Common Ailments of St. Augustine Grass

St. Augustine grass is a hardy, warm-season turfgrass found throughout the Southeastern United States. Forming a dense, coarse, blue-green turfgrass, St. Augustine usually is planted by sod or plugs and maintained at a height of 3 to 4 inches. With a low tolerance for shade, heavy foot-traffic and cold temperatures, St. Augustine has a great resistance to prolonged drought and is easy to establish in home lawn environments. Common ailments of St. Augustine grass include a variety of diseases and thatch build-up.

Large Patch Disease

Large patch disease is a fungus that attacks St. Augustine grass during the late fall or early spring. During this period St. Augustine grass is the weakest and is most vulnerable to disease. Caused by the soil fungus rhizoctonia solani, symptoms of large patch include circular areas of reddish-brown, orange or yellow discoloration, followed by eventual brown coloration as the grass dies. Fungicides containing triadimefon are effective at treating large patch in the early stages of growth.


St. Augustine grass aggressively propagates through the topsoil using stolons. This makes St. Augustine turfgrass especially susceptible to excessive thatch build-up. Thatch is a layer of living and dead organic material that accumulates between the grass roots and the topsoil. Excessive thatch build-up reduces the ability of the roots to take in moisture and nutrients because the roots extend only into the thatch, never reaching the topsoil below. Thatch is best treated by aerating the lawn with a mechanical core aerator at regular intervals during the growing season.

Decline Virus

St. Augustine Decline Virus (SAD) is a specialized disease that attacks only St. Augustine and centipede grasses. Usually forming small patches with diameters of 1 to 3 feet, infected areas initially turn yellowish, followed by a brownish color as the grass thins and eventually dies. There is no cure for SAD. Prevention is possible by using more resistant varieties of St. Augustine grass that include Serville, Raleigh and Floratam.

Brown Patch

Brown patch is a fungus that infects a wide variety of warm-season grasses that are in environments with high humidity or partial sunlight. Beginning as a small brown spot, brown patch eventually expands outward to a 2- to 3-foot diameter with the outer ring having a distinctive yellowish color. St. Augustine grass is at greatest risk for brown patch during late fall and early spring. The best preventive measure for brown patch is regular aeration during the growing season. A variety of fungicides with benomyl and chlorothalonil are effective at treating brown patch.

Keywords: diseases of St. Augustine grass, thatch problems with St. Augustine grass, ailments of St. Augustine grass

About this Author

Ryan Kane is an experienced professional pilot and freelance writer. In addition to writing about aviation related topics, Kane enjoys writing about a diverse range of science and technology topics.