Annual bluegrass, bentgrass, Kentucky bluegrass, and ryegrasses are most commonly affected by pink snow mold. However, nearly all cool-season turfgrasses as well as bermudagrasses and zoysiagrasses are susceptible.
The disease first appears as round, water-soaked spots, 1 to 3 inches in diameter, that soon turn into yellow, orange-brown, or reddish brown patches. Patches may enlarge and become light gray or light tan rings up to about 1 to 2 feet across with orange-brown or reddish-brown borders. The patches are usually rounder and smaller than those of gray snow mold. Under snow cover or with very wet conditions, varying amounts of white fungal growth may be seen on matted leaves. Where there is snow cover, the disease may blight large areas. As the snow melts, the white fungal growth at the perimeter of the patch turns pink; hence the name "pink snow mold".
The correct name for the disease many know as pink snow mold or Fusarium patch is now Microdochium patch. Over the years, the fungus which causes this disease (now called Microdochium nivale) has been reclassified and renamed many times. Although the name "pink snow mold" is not perfectly descriptive of the disease, it is used herebecause this name would not be affected by any future reclassification of the pathogen.
Pink snow mold is common and troublesome where prolonged periods of wet, cool weather occur from autumn to early summer. The disease often occurs in the absence of snow and is favored by cool or cold wet weather when grass growth is slow. Patches of the disease may increase in size if snow falls on unfrozen ground. Disease development occurs rapidly when humidity is high and temperatures are 32 to 46 F with a maximum of about 55 F.
To repair damage, rake matted grass, fertilize, and re-seed or re-sod as necessary. Somewhat resistant varieties of bentgrasses, Kentucky bluegrass, and ryegrasses are available. Keep the turf mowed in the autumn until growth stops. The turf should not go into winter dormancy in a succulent condition. Do not fertilize with nitrogen within about 6 weeks of a killing frost or when the first snow is expected. Remove mulches of fallen leaves and thatch accumulation. In addition, maintaining moderately acidic soil pH (at or slightly below 6.5) will help suppress the pink snow mold pathogen.
Apply fungicides preventively to areas which have a history of pink snow mold. One to three fungicide applications during cold, wet weather from mid- to late autumn through early spring is often sufficient; more frequent applications may be necessary to protect newly established bentgrass, particularly during an unusually warm and wet winter season.