Snow mold is those surprise white and pink circles left on your lawn after the snow melts. The circles can vary in size from a few inches to several feet in diameter. The affected grass is crusty and matted. Severe infestations kill grass and leave the lawn patchy and unattractive.
Snow mold usually grows quickly under a heavy deep snowfall on lawns without completely frozen soil. It is a cold-weather fungus that targets cool-season grasses like Kentucky Blue Grass. There are two types of snow mold fungus.
- Grey Snow Mold (Typhula Blight). Usually, it only kills grass blades. The grass has a good chance of recovering.
- Pink Snow Mold (Microdochium Patch or Fusarium Patch). Kills the crown and roots of grass plants leaving bald patches.
Snow mold fungus stops growing when the temperature remains above 55 degrees Fahrenheit. Rake up all of the dead grass to allow the area to dry out and to give undamaged grass a chance to regrow. Reseed badly damaged areas. Applying fungicide after the damage is done is usually not helpful. The fungus will not absorb the fungicide when it is not growing.
Mold spores are everywhere in the environment. You can’t eliminate them completely but you can help your lawn avoid or reduce snow mold infestation by following a lawn cleaning program for winter.
- Clean the Lawn. Remove all leaves and debris from the lawn. Bag it or mulch it. Snow mold thrives in soggy lawns layered with mats of leaf and grass debris.
- Mow the Lawn. Cut the grass shorter than normal–approximately 2” to 2 ½” long.
- Dethatch the Lawn. If the thatch in your lawn is over three-quarter inch thick, dethatch it to reduce snow mold development.
- Aerate. Aerating the lawn loosens the soil and allows more air circulation–helping to prevent snow mold.
- Less Fertilizer. High nitrogen fertilizer late in the fall feeds snow mold growth. Don’t fertilize within six weeks of the first snow.
- Add Lime. Snow mold grows best in acidic soil. Adding lime sweetens the soil and turns it more alkaline.
- Preventative Fungicide. If large amounts of snow mold are showing up every spring, consider treating the lawn before the first snowfall with a fungicide specific to snow mold.
- Snow Piles. Avoid creating large piles of snow when clearing driveways and sidewalks. They take longer to melt–giving snow mold a better chance of growing.
