I have an American Sycamore transplanted into my front yard November 2016 approx 12ft at that time. Attached are several photos of current state of leaves turning brown and falling to the ground as of today 8/13/2017. We were away for two weeks vacation, when we left no issue at all. got back yesterday and you can see the photos attached. is this a disease, if so - how do i treat it? thanks!