This is Part 3 of a three-part series on summer diseases of turfgrass.
Gray leaf spot is another turf disease can show up on your golf course under hot summer conditions. It affects perennial ryegrass, tall fescue, St. Augustine grass, and kikuyu grass mowed at 1 1/2 inches or taller. The disease can move in quickly, especially when there is heat and moisture stress.
There is no particular pattern to gray leaf spot–it looks like large swaths of stressed, scorched turf. Upon closer examination, the leaves have water-soaked lesions with a tan center and darker brown outer ring. A defining characteristic of the disease is the twisting and flagging of the leaf tips.
The following predictive model for gray leaf spot has been developed to indicate when to make preventive fungicide treatments:
Maximum daily temperature (°F) + Minimum daily humidity (%) = 140
Best Management Practices for Gray Leaf Spot Disease
The following practices will help prevent and treat gray leaf spot:
- Maintain adequate moisture.
- Maintain moderate nitrogen fertility and keep manganese levels at or above 30 ppm (Melich III).
- Use gray leaf spot-resistant varieties of perennial ryegrass and tall fescue for overseeding.
- University research has shown that the following fungicides and combinations are effective for treating gray leaf spot:
- triadimefon (Bayleton) + chlorothalonil (Daconil Ultrex)
- azoxystrobin (Heritage)
- pyraclostrobin (Insignia)
- trifloxystrobin (Compass)
Always verify that fungicides are labeled for use in your state and follow label directions for mixing and application.
Additional information on the identification and treatment of gray leaf spot, including fungicide rates and combinations, can be found on the North Carolina State University Cooperative Extension website.
Contact me with any questions about gray leaf spot or other turf-related topics. Also take time to review Part 1 and Part 2 of this series to set your golf course up for success this summer: