We have a gorgeous norwegian maple in our back yard. Last year, a gardener added topsoil to our yard that contained mold that is lethal to this species. This summer, several branches have already died from verticellium wilt. I'm told that there is no cure, and the tree is dying. The process could take as long as 30 years. We are hoping to forestall the inevitable. I've started sprinkling compost around the yard, and am watering the yard daily. The worry is that we may be overwatering, and this might also cause harm. Any advice welcome. I read that replacing the topsoil could help, then I read that this would not help because once the mold is there, it can't be removed. It would be prohibitively expensive to remove the topsoil because we've added many trees and shrubs to the yard.