Snow Molds of Turfgrass April, 1998

B-868 Snow Molds of Turfgrass April, 1998 by Gary D. Franc1 and Linnea G. Skoglund 2 Snow mold diseases of turfgrass are • Yellow to brown or black, typically dependent on snow cover pinhead-sized to 3/16 inch or prolonged periods of cool, wet diameter irregularly round weather. Disease development also bodies (fungal sclerotia) is favored by excessive thatch, poor embedded in leaves and drainage, late fall fertilization crowns (Figure 3). (before grass dormancy), and high • As grass dries, the mat disap- soil moisture. In Wyoming, two pears and the grass becomes types of snow mold are common Figure 2 crusty and brittle. and can occur together. Typhula blight (gray snow mold) and these fungal structures germinate or • Irregular small circular areas (3 Fusarium patch (pink snow mold) resume growth, infecting grass and to 6 inches diameter) of yellow are caused by the fungi Typhula continuing the disease cycle. to yellow-brown grass are incarnata and Microdochium evident. These patches can fuse nivale, respectively. These fungi Typhula blight together to cover areas of 12 inches or more (Figure 1). affect a wide range of turfgrass • Often called gray snow mold. species, especially bluegrass and bentgrass. • Found primarily in western Prognosis Wyoming. Fungal structures such as sclerotia, • If crowns are not killed, the spores, and mycelium are pro- • Develops under prolonged snow turf will regrow but will be duced on infected turf and survive cover or under heavy mulch. delayed. warm, dry periods of summer • Symptoms are often first • Under optimal disease condi- dormant in the thatch layer. When apparent in the spring as the tions, crowns will be killed and environmental conditions are snow melts (Figure 1). regrowth will not occur. favorable for disease development, Replanting or re-sodding will • Optimum disease conditions be necessary. include lush grass growth prior to snow cover, prolonged snowcover over unfrozen ground, high soil moisture, and temperatures of 32 to 35 degrees Fahrenheit. What to look for • Patches of light colored grass matted together by grayish white threads (or hyphae) as Figure 3 the snow melts (Figure 2). Figure 1 1 Research and Extension Plant Pathologist, University of Wyoming 2 Extension Plant Clinic Specialist, Colorado State University • As grass dries, affected areas Promote rapid drying and warm- become crusty. ing in spring by raking affected areas. A light spring application of • Patches may appear similar to nitrogen stimulates regrowth of Typhula blight; however, no these areas. sclerotia are present in leaves or crowns. Chemical methods Generally, fungicides are not Figure 4 Prognosis necessary for home lawns because • Usually only leaves are colo- disease can be successfully man- Fusarium patch (Figure 4) nized so regrowth will occur. aged via the cultural practices listed above. If fungicide treat- • Pink snow mold often de- • Under severe conditions, ments are necessary, the proper scribes the phase of this crowns can be killed. Replant- timing of the application is critical disease when it is associated ing or re-sodding may be for effective management. In with snow melt. necessary. general, applications must be made • Although primarily a late fall- before permanent snowfall or for winter-spring disease, the Management of Snow Fusarium patch, when tempera- fungus can infect and cause Molds tures regularly drop below 45 damage whenever tempera- degrees Fahrenehit. tures are below 60 degrees Cultural methods Many fungicides are listed for Fahrenheit with high humid- Avoid late fall nitrogen applica- snow mold control and contain ity for prolonged periods. The tions before turf dormancy. Ideally, active ingredients such as disease is not limited to snow- do not fertilize within six weeks of chlorothalonil, iprodione, PCNB, covered turf. dormancy or use only slow-release forms of nitrogen late in the propiconazole, or triadimefon. • Optimum disease develop- growing season. Label directions frequently change ment temperatures are be- as new information on disease Avoid straw mulches. tween 35 to 45 degrees management becomes available. Fahrenheit. Avoid excessive thatch. Therefore, always consult product labels for the most recent informa- • Found statewide. Prevent snow compaction and ice tion on proper chemical usage. All formation. What to look for chemical applications must be Improve soil aeration. made according to the label • Pale, yellow grass in an irregu- directions. lar outline. Often covered Minimize snow accumulation with a light pink mat of before ground is frozen. Acknowledgment: Photographs were provided by W. M. Brown, Jr. fungal hyphae and spore- Mow in fall until grass goes (Figures 1 and 3) and L.G. producing structures. dormant so that snow does not fall Skoglund (Figures 2 and 4). on a tall canopy. Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Edna L. McBreen, Director, Cooperative Extension Service, University of Wyoming, Laramie, WY 82071. 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