Beneath that pristine blanket of snow, conditions may be right for the growth of a destructive fungus called snow mold. Use these tips to spare your lawn.
If you’ve ever seen any of the the arctic horror movies named The Thing—the story has the rare distinction of having spawned three consistently watchable movies, two of them bona fide classics—you’ll know that the tranquility of a pristine field of snow can be deceiving. Of course, you’re not likely to find the Thing’s spacecraft beneath the snow in your yard, but you might find something seemingly as alien and destructive: snow mold.
Snow mold comes in two varieties: gray, caused by the fungus Typhula spp., and pink, caused by Microdochium nivalis. Pink is the more damaging variety, sometimes destroying not just the blades but also the roots of grass. During the summer, gray snow mold lingers on in the form of pinhead-sized bits of fungal matter called sclerotia. At the same time, pink snow mold waits for winter as spores hidden away in infected plant matter.
Whether as sclerotia or spores, snow mold bides its time until winter provides them with a protective blanket of snow above and a thawed or unfrozen ground below. For that reason, bursts of snow mold activity are commonest in years when an early snow keeps the soil from freezing completely. Then the mold awakens and continues to grow so long as temperatures stay within a range between just below freezing and a few dozen degrees above.
If snow mold is a problem in your lawn, you may not find out until early spring when melting snow reveals the grass underneath. The mold will appear as circular patches of matted, straw-colored grass, dotted or fringed with mold ranging in color from white to gray or pink. In particularly virulent outbreaks, the patches may overlap so heavily that it’s impossible to discern individual circles‚ just a large, amorphous blotch on your lawn.
If your lawn has already weathered severe outbreaks of snow mold in the past, you might consider ending the lawn care season with a late fall application of fungicide. In the meantime, the best defense is to take proper care of your lawn. Proper mowing can help build your lawn up against fungi like snow mold; regular raking disperses dormant fungi before they can take hold.