They also appear to be unmulched and that isn't helping.

welcome to the forums.. in every post tell us where you are.. big city name ...

are you doing xeriscape other than this plants??? .. how do you water these plant... and i agree with the mulch comment. ...

from these pix.. is seems you have very little damage... any disease would affect the whole plant.. not one or two random leaves or branches...

i wondered if someone walked by and ruffled this group of leaves.. and damage appeared when he heat hit... hard to tell from these pix ...

ken

It looks to me like some sort of fungal leaf spot - which is usually not fatal or extremely damaging, just unattractive and annoying :-) Keep the vines well pruned to ensure good air circulation and prevent creating a moist environment that would suit fungus. Also clean up any fallen leaves and remove affected ones. Be cautious with watering and mulching to avoid creating a damp environment that might promote fungal growth. It would indeed be useful to know where you are to know more about the environmental conditions they are growing in. Is there a local garden growing them without problems so you have somewhere to compare your conditions to/someone local to discuss the growing process with? What kind of wisterias are they? It's hard to tell from the pictures but it looks like they might be twining counterclockwise which could mean either Chinese or American wisteria....

We are in the central coast of California. Wisteria are popular here. We have 4 of them. One is 6 years old and beautiful with tons of blooms and recovers every year with a vengeance.

We added 3 more last year. Two are doing amazing. This one which is on one side of the pergola. The one on the other side of the pergola is gorgeous. They get the same amount of sun and water as they are on the same drip system. That’s why we’re so unsure of what is wrong with it.

My guess would be that it came in with the spores (or whatever is causing the problem) so you need to be through and careful to clean it up so it doesn’t spread to your other ones.

As a wisteria-lover, I’d love to see pictures of yours in bloom….

Have you checked to make sure the emitter on the drip system is working--not plugged up with grit or hard water deposits?

Yes but I will again