Snow mold is a common fungal disease that affects lawns in Washington State, even in areas where no significant snowfall occurs. While it is not as common as other lawn diseases in Washington, its effects on your lawn can be quite severe if you do not know how to identify and prevent an infection. Join the Simple Lawns team as we go over how to do both in this blog post!
Snow mold typically appears as circular patches of matted, discolored grass. These patches range in size from a few inches to several feet in diameter. The affected areas often have a web-like or fuzzy fungal growth on the surface, which can be white, pink, or gray in color. Gray snow mold (Typhula blight) usually has a whitish-gray appearance, whereas pink snow mold (Microdochium patch) may have a salmon or pinkish hue. Pink snow mold is often more severe than its gray counterpart, as it can infect the grass's crown, leading to more significant long-term damage.
Pink Snow Mold (Microdochium nivale)
Gray Snow Mold (Typhula spp.)
Snow mold is caused by fungal pathogens that proliferate in cool, moist environments. The primary contributing factors include prolonged snow cover, excessive thatch buildup, uncollected fall leaves, and high nitrogen fertilization late in the growing season. When snow falls on unfrozen ground, it creates an ideal environment for fungal spores to become active and begin their destructive cycle. Different types of snow mold, however, can form in different conditions that do not always have to include snow cover.
Typhula is the fungal genus of gray snow mold, and Monographella is the genus of pink snow mold. Cold, damp fall weather leading into winter is the most common cause of snow mold. This disease typically spreads underneath snow cover, but pink mold can develop even without snow. In Washington State, pink snow mold is more common than gray snow mold due to the region's relatively mild winter temperatures, frequent rainfall, and extended periods of moisture without consistent deep snow cover.
Lawn Care Mistake To Avoid
Snow mold primarily thrives in areas where moisture is trapped beneath an insulating layer of snow or debris. It is commonly found in residential lawns, golf courses, athletic fields, and other grassy areas that remain covered for extended periods. Lawns that experience poor drainage, heavy thatch accumulation, or excessive leaf cover in the fall are more susceptible to snow mold. North-facing slopes, shaded areas, and compacted soil further contribute to the growth of this fungal disease.
Here in Washington, where winter weather patterns can vary, snow mold is often observed in regions that receive consistent snowfall or have prolonged periods of damp, cold conditions without adequate drying.
Snow mold typically becomes active in late fall and early winter when temperatures range between 30°F and 60°F, depending on the type of snow mold and the type of grass infected by it. The fungus remains dormant under the snow cover and continues to develop as long as the conditions are favorable. As the snow melts in early spring, the damage becomes evident, revealing matted patches of dead or decaying grass.
Unlike many other turf diseases that thrive in warm temperatures, snow mold flourishes in the cold, making it a distinct seasonal problem. The extent of the outbreak often depends on how long snow remains on the ground, with deeper and longer-lasting snow cover leading to more severe infections.
Snow mold primarily damages the grass by weakening its structure, leading to slow or stunted spring recovery. While the disease does not typically kill the entire lawn, it can cause significant thinning, leaving lawns patchy and uneven. The most immediate effect is the presence of unsightly, discolored patches that take time to heal. A weakened lawn is more susceptible to other fungal diseases, weed infestations, and stress from environmental factors. If left untreated, snow mold can delay the return of healthy, lush grass, creating long-term maintenance challenges for homeowners.
If signs of snow mold do appear, it is essential to encourage quick drying and recovery in the affected areas. Lightly raking matted grass helps increase airflow and promotes new growth. In cases of severe damage, overseeding the lawn in spring can help fill in thin patches and restore density. Fungicide applications may be necessary, but these treatments are typically most effective when applied preventatively in late fall before snowfall occurs. The best preventative measure for avoiding snow mold are the following:
Snow mold in Washington is not overly common, but the pink snow mold variety that often appears in our lawns can be devastating to grass health. Taking the steps listed above to prevent snow mold will go a long way in maintaining a healthy lawn throughout the changing seasons. For more information or help with snow mold in the Vancouver, WA area, be sure to call Simple Lawns for all your lawn care needs!
