University of Saskatchewan

Winter Cereal Production

Snow Molds

Low-temperature-tolerant soil-borne fungi that cause snow mold can damage and kill winter cereals. The most common species of snow molds found in western Canada are:

Cottony - Coprinus psychromorbidus (low-temperature basidiomycete [LTB] and sclerotial low-temperature basidiomycete [SLTB].
Pink - Microdochium nivale (Fusarium nivale)
Sclerotinia - Myriosclerotina borealis (Sclerotinia borealis)
Speckled - Typhula ishikariensis

[ Images | Causes and Symptoms | Losses | Control ]

a) Causes and Symptoms:

Snow mold damage is usually evident as soon as the snow melts in the spring. The presence of mycelia (masses of fibrous strands produced by the fungus), the occurrence, color and size of sclerotia (hard masses of mycelia that are the resting stage of the fungi) or spores, and plant discoloration in the early spring provide the best clues for the field identification of the fungal species responsible for snow mold damage.

As the name implies, cottony snow mold has fibrous white mycelia that are present when the snow melts. Damage due to cottony snow mold is common on turfgrasses and, given the right conditions, this pathogen (disease causing organism) can cause extensive damage to winter cereals. Cottony snow mold is also responsible for winter crown rot in forage legumes.

Pink snow mold gets its name from the conidia (spore) masses of the fungus that develop a characteristic pink color on the leaves of the plant when the snow melts. It is best adapted to mild winter conditions, especially where deep snow cover maintains the soil temperature near freezing. Pink snow mold can be found on turf and forage grasses in addition to winter cereals.

Sclerotinia snow mold is commonly found on winter cereals, forage grasses and legumes, and turfgrasses in the high snowfall areas of western Canada where the winters are long. The presence of dead, bleached plants and large, black, irregularly shaped sclerotia in the early spring are the characteristic symptoms of this species of snow mold. The sclerotia can remain viable in the soil for many years.

Speckled snow mold can attack forage legumes and is highly pathogenic to winter cereals and grasses. It does not require prolonged snow cover to cause damage, but its level of damage is usually more severe following long, high snowfall winters. Speckled snow mold produces small, black sclerotia that can be found among the mycelia of the fungus and on the leaves of plants in the early spring.
[ Images | Causes and Symptoms | Losses | Control ]


b) Losses:

Snow molds can cause extensive damage to winter cereals in western Canada when conditions are favorable for their growth and development. Long, high snowfall winters usually provide the most favorable environments for snow molds and their growth is normally most prolific in areas of the field where the snow is deepest. As a result, snow mold damage usually occurs in patches that reflect the size of the snow banks and their location on the field.

In Saskatchewan, snow mold damage has been greatest on winter cereals grown on summerfallow in the Parkland region (black and grey soil zones) where the winters are long and the snowcover is most persistent. Because a protective snowcover is also necessary for winter wheat to survive the low-temperature extremes of this region, the drifting of snow from open areas on summerfallow fields and its banking along shelterbelts, fence lines, hillsides, etc., often produces winter damage due to both low-temperature stresses (in exposed areas) and snow molds (under snow banks) in the same field. In these situations, winter wheat survival only occurs in the transition area where the soil temperature is low enough to inhibit the growth of snow molds but warm enough to prevent low-temperature damage to the wheat plants.

Estimates of crop losses due to snow mold damage are usually based on field assessments using the symptoms listed above to identify the cause of winterkill. However, these symptoms quickly disappear once temperatures climb above freezing and spring rains arrive making it difficult to distinguish between low-temperature and snow mold damage. Consequently, estimates of crop losses due to snow mold are usually extremely subjective unless field inspections are made at the time of snow melt (to identify the causes) and again after crop green-up (to establish the full extent of the winter damage). Field and telephone surveys conducted later in the growing season often provide unreliable data and have occasionally greatly over-estimated the winter wheat crop losses due to snow mold in the Parkland region of Saskatchewan. Low-temperature damage is not a problem when properly managed winter rye is grown on summerfallow and, for this reason, published estimates of crop losses due to snow mold are much more reliable for rye than wheat.

Inoculum of some species of snow mold can build up quickly. Consequently, there is a greater risk of snow mold damage in rotations that include a high frequency of winter cereals or where winter cereals follow grass or legume forages.

A high probability of winterkill in the absence of a protective snowcover has meant that direct (no-till) seeding into the standing stubble of a previous crop (stubbling-in) has been the only viable winter wheat production option in Saskatchewan. In the last 25 years, crop losses due to snow mold damage have been less than one acre for every ten thousand acres (<0.01%) of stubbled-in winter wheat and rye produced in this region.
[ Images | Causes and Symptoms | Losses | Control ]

c) Control:

  1. Direct (no-till) seeding of winter cereals into standing stubble of a previous crop has proven to be an effective method of avoiding damage caused by snow mold in Saskatchewan.
  1. Crop rotations that include spring sown crops before winter cereals will assist in reducing the level of snow mold inoculum.
  2. Winter cereal cultivars with snow mold resistance are not available for production in western Canada.
  3. Fungicides that are used for snow mold control in turfgrasses are not registered for use on winter cereals.

[ Images | Causes and Symptoms | Losses | Control ]
snow-molds1 snow-molds2
Figure 1. Snow mold damage to winter wheat planted on summerfallow in east central Saskatchewan. Note the green healhy stand at the top of the hill and the extensive snow mold damage on the hillside where the snow banked during the winter. (Image Size = 129k)
Figure 2. Sclerotia snow mold damage in winter wheat (close-up). (Image Size = 68k)