Grapes

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Leave and Foilage Problems

Tan leaf spots with a dark border


Cause

Black Rot (Guignardia bidwellii), a fungal disease which overwinters in crop debris and is spread by wind and rain.

Treatment

Plant disease resistant varieties whenever possible. Clean up crop debris regularly, including fallen berries. Captan or Bordeaux mixture are two approved fungicides for black rot.

Yellow and orange leaf blotches with gray mold


Cause

Downy mildew (Plasmopara viticola), a fungal disease which overwinters in crop debris and is worst during hot humid weather (June-August).

Treatment

Plant disease resistant varieties whenever possible. Clean up crop debris regularly, including fallen berries. Captan or Bordeaux mixture are two approved fungicides for black rot.

Powdery white mold


Cause

Powdery mildew (Uncinula necator), a fungal disease which is most common during cool, humid, and windy conditions.

Treatment

Apply copper or sulfur-based fungicides at the first sign of powdery mildew.

Fruit Problems

Shriveled, black berries with brown spots


Cause

Black Rot (Guignardia bidwellii), a fungal disease which overwinters in crop debris and is spread by wind and rain.

Treatment

Plant disease resistant varieties whenever possible. Clean up crop debris regularly, including fallen berries. Captan or Bordeaux mixture are two approved fungicides for black rot.

Wrinkled, brown berries with white mold


Cause

Downy mildew (Plasmopara viticola), a fungal disease which overwinters in crop debris and is worst during hot humid weather (June-August).

Treatment

Plant disease resistant varieties whenever possible. Clean up crop debris regularly, including fallen berries. Captan or Bordeaux mixture are two approved fungicides for black rot. 

Gray fuzzy mold


Cause

Gray mold (Botrytis cinera), a fungal disease.

Treatment

Disease symptoms are often worse in cool, wet conditions. Avoid excessive irrigation, clean up and remove crop debris. Resistant varieties, and approved fungicides including Captan are available.

Shriveled berries covered with insect webbing

Cause

Grape berry moth (Endopiza viteana), the small caterpillar of a moth which spins webbing on grape flowers and fruit as it feeds.

Treatment

Inspect flower clusters several days before bloom, re-inspect the fruit clusters immediately after the bloom, and again in early August when a second generation of the moth sometimes occurs. Imidan, Sevin and malathion formulations are approved for use on the grape berry moth.