St. Augustine grass, also called carpetgrass, is a popular grass for its growth habits and its unique appearance and feel. Though it is hardy in many environmental conditions, it is at high risk of a number of fungal diseases that can cause serious damage to a St. Augustine lawn. Stopping these grass invaders requires controlling the conditions that help create a fungal problem and knowing how to treat a problem when it comes up.
In addition to its popularity in coastal areas because of its salt tolerance, St. Augustine grass is also popular in inland areas because it gains a lush, luxurious green carpet when punctiliously tended. It is also tolerant to partial shade, making it a good option for lawns growing under trees that block the sun during parts of the day.
Common varieties of St. Augustine grass disease include brown patch grass disease, take-all root rot and gray leaf spot disease. Brown patch grass disease appears as a series of patches of browning grass the size of tea cup saucers. To verify the presence of brown patch, check for dark-bluish gray edges around the spots. Take-all root rot is characterized by a diffuse, widespread lawn yellowing that slowly becomes large patches of dead grass. Gray leaf spot disease shows itself as tiny gray spots on the grass leaves which spread and eventually deteriorate the entire leaf.
Grass disease can stem from a few different causes. The main cause of fungal grass disease is an overly wet lawn. Prevent fungus-friendly conditions by watering the lawn in the early morning to give the soil a chance to dry overnight. Warm, wet evenings harbor a perfect environment for the fungal invaders that mar and kill St. Augustine grass. A St. Augustine lawn can also get diseases from poor mowing techniques or from contaminated gardening equipment that has been used on diseased grass. Generally, grass should be cut by no more than one-third its original height, and should never be cut shorter than three-fourths of an inch. Cutting St. Augustine too short damages it and leaves it susceptible to disease. To guard against disease spread from lawn equipment, sterilize the equipment, including lawn mower blades, each time they are used on a different lawn.
If grass is showing signs of disease, it has already been infected with a pathogen for several months. In climates prone to lawn diseases that attack St. Augustine grass, repeated applications of fungicide may be necessary to keep grass disease at bay. In most areas, the best time to apply preventive fungicide to a lawn is in the fall.
Problems with St. Augustine grass which can appear to be disease include overgrown thatch, chinch bugs, grubs, overfertilization and dehydration.