Gray Snow Mold

Disease

Gray Snow Mold, Typhula blight

Typhula incarnata, Typhula ishikariensis

Distribution: Home lawn, golf course

Photos

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This disease is important in northern regions of the United States, where snow cover remains on the ground for extended periods, usually 3 months or more. After the snow melts in the spring, symptoms can be observed as circular straw-colored or grayish brown infection centers in the turf. The spots range from 3 inches to 24 inches (7.6 cm - 60 cm) in diameter, but most are between 6 and 12 inches (15-30 cm). Infected turf is matted down with grayish white mycelium of the fungus often seen along the margins of the diseased area shortly after snow melt.

Typhula blight is worse in winters when snow falls on unfrozen turf. The fungus grows and infects at temperatures between 30 and 55° F (-1° and 12.7° C). The two species T. incarnata, and T. ishikariensis can be distinguished by the fruiting structures, or sclerotia, they produce on infected turfgrass. T. incarnata produces relatively large, copper-colored sclerotia with diameters that are typically larger than the width of the grass blade, while T. ishikariensis produces small, black sclerotia whose diameters are less than the width of the grass blade. T. incarnata is most significant in the eastern U.S. and Canada, and T. ishikariensis prevails in the colder regions of the world, where snow cover remains for three or more months.

  • Crops Affected: turf

    Damage

    The location of this disease is home lawns and golf courses. General symptoms are a circle, and patch. Foliar symptoms are browning. This can occur during the months of January, February, March, April, October, November, and December. Hosts of the disease are Kentucky Bluegrass, Perennial Ryegrass, Tall Fescue, Fine Fescue, Creeping Bentgrass, Annual Bluegrass, and Colonial Bent.

    Management

    It is important to avoid lush and actively growing turf going into the winter months. Nitrogen applications should be timed so that stimulated growth does not take place near the time of snowfall. Snow removal or management techniques which limit extended periods of snow cover can often be used where applicable (golf course putting greens). No resistance to gray snow mold appears to exist in the cool season turfgrass species listed.

    Chemical management is necessary where turfgrass quality and uniformity is desired. Timing is important when managing this disease, and applying a fungicide treatment prior to initial snowfall is crucial in order to achieve industry-accepted levels of disease control. Combinations of two or three different fungicides have become the norm for the management of snow mold. Several effective combinations exist including three-way combination of a half rate of a PCNB product plus a full rate of chlorothalonil plus a full rate of iprodione. Other components that have been used successfully include dicarboximides, strobilurins, and fludioxonil.

    It should be noted that the DMI fungicides, like fenarimol, triadimefon, and propiconazole, are only effective in areas like the eastern U.S., where only T. incarnata occurs. The DMI fungicides are not effective against T. ishikariensis, and must be used in a fungicide combination in areas where both species occur.

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