Types of Concord Grape Diseases

Mildews

• Concord grapes have a moderate susceptibility to powdery mildew caused by Erysiphe necator. Signs include a white, powdery substance that covers the plant's leaves and fruit along with brownish spots appearing on the normally green shoots. Downy mildew is a fungal disease cause by the plant pathogen Plasmopara viticola. This infectious disease infiltrates plant tissue, resulting in yellow lesions appearing on upper grape leaves and white fuzzy spores along the underside of the leaves. Downy mildew leads to defoliation and shriveled, discolored fruit. Concord has a slight vulnerability to downy mildew. Removal of infected plant parts coupled with fugal sprays helps control mildew diseases.

Rots

• Black rot is an early-season fugal disease caused by the plant pathogen Guignardia bidwellii. Concord grapes have a high susceptibility to black rot. Symptoms consist of rounded brown lesions on the leaves. On the grapes, discoloration and shriveling occurs along with small black fruiting bodies appearing on the dried-up fruit. Concord grapes have a small vulnerability to botrytis bunch rot. Botrytis bunch rot is a fungal disease caused by the fungal parasite Gliocladium roseum. This unsightly disease forms tan to gray hairy fungi that cover grapes. Once infected, grape plants become susceptible to other forms of diseases.

Foliage Diseases

• Concord grapes have a high sensitivity to Phomopsis leaf spot, which is a fungal disease caused by Phomopsis viticola. Phomopsis leaf spot affects the plant's shoots by forming elliptical lesions that develop black crusts. The leaves develop light green spots that change to black with yellow edges. Fruit becomes infested with light brown to black pimples that shrivel the grapes. Concord grapes have a high susceptibility to Eutypa dieback. Eutypa dieback is a fungal disease caused by Eutypa lata. This debilitating disease stunts plant growth, discolors leaves, creates dropped flowers and causes death to one side of the vine. Symptoms usually appear within three years after the infection sets in.

Cankers and Galls

• Anthracnose is a fungal disease caused by Elsinoe ampelina and to which concord grapes have a low vulnerability. This destructive canker disease attacks the leaves, shoots and berries. Rounded rust colored spots with crusty black fungus develop on leaves and shoot, creating holes in them. Grapes exhibit small rounded red spots that enlarge and sink inward, forming pink fungal spores. Crown gall is a bacterial disease caused by the plant pathogen Agrobacterium tumefaciens, to which concord grapes have a low susceptibility. Symptoms include swollen growths on the roots and stems. This disease interrupts the flow of water into the plant and causes stunted growth and discoloration.