I have several maple trees on my front lawn. All are mature and healthy looking. All are the same type maple (I don't know type). One of them has started dropping its leaves. The other maples are fine and haven't dropped one leaf. They fall off in a cluster of 3 - 5 leaves. Many, many clusters have fallen. It has been going on for 3- 4 days even though there had been no wind nor rain. What can I do?