Isle Of Wight, United Kingdom

We have a grape vine that has its root outside but grows inside our south facing greenhouse. It is at least 50 years old. Every year it produces bunches of red grapes, which have large pips in.
However, this year the grapes have been so mildewey, and the skins were splitting, that it was necessary to cut them all down - none were eadible at all. The leaves are a little bit powdery as well.
Once the leaves have turned brown we intend to prune the stems back as we normally do, but could the panel suggest a dressing or treatment that will combat the mould next year?

• 3 Aug, 2011