Our beautiful deciduous magnolia is about 20' tall and bursts forth in pale pink flowers and is full and lush with lovely bright green leaves each spring. Then in early June, the leaves start to turn yellow/brown, and they begin to drop. This year, the drop rate is high and we sweep up leaves each day. By August, the tree will begin to look sparse. I'm attaching a couple leaf photos, as well as one with the flower heads (?), which appear to have a powdery mildew and brown markings. Any idea what is wrong and is there anything we can do to assist the tree? Less water, more water, fertilizer? We really love it and hate to see it with these problems.