From the desk of Heritage Lawns of West Springfield, Inc.:

Snow Molds

Prepared by:
Gail Schumann
Assistant Professor
Department of Plant Pathology
University of Massachusetts, Amherst, MA 01003

Pink Snow Mold (Fusarium Patch) Fusarium nivale
Gray Snow Mold (Typhula Blight) Typhula spp.

Symtoms

Damage from snow mold fungi usually becomes apparent as the snow melts, exposing the grass. Snow mold symptoms consist of roughly circular patches (1”-12”) of dead and matted grass blades. In severe cases, these patches tend to coalesce and may not be clear as individual circles. Just after snow melt and while the grass remains moist, it may be possible to differentiate the two common types of snow mold found in Massachusetts by their color.

Pink snow mold may not remain pink-colored very long, however, and the web-like mycelium of both types of fungi will disappear quickly as the grass dries. A second useful identifying characteristics of gray snow mold are tiny brown survival structures (sclerotia) on the blades and in the crowns of infected plants. These vary in size and color, becoming smaller and darker as they dry. The pink snow mold fungus does not produce sclerotia.

It is useful to determine whether the disease is pink or gray snow mold because gray snow mold rarely damages more than the blades of the grass. Lawns with gray snow old can be expected to recover fairly quickly even when damage appears extensive. Pink snow mold, in contrast, may invade the crowns and roots causing more serious damage.

It is not unusual for both types of snow mold to be found in the same area. All common lawn grasses may be infected, but Kentucky bluegrass fescue lawns are the least susceptible to severe damage.

Season

Snow mold fungi are active at temperatures just above freezing in moist conditions. These conditions occur most frequently under snow cover. The gray snow mold fungus usually only causes damage after prolonged snow cover. It may also damage grass that is covered with leaves or other materials.

The pink snow mold fungus may be active in cool, wet conditions from late fall through early spring even in the absence of snow covers, which greatly extends its potential disease season.

Disease Cycle

Snow mold fungi remain inactive during the warm months when other disease fungi are most active. They survive in thatch and on plants as sclerotia (gray snow mold) or as spores or as fungus threads (pink snow mold). In the fall, Typhula species sometimes produce small, elongate, spore-producing structures that may be seen among grass blades in lawns that have not been recently mowed. They grow from sclerotia that were produced the previous spring for survival over the summer.

As cool, wet weather develops the fungi begin to grow and infect grass plants. Like all living organisms, these fungi require moisture to survive. The cold, dry air of winter prevents active growth. The shelter of leaves, snow or any other cover on the grass maintains the necessary moisture for growth.

Optimum conditions for snow mold activity occur when snow falls suddenly and remains on ground that has not yet frozen. In such cases, grass is often still lush and growing providing an excellent food base for the fungi.

Cultural Controls

Snow mold activity is greatest beneath covers that maintain moist conditions. All leaves or other material should be removed from the lawn. In addition, it is best to avoid piling snow deeply along sidewalks and driveways where it will form a long lasting snow bank. In large lawn area, the strategic placement of snow fences and landscape plants may prevent deep drifting snow.

In the spring, rake away dead and matted foliage from damaged areas to allow the new growth to begin.

Heritage Lawns of West Springfield, Inc.
Southwick, MA 01077
(413) 731-0004 • Toll Free 1-877-731-0004
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