Q.15 year old wisteria
I have two 15 year old blue wisterias trailing on the same fence, which runs along the side of my house facing south. The one in the back has been spectacular whereas the one in the front produced 5 inch flowers, which wilted and dried up and now the new leaf growth is wilting and dying too. Why is this established plant dying all of a sudden?
Check the roots for galls. It sounds like something is attacking the roots and galls are the most likely answer - if not a critter could be feasting on them.