How do we treat gray leaf spot in our HOA's St. Augustinegrass common areas?

By OurHOA · General information · Revised October 29, 2026

How HOA boards spot gray leaf spot in St. Augustinegrass, cut summer nitrogen and night watering, time fungicides, and write the landscape contract to prevent it.

Part of the HOA board handbook: vendors, projects and upkeep.

The short answer

Gray leaf spot is a summer fungus on St. Augustinegrass. It needs three things: long hours of wet leaves, heat, and soft, fast-growing grass. The board controls two of the three through the landscape contract. The plan, in order: 1. Confirm the diagnosis before anyone sprays. 2. Move all irrigation to the early morning and run it only when the grass needs water. 3. Stop pushing soluble nitrogen on shady and problem areas during the rainy season. 4. Keep summer atrazine off any turf with a history of the disease. 5. Use fungicide on new sod, high-value turf and repeat problem areas, applied by a licensed contractor, on a schedule that rotates chemical classes. UF/IFAS describes gray leaf spot as chronic but not usually damaging in established, well-managed lawns. If a mature lawn is thinning from it every summer, something in the care routine is feeding it.

What it looks like and when it shows up

The fungus is Pyricularia grisea, also called Magnaporthe grisea. In Florida, UF/IFAS says St. Augustinegrass is the only warm-season lawn grass it affects. Texas A&M describes small brown to ash-colored spots with purple to brown margins that grow into diamond shapes. In warm, humid weather the center of the spot turns gray and felty with spores. Badly hit areas look scorched, thin and yellowed, and close up nearly every blade has spots. Timing follows the rain. UF/IFAS points to warm rainy spells from May through September, when leaves stay wet for 12 hours or more, humidity tops 95 percent and air temperatures sit between 80 and 90 degrees F. NC State puts the range at 70 to 95 degrees F, needing at least 14 hours of continuous leaf wetness, and most active from June through August in St. Augustinegrass. The worst spots are predictable: shaded turf that stays damp, newly laid sod or sprigs, areas that get evening water, and lawns fertilized heavily for a summer green-up. Texas A&M notes it is worst in shaded areas that stay damp. Colorado communities rarely grow St. Augustinegrass. The same fungus attacks perennial ryegrass and tall fescue in the Midwest and the mid-Atlantic, which calls for a different program than this one.

Get a diagnosis first

Thin, brown summer turf can also be chinch bugs, drought, large patch or a bad mowing job. Chinch bugs, the main insect pest of St. Augustinegrass according to UF/IFAS, also thin it in summer, and a fungicide does nothing for them. Send a sample to a university lab before approving a fungicide program. The Texas Plant Disease Diagnostic Lab at Texas A&M charges $35 for a routine turfgrass sample, with a $20 surcharge for out-of-state samples. Its instructions: cut two or three squares about 3 by 3 inches, with at least an inch of soil and roots, from the edges of affected areas, and include some healthy grass. Ship early in the week. In Florida, the UF/IFAS Plant Diagnostic Center takes samples, and the county Extension office can explain how to send one. Ask the landscape contractor to walk the property with a board member and photograph the leaf spots up close. A written lab result settles arguments about whose fault the dead turf is.

Water and fertilizer changes that prevent it

Watering time matters more than most crews admit. UF/IFAS says irrigation between 2 a.m. and 8 a.m. usually dries quickly on sunny days. Late afternoon and early evening runs keep the blades wet through the dew period and into the next morning, which is exactly what the fungus needs. Texas A&M adds: water only when the grass needs it. Nitrogen is the other lever. UF/IFAS says excessive nitrogen produces flushes of lush, highly susceptible growth, and its turf disease guide says to apply the minimum nitrogen the grass needs, with potassium equal to or greater than the nitrogen. Texas A&M says to avoid soluble nitrogen on moderately shaded lawns in summer. In Florida, UF/IFAS notes the state limit of 0.7 pounds of soluble nitrogen per 1,000 square feet in any one application, and recommends the first feeding of the year in early April in central Florida and mid-April in north Florida. Check for a city or county fertilizer ordinance before the contractor schedules any June through September feedings. Other steps from the extension sources: - Mow standard St. Augustinegrass at 3.5 to 4 inches and never remove more than a third of the blade. - Bag clippings in areas with active disease. - Thin tree canopies over shaded turf to speed drying. - Keep atrazine off at-risk turf in summer. UF/IFAS says applications before or during disease weather raise the odds of severe gray leaf spot, and that atrazine stresses the grass above 85 degrees F.

