Okay, I am totally new to caring for our yard. We had a landscaping company put it in 2 years ago and I'm now trying to learn how to care for it. Today, I was pulling out new seedlings around a tree in our back yard and I noticed a white fuzz on the end of each of the seedlings where they were under the river rock. When I started to move the river rock, I saw that there was a huge patch of this white fuzz on the rocks, and the new growth. Our tree does not have any of the fuzz on it.

Any ideas what this is? Is it harmful to the tree? Is harmful to people (located next to my kid's play structure) What do I need to do to get rid of it.

Thanks so much!!! I am officially clueless! Haha!