Gray leaf spot is a fungal disease that severely affects St. Augustinegrass.
Gray leaf spot disease develops rapidly with high temperatures and prolonged wet weather. Other factors that contribute to disease development include excessive thatch, poor drainage and over-fertilization. The spores of this fungus are primarily spread by wind and water.
The infected areas start as olive green to brown, with water-soaked dots no larger than a pinhead. As the infection progresses, the infected areas increase in size and become ash-colored with purple to brown margins. The grass appears scorched and thin as if suffering from drought.
Fungicide application will be necessary if the gray leaf infection is severe. The earlier the applications are initiated, the greater the degree of control will be. Fungicides are usually used as a preventative measure. The fungicide will perform best if proper plant health care practices are followed including:
- Avoiding over-fertilization, and avoiding use of a quick-release nitrogen
- Watering early in the morning
- Improving drainage
- Increasing light penetration and air movement by selective pruning of trees and shrubs
- Maintaining the proper mowing height and frequently sharpening mower blades