Hello, My Wisteria is very well established about 35 years old. Always blooms beautiful purple blooms. Recently like within the last 2 months I have noticed that some of the leaves are turning yellow and falling off. This huge vine is usually quite healthy this is the first time this has happened. I live in southern California is planted in full sun. Please help with any suggestions I don't want to lose this plant. I could post a picture as well if it would help.