By Niamh
United Kingdom 
I have a mature grape vine growing in my conservatory which has succumbed to a white mould drastically reducing the yield and making the grapes inedible. The mould appears as a white powder which brushes off when the leaves are touched, and it accumualtes in thick spots on the leaves also. Spraying over the winter with copper fungicide has not helped. This is the second summer the vine has suffered with this mould.
I would love to know how to tackle this mould and get rid of it. Can you help?
Many thanks,
Niamh.
10 Jul, 2011
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Hello as no one answered you I found this on line hope it helps?
Identification
The first sign of fungus on the leaves is a form of oily-looking spots which turn pale yellow and dry out. When the humidity is high, a white, furry growth begins to appear on the underside of the leaf under each spot. The leaves then change to patterns of different shades of brown and fall early in the season leaving the developing fruit exposed to the burning sun. The grapes will then become sunburnt.
Branches that are infected at flowering time will cause irregular fruit set, and grapes as they begin to form will become hard, grey and shrivel into reddish-brown mummies. This will be followed by a white furry growth over the branches if they are not sprayed with a fungicide.
Control
Grape Downy Mildew will survive the winter on dead leaves laying on the ground, so it is important to pick up all the foliage as it falls and burn. The following seasons the first infection will occur when damp and warm temperatures begin .
Start a spraying program with COPPER OXYCHLORIDE or Mancozeb as soon as the new shoots are approximately 250 mm long. When the weather is warm and humid you should spray every two weeks, spray every four weeks if the weather is hot and dry. Then only spray if the fungus comes back again. Make sure that the spray covers all the surfaces of the leaves, branches and fruit during your program.
14 Jul, 2011