Black Rot of Grapes – Cornell Cooperative Extension of Suffolk County

Introduction: Black rot of grape, Guignardia bidwellii (Ellis) Viala and Ravaz, is an important fungal disease in home vineyards on Long Island. It can cause complete crop loss. There is a wide variation in susceptibility to this disease among native American and hybrid cultivars, where as all common cultivars of Vitis vinifera appear to be highly susceptible.

Symptoms and Signs: All green tissues of the vine are susceptible to infection. Relatively small, brown circular lesions develop on infected leaves (Fig. 1), and within a few days black spherical fruiting bodies (pycnidia) form within the lesions. Elongated black lesions on the petiole (Fig. 2.) may eventually girdle these organs, causing the affected leaves to wilt. These lesions may contribute to breakage of shoots by wind, or in severe cases may girdle and kill young shoots altogether.

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