St. Augustine is a popular lawn grass known for its tolerance to light shade. In the warm summer months, St. Augustine becomes susceptible to a number of fungal diseases that can cause unsightly spots or even complete death of the lawn. Proper maintenance and watering techniques in St. Augustine grass can help prevent and treat fungal lawn diseases.
Fungus in St. Augustine grass appears as unhealthy areas of grass which grow in size or number. A fungal problem in a lawn can cause discoloration and dead grass. The conditions that harbor fungal lawn invaders make way for other invaders like weeds and insect pests.
Fungal infections that attack St. Augustine grass include brown patch grass disease, take-all root rot and dollar spot grass disease. Brown patch grass disease is characterized by brownish-red patches of grass that are about six inches in diameter. Take-all root rot looks like diffuse blobs of yellowing grass that can spread across the whole lawn. Dollar spot grass disease is characterized by small, round spots 1 to 4 inches in diameter.
Fungal infections in grass are typically caused by overwatering or poor soil drainage. Where humid, rainy conditions occur for more than two days, a lawn can become susceptible to fungus spots. Brown patch grass disease spreads fastest in moist conditions at temperatures between 70 and 80 degrees.
Prevent fungus in St. Augustine grass by using proper watering technique. Water the grass in the morning to avoid leaving a wet lawn in the evening. Mow St. Augustine grass no more than 1/3 of its height at a time, and maintain a height of one to three inches in a St. Augustine lawn. When wet conditions are unavoidable, use a fungicide to keep fungal infections from spreading.
Grass problems that can look like a fungal infection include sod webworms, chinch bugs, grubs and Armyworms. The most common fungus-imitating insect pest in St. Augustine grass is the chinch bug, a little dark brown bug about one fifth of an inch long. Chinch bug larvae burrow in overgrown thatch and feed on the stems of the plants. Thatch is the layer of dead grass and organic material that becomes entangled at the base of the grass plants.