Check for brown shield shaped objects beneath the fluffy stuff - it looks like heavy cotton scale infestation, but you should be able to see the little shields if its that. If it is that, wipe over the trunk with a cloth very lightly moistened in methylated spirits, and all woody parts which have these on, removing them as you wipe hard. Do not apply to the leaves, and you may need more than one cloth, its a mucky job.

That's fabulous, thanks so much
Caterina