Leaf Smut and Stripe Smut Fungicides

Leaf smuts, including stripe smut and flag smut, are systemic diseases of older Kentucky bluegrass and other cool-season turf. Once a plant is infected, the fungus remains in its growing points.

What to Look For

Pale or slow-growing plants develop long gray-to-black stripes between leaf veins. Leaves split, curl, and shred as dark spores are released, and infected plants may die during summer stress.

Why It Develops

Cool, wet infection periods, susceptible older cultivars, low phosphorus or potassium, high spring or summer nitrogen, thatch, and drought stress increase injury.

Reduce Disease Pressure

• Overseed chronic areas with resistant cultivars or adapted species.
• Use soil testing to maintain balanced phosphorus and potassium.
• Avoid heavy spring and summer nitrogen.
• Prevent severe drought stress and manage excessive thatch.

What University Research and Extension Guidance Says

Kentucky reports that one well-timed systemic application in early to mid-October, watered in before drying, is more effective than multiple spring applications. Its 2024 review rates myclobutanil, propiconazole, thiophanate-methyl, and triadimefon as good to excellent in most published experiments and warns that some contact fungicides may enhance stripe smut.

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: University of Kentucky: Chemical Control of Turfgrass Diseases 2024; Purdue Extension: Smut Diseases.