Lee Burpee, Alfredo Martinez, Mila Pearce
University of Georgia
Fungus Causing the Disease: Pyricularia grisea
St. Augustine grass is most commonly attacked by gray leaf spot but it also attacks perennial ryegrass, Bermuda grass, centipede grass, bent grass and various species of fescue. Gray leaf spot is especially severe on new St. Augustine lawns.
The symptoms of gray leaf spot vary depending on the grass cultivar. On St. Augustine grass, 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 in color and oval orelongated in shape. Mature lesions are tan to gray in color and have depressed centers with irregular margins that are purple to brown in color. A yellow border on the lesions can also occur. In cool-season turf grass, the symptoms are similar to those of melting-out.
Conditions Favoring Disease:Gray leaf spot is favoredby daytime temperatures between 80ºF to 90ºF and night temperatures above 65ºF. 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.
Management Gray Leaf Spot:
- Avoid medium to high nitrogen levels during mid-summer. Use fertilizers with slow-release nitrogen sources.
- Irrigate turf deeply and as infrequently as possible to avoid water stress.
- Allow water to remain on leaves for only a short period of time. Water from 10 pm to 10 am.
- Reduce thatch by vertical cutting.
- When possible, plant turf grass that is resistant to gray leaf spot.
- Avoid using herbicides or plant growth regulators when the disease is active.
- Fungicides are available to control the disease. Consult the current Georgia PestManagement Handbook..
For more information - see these excellent publications!
Turfgrass Diseases in Georgia has photos of and control measures for this and other turf diseases - http://pubs.caes.uga.edu/caespubs/pubcd/B1233/B1233.html
Spanish Version - http://pubs.caes.uga.edu/caespubs/pubcd/B1233/B1233-SP.htm
Guide to Turfgrass Fungicides lists fungicides and their characteristics. A chart at the end of the publication shows the best fungicide for each turf disease! http://pubs.caes.uga.edu/caespubs/pubcd/B1316/B1316.html
Turfgrass Diseases Quick Reference Guide gives a quick guide to identify and manage turf diseases - http://pubs.caes.uga.edu/caespubs/pubcd/C891/C891.html
Spanish Version - http://pubs.caes.uga.edu/caespubs/pubcd/C891/C891-SP.html
Pest Management Handbook (Follow all label recommendations when using any pesticide) - www.ent.uga.edu/pmh/
Please share this information with others in the landscape industry. For more information:
Call your local Extension Agent at (800) ASK-UGA1 or locate your local Extension Office at http://www.caes.uga.edu/extension/office.cfm
For more Landscape Alerts please visit the Georgia Center for Urban Agriculture