By Gattina
Bologna,
Italy 
I lost a beautiful hydrangea last year; it became infested with what looked like small patches of cotton wool and never recovered after winter. Now, to my horror, I've found the same thing on another, very precious hydrangea and a nearby climbing rose. Up until now, both have been very strong and healthy, but both are now losing their leaves and are looking very sorry for themselves. My neighbour was very certain and told me it was a sort of fungus and I duly treated with a fungicide spray, but to no avail. I asked if it was mealy bugs and was told "No", but I'm not so sure. No photograph I've taken shows it very well, I'm afraid. Any ideas, anyone?
16 Sep, 2014
Answers
Thank you, SBG. I've been out and checked for scale casings, but can see none. Maybe neighbours aren't infallible, however confident and knowledgeable they sound.
17 Sep, 2014
woolly aphid also a possibility. you'd need a systemic insecticide as the normal insecticides don't penetrate the fluff. the systemic gets into the plant and as the aphids feed they get a dose of medicine so to speak.
when you squeeze it do you get any 'juice' out of it?
18 Sep, 2014
Erm, I've not tried that, SBG: when the rain stops I'll go and give it a try.
19 Sep, 2014
Previous question
mealy bug sounds likely so does the remains of the dead scale creature. have a look on the stems for brown/grey 'woodlouse casings' attached to the bark. if that is present then you have scale . The female sacrifices her body for her young and when they emerge she dies and you are left with a white fluff as the little ones scamper off up the plant to start feeding.
There are sprays for scale .
17 Sep, 2014