The Grapes in my Garden Seem to be Infested by Pests or Infected. What can I do?

Are the young fruits covered in a white coating?

Do the leaves have a white powdery coating on the upper surface?

Are the fruit clusters enveloped with a fluffy, grayish-brown coating?

Are the fruit webbed together with holes that seem to have been chewed from one grape to another?

Are the fruits covered with a sticky coating and black mold?

Do the leaves or leaf petioles have reddish swellings?

Do the leaves have green, pea-like swellings on their undersides?

Do the leaves have pale stipples along the leaf veins?

Have the leaves been skeletonized?

White, powdery patches on the leaves and fruits are caused by a fungal disease known as powdery mildew. Powdery mildew usually appears in damp places. Encourage good air circulation around the grapes by thinning any surrounding plants. Keep foliage dry when watering. Affected leaves and fruits should be cut off and removed.

White, cottony growths on the undersides of the leaves and fruits are caused by a fungal disease known as downy mildew. To control downy mildew, remove and destroy all diseased leaves and tendrils in the fall. Spray vines with copper several times throughout the growing season to control the disease. Do not spray copper during flowering.

Fluffy, grayish-brown coating on a grape clusters is caused by fungal disease known as botrytis bunch rot which usually appears in tight vines with poor air circulation. For prevention, thin berries within fruit clusters and remove some leaves around the fruit to increase air circulation.

Grape berry moths are likely to cause these symptoms. These small, green or brown caterpillars feed on the pulp and seeds of the fruits. Pick and destroy infested grapes. At the end of the season, collect and destroy fallen leaves because they might contain overwintering pupae.

Sticky coating is caused by grape whiteflies or mealybugs which secrete a sticky substance called honeydew. Honeydew acts as food for sooty mold that gives it the black color. To control whiteflies, spray nearby buckthorns, where the pest overwinters, with insecticidal oil during winter. Introducing Australian lady beetles will help control mealybugs.

The swellings are caused by a tiny fly called a midge. You can find small pinkish to orange maggots inside swellings. They are harmless, but the infested leaves should be pruned off.

These swellings are caused by aphid species called grape phylloxeras. Leaves, stems, and buds get distorted and later the leaves and flowers drop from the plant. Introducing natural predators will keep aphid numbers low. Insecticidal soap should be used only with severe infestations.

Pale stipples along leaf veins are caused by leafhoppers. These small, green or brown insects feed by sucking juices from leaves undersides. Leafhoppers may be the carriers of bacterial pierce’s disease, but they rarely do damage in grapes as their many predators keep their numbers low. Insecticidal soap helps with severe infestations.

Japanese beetles feed on grape leaves and leave only the veins uneaten. They are half an inch long metallic blue-green insects. You can simply knock the beetles off of the leaves.

Grape scales may be the cause for stunted and unproductive vines. They are tiny, round and immobile insects that usually hide under the loose bark where they feed by sucking sap from the vines. To control them, spray infested areas with dormant oil during winter and prune off severely infested old growths.