Gray Leaf Spot Fungicides

Gray leaf spot can rapidly thin perennial ryegrass and tall fescue during warm, humid weather. Young seedlings and lush, stressed turf are especially vulnerable.

What to Look For

Leaves develop small water-soaked spots that become gray or tan with dark margins. Severe infection blights whole leaves and creates irregular thin or straw-colored areas that may resemble drought or traffic injury.

Why It Develops

High humidity, long leaf-wetness periods, warm nights, heavy nitrogen, frequent irrigation, and young dense stands favor explosive outbreaks.

Reduce Disease Pressure

• Avoid excessive nitrogen during hot humid weather.
• Water early and reduce extended leaf wetness.
• Improve airflow and avoid unnecessary traffic on wet turf.
• Use tolerant cultivars when establishing or renovating ryegrass.

What University Research and Extension Guidance Says

NC State identifies gray leaf spot as one of the turf diseases most prone to fungicide resistance. Preventive programs should rotate effective FRAC groups and avoid repeated solo use of QoI fungicides where reduced sensitivity is suspected. Accurate diagnosis matters because symptoms can be confused with Pythium or drought stress.

Choosing and Using a Fungicide

Use the products below as a starting point, then match the active ingredient, FRAC group, turf species, use site, timing, rate, interval, and watering directions to the current product label. Preventive or very early applications are usually more reliable than rescue treatments after extensive injury. Rotate effective FRAC groups and combine fungicides with the cultural changes above.

Research and label note: University research may identify useful activity even when a current product label does not name this disease. That is research evidence, not a label direction. Apply a product only where the turf or application site and use pattern are permitted, and follow the complete label and applicable state requirements.

University sources: NC State Extension: Disease Management in Landscape Turf; University of Kentucky: Chemical Control of Turfgrass Diseases 2024.