Why Is My St. Augustine Grass Dying? A Tampa Bay Guide

St. Augustine is the most common lawn grass in Florida, and right now a lot of Tampa Bay lawns are struggling. If yours has yellow spots, brown patches or rings, here are the most likely causes and what you can do about each one.

1. It's thirsty (start here)

Tampa Bay is in a drought. Hillsborough County is limited to watering one day a week through March 31, 2027, and only between 12:01 and 4 a.m. or 8 and 11:59 p.m. Your day depends on the last number of your address (0 or 1 Monday, 2 or 3 Tuesday, 4 or 5 Wednesday, 6 or 7 Thursday, 8 or 9 Friday). The City of Tampa has its own schedule, so check yours.

Signs your grass needs water: the leaf blades fold in half, the lawn turns a blue-gray color, or your footprints stay visible after you walk on it. When you do water, UF/IFAS recommends ½ to ¾ inch at a time, which soaks the top 8 inches of soil where the roots are. Make the most of your one day rather than a light sprinkle.

2. Chinch bugs

Chinch bugs are the number one pest of St. Augustine in Florida. They suck the juice out of the grass, leaving yellow patches that turn brown and spread outward. Damage usually starts in hot, sunny spots along driveways, sidewalks and the edges of the lawn, which is why it's easy to mistake for drought.

The clue: if watering doesn't help and the brown area keeps growing, check for bugs. Cut both ends off a can, push it 2 to 3 inches into the soil where brown grass meets green, and fill it with water. Chinch bugs float to the top within about 5 minutes.

Chinch bugs in our area have become resistant to some common insecticides, so treatment is a job for a licensed pest control company.

3. Large patch (the "circles" fungus)

If you see round patches, often a foot or more across, with a yellow or orange border, it's probably large patch. It shows up when temperatures drop below 80 degrees, usually November through May, and loves grass that stays wet. Pull a blade at the edge of the patch: if it slides right out and the base is dark and rotten, that's large patch.

What helps: water only when the grass needs it (early morning, never in the evening before a cool night), and don't put down extra nitrogen in the fall. A fungicide may be needed if it keeps spreading.

4. Mowing too short, or with dull blades

This one is easy to fix. Standard St. Augustine (Floratam, Bitterblue and similar) should be cut at 3½ to 4 inches. Mowing lower stresses the grass, keeps the roots shallow and invites bugs and disease. Never cut off more than a third of the blade at once.

Dull mower blades shred the grass instead of cutting it, which gives the whole lawn a brownish look. UF/IFAS recommends sharpening blades monthly during the growing season.

5. Other things to rule out

• Gray leaf spot: small gray or tan spots with brown edges on the blades, mostly during the summer rainy season.
• Take-all root rot: yellow, thinning patches where the roots are short and black.
• Nematodes: thin, weak grass that's slow to recover after rain, often with weeds moving in.
• Too much shade: Floratam needs at least 6 hours of sun a day.
• New sod: newly laid sod needs extra water while it roots. Hillsborough County allows new lawns to be watered any day (during the allowed hours) for the first 30 days.

A note on fertilizer

In Hillsborough County and the City of Tampa, fertilizer with nitrogen or phosphorus can't be used from June 1 through September 30. Iron-only "summer blends" are allowed. Too much nitrogen actually feeds large patch and chinch bugs, so more fertilizer isn't the fix for a sick lawn.

Still not sure?

The UF/IFAS Extension office in Hillsborough County can help identify lawn problems. For bugs or fungus, call a licensed pest control company.

Sources: UF/IFAS Extension (St. Augustinegrass for Florida Lawns, Large Patch, Southern Chinch Bug), Hillsborough County and City of Tampa fertilizer ordinances, Hillsborough County watering restrictions (September 2026).