bertie muttered:

We moved in some two years ago and the purple one stretches
down one wall (approx 6 mtrs then splits (one way goes on for another
7mtr
approx. and the other about 4 mtrs) This is doing just fine, lots
of leaves
and flowers. The problem one (read disaster one) is the white
one. This leaved
up this spring and flowered as usual (lots of) but
suddenly we lost both
flowers and leaves. Its length is about 3 mtr
where it splits, one half
continuing on upwards for about another 5
mtrs, the other half is also about 5
mtrs in length. We did notice that
it looked sickly just after flowering. We
have had a fairly dry winter
(Somerset) so immediately suspected lack of
water. Its located nearly
next to the house wall so not a very good location
for water. We are
currently without any leaves although most of the wood is
still
pliable.

We had exactly the same problem in our house in Sussex. I might forewarn you
that both wisterias were planted at the same time 40 years ago (opposite
sides against the south-facing wall of the house), the mauve one has now
covered the whole front house and is snaking around the side, the white one
is about 2 foot higher than when we planted it. I'd say the white variety is
just less vigorous, or a mutation of the mauve, so it's weaker.