Well hopefully its just the weather - but die back of this kind sometimes indicates infection with phytophthera of some variety. There is no treatment for this other than to remove affected areas if possible, but only time will tell whether it is this or not.

Thanks, poss the strange weather so we've decided to watch what happens in the spring and praps have to do pruning then! Sorry for belated response.

Update on our Ribbonwood! More has died during this year & prob two thirds is now from the top down! We're going to take it down before winter sadly.

Oh dear, I was so hoping I was wrong... still, it's an opportunity to think about planting something else, though maybe you should leave it fallow for a while in case the roots were suffering from phyophthera.

Thanks for your further comment Bamboo. I think it would bebetter not to replace this tree as its right onthe edge of our pond. It was planted before the pond, so its roots had to be avoided to excavate the pond! I'm also trying to make a wild flower 'meadow' on the otherside if the tree, not so easy as one may think!