David Rance wrote:

In fact, I have my doubts as to whether Bordeaux Mixture will be of any
use with botrytis (grey mould). I can find no recommendations to its use
for botrytis in any of my books or on the web.

I had a search yesterday when Bordeaux mixture was first suggested. I
managed to find a couple of references to it being useful against
botrytis. In the absence of anything else, I am willing to give it a
try. At the very least it should protect against mildew.

Instead there seems to be
greater emphasis on cleanliness of the soil and the vine, i.e. don't
leave any dead leaves around. My advice would be to remove the
polytunnel when the grapes are approaching ripeness because it is then
that they are most prone to botrytis developing.

This is not an option. The polytunnel is 65ft x 17ft and the poly is
correctly stretched and anchored under the ground. There would also be
an issue with other plants in the polytunnel.
--
Howard Neil