Snow Molds -- Potential damage and how to recover

EDITOR'S NOTE: This article first appeared in the January/February 2014 issue of Turf News, The Ohio Turfgrass Foundation Magazine. It's reprinted with the permission of the authors.

This is the time of year that turf pathologists turn their attention to a major potential problem, snow mold!  Spring is still a long way away and there could be long periods of harsh winter weather. To date most areas have experienced super cold temperatures, snow cover, ice, and rain.

Photo 1. Pink snow mold on a green, note that spores can be moved and cause new patches to develop.

Sometimes all of these have occurred within a week or in a very short time. These environmental conditions mean that snow molds could be a concern to turfgrass managers and golf course superintendents.

Snow mold is active at temperatures just above freezing in moist conditions. The gray snow molds (Typhula incarnata, also called Typhula blight, and Typhula ishikariensis) most often occur when snow cover exceeds 40 to 60 days. Pink snow mold/ Microdochium Patch (Microdochium nivaile), however, does not require any snow cover to develop. In addition to snow molds excessive ice buildup over turf or completely saturated / flooded sites followed by sudden freezing conditions can cause damage to turfgrasses.

Bentgrasses and Poa annua are especially susceptible to damage, but all cool-season grasses can be affected. With pink snow mold, which is the most common snow mold found in Ohio, circular patches develop from several inches to over a foot in diameter. The color can vary considerably

Photo 2. Pink snow mold on creeping bentgrass in a lawn.

from pinkish, to tan or brown infected turf. Under wet conditions pink snow mold patches appear slimy (Photo 5), when dry the turf leaves appear matted and collapsed. Typhula / gray snow mold symptoms appear as circular patches of straw-colored to grayish-brown turf. The turf may also appear matted (Photo 3), with the appearance of a grayish-white mycelium at time of snowmelt. The mycelium often dries and becomes encrusted over the patch.

If damage from gray snow mold is present, little can be done to undo the damage, so your focus should be on recovery. To help determine the extent of damage, take samples of affected turfgrass and bring them into an environment that is conducive to growth (warm temperatures and light). To assess potential turf recovery, observe the growth of the plants, watching for the development of new shoots. With both snow molds recovery is usually good in Ohio but it may take time. Warm temperatures are required for new shoots and leaves to develop in damaged areas so be patient.

Photo 3. Dry matted ryegrass foliage from gray snow mold.

 

Tips to help recover from snow mold
• Remove snow and ice from turfgrass areas (this is easier said than done).
• Lightly rake the grass to promote air circulation and to allow light to penetrate the canopy and encourage new shoot and leaf develop.

• If there is any dead or matted material, rake and remove. In the case of dead turfgrass, renovate the site.
• If the site did not receive appropriate fertility in the fall, a modest application of started fertilizer would be recommended.
• For gray snow molds, the damage is done, so fungicide applications are

Photo 4.Pink snow mold in perennial ryegrass baseball field.

of little to no benefit at this time. In the case of pink snow mold / Microdochium patch (that occurs in the late winter or into the spring) fungicide applications would be recommended, especially if cool wet conditions are experienced and Poa annua is the turf under management. This pertains primarily to golf greens.

For specific fungicide recommendations, check OSU web site http://turfdisease.osu.edu
   
Or the the University of Wisconsin’s site, since they have done extensive gray & pink snow mold trials at: http://labs.russell.wisc.edu/turfpath/snow-molds/

How to identify the different snow molds

To identify gray snow molds, look for the sclerotia (a compact mass of mycelium that is the survival structure of the pathogen, on the leaf tissue and debt. Typhula incarnata has reddish-brown to dark-colored sclerotia that are rather large, up to 0.2” in diameter. Typhula ishikariensis has much smaller sclerotia that appear similar to flecks of black pepper on the leaves and debt. Active mycelium is a white to gray color.

Pink snow molds do NOT produce sclerotia, and the active mycelium is a

Photo 5. Pink snow mold in juvenile perennial ryegrass under wet conditions.

pinkish to white color, depending on exposure to light. Both gray and pink snow molds occur together, so it can be difficult to assess which is the predominate pathogen.

About the authors
Joseph W. Rimelspach, Todd E. Hicks and Francesca Peduto Hand work at The Ohio State University's Department of Plant Pathology in Columbus, Ohio.