Too bad this tree had to go. Possible that it could have got Verticillium Wilt anyway. But I think the conditions promoted the problem. The water feature was apparently built after the tree was planted, and the pond liner is almost to the trunk. Also, water upstream, flows behind a boulder and is channeled into a narrow area that accelerates the flow around the rock and up and over the liner near the trunk - a continual trickle going over the edge. Anyway, the lesson is, don't lay pond liner over roots. It interferes with gas exchange. Not sure who put the pond in.