TURFGRASS DISEASE IDENTIFICATION (P12)
Other Fungal Diseases
Gray Leaf Spot
Causal Agent: Pyricularia grisea
Susceptible Turfgrass: St. Augustinegrass, perennial ryegrass, tall fescue, and centipedegrass
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 1/4 inch in length and become bluish-gray in color and oval or elongated in shape. The mature lesions are tan to gray in color and have depressed centers with irregular margins that are purple to brown in color. On perennial ryegrass and tall fescue, symptoms first appear as small, watersoaked lesions that turn brown. Lesions may have a yellow halo. The leaf tips will have a twisted or fishhook shape.
Conditions Favoring Disease: Gray leaf spot favors temperatures between 80°F to 90°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 and humid periods.
- Avoid medium to high nitrogen levels during mid-summer.
- 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.
- Reduce thatch by vertical cutting.
- When possible, plant turfgrass that is resistant to gray leaf spot.
- Avoid using herbicides or plant growth regulators when the disease is active.
- Apply contact and/or systemic fungicides on a preventive basis.
Occasionally occurs in: CT, KS, MA, NE, NH, NY, OK, RI, TX, VT.
Frequently occurs in: AL, AR, DE, FL, GA, IL, IN, KY, LA, MD, MO, MS, NC, NJ, OH, PA, SC, TN, VA, WV.
Causal Agent: Drechslera spp. and/or Bipolaris spp.
Susceptible Turfgrass: Creeping red fescue, Kentucky bluegrass, annual bluegrass, perennial ryegrass, tall fescue, and some varieties of bentgrass and bermudagrass
Symptoms: Leaf spot (melting-out) causes purplish-brown to black spots with tan centers on the leaf blade and sheath. The lower leaves of the infected plants become shriveled and blighted. When melting-out infection is severe, almost all of the leaves and tillers die, causing severe thinning of the stand—or melting-out. On cool-weather turfgrass, melting-out typically follows the appearance of leaf spots.
Conditions Favoring Disease: Leaf spot favors temperatures between 40°F and 80°F. It occurs in areas that experience more than 10 hours a day of foliar wetness for several con secutive days. It also favors high amounts of nitrogen and a low mowing height.
- Increase the height of cut.
- Reduce turf stress by using lightweight equipment.
- Avoid the application of high rates of water-soluble nitrogen in the spring.
- Minimize the amount of shade.
- Irrigate turf deeply and as infrequently as possible.
- Reduce thatch in the early spring or fall for cool-season turfgrass and in the summer for warm-season turfgrass.
Frequently occurs in: All states.