I have a two Weeping Willow Trees, they are planted on a low grade hill but not in a real moist area. They were about 8 ft tall when planted about 8 years ago and are now about 20 ft tall. They are beautiful trees, however, this year the back side of one tree has all brown leaves. Is the tree dying? Is there anything I can do to save the tree? Could I try cutting it back, if so how and is there a better time of year to cut it?