Q: I have what looks like spider webs on my lawn. What causes this and will they hurt the grass?
A: It is a fungus commonly called snow mold. There are two different kinds caused by different fungi and you can have both at the same time. One looks whiteish-gray, the other is pink or tan and pink. Both appear as roughly circular patches of dead or matted grass and in wet spots there is often webbing that disappears when it dries. Snow molds are commonly seen in the spring when temps are just above freezing. They go dormant and disappear when it warms up, but they are still alive and waiting to return when the conditions are more favorable.
The fungi do kill the grass, but just the existing leaves. The crown of the plant, which is where new growth comes from, is not harmed. New leaves formed after the weather warms up are usually fine, but it may take a month or more before they fill in and you can’t see a dead spot.
This spring, gently rake the damaged areas to remove the dead thatch. This allows sun to reach the new grass and helps dry out the area. Don’t rake healthy grass until the ground dries up or you will pull it up by its roots. (We tend to be eager to get out and do lawn work in the spring, but if the ground squishes underfoot, it’s still too wet.)
Next fall keep your lawn mowed until it stops growing. Rake leaves so they don’t mat. Although fall is the best time to fertilize lawns, don’t give it a lot of nitrogen less than a month before the first snow. Slow-release nitrogen is a better choice for fertilizing. Long, lush, nitrogen-rich grass covered by lots of snow encourages the fungi.
There are some fungicides available, but they usually aren’t needed by the average homeowner.
There are varieties of grass that are more resistant to snow molds than others. If you have lots of problems or snow mold really bothers you, you may want to replace your lawn with a different variety.
Written by U of M Extension Master Gardeners in St. Louis County. Send questions to email@example.com.