St. Augustine Grass: Common Problems and How to Fix Them

St. Augustine grass is the king of Florida lawns — lush, dense, and beautiful when it's healthy. It's also one of the more finicky grass types out there. If you're a Florida homeowner, you've probably already experienced at least one St. Augustine crisis.

Here's a rundown of the most common problems and exactly what to do about each one.

Chinch Bug Damage

What it looks like: Irregular yellowing and browning that usually starts along sidewalks, driveways, or hot sunny edges of the lawn. The damage expands outward as the bugs spread. Looks like drought stress but doesn't respond to watering.

How to confirm it: Part the grass at the edge of the damaged area and look at the soil level. You'll see small (1/6 inch) black bugs with white wings scrambling around. You can also do a "float test" — press a coffee can into the soil at the damage edge, fill with water, and watch for bugs floating to the surface.

The fix: Bifenthrin (granular or liquid) is the most reliable treatment. Apply to the entire lawn, not just the damaged area, since bugs spread. Re-apply in 3–4 weeks. Water the lawn first before applying granulars to activate the product.

Brown Patch Fungus

What it looks like: Near-perfect circular brown patches that grow outward. The pattern is the giveaway — circles, not irregular shapes. In the early morning dew, you may see grayish-white fuzzy mycelium at the edge of the patch.

How to confirm it: Pull grass from the edge of the damage. Blades will come out easily with a rotted, dark base.

The fix: Switch to morning-only watering immediately. Apply a systemic fungicide like azoxystrobin (Heritage G) or propiconazole. Repeat every 14–21 days. Be patient — recovery takes weeks.

Take-All Root Rot

What it looks like: Yellowing and thinning that starts in patches and can spread to large sections of the lawn. The grass looks yellow-green, weak, and thin rather than brown and dead.

How to confirm it: Pull up affected grass — the roots will be short, black, and rotted. Healthy St. Augustine has white, firm roots extending several inches.

The fix: This one's tricky. Peat moss applications (about 1 cubic yard per 1,000 sq ft) help by acidifying the soil, which suppresses the fungus. Propiconazole or azoxystrobin fungicides applied in spring and fall can help manage it. Avoid heavy nitrogen fertilization which feeds the fungus.

Gray Leaf Spot

What it looks like: Small olive-gray to brown spots on individual grass blades, often with yellow halos. Heavy infections make the whole lawn look thin and stressed.

How to confirm it: Look closely at individual blades. The spots have a distinct oval or diamond shape.

The fix: This is a warm-weather fungus that hits hardest when you fertilize during summer heat. Stop any nitrogen applications. Apply propiconazole or mancozeb fungicide. The disease usually backs off when temperatures drop in fall.

Drought Stress

What it looks like: Grass blades fold in half lengthwise (they're trying to conserve moisture). The lawn turns a blue-gray color before going brown. Footprints stay visible for several minutes after walking on it.

The fix: Water! But do it correctly — deep and infrequent beats shallow and frequent. Florida lawns need about ¾ to 1 inch of water per week, ideally in a single deep watering in the morning.

Nutritional Deficiencies

Iron deficiency: Yellow-green color, especially in newer growth. Very common in Florida's alkaline soils. Fix: liquid iron supplement or chelated iron granules.

Nitrogen deficiency: Pale green or yellow color across the whole lawn. Fix: balanced slow-release fertilizer (15-0-15 or similar is popular in Florida).

Potassium deficiency: Drought stress symptoms even with adequate water. Tip burn on blade edges. Fix: potassium sulfate or a fertilizer with high K (the third number on the bag).

Thatch Buildup

What it looks like: A spongy, bouncy feeling when you walk on the lawn. Poor response to fertilizer and water. Increased pest and disease problems.

How to check: Plug out a section of turf. If the brown layer between the soil and green grass is more than ¾ inch thick, you have a thatch problem.

The fix: Power dethatch in spring or fall when the grass is actively growing. It looks brutal (the lawn looks destroyed for two weeks), but St. Augustine recovers quickly.

Proper St. Augustine Care Calendar

Spring (March–May): Fertilize once, apply pre-emergent for weeds, watch for first chinch bug activity as temperatures climb.

Summer (June–August): Minimal fertilization (no heavy nitrogen), watch for fungal disease, maintain consistent mowing at 3–4 inches.

Fall (September–November): One more round of fertilizer (low-nitrogen, higher potassium), best time to overseed thin areas.

Winter (December–February): St. Augustine goes semi-dormant. Don't fertilize. Water only when there's no rain for 3+ weeks.

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