What Causes Fescue to Turn White in Winter?

Snow Molds

• There are several common fungal diseases that can cause a fescue lawn to turn white, but the one characterized by a tendency to appear during cold weather is snow molds. As the name implies, this ailment is common not only in cold weather but immediately after snowfall. There are two distinct kinds of snow molds. Gray snow mold (also called Typhula blight) is caused by the fungus Typhula spp., and pink snow mold (also called Fusarium patch) is caused by the fungus Microdochium nivalis.

Symptoms

• The only way to confirm whether snow molds are the cause of the white patches in your lawn is to look for the symptoms associated with snow molds. The causal fungus grows underneath snow patches and continues to grow until snow melts. After snow melts, you will notice white, pink and gray patches that will enlarge as long as the grass remains cool and wet. Mushrooms and hard fungal structures called sclerotia can emerge from the infected patches as well. As soon as temperatures rise above 45 degrees (for gray snow mold) or 60 degrees (for pink snow mold), the fungus becomes inactive and the grass should green up quickly.

Prevention

• Lawn care practices at the end of the summer have been shown to help prevent the emergence of snow molds. Mow your fescue as long as it is growing but not after it stops growing. Similarly, fertilizer applications should be timed so that they do not affect the fescue's ability to go dormant in the winter, which in most cases will be when the fescue is still green but after leaf blade growth has stopped. Clear up all leaf and grass debris piles, since snow molds are more likely to grow underneath these. Also avoid piling snow into a snowbank along sidewalks and driveways that are adjacent to the lawn.

Control Approaches

• Snow molds almost never cause serious damage to turf grass because the fungus that causes snow molds becomes inactive when the weather warms; at most, the infected white fescue patches will take longer to turn green after the winter than the rest of the lawn. Fungicide treatments are very rarely necessary and are mostly ineffective anyway. If snow molds are a persistent problem on your fescue lawn, adjust your mowing and fertilization practices and simply allow the fescue to outgrow any damage that it suffers as a result of snow molds.