I have a wisteria that is mature and the last two years leaves have turned yellow and started falling in August or late July. I'm not sure about last year but this year the leaves that have fallen have black spots which may just be part of the leaf dying process, I'm not sure. Any help you can give me is greatly appreciated.
Leaf spots are common on wisteria and are caused by different fungi. The wet spring and summer weather probably contributed to the problem. This time of year the plant is getting ready for fall and sprays are not necessary. Fungicides are protective, not curative and the growing season is about over. Pick off attached or rake up fallen leaves and destroy them to help manage the growth of fungi next year.
Feel free to contact our office if you have other questions.
Let me know if I can help you further!
Jefferson County Cooperative Extension Service
810 Barret Ave
Louisville KY 40204