Diagnosing and Managing St. Augustine Grass Diseases

St. Augustine Decline (SAD) Virus: Rare in Georgia

SAD is primarily found in Arkansas, Louisiana, Mississippi, and Texas—virtually unknown in Georgia. Symptoms include gradual yellowing and die-back over three years, spread by mowing equipment. The only control is planting resistant varieties like 'Raleigh'.

More Likely Culprits for Lawn Decline

Cold injury, hard soil, drought, soggy soil, and excess shade are far more common causes. For a definitive diagnosis, submit a sample of unhealthy (not dead) grass to your county Extension office for free analysis.

Brown Patch: The Primary Fungal Threat

Brown patch thrives on heavily fertilized St. Augustine when nights exceed 68°F and days exceed 80°F. Dead patches start small but can merge into areas over 3 feet wide, sometimes forming a "doughnut" pattern with a green center.

Brown Patch Management

• Fertilize moderately in summer.
• Irrigate in very early morning.
• Apply labeled fungicides if needed, following rates and timing precisely.

Cultural Practices to Prevent Brown Patch

• Avoid excessive nitrogen—use only enough for a reasonably green lawn.
• Water deeply (5–7 inches) only when soil is dry, between 10 PM and 10 AM.
• Don't wait for fungicides; proper fertilization, watering, and mowing are your best defense.

How to Collect a Disease Sample for Diagnosis

1. Find the disease margin where live grass meets dead grass.
2. Cut a 4×4-inch square with half live, half dead grass, including roots.
3. Keep sample cool and moist—place in an unsealed bag, refrigerate if not delivered same day.
4. Submit to your county Extension office on Monday or Tuesday for fastest lab processing.
5. Results arrive in about 10 days.