GRAY SNOW MOLD ON TURFGRASS Typhula spp.   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 sp.) 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

Gray snow mold (Typhula blight) is caused by Typhula incarnata and related species. It is a true snow mold and appears as roughly circular bleached patches up to 60 cm in diameter (Fig. 1). Soon after the snow melts, the infected grass may be matted and surrounded by a white to gray halo of fluffy fungal growth. Examination of the diseased plants reveals tiny tan or brown pea-like structures (sclerotia) on or imbedded in infected leaves. The severity of the disease will vary. It is particularly severe when turf has been subjected to a prolonged, deep, compacted snow cover. Although the disease is unsightly, it rarely kills the grass.

Figure 1: Infected spots on turf.

Figure 2: Clavual of sporocarps in close-up view of infected turf.

Disease Cycle

The disease cycle for this fungus is nearly opposite that of most others. This fungus produces sclerotia (resting structures) to help it survive the summer months. In late fall when conditions are favorable, these sclerotia may produce mycelium or basidiocarps (Fig. 2) that produce spores. Mycelium from the spores or sclerotia grow out and infect new plants under cover of deep snow during the winter. Where gray snow mold has occurred once, it is likely to recur if left unmanaged.

Disease cycle of Gray Snow Mold. (Provided by Compendium of Turfgrass Diseases, 2nd edition, APS Press)

Control Strategies

Development of gray snow molds can be reduced via 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 molds have caused damage, rake the matted grass in order to encourage new spring growth. If re-seeding areas where these diseases have been a problem, use disease resistant turfgrass varieties.

If snow molds have 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. Homeowners may use Heritage or some fungicides containing the active ingredients triadimefon or quintozene. Apply according to label directions. Additional products may be available for use by commercial applicators. Commercial applicators should refer to the appropriate pest management guidelines for more information or contact their local Cooperative Extension Office for more information on currently registered products. Where multiple applications are required, alternate the use of 2 or 3 recommended fungicides, but note that use of an Azoxystrobin fungicide (Heritage) may increase the severity of Dollar Spot. In all cases, read and follow pesticide label directions.

Updated, SLJ, 1/07