Branch and twig borer—Melalgus confertus
Adult branch and twig borers are often seen walking on canes or feeding on bud axils or shoot crotches.
The adult borer is a dark brown beetle, cylindrical in shape. The immature stage (grub) is white, fleshy, enlarged just below the tiny brown head, and appears legless. It is typically curled up in a C shape.
Adult branch and twig borers are present on vines from early March through April. Males are frequently found attending females while they feed. Eggs are laid singly in protected areas. Larvae emerge in May or June and bore into dead grapevine wood where they continue to feed. The larva remains in its burrow for 10 months. It then prepares a hollow cell in which to pupate. Adults emerge from pupae within 2 weeks of pupation. Branch and twig borers have one generation per year.
New shoots (8 - 10 inches long) wilt or break off during windy weather. Close inspection reveals a hole or gnawed area in the crotch formed by shoot and spur. Larvae burrow into wood at dead or dying parts of vines, plugging the tunnel behind them with sawdustlike frass and chewed wood.
Prune out dying and dead parts of vine and remove or burn all prunings before March, as these are breeding sites for the beetles. Keep area free of prunings and wood cut from fruit and nut trees and ornamentals. The many species of general predators found under the bark of grapevines may assist in maintaining lower populations. Treatments with commercial formulations of the entomopathogenic nematode Steinernema carpocapsae, which can move through frass tubes to infect larvae, may be of some benefit. Pesticides should not be necessary.