Grapevine Bugs

In cold climates of the U.S., American bunch grape (Vitis labrusca) is the main type of grapevine you're likely to grow in your garden. In warm winter climates, you probably grow European grape (Vitis vinifera). Both species grow in U.S. Department of Agriculture plant hardiness zones 6 through 9, depending on the cultivar. A number of insect pests attack both grape species and their cultivars. The insects vary across the country.

In the eastern U.S., Japanese beetles feed on grape leaves, eating the soft tissue and leaving the veins. Shake the small, green and bronze beetles off in the early morning into a pail of soapy water. Grape flea beetles are small, metallic, jumping, metallic blue to green insects. Both adults and the grublike larvae eat grape leaves. The adults overwinter in debris near the grapevine, so eliminate the beetles by removing litter and fallen leaves each year. Colorful yellow, cream and black caterpillars of the grapeleaf skeletonizer chew away the soft leaf tissue between veins. Adult moths are metallic blue-black with an orange collar. Be watchful for just-hatched groups of small caterpillars and pick them off promptly before they disperse.

In fall, the normally predatory multicolored Asian lady beetle may feed on damaged grapes. Prevent them being a pest by removing any damaged fruit from grape clusters before they attract the beetles. The grape berry moth lays eggs on grapevines and the larvae eat buds, blossoms and developing grapes. The insects overwinter as pupae in leaf litter under the vines, so removing dead leaves before spring bloom gets rid of the pupae before they hatch into moths. Although they don't harm the grapevine, yellowjacket wasps can feed on juices from damaged grapes in late summer and fall. To prevent getting accidentally stung by them, remove damaged grapes and be watchful when harvesting fruit.

The grape phylloxera causes galls on both the leaves and roots of grapevines. The leaf galls are about 1/4 inch wide and look like paler green raised bumps. The tiny yellow-brown bugs have a complex life cycle that alternates between leaf and root forms. The leaf galls don't cause much damage to the plant but the root galls, which are knotted swellings, can lead to root decay. American grapes are resistant to grape phylloxera damage, but European grapes aren't, and should be grafted onto American grape rootstock. The larvae of a brown snout beetle called the grape cane gallmaker live in reddish galls produced just above leaf nodes. For control, prune away the gall areas by mid-July before new beetles emerge from the gall.

A brown moth with a stout, yellow-banded abdomen and transparent hind wings lay eggs on or near grapevines that hatch into cream-colored larvae. The larvae burrow into grape roots, feeding on them for two years. Root damage can cause stunted growth or death of the plant. It's hard to evaluate because the damage is all underground. Prevent infestations by controlling weeds around grapevines to reduce egg-laying sites and to expose the larvae so they die before they can burrow into the roots.