Also called buffalo grass, St. Augustine is a warm-season grass commonly found in the southern United States. Sometimes brown spots appear on the grass that affect its health and mar its appearance. These brown spots can be caused by a few different sources and need immediate attention to prevent the problem from spreading.
St. Augustine History
St. Augustine (Stenotaphrum secundatum) is a perennial pasture and lawn grass native to the West Indies, Mexico and western Africa. Explorers before the 1800s found this grass growing along the Atlantic coast of Africa, North and South America and Hawaii. The University of Hawaii's Cooperative Extension mentions the presence of this grass on the islands around 1816.
Brown Spot Types
St. Augustine is susceptible to brown spots or patches that look unsightly against the lush green grassy carpet. The major causes of brown spots include drought, brown patch, take-all-patch, grubs and chinch bugs.
Brown patches form when the grass is watered once every 10 days with less than 1 inch of water. Brown patch fungal disease (Rhizoctonia solani) occurs in fall or spring in St. Augustine lawns that are overwatered or poorly irrigated. Another fungal disease, take-all-patch has an infection pattern slightly similar to that of brown patch, but symptoms appear in the summer instead of spring or fall. Grubs are tiny pests that chew the roots of grass in autumn and summer, causing patches of brown spots throughout. Chinch bugs are tiny pests that feed on the juice in grass blades instead of the roots.
Spots caused by a lack of watering are actually linear rather than perfectly round and are always located in areas that receive direct sunlight. Brown patch disease forms doughnut-shaped patches in the lawn grass with green grass inside surrounded by dying or dead grass that is brown. Grubs are responsible for creating brown spots in the lawn that come out easily when pulled. These thick, white, curved pests are easily visible under the roots. Grass damage by chinch bugs is similar to that of grubs, but the grass does not come out as easily when tugged because these pests leave the roots intact. The small white bugs are visible when the infested grass is brushed through with a hand.
Provide an inch of water per week to the St. Augustine lawn so it recovers from drought, but provide an additional half-inch of water if you notice signs of wilting such as folding or grass blades not recovering from foot traffic. Use a fungicide that contains thiophanate-methyl, propiconazole, terrachlor or myclobutanil specifically formulated to treat brown patch disease. Spread a half-inch-thick layer of sphagnum peat moss over brown spots caused by take-all-patch fungus so it acidifies the soil below, kills the fungus and recovers the grass. Treating or controlling grubs is difficult because they are quite large and located below soil surface. Drench insecticide over the soil where these pests feed in midsummer to prevent future grubs from settling there. Treat chinch bugs with timely applications of insecticide.