The foliage wilts turning black and limp, followed by die back
of the whole plant. Clematis are particularly susceptible.
Various fungi which are either soil borne or which have entered
the plants through pruning cuts or other wounds. There are no
chemical controls. Affected plants should be dug up and
destroyed. With clematis you can try to prevent damage by
planting the rootball about 8cm (3in) below the level they were
in the pot. This means that there are still some buds buried
underground that remain viable after a wilt attack and can grow
even if the rest of the plant has died. Cut back the wilted
clematis to ground level and wait for new shoots from below
ground.