Photo courtesy of Spring-Green Lawn Care

When it comes to winter diseases in lawn and turf stands, weather is a factor in determining the existence and the severity of the disease. In fact, it’s part of the “disease triangle” that will determine if a lawn care operator will have to treat a lawn for a disease.

“The disease triangle consists of a pathogen, which is already in the soil, the host plant, which is your turf, and the environment,” says Harold Enger, director of training at Spring-Green Lawn Care.

The first two factors are fairly constant. Weather, especially cold, snow and rain, will in large part determine the occurrence and severity of winter diseases in both warm season and cool season turf. Enger says a fourth factor is time. The longer extreme conditions exist, the more severe the problem will likely be.

As for weather, forecasters are giving some clues to what the weather conditions might be like this winter for different parts of the country.

La Niña to replace El Niño.

According to AccuWeather, the El Niño that resulted in a mild 2015-16 winter for a lot of folks officially ended in June. Right on the heels of this weather phenomenon is a rather weak La Niña system, which they’re predicting will result in a snowy winter in the East and dryer weather in the flood-soaked South.

Weather forecasts aside, lawn care operators know to err on the safe side and prepare for the worst when dealing with Mother Nature. Here is what lawn care operators around the country are doing to prepare and treat winter diseases in turf.


Meteorologists think the Pacific Northwest will bear the biggest brunt of La Niña and are predicting stormy weather for the region. However, it’s not supposed to be really cold. The weather and climate are quite variable in this region. LCOs are always on the lookout for snow mold, regardless of weather forecasts.

“Snow mold is one of the biggest threats to turf in this region, especially in areas of the Northwest that receive snowfall,” says Hamilton Allen, training director with Senske Services, based in Seattle. There are two kinds of snow mold that they deal with in this region: gray and pink. Gray mold requires snow while pink mold doesn’t. Hamilton says they see more of the pink snow mold in Washington state, although it really depends on where exactly you’re located. Snow mold is usually treated with a general fungicide up until the end of November. Treatments are usually effective, especially if the turf is fairly healthy.

“But it depends on the pressure, the health of grass and height. If you’re not taking care of your lawn, the issues can be much greater,” Hamilton says.

He says the snow creates a humid environment for fungal spores to develop. Hamilton suggests cutting the grass fairly short before it goes dormant to prevent a “humidity pocket” from forming. Nitrogen, of course, will stimulate green growth and should be avoided in fall treatments of turf.

Hamilton says his company will respond to any complaints regarding snow mold but they usually only treat commercial and large lawns, unless the problem is pervasive. “If we get a call about snow mold, we note it in our system and keep an eye on it,” he says.


If the AccuWeather forecasters are right, the East Coast could be in for a snowy winter, which would mean a greater occurrence of snow mold. Gray mold is the most prevalent form of snow mold in this region.

One of the biggest turf diseases affecting warm season grasses in the southeast is large patch. To treat, wait until the temperature is hovering around 70 degrees and apply a fungicide that is labeled for these diseases.
Photo courtesy of Spring-Green Lawn Care

With 40 years in the business, Spring-Green’s Enger has a pretty good handle on winter lawn diseases in general. He says in the cool season zones, like the Northeast and Midwest, snow mold generally occurs on turfgrass that hasn’t hardened off before the snow falls.

“If the temperatures are in the 40’s and 50’s and then it snows, it’s a great condition for snow mold to develop,” Enger says.

He says gray snow mold is mostly a cosmetic problem and can be easily remedied by spreading out the mycelium that appears on the surface of the grass with a rake or even your finger. LCOs normally only treat commercial turf, such as a golf course or a high profile lawn, for snow mold. In residential lawns the problem will clear up on its own as the weather warms up in the spring. “I’ve never seen grass killed by it,” Enger says. “Generally the grass grows back and is just fine.”

Deron Snyder, owner of Northeast Pro Turf in Moravia, New York, treats mostly golf courses and athletic fields for snow mold diseases. He says many homeowners don’t even know they have the disease in their lawns since it disappears within a few weeks of a warm up.

Where snow mold is known to be a problem, they’ll wait as long as they can in the fall before applying a fungicide. “We’ll delay it as late as we can, up until Thanksgiving” Snyder says. He says they use the systemic fungicide Turfcide 400, flowable as well as granular, as a preventative measure for the disease.

He says he prefers to use the granular because you can winterize your spray equipment and have it stored before the snow flies and use the granular spreaders late into the fall. “Most guys like to do a pretreatment, then wait as long as they can to apply the snow mold treatment,” Snyder says. “The nice thing about granular, they can wait as long as they can to apply it.”


Clint Culver, owner of Nitro Green Professional Lawn and Tree Care in Helena, Montana, says his crew tries to get down a fungicide application by Thanksgiving.

“We wait as long as we can before we apply a fungicide,” Culver says. Nitro Green treats primarily sports turf, rather than residential, even though they have double as many residential clients as commercial ones. Because turf stands are getting soggy by fall in this particular region of the West, they’ll spray with the hoses from the truck rather than risk taking any heavy equipment out on the turf.

Proper cultural practices are also important in the West for residential and commercial properties. Culver says he tells property owners to cut the lawn fairly short in the late fall and to not pile snow with blowers or plow trucks.

Taylor Haught, Phoenix branch manager at Somerset Landscape, says it’s important to overseed their dormant Bermuda grass lawns with a quality perennial rye seed. The most predominate disease is a warm season pythium that can wipe out a large section of overseeded rye grass.

“Pythium is mostly onset by poor management/cultural practices such as over-watering, fertilizing and mowing,” says Taylor Haught, Phoenix branch manager. “Once there is an outbreak, the rye grass will die and must be reseeded in order to regain a uniform lawn.”

Haught says there is no cure for warm season pythium, only prevention, and it is important to not over water and over fertilize. The team at Somerset runs soil and water analysis and looks out for dangers in high sodium settings.

The second disease to look out for, Haught says, is rapid blight. Rapid blight is mostly brought on by high sodium content caused by routine applications of gypsum and/or calcium treatments,

“Applications of gypsum/calcium will allow the sodium to leach through the soil and reduce favorable conditions for rapid blight to grow,” he says.

Once an area is diseased, there are chemical treatments with the active ingredient pyraclostrobin that can provide the corrective measures needed.

“This year should be better than most because of the perfect/ideal weather we have had to germinate and grow rye grass,” he says. “Gypsum and calcium are the key to beautiful, well-kept lawns.”


Dealing with winter diseases in the South and Southeast is kind of like predicting the weather. There are a lot of different variables that come into play, including the type of turf, amount of rainfall and temperature.

The two biggest turf diseases affecting warm season grasses in this area are large patch and spring dead spot. Spring-Green has a location in the Columbia South Carolina area and treats these diseases in commercial and residential lawns. Enger says that spring dead spot, common in bermudagrass, is a fungal disease that works on the roots of plants, starting in fall, and shows up as ugly dead spots in the spring.

Large patch attacks zoysiagrass and, like dead spot, works on the roots of plants. Enger says the treatment method for both diseases is to wait until the temperatures are hovering around 70 degrees and treat it with a fungicide that is labeled for these diseases. As for cultural practices, he says to mow at about 2 ½ inches and do what the university horticulture programs recommend and chew up the leaves with a lawn mower, but don’t remove them.