Dealing with snow mold on your grass

Snow mold is a common fungal disease in east Idaho lawns. All cool-season grasses are susceptible, some more than others. The longer the grass is covered with snow the greater the opportunity for snow mold to develop.

This has been a prime year for snow mold development.

Symptoms and Signs

Snow molds prefer cool temperatures and high humidity. There are two types of snow mold — pink snow mold and gray snow mold. As the snowbanks finally recede this spring you will see both the signs and symptoms of snow mold in many lawns.

Pink snow mold starts out as two-inch, circular patches with pink to white mycelium at the edges of the patch. These patches may expand up to twelve inches across.

Signs of gray snow mold are first seen as the snow melts and reveals a gossamer layer of white to gray mycelium.

Matted leaf blades may or may not be a symptom of snow molds, but when snow molds are present the leaf blades will always be matted.

Disease cycle

Pink snow mold can occur any time of year with favorable wet, overcast days and temperatures are 32 F to 60 F. When conditions provide dry, sunny days the pathogen will become inactive.

Gray snow mold will start to germinate with wet fall weather at 50 F to 60 F. Persistent snow cover favors gray snow mold.
In both cases long leaf blades that are wet and matted to the ground favor development of the pathogens.

Control options

Application of fungicides after the disease appears is not effective. Fungicides are preventative rather than curative. Areas such as golf courses may apply fungicide in the fall to help prevent development of the disease under the snow.

Fungicides are not recommended for home landscape control of snow molds. If, as the snow recedes you notice that the grass has been matted down under the snow, a quick rake over the grass will help release humidity and allow sunlight into the turf.

Actual control of leaf mold begins in the fall. After the lawn has gone dormant do one final, short mowing, about 2 -2.5 inches high. The final application of fertilizer should be about half rate and applied after the grass has gone dormant so there won’t be succulent, new growth going into winter. Pink snow mold spreads rapidly through lawns with a thick layer of thatch.

Horticulture Educator Ron Patterson can be reached at (208) 529-1390.