Please help! My eunonymous, grown from a tiny plant and now 4ft plus, is covered with a black sooty like substance, now both leaves and stem. I thought it was sooty mould but was told that this does no harm. Now part of the shrub seems to be dying back - sections of the leaves are now without colour and look like die back at least.
This is one of my favourite plants in the garden, so I am desperate to nurse it back to health. Any help gratefully received.