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How to Handle Snow Mold on Your Lawn

Q. Dave in Randolph, New Jersey writes: "As this winter's relentless snow finally began to melt, it exposed small patches of fuzzy mold on some parts of my lawn. Could this be snow mold? The lawn is in full sun and was planted new last August. I had a truckload of screened topsoil delivered, levelled the area, and planted Tall Fescue. (Yes, I now know that fescue is better for shady spots; d'oh!)….

A. Let me hit 'pause' here to reassure Dave on his choice. "Fescue" is the name of a large family—or more correctly, 'genus'—of plants. Dave is correct that fescues in general are more shade tolerant than other cool-season grasses, but that doesn't make them 'shade-only'. In fact, in regions where winters are cold but summers can get hot, our lawn care expert Dr. Nick Christians recommends Dave's 'tall fescue' over all other grasses, calling it the most heat tolerant of all the cool-season grasses.

So Dave did not make a mistake. In situations where the lawn area is shady, and especially if you have shade in a region with mild summers, the preferred choice would be fine fescue. But 'turf-type tall fescue' will thrive in sun and stand up well to mid-summer heat and drought. Dave is doing great so far.

He continues: "I did not fertilize or use any chemicals on the new lawn since my well is in the same area. The grass filled in very nicely, and I had a full, green lawn which I kept free of leaves and cut at three inches with a mulching mower with a sharp blade. I didn't have to water after the grass was up because we had sufficient rain. The lawn was under snow cover since January, and no one has put a foot on it since."

So Dave seems to have done everything perfectly. He concludes: "I've read that snow mold can make dead patches in the lawn, which is not what I was hoping to see in front of my home! Is there anything I can do now that the snow has finally melted? Or am I going to have to re-seed? The only advice I can find online is chemicals, chemicals, chemicals…."

That's generally the case with online advice: if it's moving, spray it with insecticide. If it looks diseased, break out the fungicide. (Or if you're at a certain certifiably weird site, a shampoo and a beer…)

Now—although it SOUNDS like a cultural problem (one caused by poor plant care), snow mold IS a disease. Actually, it's two diseases: you got your 'pink snow mold' and you got your 'gray snow mold', each caused by a different disease organism. But it's also somewhat cultural, in that certain conditions have to occur to allow these organisms to flourish. And poor Dave got nailed by those conditions across the board.

Snow molds most frequently appear when you have an early snow that covers a lawn while it's still actively growing. Most often, that overly-active growth is fueled by a late feeding of old-school fast-release high-nitrogen fertilizers. But in Dave's case, it was just the natural vigor of a young lawn that was close to perfectly installed. It would have been much worse if he had fed the lawn—and worser still if there had been leaves on the lawn when the snow fell; that's a sure-fire recipe for mold.

Fear of snow mold is why some people think they should cut their lawn low going into winter, so that it won't be overly tall when and if they get an early and persistent snow cover. Sounds like a good idea, right?

I certainly don't recommend it. Any 'pruning' of a non-dormant plant will stimulate growth, and lawn mowing is really just a form of pruning. Plus, cool-season lawns grow at their fastest and use up their energy reserves the quickest when they're cut lower than three inches. So this well-intentioned idea would actually cause the grass to be growing rapidly and be really weak if and when that feared snow arrives.

Back to Dave: He has a very good chance of these patches clearing up on their own. Snow molds are most persistent on shady lawns when Spring weather is cold. (Ideally, he would have liked our temps to be warmer early this Spring—so would the rest of us!). Anyway, his full sun exposure is going to help a lot. In addition, he should gently rake the patchy areas to improve the air circulation there.

And there is an organic fungicide he can apply called Bacillus subtilis. It's widely available under a number of different brand names, suppresses a wide variety of diseases, and won't harm other living things or the water in his well. I would do the gentle raking and then spray the organic fungicide on the affected areas a few times this Spring. Stop spraying when the weather gets really warm and moisture becomes less abundant.

And finally, let's address his question about "reseeding". He will have to add some seed to his lawn, but not now. And it has nothing to do with the snow mold.

Anyone who's growing a fescue lawn needs to overseed every couple of years, no matter what. Fescues are superior grasses in many ways, but they don't creep sideways to fill in bare spots and damaged areas the way bluegrass can. So any kind of a fescue lawn should get some fresh matching seed every few years—but in mid-August, when the soil is still nice and warm but the upcoming weather is getting cooler; not in the frozen soils of Spring.

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