PINK SNOW MOLD ON TURFGRASS Microdochium nivale   F A C T S H E E T

Introduction

Winter diseases of turfgrasses are often associated with melting snow or cold, wet periods. Bluegrasses (Poa sp.), fescues (Festuca sp.), and ryegrasses (Lolium sp.) may be attacked, but bentgrasses (Agrostis palustris) are most susceptible. Two diseases, Gray Snow Mold (Typhula Blight) and Pink Snow Mold, are common in New York, and may occur singly or side-by-side. Since different fungicides may be used to control each of these diseases, it is necessary to distinguish between them.

Symptoms

The fungus that causes Pink Snow Mold produces roughly circular bleached patches up to 60 cm in diameter. Often the mycelium of the fungus is readily visible. In contrast to Gray Snow Mold, however, a pinkish cast to the symptomatic area might be observed under wet conditions. Moreover, no tan sclerotia are associated with the diseased plant tissue as seen in Gray Snow Mold. This disease can become severe when turf is subjected to prolong periods of cool, wet weather from early autumn to late spring, and does not require snow cover to develop. A severe infection by M. nivale kills the turfgrass.

Figure 1: Patches caused by the Pink Snow Mold fungus (provided by Dr. Eric B. Nelson, Cornell University) Figure 2: Mycelium of the fungus (provided by Dr. Eric B. Nelson, Cornell University)

Disease Cycle

The fungus Microdochium nivale survives unfavorable periods as dormant mycelium in infected plants and plant debris. As conditions improve for fungal growth, the fungus may begin to infect plants with little symptom development. Wet weather conditions with temperature around 16^oC will promote rapid spread of the disease. Dry, warm weather causes the fungus to revert to its dormant state. The fungus can be transmitted throughout the year on equipment, people, animals, wind or water.

Management Strategies

Development of pink snow mold can be reduced by various cultural methods. Avoid late fall applications of fertilizer that would stimulate succulent growth. Such growth is very susceptible to infection. Also continue to mow turf as long as it continues to grow in the fall, and avoid compacting snow over the lawn. Where snow mold has caused damage, rake the matted grass in order to encourage new spring growth. If reseeding areas where the disease has been a problem, use disease resistant turfgrass varieties.

If pink snow mold has been severe or wide-spread in past years, or if susceptible varieties or species are being grown, a preventative fungicide program may be used. Fungicide applications should be made in late autumn just before permanent snow cover is expected and, if possible, during a mid-winter thaw. For home lawn applications, homeowners may treat with Heritage (azoxystrobin), Bonide Infuse Systemic Disease Control Lawn & Landscape (thiophanate-methyl), or a registered fungicide containing the active ingredient propiconazole. Note that Heritage should not be used where it may come in contact with certain Malus spp.--See label for details.

Where multiple applications are required, alternate the use of 2 or 3 of the recommended fungicides. Additional products may be available for commercial use. Commercial applicators should refer to the appropriate commercial pest management guidelines, or contact their local Cooperative Extension Office for more information on currently registered products. In all cases, read and follow pesticide label directions, and be certain any formulation(s) of pesticide(s) you purchase are registered for the intended use.

Updated, SLJ, 3/09