I have two 16-year-old doublefile viburnums planted an acre away from each other that are both exhibiting stem dieback, starting from the tips of the branches. The tips appear to be dead as they break off very easily and have split bark. We are having a very wet spring following several years of drought. From what I can determine, there are two diseases that could be the culprit: verticillium wilt (VW) or botryoshaeria canker (BC). If it's VW, I assume the plants are history. If it's BC, I can probably save the shrub by cutting back into healthy wood. Any thoughts as to which disease it is or recommendations?