grey rot, sometimes known as grey mould and sometimes just rot, the malevolent form of botrytis bunch rot and one of the most harmful of the fungal diseases that attack vines. In this undesirable bunch rot form, the Botrytis cinerea fungus rapidly spreads throughout the berry flesh and the skin breaks down. Other fungi and bacteria then also invade the berry and the grapes become rotten. Badly infected fruit develops off-flavours, acidity is significantly reduced, and phenolics are oxidized by laccase; badly infected vineyards themselves have a characteristic mouldy and often vinegary smell. Wines produced from such fruit smell mouldy and red wines look pale and grey-brown. When the Botrytis cinerea fungus attacks healthy, ripe, white wine grapes and the weather conditions are favourable, it results in so-called noble rot, which can produce some of the world’s finest sweet wines. If the grapes are dark-skinned, unripe, or damaged, or the weather is unremittingly humid, the fungus wreaks so much damage that it is called grey rot.
