Typhula Blight and Fuasarium Patch
The snow molds usually appear in the spring as the snow melts from lawns. There are two common types of snow mold: Typhula Blight and Fusarium Patch. They usually can be distinguished by their symptoms, develop under slightly different conditions, and are controlled by different fungicides. Typhula Blight is caused by the low temperature fungi, Typhula incarnata and T. ishikariensis, especially active under the snow covering unfrozen ground.
Typhula Blight damage first appears when the snow is melting. Roughly circular patches 2 to 40 inches or more in diameter develop. These patches are straw colored, and enlarge as long as the grass remains cold and wet from melting snow. The grass in the patches has a matted appearance, and may have a visible gray colored mold growth on the whole patch or on the advancing margin. Hard fungus bodies called sclerotia develop on or are imbedded in the leaves and crowns of affected plants. These sclerotia are more or less spherical in shape. The sclerotia of T. ishikariensis are the size of a pinhead and black; those of T. incarnata are up to 3/16 of an inch in diameter and brown. These sclerotia's presence help diagnose Typhula Blight.
The Typhula fungi survive the summer in the soil or thatch as sclerotia. Active growth of the fungus resumes in the absence of light under snow cover on unfrozen ground. Growth takes place at temperatures as low as freezing (to slightly below freezing) and continues after snow melt in the spring for as long as the grass remains wet and the temperatures cold. Typhula activity stops when the temperature exceeds 45 F or the surface is dry.
Management practices for control of Typhula Blight are similar to those for Fusarium Patch. Fungicides are seldom needed in bluegrass lawns.