What is this Mold on the Lawn amongst the Snow Mounds on my Ann Arbor lawn?

Snow mold is a fungal disease that appears in the early spring as the snow melts. The damage is usually concentrated in circle shapes that range from three to twelve inches in diameter. There are two types of snow mold: Grey snow mold (Typhula blight) and pink snow mold (Microdochium Patch).

Grey snow mold is a lawn disease that likes cold, damp weather. Ideal conditions are temperatures around 30-40 degrees for an extended period of time. The disease grows in long grass over winter under snow or a wet layer of leaves. Pink snow mold infects the crown plant and can cause more severe injury than gray snow mold which only infects the leaf tissue. The control of either lawn disease may require a combination of methods. In severe, recurring cases, a combination of chemical, cultural, and biological controls may be required. In less severe cases, a light raking of the affected area may be the best answer.

Snow mold can also create allergy problems. Snow mold allergy is similar to greases, weeds and pollen allergy. One thing we have to remember is that mold is able to grow in extremely cold temperature, so winter can be the best season for mold to grow. Mold is not a seasonal allergen like pollen. It could occur in all seasons and get worse during the winter. Therefore, if we often find some health problems or discomfort during the winter, it is very possible for us to have snow mold allergy.

Controlling either of the grass diseases is easy if the infection is not severe. A light raking of the matted area will loosen the grass and allow the new plants to grow. Be sure to rake lightly, as the ground is usually very wet and the existing grass can be easily raked up. In severe infestation, raking is also recommended, but on a larger scale. It is not advisable to use a power rake as it may also damage the existing grass.

If you do have an outbreak of Snow Mold, it is a good idea to reduce any piles of snow that may remain, especially in shady areas. The longer the snow remains the more moisture and cool temperatures are present. Applying a chemical disease control material to grass already damaged by Snow Mold will do little to change the severity or need for lawn renovation. Most of the chemical controls should be applied in the late fall as a preventative treatment.