Why Is My Lawn Turning Brown? A South Florida Diagnosis Guide

Brown patches in a St. Augustine lawn are the single most common complaint we hear from Palm Beach County homeowners. The frustrating part is that half a dozen very different problems all look roughly the same from the porch.

Diagnosing correctly matters, because the treatments contradict each other. Water a fungus problem more and you feed the fungus. Treat for insects when the real issue is a broken sprinkler head and you have spent money for nothing.

Chinch Bugs

Chinch bugs are the number one lawn pest in South Florida, and St. Augustine is their preferred meal. They pierce the blades and suck out the juices, so the grass yellows and then dies.

What It Looks Like

• Irregular yellow patches that turn brown and expand outward
• Damage starts in the hottest, sunniest parts of the yard
• Very often along driveways, sidewalks, and curbs where reflected heat is worst
• Grass that does not green up after watering, because the plants are dead rather than dry

How to Confirm It

Look at the thatch line first. Part the grass at the edge between green and brown, right down at soil level, and watch for small fast-moving insects. Adults are dark with light markings across the back; the young are smaller and reddish.

The reliable check is the can flush test. Cut both ends out of a coffee can, push it a couple of inches into the soil at the edge of the damage, and fill it with water. Keep it topped up for several minutes. If chinch bugs are present they float to the surface.

Treatment is best handled by a licensed applicator, who can select and apply an appropriate product and follow the label. Our pest control and lawn treatment programs monitor for chinch bugs during the hot months, when populations build fastest.

Large Patch or Brown Patch Fungus

This is a fungal disease, and it behaves very differently from insect damage.

• Roughly circular patches, often with a darker or yellow outer ring
• Patches expand outward and sometimes join into larger irregular areas
• Appears during cooler, wet stretches, so more common in the winter and shoulder seasons
• Blades pull away easily from the runner at the base, and the base looks rotted

The circular shape is the tell. Insects rarely produce neat rings; fungus spreading outward from a point does.

The first response is cultural, not chemical. Cut back watering, water only in the early morning so blades dry during the day, improve airflow by thinning overhanging branches, and avoid heavy nitrogen while the disease is active. If it keeps spreading, a licensed applicator can apply an appropriate fungicide.

Dry Spots and Irrigation Gaps

Sometimes brown grass is simply thirsty grass, and the cause is a coverage problem rather than a schedule problem.

• Browning is fairly uniform across an area rather than patchy
• Footprints stay visible after you walk across it
• Blades fold or roll inward
• The same spots dry out every time, often near a blocked or misaimed head

Run each zone and watch it. A tilted head, a head blocked by a shrub, or one sunk below grade will show up immediately. The can test described in our guide to watering a South Florida lawn will quantify how uneven the coverage is.

Dog Urine

Small, well-defined round spots, often with a ring of unusually dark green grass around the edge, usually mean a dog. The nitrogen concentration burns the center while fertilizing the margin.

Watering the area heavily right after the dog uses it dilutes the concentration. Damaged spots normally need patching once the habit is managed.

Grubs

Grubs are beetle larvae that feed on roots underground. Because they sever the roots, the tell is unmistakable: grab a handful of affected turf and pull. If it lifts away like a loose piece of carpet with no root resistance, you have a root-feeding problem.

Grubs are a less frequent cause of brown patches here than chinch bugs, so run the carpet test before assuming them. Treatment should be applied by a licensed professional, timed to when the larvae are actively feeding.

Working Through It

Start with the cheapest diagnostics. Walk the lawn and look at patch shape, check whether the grass is dry or dead, run the irrigation and watch the coverage, then do the can flush and the carpet tug. Those five minutes usually identify the culprit.

Once the cause is dealt with, thin and bare areas can be repaired with plugs or sod patches. Our guide to fixing bare spots in a St. Augustine lawn covers that, and the important part is fixing the cause first so the new grass does not go the same way.

Talk to Ocean's Edge About Your Property

Every property in Palm Beach County is a little different, and the right plan depends on your soil, your exposure, and how you actually use the yard. Call us at (561) 779-5765 or request a free on-site evaluation. We will walk the property with you, talk through the options, and put together a plan at no cost.