I was given a small wisteria 3 years ago (about 2 ft tall) which appeared to have been grown from a graft. In the first summer, the 2 stems shot up to about 8 ft tall and spread out laterally by about 3 ft. The leaves looked fine. In the second year, all appeared well apart from the fact that the leaves on the 2 lateral shoots died. This year, despite the cold end to the winter, it budded up and has come into leaf but I have noticed today, that the leaves on one of the upright shoots are dying off. It is South facing and in the sun all day. It has been watered, although not excessively as I know they do not like to be waterlogged. There is no discolouration to the leaves and there does appear to be any infestation or fungus development. Could anyone throw some light on the likely problem? Thanks for your thoughts in advance.