Pests & Diseases of Grape Plants

Black Rot

• A very serious disease of grapes is black rot, which is caused by the fungus Guignardia bidwellii. Grapes plants are most susceptible to this disease during warm, wet seasons. The fungus attacks all areas of the vine, but it particularly damages the fruit, causing grapes to dry up and turn black.

Downy Mildew

• Another serious fungal disease of grape plants is downy mildew, caused by the fungus Plasmopara viticola. This fungus also attacks all areas of the vine, but it especially affects the leaves, leaving yellowish, oily lesions between the veins. White cottony growth then appears on the lower surface of the leaf. Berries become grayish and drop when the plant is affected by downy mildew.

Powdery Mildew

• Powdery mildew typically happens in the fall. It is caused by a fungus that produces a light gray or white powdery substance on the surfaces of leaves. Although it looks bad, this disease is rarely fatal to grape plants.

Botrytis

• Gray mold, also known as Botrytis blight, is another fungal disease that affects grape plants. The disease causes leaves to rot off. Affected areas may be covered with gray mold, particularly in cool, damp weather.

Japanese Beetle

• A major pest of grape plants is the Japanese beetle, which is a small, metallic green beetle with copper-brown wings and small tufts of white hairs under its wing covers. Japanese beetles typically damage the leaves of the plants but rarely kill the grape plant. Shake beetles from the plants to prevent damage to the leaves of the vine.

Leafhopper

• Leafhoppers are pests that damage grape plants by piercing the plant and sucking out the nutrients. They move with a crab-like motion, and their presence on grape plants is easily recognized by large white blotches or drying and yellowing of the leaves. Sometimes the leaves will curl, depending upon the species of leafhopper.

Leafrollers

• Leafrollers wrap leaves around themselves and proceed to eat the leaves from inside their protection. Grape plants infested with leafrollers will have signs of chewed leaves, which will turn brown and drop in late summer.

Mealybugs

• Mealybugs are grape plant pests that are named for the white waxy secretions covering their body. There are several types of mealybugs, including scales, whiteflies, and aphids. They are especially a nuisance in warm, wet climates and attack all areas of the grape plant by piercing and sucking the sap, leaving a sticky substance on the plant.