifts like a loose carpet, with little root holding it down, grubs are a strong suspect. Peel back a square foot of turf at the edge of a patch and count what you find near the surface. A handful of grubs per square foot is generally worth treating; one or two is normal and rarely the cause of widespread browning.

If you confirm grubs, a grub-control product applied per its label is the usual fix, watered in afterward. If the grass lifts easily but you find no grubs, keep looking: the roots may have rotted from fungus or excess moisture.

Fungus: look for rings and morning signs

Lawn fungus thrives when grass stays wet — humid nights, evening watering, or poor air circulation in shade. Common patterns include rings of brown grass, patches with a darker border, or blades with spots.

Check the lawn early in the morning — some fungi show a fine web-like growth or grayish cast that vanishes by midday. Frequent light watering instead of a deep soak also favors fungus, keeping blades wet and roots shallow.

The first fix for suspected fungus is cultural, not chemical: water in the morning so grass dries during the day, avoid daily watering, and mow at the right height so air moves through the turf. Fungicides work best matched to the specific fungus, so if patches keep spreading after a week or two of better habits, get an identification from a lawn pro rather than guessing at a product.

Drought and heat stress: the whole lawn talks at once

Drought stress rarely shows up as one neat patch. It usually hits the sunniest, thinnest, or most compacted parts first — south-facing slopes, areas near driveways and sidewalks that radiate heat, and spots with shallow soil. The grass wilts, footprints linger, and the color fades from green to dull gray-green to brown.

The screwdriver test helps: push a screwdriver into the soil in a brown area and in a green area. If it goes in easily in the green area and barely dents the brown one, the brown area is dry and possibly compacted. The fix is a deep soak, once or twice a week, wetting the soil several inches down — far better than a daily sprinkle. Brown does not always mean dead: dormant grass often greens up within a couple of weeks of consistent watering, while grass killed by grubs or disease usually does not.

Dog urine, scalping, and fertilizer burn

These three come from normal yard use, and they are also the easiest to fix.

Dog urine leaves small, round, straw-colored spots, often with a green ring. Water the spot right after the dog goes to dilute the nitrogen. Reseeding a dog spot without changing the habit just sets up the same spot again.

Mower scalping happens when the mower cuts too low, especially on uneven ground or when tall grass loses over a third of the blade at once. Scalped areas look brown and ragged, often in stripes or on high spots. Raise the mowing height, mow more often during fast growth, and never cut more than about a third of the blade at a time.

Fertilizer burn shows up as brown stripes or patches a few days after fertilizing, especially if granules were spread unevenly, spilled in one spot, or applied to dry grass without watering afterward. Water the area deeply to flush excess salts from the root zone, and do not fertilize again until the grass recovers. Next time, spread at the labeled rate with a spreader and water after applying.

What to fix first

When several causes are possible, work in this order:

1. Rule out water first. Do the screwdriver test. Water problems are the most common and the cheapest to fix. 2. Do the tug test for grubs. It takes two minutes and settles the grub question before you buy anything. 3. Look for a recent event. Did you mow very short, fertilize, or have a long wet spell? A cause matching the timing is usually the right one. 4. Change one habit at a time. Water in the morning, raise the mower, or dilute dog spots — then give it a week. 5. Reseed only after the cause is handled. Seed in grub-damaged soil, an active fungus problem, or a dog spot still in daily use will fail like the old grass did.

When to stop and call a pro

Most brown patches are a do-it-yourself diagnosis, but get help if patches spread fast, the whole lawn thins despite water and reasonable care, you find heavy grub counts in many areas, or you suspect a fungus you cannot identify. A lawn pro can identify the fungus or pest, test the soil, and tell you whether the grass is dormant or dead — which decides whether you water and wait or reseed.

Call a pro before applying any restricted pesticide or fungicide, and always follow the label exactly, including keeping children and pets off treated areas for the stated time. Mention septic systems, wells, or nearby water before anyone treats the lawn.

On ZIP Pros, describe the patches once — shape, whether the grass pulls up, and what changed lately — and get free quotes from local lawn care pros.