I have a 3 year old Tri Color Beech. I live in Michigan by a lake and we have underground sprinklers. The problem is, the tree will leaf out and look beautiful for about a month, now the leaves are turning brown. This has happened the last two years. I have looked at other Beeches in the area and they are not turning brown. Last year I did not fertilize, this year I did. What could be wrong?