This is a 5 or 6-yo air layered Wisteria which was repotted last year into its cascade pot and grew well in the summer afterwards. This season, however, it started off earlier than its younger pot grown one (in a cold and damp March here in the UK). Initially all looked well, but the past few days I've noticed that many of the leaves are whitening or at least getting white spots where the chlorophyll seems to have gone out of the leaf. It's fed weekly with Green Dream (UK) feed and has been sprayed as a precaution against aphids 2 weeks ago as we had a mild winter so the bugs were out in force much earlier in the season than usual.

One of the photos shows the underside of the leaves but in truth there's nothing visible on either surface. It's kept in a south facing town yard with sun for the first 4-5 hours of the day I've other bonsai (Hawthorn, Maple, Spirea, Apple. Elm etc) all of which are fine with no evidence of anything similar, and the younger Wisteria is also fine (kept in similar conditions except in a small container).

As the tree is still growing well currently I'm keen to not make assumptions that it'll come good when perhaps it won't so keen to see if anyone's come across a similar problem.

Oops - didn't mean it's fed weekly with GD - I have a weekly feeding regimen but it's different for different plants - the GD feed tends to last 2-3 weeks before needing replenished.