Brown Patch in Warm-Season Lawns: Complete Guide

Brown Patch disease creates distinctive circular or irregular patches of brown, dead-looking grass that can range from a few inches to several feet in diameter. In Florida lawns, these patches often appear seemingly overnight after periods of high humidity and warm nighttime temperatures. The affected grass blades turn a tan to brown color and can easily be pulled from the soil because the fungus attacks the leaf sheaths at the soil line.

One of the telltale signs of Brown Patch is the "smoke ring" - a dark, grayish-purple border that appears around the edge of the patch, especially visible in the early morning when dew is present. This ring represents the active edge of the fungal infection where the pathogen is actively destroying grass tissue. In St. Augustine grass, the lesions on individual blades appear as irregular tan spots with dark brown borders.

The center of older Brown Patch infections may actually begin to recover and green up while the outer edges continue to expand, creating a distinctive "frog-eye" pattern. In severe cases, multiple patches can merge together, creating large areas of damaged turf. Florida's warm, humid climate provides ideal conditions for Rhizoctonia solani, the fungus responsible for Brown Patch, to thrive from late spring through fall.

Unlike drought stress which causes grass to wilt and curl, Brown Patch-affected grass maintains its shape but changes color. The transition from healthy green to diseased brown typically occurs over just a few days, making early detection and treatment critical for limiting damage to your Florida lawn.