St. Augustine grass (Stenotaphrum secundatum) is a low-growing, coarse-textured, very dense and vigorous lawn grass. Because of its lack of winter hardiness, this grass is restricted to growing only in areas with warm climates. It prefers full sun to moderate shade and grows on a variety of soils. St. Augustine grass is not drought tolerant, is considered a high-maintenance grass and is susceptible to some plant diseases.
St. Augustine Decline (SAD virus)
Symptoms of St. Augustine decline are yellow, mottled grass blades that become more uniformly chlorotic over time--with both young and old grass affected. The early stage of this disease is sometimes confused with the iron deficiency that usually occurs in young grass. St. Augustine decline is transmitted through lawn and garden equipment. The spread of the virus can be reduced by cleaning tools with a 10% bleach solution. There are no chemical controls for the SAD virus. The best method to reduce the spread of the disease is selection of resistant grass varieties such as Floratam, Raleigh, Seville and Floralawn.
Brown patch is a major disease of St. Augustine grass that occurs in warm, humid weather. It is encouraged by excessive nitrogen and is generally most noticeable during spring and fall months. Brown patch is also known as Rhizoctonia blight (it's caused by the fungus, Rhizoconia solani). Symptoms of brown patch are 1- to 3-foot-diameter circular patches on lawns that appear early in the morning while dew is present. The outer edge of the circle will be a dark gray to purple ring, called a "smoke ring," that will disappear later in the day, leaving behind a circle that dries out to light brown. Brown patch can be controlled with fungicides.
Gray Leaf Spot
Gray leaf spot, a common disease of St. Augustine grass, is caused by the fungus Bipolaris sorokiniana during the summer rainy season. It is primarily a problem on new grass growth. Gray leaf spot develops quickly and is especially prolific in damp, shaded areas or in low-lying spots in the path of water runoff. Symptoms of gray leaf spot begin as small brown spots with purplish-brown edges become elongated. Leaf sections will turn yellow and--in severe infestations--stems and leaves wither and die, giving the affected lawn area a scorched look. Gray leaf spot can be controlled with fungicides. However, there are good culture practices to reduce fungal disease--including watering early in the day so the lawn does not remain wet for extended periods, removal of leaf clippings in affected areas, and avoiding high rates of nitrogen fertilizer during summer months on shady lawns.