TURFGRASS DISEASE MANAGEMENT
Turfgrasses are most susceptible to disease when they are stressed or growing slowly. As a result, the most severe disease problems on cool-season grasses occur during the summer, and most diseases in warm-season grasses develop in the fall and spring. Grasses that are healthy and vigorously growing are far more resistant to disease than grass that is poorly managed, and they will also recover more quickly should disease develop.
Fungicides can be used to control turfgrass diseases. Fungicide applications may be preventive, if made before symptoms of the disease appear, or curative, if made after symptoms appear. Preventive fungicide programs are recommended for diseases that occur annually. Curative fungicide applications are less effective and usually require increased application rates or shorter application intervals. Whenever possible, schedule preventive fungicide applications based on the weather conditions that favor disease development, not based on the calendar. A disease must be identified accurately in order to select the best fungicide for its control.
Many systemic fungicides lose effectiveness due to the development of fungicide resistance. Fungicide resistance occurs when fungicides from the same chemical class are applied repeatedly. Repeated applications allow strains of the pathogen that are naturally resistant to the fungicide to build up in the population. When resistant strains become dominant in the population, the fungicide no longer controls the disease, and significant damage may occur when conditions become favorable for disease development.