Snow Mold

While colder winter weather might slow the growth of grass, it doesn't mean fungus isn't infecting the turf. Snow mold, an umbrella term for multiple fungi, can appear after lengthy periods of snow cover and even, somewhat misleadingly, when snow isn't present. Paul Koch, associate researcher and turfgrass diagnostic lab manager at the University of Wisconsin-Madison helps us break down snow mold, how it can be identified and treated.
 

Growth and identification. Snow mold is generally broken into three categories. Gray snow mold (Typhula incarnate), speckled snow mold (Typhula ishikariensis and also sometimes referred to as gray snow mold) and pink snow mold (Microdochium nivale). Gray and speckled snow mold are usually found in the northern tier states, while pink snow mold can be found pretty much anywhere in the country, Koch says. "In fact, a few years ago they had a decent (pink) snow mold outbreak in Mississippi," he says.

Pink snow mold needs wet, cool conditions and not necessarily snow fall for the fungus to become active and grow out of the thatch and infect the turf, Koch says. In the spring, once it is no longer infecting the turf, it will go dormant and survive in the thatch and soil on organic matter.

In the spring, gray and speckled snow mold produces sclerotia, which is hard and pebble-like and serves as the funguses long-term survival structure, Koch says. "(Sclerotia) survives the summer and into the fall," he says. "Once the fall starts to cool down, the sclerotia will germinate and produce new mycelium and the fungus will then infect under snow cover." Speckled snow mold is normally seen in areas of continuous snow cover for more than 90 days, while gray snow mold requires about 60 days.

When it comes to identifying the different fungi, there are differences. Following snowmelt, LCOs should be able to see sclerotia with the naked eye, Koch says. If it is gray snow mold, the sclerotia will look like a little red pebble on the leaf blades. "Lawn care operators in the far northern part of the country that will see more of the speckled snow mold, they also have sclerotia but it's very small and black – almost looks like pepper on leaf blades," he says.

Pink snow mold doesn't produce sclerotia, Koch says. So if it looks like snow mold but doesn't have sclerotia, it's probably pink snow mold.

"As far as looking more at the symptoms themselves, snow molds are normally more of a patch, so it's going to be somewhat circular," Koch says. The gray snow molds will have more of a gray, dimmer color. Pink snow mold will be more of a tan color and may have a reddish hue outside of the patch.

Prevention and treatment. Lawns that are more susceptible to snow molds are ones that had a lot of fall fertility put down and are actively growing during winter, Koch says.

"Limiting your late fall nitrogen applications will limit your snow mold development, so that is a cultural control that can be done," he says. "Making sure you have the leaves raked off the lawn. Leaves will trap moisture and can promote snow mold development. If there is any drainage problems, if the lawn is very wet for portions of the winter that will be more susceptible to snow mold development."

Snow mold forms from previous infections. "If you can control snow mold very well for several years, you're less likely to have it in a future year because there's just less of it there from a previous year," Koch says.

So, in cases where it's needed, one fungicide application or a granular application can work well for control. Koch says there are many options, but some of the active ingredients that work well are azoxystrobin, propiconazole, pyraclostrobi and triticonazole.

The author is an associate editor at Lawn & Landscape. She can be reached at clawell@gie.net.
Credit: University of Wisconsin – Madison