Grape vines need to be pruned back in mid winter every year...

With the wet conditions this year so far, I'm not surprised your vine has got mildew. MG is right to a point. Yes Vitus should be pruned every winter, but there are some that leave one Rod to form fruits. You could prune yours in Winter, fear not it will grow again and you could train to cover shed, and by keeping on top of the extra growth you could hold mildew at bay. But are you growing it for the fruit or as a way to enhance your shed? that answer would define the pruning route you should take.

Our grapevine about 25 years old has occasionally had mildew. I think dryness at the root is one reason. We have never specially watered our vine. Just prune it back later in the autumn to as bare a stem as you can get. The shame is that you may miss that wonderful colour that comes in vines in autumn. We grow ours for grapes if they ripen well......not this year, but lots of grapes for the starlings and blackbirds and decoration and autumn colour.

Dorjac, grape vines should not be pruned back until mid winter Seaburngirl prunes hers on 26 December. If you prune before sap has gone down then the cuts are likely to 'bleed'.

many thanks for your replies regarding my grapevine

regards
Jen