Increase control of turf-damaging snow mold by taking a preventive approach

The turf on top was untreated before snowfall for snow mold. The turf at the bottom of the photo was treated with Interface and Triton FLO before the temperatures dropped.

Winter usually marks a period of hibernation, when Mother Nature slows down, plants go dormant, lakes freeze and we wait until the spring before we get back to the business of living. But, if you’re a snow mold, winter is the perfect time to be lurking underneath the snow, killing turfgrass while the rest of us await spring.

In areas where there is lasting snow cover, you’ll only get one shot to control them before lawns get buried. In cold, wet climates, there’s constant disease pressure and often little you can do to get on lawns or other areas of fine turf when they’re wet. Unfortunately, the damage done by snow molds can last through the spring, at least until it’s warm enough to get significant regrowth of cool-season turf. For those in the most northern climates, every day of the season counts and waiting for fine turf to recover from unsightly snow mold damage can be painful, with full recovery sometimes taking months.

Cultural Control Strategies

Although gray and pink snow molds and Microdochium patch occur under different conditions, there are some general strategies that work well for controlling all of them. These include:
1. minimizing fall nitrogen applications to allow turf to go into a hard dormancy in the winter;
2. continue mowing turf regularly until winter dormancy to avoid the build-up of excess vegetation and organic matter that favor fungal development; and
3. improving soil and surface drainage to reduce excess moisture.

Snow molds come in different varieties. Two different species of Typhula cause two different “gray” snow mold diseases, while the fungus Microdochium nivale causes two diseases: pink snow mold and Microdochium patch. Each of these diseases has specific conditions they occur under, and although there are things in common that you can do to avoid these diseases, there are some significant differences in controlling them.

A plot of untreated turf at the University of Wisconsin trials with snow mold damage.

Although the biology of these fungi that cause these diseases is different, the snow molds all cause disease in a similar way. Both Typhula and M. nivale can colonize turf in the fall and early winter before daytime temperatures drop below freezing. When it snows, the stage is set for snow mold to really cause damage. Since snow is mostly air, it’s a great insulator. Even when air temperatures are well below freezing, the temperature directly underneath the snow can remain above freezing, allowing snow mold fungi to do significant damage to the turf underneath. The extent of damage caused by snow molds under snow (or the success of fungicide programs used to control them) is often not seen until the snow melts away in the spring. It’s a little like Forrest Gump’s box of chocolates in that “you never know what you’re gonna get” until then.

M. nivale, however, can cause disease even when there isn’t snow cover. As long as it’s cold and wet, this fungi can cause disease. More on this later.

This plot has been treated with 6 fluid ounces of Interface and 0.85 fluid ounce of Triton FLO.

Gray and gray speckled snow molds

Gray snow mold diseases include both gray snow mold (caused by Typhula incarnata) and gray speckled snow mold (caused by Typhula ishikariensis). Both of these diseases tend to develop when there is 60 days or more of lasting snow cover. T. incarnata and T. ishikariensis can both be present on turf, but T. incarnata needs at least 60 days of snow cover and T. ishikariensis needs at least 90 days of snow cover to develop. These two diseases appear similar, causing gray blighted patches of turf 1 to 2 feet in size that often coalesce together. In these patches, T. incarnata will produce reddish-brown colored sclerotia about 3/16 of an inch in size, while T. ishikariensis will produce smaller dark brown to black sclerotia about the size of a pin head.

Both Typhula species start infections of turf in the fall when air temperatures are in the 50 to 65 degree Fahrenheit range. Under snow cover, they can continue to cause damage to turf when temperatures below the snow are 32 degrees Fahrenheit or slightly lower, and continue to cause damage during snow melt until daily temperatures are above 45 degrees Fahrenheit and conditions are dry.

Pink snow mold and Microdochium patch

Pink snow mold is caused by M. nivale. Pink snow mold can be active at temperatures of 32 to 48 degrees Fahrenheit, and tends to be more common when snow cover is light or only for short periods of time. Damage under snow appears as white patches a few inches to a foot in size that have reddish-brown borders and can have a slightly pink color in the patches where pink spore masses (sporodochia) are being formed.

