Question
I have 2 wisteria vines growing over an arbor and this is their first year to grow and bloom.  I just looked outside and one of the plants looks like most of the leaves are withering.  The other plant looks okay for today.  I live in Nashville TN and we have had much rain and this week mild temperatures.
I can not see any bugs and don't want to loose these plants...Have any suggestions?

THanks

Answer
Good morning, Judy-
First, congratulations on getting your wisteria vines to bloom. It's always worth the 2-3 year wait, and not everyone is so lucky.
Now, as for your withering leaves, there are several possible culprits.

1. Powdery Mildew: Sometimes, leaves will turn brown as a symptom of a fungal disease called "powdery mildew." This disease - which can spread to other plants (including your other wisteria) can be difficult to see on wisteria without a loupe or magnifying glass. You might see fuzzy white growths on the brown patches, or you might not see anything at all.  Treatment is easy, though, just use a copper-based fungicide, being careful to spray both sides of the leaves. It won't hurt any other plants, pets, or people.

2. Spider Mites: I see that you have emphasized that you do not see any insects, but spider mites are very hard to detect with the naked eye. Spider mite activity typically results in foliage that looks "singed" or burned. If you use a magnifying glass, you can usually spot adult spider mites and their eggs on the lower section of a leaf. Cool temperatures (frost) will kill them off, but controlling them until then will require proper pesticides ( a good organic one is Neem) or the introduction of biological predators (e.g., ladybugs).

3. Exposure: Is the brown wisterial getting more sun than the other one? This is a long-shot theory, since wisterias don't often get "sunburned," but I am just wondering. Does the sun strongly reflect off a large light-colored surface (e.g. side of a house) onto one plant more than the other? Just something to ponder.

4. Water: You have also emphasized that the plants have received plenty of rainfall. Was the watering consistent all summer? If one of the plants was stressed earlier in the summer due to lack of rainfall or hose-watering, then the symptoms could be showing up now.  It can take about 4-6 weeks for some dought-stress symptoms to manifest themselves.

Well, those are the only 4 things I can think of: one disease, one insect, sun-scorch, or uneven watering.
Let me know how things work out, and send me a photo or two if you are so inclined. Good luck!