Hi Sue, sounds as if it could be verticillium wilt, but it could also be botryosphaeria fungus, which isn't likely to kill the whole shrub, wheras verticillium wilt almost certainly will, what I would do, until you know for certain, is cut back to a couple of nodes behind the affected part, destroy the prunings by burning, an use a copper fungicide spray on the whole plant, if you get no further trouble, then it will more than likely be botryosphaeria fungus, hope this helps, Derek.

Thank you Derek. I've put the offending branch on the bonfire pile but everything's much too wet to burn now. It will have to wait until after the young rooks have fledged if it doesn't dry out before nesting time! (The bonfire site is almost under the rookery) I haven't used a copper fungicide before - never had much need of fugicides at all - can you recommend one?

Hi Sue, I've never used 1 at home either, and I don't think the commercial products are available to amateurs, all I can suggest is going to a g c, see what's available, and decide which 1 you want to use, sorry, Derek.

I agree with Derek. prune the stem back every 6" until you have a 'clean section of wood with out the discolouration you have found.

Right, I've cut it back right to the parent branch - the staining only disappeared in the last inch so it was a near thing. Fingers crossed now!