When fungicide is worth paying for

Fungicide makes sense in three cases: new sod or sprigs going in during the rainy season, high-visibility turf at the entrance or pool, and areas with a lab-confirmed history of the disease. For an established, well-kept lawn, fixing water and fertilizer is cheaper. UF/IFAS says fungicides work best applied preventively, while the weather favors disease. Its ranking: - Strobilurins (QoI), such as azoxystrobin, are among the most effective. - Sterol inhibitors (DMI), such as propiconazole, give some control and work best tank-mixed with a strobilurin when pressure is high. - Chlorothalonil, a contact fungicide, works if applied often, at moderate to low pressure, or as a tank-mix partner. Resistance is real. UF/IFAS and NC State both report strobilurin-resistant populations of the fungus. Require the contractor to rotate chemical classes and follow the resistance rules on each label. NC State's general preventive program repeats every 14 to 21 days, with shorter intervals when weather strongly favors disease. The product label sets the actual rate and interval. No cultivar is immune. UF/IFAS lists Floratam, the most planted St. Augustinegrass in Florida, as susceptible. When replacing turf, ask the sod farm for its cultivar's gray leaf spot rating.

A season on the calendar

A sample schedule for a Texas Gulf Coast or Florida community. Shift by a month for north Texas or north Florida. - March: walk the turf with the contractor. Map shady, damp and previously damaged areas. Confirm the controller start times are before 8 a.m. - April: first fertilizer of the year at a moderate rate. No new sod in known problem areas if it can wait until fall. - May: start preventive fungicide on new sod and high-value areas if the history justifies it. Hold atrazine on those areas through September. - June to August: weekly scouting by the crew. No soluble nitrogen on shaded turf. Bag clippings where spots show up. Send a lab sample from any new thin area. - September: compare the map with March. Note which zones still had disease and why. - October to November: tree thinning, drainage repairs and resodding, before next year's rainy season.

Contract wording and license checks

Clauses the board can adapt for the landscape agreement: "Contractor shall schedule all irrigation on St. Augustinegrass common turf to finish by 8:00 a.m. and shall not run irrigation between 2:00 p.m. and midnight except to establish new sod with Association approval. From June 1 through September 30, Contractor shall not apply soluble nitrogen to areas the Association designates as shaded or disease-prone. Contractor shall report suspected turf disease to the Association within 7 days with photographs and shall submit a sample to a university diagnostic lab before beginning any fungicide program. Fungicide programs shall rotate chemical classes as the label requires. For each application, Contractor shall provide the product name, EPA registration number, rate, areas treated and applicator license number." The person applying fungicide needs the right state license. Texas Occupations Code section 1951.003 counts controlling pests or diseases of plantings next to a residence, for pay, as structural pest control, which needs a license. In Florida, the limited landscape maintenance certification in Statutes section 482.156 says outright that it does not authorize applying pesticides to turf, so a crew holding only that card should not be spraying fungicide on the lawns. Colorado's Pesticide Applicators' Act, C.R.S. title 35, article 10, requires a commercial applicator license for hire. Rules differ by state and by your governing documents. Treat this guide as education, not legal advice. Our guide on hiring an HOA landscaping contractor covers bids, insurance and scope.

Mistakes boards make

- Approving a fungicide program for brown turf that turns out to be chinch bugs. Get the lab result first. Our guide on controlling chinch bugs in HOA St. Augustine turf covers that pest. - Leaving controllers on evening start times because the crew set them that way years ago. - Feeding the whole property heavily in June so the community looks green for an annual meeting. - Laying new sod in a shady area in July and then blaming the sod farm. - Running the same strobilurin product all summer until it stops working. - Spraying a weed-and-feed with atrazine across diseased turf in the heat. A notice for owners who ask why the sprinklers run before dawn: "The board has moved common-area irrigation to early morning hours on the advice of university turf specialists. Watering after sunset keeps the grass wet overnight and feeds gray leaf spot, a summer fungus in St. Augustinegrass. Please report sprinklers running in the evening to the board."

Sources

These guides are general education for HOA boards and residents, not legal, tax, or financial advice. Rules vary by state and by your community's governing documents - check with a professional for your situation.

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