Parasites of Grapevines

Grape Phylloxera

• Grape phylloxera, tiny aphid-like insects, cause tiny growths known as galls on grape leaves. High numbers of galls cause leaves to die and drop off, which delays ripening, affects grape quality and makes the vines susceptible to winter damage. Aphid eggs overwinter inside the wood of the grapevine and hatch in the spring with the nymphs moving onto the leaves and creating new egg-filled galls. Control phylloxera by spraying vines with carbaryl during the blooming stage.

Grape Flea Beetles

• Tiny grape flea beetles, roughly 1/10 of an inch long and deep blue with purplish or green undertones infest vines. Flea beetles overwinter as adults under the soil around the grapevines emerging in early spring to mate, lay eggs and feed on grapevine buds. Damage to the buds can prevent them from developing and bearing fruit. Monitor and control these pests in the early spring. You may see the beetles on the leaves or observe them springing up when leaves are disturbed. Good gardening practices help control grape flea beetles. Remove debris and leaf litter regularly. If more than 4 percent of the buds are infested, the University of Minnesota Extension recommends spraying an application of carbaryl or pyrethrin.

Japanese Beetles

• Japanese beetles, which commonly plague rosebushes, can also wreak havoc on grapevines. Adult beetles have iridescent, greenish-black heads and thoraxes with copper-colored wings. Japanese beetles feed on grape leaves and cause serious damage, often defoliating young vines. The larvae are large, white and shaped like a semicircle. Overwintering beneath the soil, they emerge in June as adults. The Virginia Fruit Extension reports that a biological control agent called Bacillus popillae kills the larvae but is ineffective against adults. Parasitic wasps and tachinid flies can control levels of the adult beetles. Carbaryl is also effective.

Grape Berry Moth

• Grape berry moths, which feed only on the grapes, can destroy up to 90 percent of the fruit on untreated vines. The small, brownish moths are about 3/8 of an inch long and can be seen taking rapid zigzag flight from late afternoon to dusk. Grape berry moths overwinter in cocoons on the soil at the base of the vines with adults emerging in May before blossom time. The purplish larvae feed on stems, blossoms and immature grapes, leaving a telltale red or purple blemish at the entry point. Detect them by the webs they create in flower and berry clusters as well. According to Michigan State University, treat light infestations by plucking affected grapes by hand. Spray heavier infestations with insecticide after the grapes have bloomed. Additional treatments may be necessary in late summer.