Wysteria is dropping leaves
My wisteria is suddenly losing a lot of leaves. They are not yellow. If you shake a branch, more fall off. Don't see any bug sucking marks. With all the rain, the area is is planted in did get a lot of rain. I have rubber mulch in the area, and some plastic near the base so it doesn't drown (soil is a lot of clay I think) It's been there about 3 years.
We're uncertain what you mean by the plastic near the base. Could you send photos in a reply showing the situation? Close up and wider angle would be good. Or provide further written explanation.
You also say the wisteria got a lot of rain. Does water pool there? Is there standing water for any length of time? If so, how long?
I put a plastic sheet barrier loosely around the base so the young plant didn't drown. It gets enough water and extra heavy water doesn't drain into the roots. Water does not pool there, but does nearby. The standing water seems to drain pretty quickly.
The yellow dropping leaves points to a root problem. It's possible the plant was not getting enough water. Plant roots need water. As long as the soil drains well and there is not standing water for more than, say, an hour at most, it's fine. The water quickly runs through the soil.
Remove the plastic.
Mulch should never be impermeable if there are plant roots underneath. You want water to get to the roots. If you mulch to keep off weeds, mulch should be no more than 2-3" deep and kept away from the base of the plant by a few inches. Never heap mulch on the base of any plant
The plastic "barrier" is about 4 inches away from the base of the plant so it CAN get water. The mulch is only about 1/2 in deep and, as I said, rubber mulch so it is not compacted. The leaves are NOT yellow, they are still green. I was looking at the nearby pooling water during yesterday's rain and the excessive water was not around the bush thankfully. Until about 2 weeks ago, the plant was growing well, with new shoots and vines. Vines are still looking healthy.
We still suggest you remove the black plastic, or at least punch holes in it. Sounds like the plant doesn't need it. When removing it, you'll be able to see if the soil is too wet or too dry.