I have no idea what that is - is this a grape vine or another type of vine? I'm hoping our member Tugbrethil knows what this is...

Could it be putting out feeler roots to find something to climb up. I have seen similar rubber plants and ivy. Not sure it's just a guess.

Definitely aerial roots, and it looks like a member of the grape family. Usually, when this happens here in Arizona, it means that the trunk was girdled, and the vine is desperately trying to find some other place to root.

that's what I thought T. What would you suggest. Layering the roots in suitable compost, layering like S'berries and then taking a new plant?

Probably the best way of saving the variety. Another way would be to wait until after normal leaf drop, and take hardwood cuttings, but if it is showing stress now, it may not live long enough, or have enough reserves for the cuttings to winter over.

Many thanks to all of you.
Some clarifications: yes it is a grapevine about 6 years old.
It is south-east facing growing on a barn wall. It had leafed, flowered and has grape bunches this year.
It all started earlier this summer when I sprayed her with Bordeaux mixture on a hot evening: she started losing leaves and growth that simply browned and fell off the plant.
These 'aerial roots' are all along the trunk extending 4-5 metres.
I shall wait until she drops all her leaves and cut her back to the original stem to see if she comes back next year. She was very strong growing plant and used to grow 1 to 2 metres along the barn each year.
Again, many thanks for your help and advice: will keep you informed how it goes!

How strange! We spray Bordeaux mix at all hours with no problems at all! How strongly did you mix it, Alfredo? You didn't mix anything like summer oil or wettable sulfur dust with it did you? If not, I would suspect some other cause of the leaf drop.

the mixture was standard strength omitting any dosing mistake by myself.
The growth things are slowly extending and I shall check if there is any restriction on the trunk.
Did you look at my photo of the whole plant? That was last year in Summer: she was beautiful and growing in strength!
thanks for your ongoing interest...

I just looked at the picture, and it looks in perfect health then. Two possibilities come to mind:
Since the lawn appears to come right up to the base of the vine, is it possible that there has been strimmer injury to the base, maybe from hired help?
Before spraying with giberellic acid became a common method of stimulating larger grapes, the growers used to partially girdle their vines in spring. That involves cutting 1/2 to 2/3 of the way through the phloem--the inner layer of bark that transmits the sugars from the leaves down to the roots--to force more energy to the fruit. Done properly, it slows the vine down slightly, but rarely does serious damage. One false move during the process could be disastrous, though! Did a friend or hired man offer to "make your grapes better" this year?
Both of those possibilities should be obvious upon inspection.