Grape Bunch Rots

Grape bunch rots Common name Grape bunch rot Botrytis bunch rot Gray mold of grape Causal agent Grape bunch rot is a fungal disease related to the pathogen of the genus Botrytis. It commonly affects grape species. Scientific name Botrytis cinerea Symptoms & Signs The most apparent symptom of grape bunch rot is the grayish mold over the berries. It can cause drying and shriveling of the grapes, leading to premature cluster drop. The berries are soft and mushy, with white cultivars turning brown and purple cultivars turning red. Sometimes, the pedicel also shows lesions causing girdling and eventually fruit drop. Transmission The fungus overwinters in mummified grapes or debris and produces spurs or conidia in the spring, which spreads the disease. Spores travel to other plants by insects, water, wind, and contact. Warm, moist conditions between 54 to 75 degrees F increases the risk of infection. Time of concern Early spring to late summer Common hosts Vitis vinifera grape French Hybrid grape