Large Patch or Brown Patch
The fungus responsible for large patch, commonly referred to as brown patch, attacks most species of grasses but is more serious on bentgrass, bluegrass, bermudagrass, centipedegrass, and St. Augustinegrass.
Large patch is prevalent in spring or fall. You will see brownish to gray irregular, circular areas a few inches to several feet in diameter. In certain grasses, a narrow, dark, smoke-colored ring may border the diseased area. These water-soaked or scalded spots spread rapidly, becoming large, brown areas.
Generally, large patch fungus attacks the base of leaf sheaths where they are joined to stolons. Leaves turn yellow in St. Augustinegrass and a reddish color in centipedegrass before dying. Uncontrolled, it can attack the roots and kill large areas of the lawn. Large patch is severe on St. Augustinegrass in the spring, especially at temperatures of 60 to 75 °F. At temperatures of 80 °F and above, and under low moisture conditions, the activity of the fungus decreases. Large patch can be caused by too much nitrogen fertilizer, watering late in the afternoon, and by thatch buildup.
Control: 1) Use recommended varieties and good cultural practices for watering, fertilizing, and mowing. 2) Control thatch. 3) Limit the amount of nitrogen fertilizer. 4) Refer to Tables 14 and 15 for recommended fungicides.