Dead areas of turfgrass are usually the result of one, or more, of three factors – disease, insects, and poor cultural practices.Brown patch is a fungus disease most likely to be observed between November and May when temperatures are below 80 degrees. It is normally not seen in the summer. It is distinguished by dying blades of grass attached to a living, horizontal stem. This results in the appearance of green blades protruding through dead grass blades. If the affected grass has an all-dead appearance, the damage may be a result of grub feeding (especially in April and October). If grub damage is the problem, you should be able to lift the dead grass up like a carpet, since the grubs have removed the roots which normally anchor the turf. Chinch bug damage during hot weather can also be a problem. This damage usually begins as a small, irregular circle and spreads outward, often beginning near concrete pavement or sidewalks. Of course, drought damage caused by malfunctioning sprinkler heads or the rapid drying of turf over shallow deposits of soil can also result in dead areas of lawn. After determining and correcting the problem, if the grass is truly dead, you will need to re-sod or replant plugs of turf in those areas.

Recommended Resources
St. Augustinegrass for Florida Lawns
Key for Identification of Landscape Turfgrass Diseases
Southern Chinch Bug Management on St. Augustinegrass