causes of black nodules wisteria stems
What causes black warts on the stems of Wisteria?
Certified GKH Gardening Expert
It is not uncommon for roots of wisteria to have black-looking nodules on them but on the stems, this could be attributed to pests or a fungus. I would recommend treating with neem oil. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm