Snow mold is active at temperatures just above freezing in moist conditions. The gray snow molds (Typhula incarnata & ishikariensis) most often occurs when snow cover exceeds 40 - 60 days, pink snow mold (Microdochium nivaile) does not require any snow cover to develop. The freezing and thawing of snow and excessive ice build up on grass is the major cause of snow mold and can cause winter damage to turfgrasses. If gray snow mold damage is present little can be done to undo the damage and the focus should be on recovery. To help determine the extent of damage take samples of affected turfgrass and bring into an environment conducive to growth (warm temperatures & light). Observe growth of the plants and development of new shoots to assess potential recovery. It would be recommended to photograph and document the process to demonstrate the potential recovery of the turfgrass.
Tips to Help Recover from Snow Mold:
- Remove snow and ice from turfgrass areas (this is easier said than done).
- Lightly rake the grass to promote air circulation and light to penetrate the canopy and encourage new shoot and leaf develop.
- It there is any dead and matted material, rake and remove. In the case of dead turfgrass renovation of the site would be recommended as soon as possible.
- If the site did not receive appropriate fertility in the fall a modest application of started fertilizer would be recommended
- Bentgrasses and Poa annua are especially susceptible to damage but all cool-season grasses can be affected.
- For gray snow molds the damage is done, so fungicide applications are of little to no benefit at this time. In the case of pink snow mold or Microdochium Patch (the common name for the disease when it occurs without snow) fungicide applications would be recommended especially if there are wet conditions experienced during the spring. Some fungicides to consider for pink snow mold would be fludioxonil, iprodione + chlorothalonil, iprodione, propiconazole, pyraclostrobin, thiophanate-methyl or trifloxystrobin.
How to identify the different snow molds:
To identify gray snow molds look for the sclerotia (compact mass of mycelium that is the survival structure of the pathogen) on the leaf tissue and debt. Typhula incarnata has reddish brown to dark colored sclerotia that are rather large, up to 0.2 inches in diameter. Typhula ihikariensis has much smaller sclerotia that appear similar to flecks of black pepper on the leaves and debt. Active mycelium is a white to gray color.
Pink snow molds do NOT produce sclerotia and the active mycelium is a pinkish to white color depending on exposure to light. Both gray and pink snow molds occur together so it can be difficult to assess which is the predominate pathogen. Authors: Joseph Rimelspach
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