Cercospora leaf spot disease affects St. Augustine grass from late spring through summer. It is found frequently during periods of heavy rainfall. Areas of grass that are under stress are susceptible to the development of this disease. Areas in low light or under low fertility have the best conditions for it to occur.
The first signs of Cercospora leaf spot are narrow dark brown leaf spots that become larger, turning into oblong or irregular shaped lesions, with dark tan centers and dark brown to purple margins.Under extreme humid conditions during the summer, spots in the center of the lesion may turn whitish in color. If many blades of grass have numerous spots, extensive yellowing and withering can happen to the problem area in a St. Augustine lawn.
This disease can be prevented if a proper fertilization program is followed. Using a slow-release fertilizer with a balanced rate of nitrogen and potassium prior to summer reduces the chances for this disease causing lawn problems. Correct watering such as timing, frequency, and amount, needs to be followed to help in preventing it.