I have 2 Wisteria plants, bought from same nursery at the same time about 4 years ago. They are planted about 8 feet apart and grow up an arch shaped trellis and meet at the top. Both get about 4 hours of direct sun per day and are watered twice a week during the summer. The one seems to be doing pretty good but on the other the leaves are getting pale, rust covered looking, and drying out starting from the tips. The other plant shows some of these same signs but not nearly to the extent of the other one. Could this be from too much water and/or fertilizer. I fertilized in the spring but not since then.
I would have the soil tested. The soil may have too much phosphorus in it, which can block the uptake of iron, which causes chlorosis. It may also be lacking other trace minerals which could make it sickly. A soil test at your local extension office is the best way to pinpoint the deficiencies in the soil.
I would also check for crown or root galls. Here is some information on them that may be helpful: