Gray Leaf Spot

Pyricularia grisea

Warm-Season Grasses Highly Destructive Fungus

Symptoms

Oblong to diamond-shaped lesions with gray centers and dark brown borders. Severe infections cause a "blasted" appearance as large areas of turf turn brown rapidly.

Early lesions are small, water-soaked, and olive-green to brown
Mature lesions are oblong to diamond-shaped with gray to tan centers and dark brown to purple borders
Gray sporulation visible in the center of lesions under moist conditions
Severe foliar blighting causes large areas to turn brown — easily confused with drought stress
On St. Augustinegrass, irregular yellowing progresses to large brown patches

Signs

Gray sporulation (conidia and conidiophores) visible in the center of mature lesions under moist or humid conditions — gives lesions their characteristic gray color
Conidia are pyriform (pear-shaped), two-celled, and hyaline — visible under a compound microscope
Heavy sporulation on seedling tissue can give newly infected stands a grayish cast

Biology

P. grisea produces conidia that are dispersed by wind and water splash. Infection occurs during extended periods of leaf wetness at high temperatures. New seedlings are extremely susceptible. The pathogen can complete multiple disease cycles in a single growing season.

Favorable Conditions

Temperature range: 80–95°F with 10+ hours leaf wetness

Temperatures between 80–95°F with extended leaf wetness
High nitrogen fertility promoting succulent growth
Overcast, humid conditions with frequent rainfall
New seedlings or recently overseeded ryegrass stands
Poor air circulation and shade

Cultural Practices

Avoid high nitrogen applications during summer — use slow-release sources
Water early morning and avoid evening irrigation
Improve air circulation; reduce shade where possible
Delay overseeding ryegrass into warm-season grasses until temperatures moderate
Avoid mechanical stress during high-risk periods
Use resistant cultivars where available

Related Reports

No published reports yet for this disease.

Reports will appear here as they are peer-reviewed and published.