This disease is caused by a fungus.  It may be mistaken for chinch bug damage or drought symptoms.

 

Symptoms are circular to irregular in shape and may resemble symptoms of brown patch. Patches of diseased St. Augustinegrass or centipede at first appear yellowish-green and then die. As diseased stolons die, severe thinning occurs in areas of several feet to even entire lawns. 

 

It is important to remember that this is a root disease and by the time leaf symptoms are noticeable, the root systems have already been severely damaged. Another key symptom is the ease of lifting stolons from the soil since the roots are essentially gone. You can lessen the disease by following cultural practices that reduce turf stresses. Eliminate excessive irrigation. Avoid applying high rates of lime, and maintain a soil pH of 5.5 to 6.0. Mow at recommended heights and intervals with a sharp blade. Avoid ammonium nitrate fertilizer, and use acidifying fertilizers such as ammonium sulfate or slow-release urea. Maintain recommended levels of potassium.