I have two pear trees (not the fruit kind) and one dying (I think) maple. All three trees where planted on top of a clay area. Some dirt was brought in at the time of planting, but not enough. A greenish mold grows and then the bark starts to split. This is over some time, of course. What can I do to stop this? The two pear trees are newer, and I replaced the dying maple that was there. Don't want the same thing to start with them. I live in Michigan.