botrytis bunch rot, vine disease which, of all fungal diseases, has the greatest potential effect on wine quality. The disease can have a disastrous effect on both yield and quality when the fungus affects almost ripe, or damaged grapes, typically in humid weather. This malevolent form is known as grey rot, the most common of the bunch rots. On the other hand, if it affects ripe, healthy, whole, light-skinned grapes, and the weather conditions are favourable, botrytis develops in a benevolent form called noble rot, which is responsible for some of the world’s finest sweet wines. (If it affects red grapes, it always damages pigments, resulting in wines with a brownish tinge and, often, off-odours associated with rot.)
