Why Is My St. Augustine Grass Turning Yellow? (Florida Fix)

Yellow St. Augustine in Lake County almost always points to one of five things. Diagnose by pattern first — where the yellow is and what shape it makes — then act fast. A small spot today is a dead patch in two weeks.

1. Chinch bugs (#1 killer in summer)

Pattern: Irregular yellow-to-brown patches in the sunniest parts of the lawn (driveways, sidewalks, south-facing slopes). Spreads outward.

Test: Cut the bottom off a coffee can, press into the yellow edge, fill with water. Chinch bugs float up in 5 minutes.

Fix: Bifenthrin or imidacloprid treatment to the affected area plus a buffer zone. Re-treat in 2–3 weeks.

2. Iron / nitrogen deficiency

Pattern: Whole lawn (or large zones) pale yellow-green. Newest growth is the yellowest.

Fix: Liquid iron foliar spray for fast green-up (3–5 days). Follow with a slow-release Florida-friendly fertilizer (15-0-15 or similar).

3. Overwatering / fungus (Take-All Root Rot, Brown Patch)

Pattern: Circular yellow rings or patches, often in low-lying or shaded areas. Roots pull up easily.

Fix: Cut irrigation back to 2x/week. Treat with a systemic fungicide (azoxystrobin). Aerate compacted areas.

4. Dog urine

Pattern: Small round yellow spots, often with a green ring around the edge.

Fix: Deep-water the spots, train the dog to one area, reseed/patch in fall.

5. Mower scalping

Pattern: Yellow strips along high spots, after a mow.

Fix: Raise mower deck. St. Augustine should be cut at 3.5–4 inches in Florida — never shorter.

When to call a pro

If the yellow is spreading more than a foot a week, or covers more than 25% of the lawn, get eyes on it before you lose the whole yard. Our maintenance crews diagnose and treat as part of weekly service.