Snow molds are fungi that are classified as psychrophilic, or cold-loving, and will attack plants under a layer of snow. The snow cover provides the fungus with a dark, humid environment suitable for fungal growth. It also predisposes the plants to disease by increasing the contact of pathogens in the soil with plant tissues and depleting carbohydrates stored in the plant as metabolism slows down. Two of the most common snow molds are pink snow mold (also known as Microdochium patch) caused by the pathogen Microdochium nivale, and gray snow mold (also known as Typhula blight or speckled snow mold) caused by Typhula incarnata and three types of Typhula ishikariensis. Both pink snow mold and gray snow mold can occur together and almost all grass species are susceptible to both of these diseases.
The first symptoms of pink snow mold are circular patches of infected turf after long periods of cool, wet weather. The patches will be approximately 2 inches in diameter at first and will change colors from orange-brown to dark reddish brown and finally light gray or tan. There may also be a faint growth of white or light pink mycelium at the edges of the patch, but the pink color is usually only noticeable in early daylight hours. The patches can enlarge to a size of 8 to 12 inches in diameter. Plants in the center of the patches may start to recover from the disease while the pathogen is still invading plants on the edge of the patch creating a "frogeye" symptom. Under long periods of low temperatures and leaf wetness the patches can combine creating large areas of blighted turf. As the snow melts, the most common symptom is mostly circular patches that are a dull white color. Newly exposed patches near the receding snow line have an abundant growth of white to light pink mycelium on leaves that have been matted down. Under prolonged periods of leaf wetness, numerous, small clusters of pink spores will be produced on the surface of the leaves. As the snow recedes, the patches of infected turf will have a bleached color and may be confused with symptoms of gray snow mold. The symptoms of gray snow mold are a little different. Once snowmelt has begun, areas of light yellow, straw-colored turf will appear. The leaves are usually Introduction Symptoms matted down and covered with either a thick or thin layer of white to gray mycelium. As the grass dries, the mycelium will dry out and disappear turning the leaves a gray or silver color. There may also be a ring of gray or white mycelia present at the edge of the infected area. Under optimal conditions, the diseased areas can coalesce causing a large area of turf to be affected. However, only the leaves of infected plants are killed while the crown is not affected. So new leaves will be produced from the crown during the spring. A characteristic