Microdochium patch is also caused by M. nivale, but doesn’t need lasting snow cover and can develop anytime daily temperatures are below 68 degrees Fahrenheit and there is rain, heavy mist or fog, or any type of prolonged wet conditions. Symptoms include white to pinkish patches a few inches to a foot in size, which often have a water-soaked, greasy appearance on the advancing margin of patches and rings of infected turf.

Snow mold control

For “real” snow mold under conditions of snow cover, turfgrass pros will only get one chance to make the right fungicide choices before snowfall. Two things are really important: the timing of the application and selecting the right combination of fungicides to last through the winter under snow. Fungicides must be applied prior to snow fall, but early applications in the fall may not last long enough through the winter. A preventive fungicide application needs to be made in the fall through early winter before snow accumulation is expected. The timing will vary for different areas in the United States, but having fungicides down before snow season is key for control. Needless to say, fungicide applications after snowfall are not very effective, no matter what combination is used.

Because snow mold fungicides are often needed to provide 60 to 150 days of control, one fungicide alone won’t do the job, so choosing the right combination is critical. The longer the expected period of snow cover, the more fungicide or fungicide products may be needed. Often, combinations of different classes of fungicides are needed to get effective control when such a long period of control is expected from a single application.

Interface fungicide provides two strong fungicides (iprodione and trifloxystrobin) that are effective against snow molds. When less than 60 days of snow cover are expected, Interface alone at 6 fluid ounces is an effective solution for snow mold control. When 60 to 150 days of snow cover are expected, 5 fluid ounces of Interface should be mixed with 0.85 fluid ounce of Triton FLO to provide a three-way-mix of iprodione, trifloxystrobin and triticonazole. For over 150 days of snow cover, 6 fluid ounces of Interface plus 0.85 fluid ounce of Triton FLO should do the job. For added control, 4.5 to 5.4 fluid ounces of Reserve can be substituted for the 0.85 fluid ounce of Triton FLO at 60 to 150 and greater days of expected snow cover, respectively.

Granular Fungicide Gets EPA OK

Headway G received registration from the U.S. EPA for use on residential and commercial lawns. The formulation of azoxystrobin and propiconazole controls more than 20 turf diseases, including gray and pink snow mold.
“Granular products are preferred by many professional lawn care operators,” says Bob Goglia, brand manager for Syngenta. “The introduction of this product into the lawn care industry gives lawn care operators a reliable broad-spectrum fungicide that requires no mixing and no traveling with a water tank, while providing confidence that it will minimize customer call-backs.” The granular formulation allows for application even when wind conditions prohibit spraying.
Headway G is not currently registered for use or sale in all states. Check with your state or local extension service prior to buying or using this product.

Stressed turf is susceptible

Although it may seem strange, the late summer and early fall may be good times to start thinking about snow mold control. Fall diseases like dollar spot and Bipolaris leaf spot can cause significant damage, weakening turfgrass as it goes into winter conditions and making it more susceptible to snow mold damage.

Microdochium patch can occur throughout the fall, winter and spring in areas where it is cold and wet and daily temperatures are below 68 degrees Fahrenheit. Often, Microdochium patch outbreaks are associated with extended rainy weather when it’s nearly impossible to get equipment on water-saturated turf. In these cases, many turfgrass pros are forced to spray curatively after the disease has developed.

Fungicide applications with both good knock down activity and long residual control are needed for this disease. Since there can be prolonged periods of weather favorable for the disease and multiple cycles of the disease in the fall through spring, fungicide resistance can be a problem so it’s important to rotate amongst fungicides with different modes of action. Fungicides with different modes of action delay the development of fungicide resistance.

Snow mold and Microdochium patch control need to be done preventively. Combining cultural controls with timely fungicide applications are extremely important. Once heavy snow falls or winter rains come, it is often way too late to do effective management of the disease. Start prepping for these diseases in the fall to make life much more enjoyable in the spring when the last thing you’d want to see is dead grass.

The author is a technical service specialist with Environmental Science, a division of Bayer CropScience LP. Prior to joining Environmental Science, Wong served as associate specialist in cooperative extension at the University of California, Riverside.