Let It (Snow) Mold

The turf disease is bad enough to ruin a superintendent's spring. But it can be controlled. Here's how.
By John Fech and Loren J. Giesler

Snow mold is one of those maladies on the golf course that can cause major frustration. Without a doubt, golf course superintendents that have felt the sting of snow mold injury agree that it's a disease that can cause wholesale, widespread damage to the turf, as well as that sick feeling in your gut. Yet, like other serious issues in life, knowing more about it can lessen its load.

Guessing game

Because of the nature of the conditions that cause snow mold, the likelihood of occurrence is a bit of a guessing game. Perhaps more so than any other disease, snow mold infection is highly dependent on what happens over the winter. For the most part, the "what" is a set of weather conditions over which none of us have any control.

Symptoms and favorable conditions

The two most common snow molds are Microdochium patch (pink snow mold) and Typhula blight (gray snow mold). In some winters, early symptoms can be observed. However, it's normally not easy to tell what's going on until winter is over.

Pink snow mold can injure turf from the middle of fall to early spring during conditions of prolonged cool, wet weather. Most often, infection occurs with temperatures in the 32- to 50-degree Fahrenheit range with light drizzle or fog. The greatest damage will result when heavy, wet snow falls on unfrozen, nondormant turf. The development of pink snow mold has also been linked to high nitrogen fertilization in fall.

Gray snow mold is one of the most common snow molds. It's normally not detected until winter is over.

Symptoms of pink snow mold on bentgrass greens and tees are roughly circular, rusty brown patches that range from 6 inches to 3 feet in diameter. On other species, including Kentucky bluegrass, perennial ryegrass and fine leaf fescues, more or less circular spots 6 to 12 inches in diameter are seen. Within the affected areas, turf blades and stems appear bleached and matted. Under wet or moist conditions, a white to salmon pink moldy growth is visible at the edge of the patches. Because of the contrast in color and stem architecture between the diseased spots and dormant turf, the scattered spots can sometimes be detected, even in midwinter.

Symptoms of gray snow mold usually develop where snow is piled high and is slow to melt.

Gray snow mold

Gray snow mold is encouraged by a different set of weather conditions. Strictly a cold weather disease, Typhula blight causes the bulk of its damage when turf is covered with ice and snow for an extended period of time.

Patiently waiting their turn to cause damage to the course, the sclerotia that cause gray snow mold lay embedded in the thatch and older, infected grass blades. When snow cover and extended periods of freezing or near-freezing temperatures are present, they germinate and infect grass plants.

Symptoms of gray snow mold are most likely to develop where snow has been piled or drifted into place and is slow to melt. When infected, patches of rough-looking, bleached tan areas become visible. Usually between 8 inches and 1 foot in diameter, the blotchy areas become evident as melting snow recedes from affected areas. When wet, they are often covered by a whitish-gray moldy growth. The presence of small orange to black roundish sclerotia embedded in infected leaves helps to distinguish gray snow mold from other winter maladies. The use of a 10x hand lens is usually necessary to observe them.

Pink snow mold can injure turf during conditions of prolonged cool, wet weather - from the middle of fall to early spring.

Look-like symptoms

Damage from direct ice kill or low temperature injury can mirror that of snow mold. After the rapid onset of extremely low temperatures, similar looking symptoms can appear. In this case, low temperature injury results from tissues being mechanically disrupted by internal ice crystals and fluctuating hydration of the plant crown.

Another form of low temperature injury is winter desiccation, common on elevated areas of the golf course such as tees and greens. Topdressing and winter covers can be used as preventive measures to avoid damage. A third type of winter injury that can be mistaken for snow mold occurs when ice covers turf for long periods of time and excessive moisture combines with freezing conditions. When large sheets of ice form, injury can result from the suffocation of the turf and produce irregular areas of damaged turf. This symptom results from ice cracking and oxygen being available only at these locations. Ice injury often occurs in pockets or depressed spots where water can accumulate prior to freezing.

Cultural control

Preventing snow mold through various management practices is worth the effort. Lush growth is a key trigger for the encouragement of snow mold injury. First, preventing the accumulation of snow and ice through devices such as snow fences will help to reduce the likelihood of snow mold development.

Secondly, balanced fall fertilizer applications with at least a 50 percent component of slow-release nitrogen will help to reduce succulence going into winter. Third, continued mowing until dormancy to prevent blades from falling over excessively will help prevent a localized microclimate that facilitates development of snow molds. Finally, once snow mold symptoms have been observed in early spring, "recovery" fertilizer applications to encourage new growth will help produce replacement shoots for the ones damaged by the disease.

Chemical control

On high-value turf and where snow mold infection has caused damage in previous years, preventive fungicide applications are justified. In most scenarios, a late fall application followed by subsequent follow-up treatments during winter thaws provide effective relief from snow mold diseases. Keep in mind that dormant turf does not incorporate and translocate the systemic fungicides used in fall applications, so it is important to make these applications before the turf is fully into winter dormancy.

Preventive fungicides that have been reported to provide good to excellent results for pink snow mold include fludioxonil, iprodione, PCNB, propiconazole, pyraclostrobin, thiophanate-methyl and trioxystrobin. Be sure to read and follow all label instructions carefully for best results.

Products that have demonstrated good prevention of gray snow mold are products containing PCNB or combinations of chlorothalonil with one of the following active ingredients: iprodione, thiophanate-methyl, fludioxonil or azoxystrobin.

John Fech is an extension educator specializing in turf and ornamentals at the University of Nebraska-Lincoln. Dr. Loren Giesler is an Extension Plant Pathologist at the University of Nebraska-Lincoln.