What causes white fungus patches on my NB lawn every spring?

Those white or greyish-pink fuzzy patches appearing on your New Brunswick lawn in early spring are almost certainly snow mold, a fungal disease that develops under snow cover during the long Maritime winter. NB is particularly susceptible because of the combination of prolonged snow cover, fluctuating freeze-thaw cycles, and high humidity — conditions that create an ideal breeding ground for these fungi.

There are two common types in New Brunswick. Grey snow mold (Typhula spp.) produces circular patches 6-24 inches in diameter with a grey-white matted appearance, and is the most common variety across the province. Pink snow mold (Microdochium nivale) creates similar patches but with a pinkish hue around the edges and can actually occur even without snow cover during cool, wet conditions — making it common in the rainy springs typical of Saint John and the Fundy coast. Grey snow mold rarely kills grass crowns and lawns usually recover fully, while pink snow mold can be more damaging if left unchecked.

The good news is that most NB lawns recover from snow mold on their own within 3-4 weeks once temperatures warm and the grass begins actively growing. To speed recovery, gently rake the affected areas with a leaf rake as soon as the snow melts to break up the matted fungal growth and improve air circulation. This simple step can dramatically accelerate healing by allowing sunlight and air to reach the grass crowns. Avoid heavy foot traffic on affected areas while the lawn is still wet and soft from snowmelt.

Prevention is far more effective than treatment. In fall, continue mowing your NB lawn until growth stops entirely — usually mid-to-late October in Fredericton and early November in milder coastal areas. Your final mowing height should be 2-2.5 inches, shorter than your summer height of 3-3.5 inches, because tall grass folds over under snow and creates a moist environment where fungi thrive. Avoid applying nitrogen fertilizer after mid-September, as lush late-season growth is highly susceptible to snow mold. Also rake up all fallen leaves before snow arrives, since leaf layers trap moisture against the grass.

For lawns with chronic snow mold problems, consider improving drainage in low-lying areas where snow accumulates, reducing thatch buildup through core aeration in early fall ($100-250 for a typical NB lawn), and overseeding with more resistant grass varieties like perennial ryegrass. If snow mold damage is severe and large patches fail to recover by mid-June, overseed those areas and keep them moist — or consult a lawn care professional for a targeted fungicide application.

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