Leaf spot/melting out on lawns

Leaf spot and melting out are two phases of the same disease complex on cool-season turfgrasses. The leaf spot phase creates visible lesions on individual blades and looks alarming without causing severe stand loss. The melting out phase -- when the pathogen moves from leaf tissue into crowns and.

Leaf spot and melting out are two phases of the same disease complex on cool-season turfgrasses. The leaf spot phase creates visible lesions on individual blades and looks alarming without causing severe stand loss. The melting out phase — when the pathogen moves from leaf tissue into crowns and roots — is when the actual stand damage occurs, and it often arrives weeks after the visible leaf spots.

Pathogens and host range

Per Penn State Center for Turfgrass Science, the leaf spot and melting out complex on cool-season grasses is caused primarily by:

• Bipolaris sorokiniana (formerly Helminthosporium sativum) — common on Kentucky bluegrass and tall fescue
• Drechslera poae — primarily on Kentucky bluegrass
• Drechslera siccans — on ryegrass

The diseases affect all common cool-season grasses, with Kentucky bluegrass and perennial ryegrass being most susceptible. Tall fescue is affected but less severely.