St. Augustine grass is a warm season grass that is found in much of the southern United States. Many varieties of St. Augustine are known for their shade tolerant properties. St. Augustine is a high maintenance grass that demands proper watering, regular mowing and adequate fertilization to maintain its lush carpet. Improper maintenance or cool, wet weather can cause a fungus problem in St. Augustine grass.
Fungal infections in St. Augustine grass can happen quickly and consume a lot of turf in just a few days. Though fungal problems in St. Augustine can look similar to other lawn pests like chinch bugs, each type of fungus that grows on St. Augustine has distinguishing characteristics that set it apart from other lawn problems.
Gray Leaf Spot
Though many other grasses are resistant to the fungus that causes gray leaf spot disease, the gray leaf fungus is a particular problem in St. Augustine grass. Gray leaf spot symptoms start as small reddish-brown spots about an inch to 1 1/2 inches wide. Spots can grow together and form large areas of infected grass. Gray leaf spot can tend to look like drought symptoms, but it is present when the weather has been wet and humid.
Brown Patch Disease
Brown patch disease is a common fungal problem that strikes most often in St. Augustine grass. The disease is characterized by spots between 6 inches and 12 inches wide that change in color from yellow to reddish brown. According to the University of Florida, brown patch grass disease invades St. Augustine at temperatures below 80 degrees, thriving best at around 73 degrees. High concentrations of nitrogen in combination with warm, wet weather can trigger an attack of the fungus. A distinguishing symptom of brown patch disease in St. Augustine grass is black, rotten material where the stem meets the root area.
Take-All Root Rot
A threat to many grasses, St. Augustine is particularly plagued with the effects of the fungal disease called take-all root rot. Characterized by spreading, patchy yellow-green spots of grass that can be many feet wide, take-all root rot can quickly kill an entire lawn. The fungus that causes take-all root rot can also affect Bermuda and Zoysia grasses.
The best way to keep a fungus problem from growing on St. Augustine grass is to perform regular and proper maintenance on the turf. Mow St. Augustine to the correct height, between 1 and 3 inches. Water St. Augustine in the morning to avoid leaving a wet, fungus-harboring carpet of grass in the cool evening. If a fungal infection strikes, fungicide can be applied in the early stages to keep the fungus from spreading.