Lawn Fungus in Central Florida: Preventing Gray Leaf Spot & Large Patch

Two Fungus Problems, Two Very Different Seasons

Central Florida's warm, humid climate is hospitable to more than one type of lawn fungus, and which one you're dealing with usually depends on the time of year. The two we see most often on St. Augustine lawns are gray leaf spot in the hot months and large patch during the cooler ones.

Gray Leaf Spot (Summer)

Gray leaf spot is caused by the fungus Pyricularia grisea and shows up as small oval-to-elongated lesions on the grass blades with tan-to-gray centers and brown borders. In a bad outbreak, the lawn can take on a scorched, grayish look from a distance.

It's worst in hot, humid weather when grass blades stay wet overnight, and it's made worse by heavy nitrogen fertilization, which pushes soft new growth that's more susceptible. This is one of the reasons disease-resistant varieties like Cobalt tend to hold up better through Florida summers than standard St. Augustine.

• Water early morning only (ideally before 10am) so blades dry out during the day instead of staying wet overnight.
• Avoid heavy nitrogen applications during summer — this also happens to line up with your county's fertilizer blackout window.
• If an outbreak is already underway, a fungicide labeled for gray leaf spot on St. Augustine is the standard treatment; timing and reapplication intervals matter, so follow the label closely.

Large Patch (Fall/Winter)

Large patch, caused by a Rhizoctonia fungus, shows up as roughly circular brown patches — sometimes several feet across — usually appearing as the weather cools from late fall through winter. It's favored by excess soil moisture, poor drainage, and thick thatch, and it gets worse when lawns are watered too often or too late in the day during cool weather.

• Cut back watering frequency as temperatures drop — this is also just good general winter lawn care.
• Preventive fungicide applications in early-to-mid fall, before symptoms appear, are far more effective than treating an active outbreak in January.
• Improving drainage and reducing thatch buildup both lower the risk going into winter.

General Fungus Prevention That Applies Year-Round

• Water early morning, never in the evening.
• Don't over-fertilize, especially with nitrogen, outside of the recommended spring and fall windows.
• Keep mower blades sharp and never mow wet grass — torn, wet blades are more vulnerable to infection.
• Improve airflow and sunlight where possible (thinning overhanging tree limbs) in chronically damp, shaded areas.

Strada Landscape, Inc. specializes in residential sod installation throughout Orlando and Central Florida, including Windermere, Winter Park, Dr. Phillips, and Lake Nona.