Like all disease-causing pathogens, Microdochium nivale is an opportunistic pest. Because it thrives under a wide range of conditions, the pathogen that causes Microdochium patch, or pink snow mold, has an open door to cause damage on cool-season turf on golf courses.
Although it might seem early to begin thinking about pink snow mold prevention, the time to make preventive fungicide applications is just a matter of weeks away for many superintendents.
"This is by far the biggest problem for golf courses in Oregon," said Alec Kowalewski, Ph.D., of Oregon State University. "It's a problem here from October through spring."
Microdochium patch can be found in all types of cool-season turf where conditions are conducive.
Although it is commonly found where snowfall is significant, the disease also can be a problem where snow accumulation is not as much of a concern.
According to university research, it is more likely to occur under snow cover when the soil is not frozen, and begins with the infection of turfgrass leaf tissues by mycelium of Microdochium nivale residing on the plant. Mycelia typically spread under snow cover causing infections that result in patches of blighted leaves, stems or crowns. Spores formed on diseased tissue can promote new infections even after snow cover is not present. The pathogen survives as dormant mycelium in organic matter and in the soil during spring, summer and fall.
Typically, the deeper the snow cover and the longer the snow remains on the turf surface, the greater the extent of symptom development and turfgrass injury, according to research at Penn State University.
Ideal conditions for the development of pink snow mold include temperatures slightly above freezing at the snow/turf interface when the plant tissue is wet.
University of Illinois research indicates that disease development occurs rapidly when humidity is high and temperatures are 32 to 46 degrees Fahrenheit, with a maximum of about 55 degrees. Once snow melts and no longer covers the turf, disease activity usually subsides but can become active again if cold, wet, and overcast conditions persist.
Symptoms include pink, white or tan patches of matted leaf blades inside an outer ring of copper-colored turf. Patches typically range from 2 inches to 10 inches in diameter, and fluffy white mycelium can sometimes be present around the patches in later winter or early spring during periods of high humidity.
On creeping bentgrass greens, streaks of off-colored turf that follow surface drainage patterns might appear during the spring, according to research conducted at Purdue University.
According to research at Penn State and Illinois, there are several cultural practices that can help minimize the onset of pink snow mold.
- Keep the turf mowed in the autumn until growth stops.
- Put turf to bed for winter dormancy in a hardened state, not in lush condition. Do not fertilize within about six weeks of the first frost or snow.
- Remove organic matter and thatch thatch accumulation.
- Maintain moderately acidic soil pH — at or slightly below 6.5.
There are many chemical options for controlling Microdochium patch, including chlorothalonil as well as DMI and Qol class fungicides.
Although it is commonly found where snowfall is significant, the disease also can be a problem where snow accumulation is not as much of a concern, says Kowalewski.
Microdochium patch can be found in all types of cool-season turf where conditions are conducive.
Much of the Pacific Northwest does not get a great deal of snowfall, but prolonged periods of cool, wet weather there still make for ideal conditions for the pathogen to settle in for an extended period.
"In Portland, Salem, Seattle and Eugene it doesn't really snow very much," Kowalewski said. "But the fungicide wears off, and we have to make repeated applications about every 21 days through winter and spring."
Kowalewski says some superintendents in the Northwest relax fungicide applications in December and January when temperatures drop below freezing, when spread of the disease would cease.
"Those are the risk-takers who do that, because it's too cold," he said. "But there aren't many doing that."