Released: February 08, 2007

Cold, Wet Soil Can Trigger Snow Molds in Turfgrass

MANHATTAN, Kan. – Mother Nature seems to enjoy her little surprises. In fact, where snow fell in the High Plains before the ground was fully frozen, she may be preparing two “gotchas” for lawns and golf courses. One of the surprises already is springing up to the south, as far away as Mississippi.

“Most plant diseases shut down during cold weather, but these two are exceptions. Although they attack grasses, not snow, they’re popularly known as gray snow mold and pink snow mold,” said Megan Kennelly, plant pathologist with Kansas State University Research and Extension.

The fungus-caused diseases can occur together on the same site, she said. The fungi live in and around grass year-round. But, they become active only when winter weather creates the right mix of wet and cold.

“Pink snow mold – also known as Microdochium patch – doesn’t even require that its moisture be snow. Repeated cycles of frost-thaw can activate it. Foggy or drizzly weather can trigger it, too, if the temperature is right,” Kennelly said..

In contrast, gray snow mold – a group of closely related Typhula fungi – seems to prefer turf, Kennelly said. It usually develops after turfgrass has been under snow cover for about two months. It needs the snow to insulate the ground and keep soil surface temperatures just above freezing.

Both kinds of mold cause bleached-looking circles about 2 feet across. In most cases, the circles appear as snow melts.

While the damaged areas are still wet, dense masses of the fungi’s branched, threadlike hyphae may be visible. The structures are white to pink in pink snow mold and white to gray for gray snow mold.

Gray snow mold usually will have sclerotia, too: hard, pea-size, light-brown to black structures.

Snow molds appear to be a bigger problem for golf courses than for home lawns, especially if the diseases infect putting greens, Kennelly said.

“Golf course owners are selling an experience, which includes their turf’s appearance. On greens, however, mixed areas of dead and living bentgrass leaves could also affect how a ball rolls,” she said.

The plant pathologist’s recommendations for golf courses can include applying chemicals, shoveling snow from susceptible areas, and applying dark-colored sodium humate or the like to promote melting. (Details are on the Web at http://www.plantpath.ksu.edu/DesktopDefault.aspx?tabid=632.)

“Although the symptoms look dramatic, I don’t recommend fungicides for home lawns, except in extreme situations. Infected turf eventually recovers. And, if homeowners just make a few changes in lawn management, the diseases aren’t likely to become a frequent problem,” Kennelly said.

Her suggestions for ways to keep snow molds in check include:

* Keep mowing grass until it quits growing in late fall. Turf left taller than 3 inches when winter arrives will matt under any snowfalls, thus creating a favorable environment for the fungi.

* Don’t fertilize in fall beyond the recommended times. Too-late applications signal turf to produce lush top growth, and, lush growth is more susceptible to snow molds.

* Rake leaves in fall, so they can’t matt down and foster an insulated moisture buildup.

* Rake lawns in spring to remove debris, air out the turf and promote drying.

-30-

K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by:
Kathleen Ward
kward@oznet.ksu.edu
K-State Research& Extension News