Grape Vine Pests and Diseases

Grape Cane Gallmaker

• The grape cane gallmaker (Ampeloglypter sesostris) causes damage to new shoots as they appear in the spring months. A reddish-brown snout-nosed beetle, the insect occurs widely throughout the Eastern and Midwestern regions of the United States. In May and June, the female lays her eggs within the new shoots of the grape plant by hollowing out a tiny cavity. Within a cavity, the female will lay a tiny egg. She will carve out approximately 14 cavities, but only a few contain eggs. The eggs hatch after a seven to 10 day gestation period. The tiny larva remains inside the cavity, feeding on the wood of the grape shoot.

  The cavity forms a gall, or tumor-like protrusion, on the the shoot. Overall, the shoot is not damaged by the gall and continues to produce grapes. The shoot is a bit more susceptible to breakage, according to the Cornell University. Because the bug does only minor damage, it is not usually controlled unless the infestation is severe. Spraying with an approved pesticide will usually gain control.

Grape Berry Moth

• The grape berry moth (Endopiza vitana) occurs throughout the eastern United States. The insect feeds widely on the fruit of the grape vine. If control is not used, more than 90 percent of the crop will be destroyed, according to the University of Michigan. The larvae of the grape berry moth feed on the shoots, flowers and fruit of the vine in the spring. Up to three generations of the insects occur per season.

  Apply post-bloom insecticide sprays against the grape berry moth for successful control. Later applications of insecticides in mid and late summer will help control severe infestations.

European Red Mite

• The European red mite (Panonychus ulmi) has become a problem in the eastern United States. The insects feed heavily on a grape vine's foliage by piercing it with their mouths and sucking the nutrients out. The foliage eventually turns bronze and dies. The damaged foliage and shoots end up affecting the vine's ability to produce ample grapes.

  The females of the European red mite appear dark red, and the male is slightly lighter in color. The mites congregate along new shoot growth. Miticides and summer oil applications will control the mites. Predatory mites often control the European red mites without the need for miticide applications. Such applications will kill not only the European red mite but also the beneficial mites.

Eutypa Dieback

• Eutypa dieback (Eutypa lata), a fungal disease, occurs predominately on grape vines that are older than 5 or 6 years. The disease causes stunted, deformed growth and tattered foliage. Dark wedge-shaped cankers develop on the wood of the grape vine.

  Promptly prune away and destroy all canes infected with the disease to gain control. Prune after a rain shower so the spores of the fungus are not easily spread, recommends Texas A&M University. Unfortunately, no chemicals are licensed to treat the disease.

Downy Mildew

• Downy mildew (Plasmopara viticola), a fungus, causes the foliage of the grape vine to develop a white, cotton fungus covering. The leaves turn brown and die once the covering occurs. The grapes begin to rot and turn white when infected at a young age. When berries are infected in a mature state, they begin to change color. Light berries turn gray-green, and dark berries turn pinkish. The grapes easily fall from the vine.

  The fungus grows best when the weather is warm and wet. Apply preventative fungicides before the white covering of the fungus occurs. Use mancozeb and copper compounds to prevent downy mildew.