St. Augustine Lawn Care: Diagnosing Brown, Straw-Like Grass and Fire Ant Issues

Understanding the Problem

A homeowner in Zone 9a reports that their St. Augustine (Floratam) lawn, previously green and growing well, has suddenly developed patches of dried, straw-like grass with only a few surviving sprigs. Daytime temperatures reach 85–88°F, while nights drop to around 55°F. The lawn is watered twice weekly and was fertilized in February with Ironite. Fire ants are also present and treated as mounds appear.

Expert Analysis

The straw-like appearance indicates the grass is dead, not merely dormant. Temperature fluctuations between 55°F nights and 85–88°F days are not cold enough to cause such damage; St. Augustine typically goes dormant only when nighttime temperatures consistently fall into the 40s or below for 10–15 days.

Given the sudden onset during active growth, the most likely culprits are:

• Chinch bugs – active in sunny areas, causing rapid, irregular die-off.
• Lawn disease (fungus) – often appears as circular patches that expand slowly.

Fire ant treatments alone would not cause this pattern.

Immediate Recommendations

1. Do not fertilize now. Fertilizing a stressed lawn (from insects or disease) worsens the problem.
2. Identify the cause. Check for chinch bugs by parting grass at the edge of damaged areas; look for small black insects with white wings. For disease, look for distinct circles with a yellowish halo.
3. Treat accordingly. If insects are confirmed, apply an appropriate insecticide. For fungal issues, a baking soda solution (1 tablespoon per gallon of water) can be effective as an organic option.
4. Adjust watering. Water deeply (1–1.5 inches) once or twice a week rather than frequent shallow watering. This encourages deep roots and reduces disease pressure.
5. Use proper fertilizer. Ironite is an iron supplement, not a complete fertilizer. Apply a balanced lawn fertilizer (3 lbs per 1,000 sq ft) every 45–60 days during the growing season.

Long-Term Lawn Health

A consistently maintained lawn—proper mowing, deep infrequent watering, and regular fertilization—resists pests and diseases better. Once the issue is resolved, consider re-plugging dead areas and establishing a routine care schedule.

If uncertain, consult a local pest control expert or lawn care professional for on-site diagnosis, especially for chinch bugs which are common in St. Augustine lawns during warm weather.