Sour bunch rot
Sour rot is a wet rot that spreads rapidly throughout clusters and smells like vinegar. It is caused by acetic acid bacteria and various undesirable yeasts and fungi. Unlike Botrytis bunch rot, it usually lacks fungal sporulation. Low-grade powdery mildew infections and grape berry moth infestations can predispose clusters to infection. Fruit flies are common and help spread the disease. Tight-clustered cultivars are more susceptible than others. Prolonged periods of wetness or high relative humidity are conducive to sour rot development.
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