Ascochyta Leaf Blight on Lawns: Symptoms, Causes & Cultural Control

Sudden large brown or bleached patches during wet-dry weather swings often signal Ascochyta leaf blight — a foliar fungus that rarely kills grass crowns or roots.

Identification

Common on Kentucky bluegrass, tall fescue, perennial ryegrass. Confirm with hand lens: tiny yellow-to-dark-brown, flask-shaped fruiting bodies on discolored blades.

Management (Fungicides Rarely Needed)

• Dethatch and aerate annually (fall) to improve water penetration and reduce spore habitat.
• Irrigate evenly — avoid soggy soil and standing water.
• Mow at 2½–3 inches with sharp blades; reduce frequency to allow healing between cuts.
• Balanced fertilization; avoid heavy spring nitrogen (promotes succulent growth needing frequent mowing).

Good cultural practices let grass outgrow this transient disease.