I have a wisteria that is approximately 35 years old. Despite neglect in its early years it has thrived and is trained along a pergola. It has a central trunk - it was originally grown as a standard - but also has five or six long established branches emanating from the trunk. Last year two of these branches did not produce either leaves or flowers and were cut back. This year there has been a noticeable lack of flowers and those that did appear seemed to die before they fully opened and there is hardly any foliage at all, albeit there are leaf buds which have died. I don't know what has caused the die back but the base of the trunk looks as though it has rotted. Is there anything I can do to save it?