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Snow mold: an ounce of prevention now ...

I remember an early spring day in the 1980s. I was working at the Garden Line office and wishing I were outside. It was warm and sunny and the snow was melting quickly.
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I remember an early spring day in the 1980s. I was working at the Garden Line office and wishing I were outside. It was warm and sunny and the snow was melting quickly. One of the last calls of the day dealt with a grey, cotton-like growth that was visible under the retreating snow. The caller wanted verification of the problem, and I needed a slide of snow mold. Their residence was en route to my home and I had my camera in the car. So I was pleased to make a "house call."

It was, indeed, snow mold, a combination of several fungal organisms that thrive under moist conditions at temperatures around freezing (0-7 C). The cotton-like patches are the mycelium or vegetative part of the fungi and can range from a few inches to several feet in diameter. In severe cases, they can kill large portions of a lawn.

Grey snow mold (Typhala incarnata and few related species) is more commonly found in our area, generally attacking only the above-ground grass blades. Pink snow mold (Microdochium nivalis) occurs less frequently but is more damaging as it also attacks grass roots.

The standard recommendation in spring is to encourage a rapid snowmelt, usually by raking out the snow. The fungi become inactive when exposed to sunlight, once temperatures are above 15 C and when the lawn is dry.

Now (late fall) is the time for that ounce of prevention, especially if snow mold has been a problem. To reduce its impact, allow your lawn to harden off prior to winter. Avoid over-fertilizing, especially with nitrogen, in the fall. The last application should be no later than Aug. 15. Nitrogen promotes a lush succulent growth that is extremely vulnerable to fungal attack.

Your lawn should go into winter no taller than two to three inches. Longer grass becomes matted under the weight of the snow and provides an ideal environment for snow mold proliferation. It attacks the leaves first, then later the crown of the grass plant.

Thatch is partially decayed organic matter, on the soil surface, among the living grass blades. If the thatch layer is more than one half inch thick, it too serves as excellent habitat for snow mold and as well as an "over-summering" site for spores. Use a mulching mower to decrease the size of clippings and dethatch your lawn each spring if the layer becomes excessive. Rake the lawn in the fall, removing leaves and other organic material that provide initial sustenance for snow mold.

Snow mold is favoured by early snowfall on unfrozen ground. Although we have no control on the weather, snow fencing can be used to discourage the accumulation of deep snow drifts and encourage even snow distribution. Damage is generally worse where the snow lingers longest, thus the benefit of raking it away when the damage is first noticed.

Snow compaction is also thought to favour snow mold. So place your ice rink on the vegetable garden rather than the lawn.

No fungicides for snow mold control are registered for domestic use in Canada. If snow mold persists year after year despite preventive measures, and your lawn was established over 20 years ago, consider re-seeding or sodding with some of the more recent Kentucky bluegrass cultivars that are more resistant to snow mold.

Sara Williams is the author of the new, revised and expanded Creating the Prairie Xeriscape as well as the Saskatoon Forestry Farm Park & Zoo: A Photographic History. She will be leading tours to Morocco, Turkey and Ireland in 2015. Call Ruth at 1-888-778-2378 (ruth@worldwideecotours.com) for information.

- This column is provided courtesy of the Saskatchewan Perennial Society (www.saskperennial.ca; hortscene@yahoo.com). Check out our Bulletin Board or Calendar for upcoming garden information sessions.