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Both indoor and outdoor grapes suffer from fungal diseases which affect leaves and fruit. The three top grape diseases are downy mildew, powdery mildew, and grey mould. Four grapevine viruses have also recently been detected in the U.K. but are not currently known to be widespread.
Grape powdery mildew
The three main diseases that affect grapevines in the UK are;
Grapevines are also rather susceptible to the root disease honey fungus.
Recently, RHS researchers have detected four viruses affecting grapevines in the UK - caused by Grapevine virus A; Grapevine rupestris stem pitting associated virus; Grapevine fleck virus; and Grapevine leafroll-associated virus 1
Resistance: A number of grape cultivars show some resistance to powdery mildew including the wine varieties 'Leon Millot', 'Orion', 'Seyval Blanc' and 'Triomphe d'Alsace' and the outdoor dessert variety 'Brant'.
There are no products available to amateur gardeners for the control of either downy mildew or grey mould.
The products SB Plant Invigorator, Resolva Natural Power Bug and Mildew Control, RHS Bug and Mildew Control, Ecofective Bug & Mildew Control and the Ecofective ‘Defender’ range contain a blend of surfactants and nutrients and can be used on any edible or ornamental plants, with no harvest interval. They have a physical mode of action and may be used against powdery mildews, as well as a range of pests such as whiteflies, aphids, spider mites, mealybugs, scale insects and psyllids.
Inclusion of a product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.
Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)
Downy mildew: the downy mildew pathogen survives over winter as resting spores in dead, infected leaves. These initiate new infections in the spring. Subsequent infections occur from airborne spores produced on these initial infections. Wet conditions are required for infection to occur and the disease is very seldom seen on vines grown under glass. The pathogen is an obligate biotroph (it feeds on the living cells for extended periods without killing them, and cannot live on dead plant material). Vitis vinifera is susceptible; other Vitis spp. and related Parthenocissus spp. (Boston ivy, Virginia creeper) and Ampelopsis are less affected.
Powdery mildew: the powdery mildew fungus over-winters in the buds and when these emerge in the spring it produces airborne spores which spread the disease. The pathogen originated in north America, but is now present wherever vines are grown. Leaf infection reduces plant vigour. When fruits are infected they split as they expand and this allows secondary infection by grey mould (Botrytis cinerea).
Grey mould: this pathogen produces abundant airborne spores on dead plant material, where it is able to grow as a saprophyte (feeding on dead organic material). It normally only infects plants through wounds, or particularly vulnerable organs (flowers or ripening fruit). When ripening grapes become infected they usually either fall prematurely or rot and then become mummified. When exactly the right climatic conditions occur, the so-called 'noble rot' develops, leading to fruit with a very concentrated sugar content which is used to make certain very desirable and expensive vintages; such conditions are, unfortunately, not likely to occur in the UK and are most unlikely in vines under glass.
Grapes: indoor cultivation
Grapes: outdoor cultivation
Grapes: pruning and training
Grapevine blister mite
Grapevine New Disease Report by RHS Scientists
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