Wisteria Carbuncle Problem
We have a number of ten year old Chinese purple wisteria, some of which are experiencing a clumpy growth on the stems. These growths may be as much as 6 inches in diameter, are brown and clumpy. I see none anywhere near the root area, so do not believe this is classic crown gall. Also, other than these unsightly growths, there is no real damage to the plants; no leaf dying, flower problems, or anything. What might it be?
There are several cankers and galls which can affect wisteria. Probably you should have the clumpiness examined by a professional, either at a nearby nursery or at the extension service. This link will help you locate the nearest one of those:
Meanwhile, here are a couple of articles that might offer some insights: https://www.gardeningknowhow.com/ornamental/vines/wisteria/wisteria-diseases.htm