AKA: Going Out, Leaf Blotch, Melting Out
Fungus: Helminthosporium spp
Symptoms: Leaf spot, melting out and going out symptoms include general thinning out of grass in scattered areas, often general browning is evident on affected plant. Circular to elongate purplish, brown to dark brown, or reddish brown spots with white, tan, brown or straw-colored centers on leaf blades, leaf sheaths and stems. Crowns and roots frequently are attached. In hot, windy weather, such plants generally die. Leaf blotch is manifested as tiny purplish to reddish spots on leaf blades and leaf sheaths. Seedlings are very susceptible but developing plants rapidly become resistant. Affected seedlings may die. Small lesions may develop on roots and crowns.
Grasses susceptible: Kentucky bluegrass, ryegrass, bentgrass, and fescue. Improved selections of bluegrass – Marion, Pennstar, Anheuser Dwaft – exhibit a high degree of resistance: Cougar and Delta are moderately resistant: Arboretum and Park are highly susceptible.
Conditions favoring disease: Various species of Helminthosporum are pathogenic over a wide range of temperature conditions (50 to 90 degrees F) under high humidity. Leaf spot generally appears first on grasses in shaded areas and is most severe and damaging on closely clipped turf. Leaf blotch damages young seedlings or adult plants weakened by excess thatch, deficient nitrogen and unfavorable growing conditions.