UGA Department of Plant Pathology and UGA County Extension Coordinator Coweta County GA

Turfgrass disease samples keep coming to our Department of Plant Pathology Plant Disease Clinics. Gray leaf spot (GLS) is showing up now, which is earlier than historically seen and a bit further north (Coweta County) than expected for this time of the year (early June).  Therefore, is time to scout and manage GLS: Gray leaf spot is a fungus disease that affects St. Augustinegrass, perennial ryegrass and tall fescue in Georgia. Hot humid summer weather and high nitrogen levels can make turf susceptible to this disease.

The fungus causing the disease is Pyricularia grisea. Symptoms: The symptoms of gray leaf spot vary depending on the grass cultivar. On St. Augustinegrass, gray leaf spot first appears as small, brown spots on the leaves and stems. The spots quickly enlarge to approximately ¼ inch in length and become bluish-gray and oval or elongated in shape. The mature lesions are tan to gray and have depressed centers with irregular margins that are purple to brown (see image). A yellow border on the lesions can also occur. In cool-season turfgrass, the symptoms are similar to those of melting out. Conditions Favoring Disease: Gray leaf spot is favored by daytime temperatures between 80°F to 90°F and night temperatures above 65°F. It is also found in areas with high nitrogen levels and that are stressed by various factors, including drought and soil compaction. This disease is most severe during extended hot, rainy and humid periods.

Symptoms of gray leaf spot (GLS) in St Augustinegrass. (Photos S. Butcher, A. Martinez)

Disease Management Tips:

  • Proper soil fertility is essential to avoid plant stress and maintain strong growth. Adjust nutrients as per a soil test.  Avoiding nitrogen to tall fescue and/or ryegrass, or high nitrogen levels to warm season grasses (St Augustine) during mid-summer is crucial for GLS management.  
  • Appropriate mowing practices are important to curtail the disease, such as mowing as frequent as needed for 1/3 removal of leaf blades as well as collecting clippings when disease symptoms are obvious and severe.
  • Irrigate turf deeply and as infrequently as possible to avoid water stress. Allow water and humidity to remain on leaves for only a short period of time.
  • Reduce thatch, as it can serve as a spore/mycelium reservoir.
  • When possible, plant turfgrass that is resistant to gray leaf spot.
  • Avoid using herbicides or plant growth regulators when the disease is active that can restrict plant growth or create additional plant stress.
  • In Georgia, there are several fungicide products that are effective against gray leaf spot. Fungicides that contain active ingredients in the dimethyl inhibitors (DMI) and/or strobilurins chemical groups are efficacious against GLS. For a complete and updated list of available fungicide products, refer to the latest edition of UGA Extension Bulletin 984, Turfgrass Pest Control Recommendations for Professionals. Various publications on turfgrass pests are available on the turfgrass website:

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