Home & Garden Tips
Grey Leaf Spot on St. Augustine grass
By Roosevelt McWilliams County Extension Agent

Compared to finer textured grasses like the Bermudas, St. Augustine has large flat stems and broad coarse leaves. It has an attractive blue-green color and forms a deep, fairly dense turf. It spreads by long aboveground runners or stolon. While it is aggressive, it is easily controlled around borders. It produces only a few viable seed and is commonly planted by vegetative means.

St. Augustine is the most shade tolerant warm season grass in Georgia. Perhaps the greatest disadvantage of this grass is its sensitivity to the chinch bug. While insecticides can control this insect, frequent applications are required.

I am beginning to see this common grey leaf spot fungus as I visit homeowners around the county. It is very common on St. Augustine grass during the summer and early fall. Occasionally we may also see this disease on tall fescue.

Symptoms on St. Augustine grass are initially a small, brown water soaked spot that enlarges to have a tan to grey center and a purplish brown border. Spots usually are round to oblong. Areas of grass severely affected by the disease look like they have been scorched by drought.

If you look at the leaf spots under a microscope, the spores are teardrop or ice cream cone shaped and have one to two septation when mature. The control is similar to that for brown patch. Limit nitrogen as excessive applications of N favor the disease. Proper watering is important.

The turf should be irrigated early in the day or during night. You should avoid watering early in the evening prior to sunset. Watering should be thorough (wetting the lawn to a depth of 5-7 inches) and as infrequent as possible to provide adequate moisture. Frequent shallow watering should be avoided.

If you water an inch of irrigation water per week it will be sufficient. The weeks when we have rain no irrigation may be required. Drought-stressed grass is more likely to be infected. Stress from herbicide applications during days when the temperature is 85 degrees Fahrenheit or higher also predisposes the grass to the disease.