MSU Extension Integrated Pest Management

Botrytis bunch rot

Disease

Botrytis bunch rot

Botrytis cinerea

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Botrytis bunch rot is a fruit rot, but it can also affect other plant parts. In spring, buds and young shoots may be infected and turn brown. In late spring, V-shaped or irregular brown patches may appear on leaves. Inflorescences may become blighted and wither away. Some flower infections remain latent until veraison. Once infections become activated, they spread rapidly from berry to berry. Compact clusters, powdery mildew infection, hail and insect damage, high nitrogen content and rain cracking can predispose grapes to infection. The disease is favored by temperatures of 59 to 68ºF (15 to 20ºC) and spreads rapidly during rainy periods, especially close to harvest. In certain cultivars, slow developing late-season infections are termed “noble rot” because they contribute to the production of exceptionally sweet wines. The fungus overwinters in mummified fruit and other infected plant parts.