“St. Augustine grass fungus” can refer to several different diseases, and the treatment depends on the disease you actually have. The major problems include large patch, gray leaf spot, and take-all root rot.
Large Patch
Large patch commonly appears during warm, humid periods and is often most noticeable in spring and fall. Excess nitrogen can make the disease worse. Management starts with correct fertilization and irrigation; fungicides may be useful when the disease is correctly identified and the product is labeled for it.
Gray Leaf Spot
Gray leaf spot is especially common during warm, rainy weather and often attacks young, actively growing St. Augustinegrass. Avoid excessive nitrogen and prolonged leaf wetness. Fungicides can be appropriate when disease pressure is high and the diagnosis is confirmed.
Take-All Root Rot
Take-all root rot affects the roots and can produce yellowing, thinning, and irregular dead areas. It is associated with high moisture and turf stress. Cultural management—especially correcting stress and drainage problems—is a key part of control.
Do Not Treat Every Brown Patch the Same
Brown or thinning St. Augustinegrass can also result from drought, insects, herbicide injury, nutrient problems, or winter damage. Identify the cause before applying fungicide.
Prevention
- Water based on soil moisture rather than a rigid schedule.
- Avoid excessive nitrogen fertilization.
- Improve drainage and reduce prolonged leaf wetness.
- Mow at an appropriate height with a sharp blade.
- Use a fungicide only when the disease is identified and the label includes that disease and turf type.
Bottom Line
There is no single treatment for “St. Augustine fungus.” Diagnose whether you are dealing with large patch, gray leaf spot, take-all root rot, or a non-disease problem, then use the management strategy appropriate to that diagnosis.
Sources: UF/IFAS Extension and Texas A&M AgriLife Extension identify large patch, gray leaf spot, and take-all root rot as major St. Augustinegrass diseases.
