By Steve147
United Kingdom 
i bought a house with a large grapevine in the conservatory and with huge harvests of grapes for the first two years. then trouble started with the quality the grapes and the vine itself. each spring it starts out fine and it looks healthy, but then a dusty sort of mildew covers all the leaves and then the bunches of grapes untill the grapes start to wrinkle and die. does anyone know what to do about this condition and how to prevent it. i would be most greatfull
21 Feb, 2010
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This is botrytis and is a common problem on indoor vines. Try spraying with Bordeaux mixture (copper based fungicide) from late winter before leaf bud to when the flowers begin to set. As explained below, you need to thin your vines to remove excessive leaves and growth which create a humid atmosphere where the fungus can flourish, and also to enable the spray to reach all the infected parts.
This site has some advice:
"Cultural Control
Excellent control has been achieved using canopy management and leaf removal in particular. Removal of basal leaves or basal lateral shoots at or immediately after berry set has resulted in significantly reduced incidence and severity of disease. In warmer growing areas, be careful not to remove excessive numbers of leaves, which can lead to sunburned fruit. This condition is made worse when leaves are removed later in the season. If leaves are removed at cluster set, the berries acclimate readily to the sunlight and develop a thick cuticle that helps prevent sunburn as well as Botrytis infection."
http://www.ipm.ucdavis.edu/PMG/r302100111.html
21 Feb, 2010