Insects Attacking the Roots

The adult is a clear-wing moth, with the forewings brown and the hindwings clear with brown borders. The body mimics that of a wasp, brown with yellow markings. Male moths measure about 5/8 inch in length, while the female is larger, about 3/4 inch long. The moths emerge from the soil during July and August. Eggs are deposited individually on grape leaves or weeds, or dropped on the ground close to the trunk. The larvae hatch and burrow into the soil, find their way to the roots and crown, and feed on them. Larvae continue to feed within the vine's root system for about 22 months. A fully developed larva is about 1 1/2 inches long and white with a brown head capsule. Mature larvae move to places just under the surface of the soil and pupate in earthen cells. Adults start emerging in July and continue to emerge through August.

Damage Symptoms

Larvae attack the roots and crown of grapevines. They tunnel into the roots or crown and feed internally. Feeding and boring weaken the grapevine and may eventually kill it. Larvae also provide entry points for disease organisms. Vines that are severely infested may wilt under stress, sometimes only part of the vine will show stress.

Management

Weed control is important in managing this insect pest. Weed control decreases the number of oviposition sites and provides an area under the trellis suitable for applying an insecticide. Researchers in North Carolina also have achieved good control of root borers with polyethylene mulch, this technique can be easily accomplished at planting. It works well for a while but the mulch must be maintained over the years in order to be successful.

An alternative method of control using pheromone rope ties to disrupt the males of the grape root borer is being tested by researchers at Ohio State University. This method prevents the male root borers from locating the female borers and mating, thus reducing the number of fertile root borer females in a treated vineyard. Ties are dispensed manually at a rate of 100 ties/acre. They should be placed on the top trellis wire every 6 or 7 vines. Results from these trials look promising, but bringing the borer population down to acceptable levels requires several years. Another method of utilizing the grape root borer pheromone for control is being studied at two southern Ohio vineyards. This method utilizes the sex pheromone and 1C pherocon traps. Traps baited with the pheromone are placed throughout the vineyard in an attempt to reduce the number of males available for mating. This study has been underway for3 years now and the male population is continuing to decline by an average of about 30% per year. External woodlots containing wild grapes are a good source of grape root borers. Such areas adjacent to vineyards should be considered when trying to manage this pest. Extermination of wild grapes from within these areas may help to reduce root borer pressure.

Chemical control of this pest is difficult due to its cryptic nature. Chlorpyrophos is the only chemical currently labeled for control of grape root borer. This treatment should be applied to the ground immediately under the grape trellis when the first adults are captured in the pheromone traps. This application provides a toxic barrier which newly hatched larvae must penetrate to gain access to the grape vines root system.

Monitoring

Pheromone traps are the only means to easily monitor this pest. Response by male root borers to this sex pheromone is strong. A minimum of 3 pheromone traps should be placed transecting the vineyard in a diagonal manner. Traps should be in place by late June and checked on a weekly basis thereafter. A single pheromone cap within a trap will last the entire season.

Trapping out utilizes the sex pheromone placed within 1C pherocon sticky traps. This method is still experimental at this time but certainly appears to be working. Traps are placed around the vineyard perimeter in late June at 35 to 50 foot intervals. These traps should be checked on a weekly basis. Where infestations are high, many borers will be trapped resulting in the need for removal of some of the trapped adults or replacement of the trap bottoms. This method requires a continued effort year after year to reduce pressure subsequent years.

Chemical control of emerging adults or entering newly hatched larvae will give some assistance if repeated over a wide area.

In the case of the root form of grape phylloxera, the insects overwinter as immature forms on the roots. These forms mature in the spring and produce eggs that hatch into nymphs. The nymphs then start new galls on the roots.

Winged forms develop in the spring, summer or fall and emerge

from the soil to lay eggs on stems. These eggs hatch and produce the true sexual forms that produce the overwintering eggs laid under the bark. Several generations of each form of phylloxera may occur each season. Although the two forms behave differently, both belong to the same species of phylloxera that occurs on the leaves and roots of grapes.

In many areas of the world, susceptible cultivars are grafted onto resistant rootstocks to prevent damage by the root form. However, the foliar form still may occur in such cases. Currently only one insecticide is labeled for the foliar form of grape phylloxera. There are some natural predators which feed upon the foliar form of grape phylloxera, but none of these provide adequate control of the pest. There is no known completely successful chemical control for the root form of gape phylloxera. Eastern growers usually do not have a problem with the root form of the phylloxera but it does serve as a resource for the foliar form.

Both adults and larvae of the grape rootworm feed on grapevines. Adult beetles feed on the leaves, and larvae attack the roots of the grape plant. The activities of the larvae, or grubs, are much more detrimental to grapevines than the feeding of adults.

Adult beetles first begin to emerge from the soil about two weeks after bloom. The adult is grayish-brown, elongate and about 3/8 inch long. By mid- to late June, most o

f the beetle population has emerged. The beetles chew on the foliage, making chain-like holes in the leaves. Mating occurs and the females lay their eggs under the bark on the vine. Most larvae hatch from the eggs by about mid-July. The small, white grubs drop to the ground and

find their way to the roots where they proceed to feed. Most larval feeding occurs during late summer and early fall. The grubs overwinter beneath the soil surface, pupate in the spring and emerge as adults. There is only one generation each year.

If large populations of the grubs build up in a vineyard, vines may be affected adversely. In situations where many or most of the smaller roots of a grapevine are destroyed by larvae of the grape rootworm, the vine may be seriously weakened and its vigor drastically reduced, and death may follow. Control measures should be directed at the adult as this stage of the insect is the most vulnerable. Look for the beetles and their feeding damage during late June to mid-July.

Grape Trunk Borer, Clytoleptus albofasciatus (Laporte and Gory) (Coleoptera: Cerambycidae)

Immature forms, or larvae, of the grape trunk borer sometimes infest dead wood of the trunks of the older grapevines. . Larvae do not feed on living wood tissue. The adult beetle is brown to black with red and yellow markings. Its antennae are nearly as long as the entire body. The beetle is about 5/8 inch long.

The beetle lays eggs on grape trunks. Newly emerged larvae burrow into the grape trunk at cracks, old pruning scars and pruning stumps where dead wood is present. Larvae feed inside the trunk for two seasons; a fully grown larva is white and about 3/4 inch long. During the second season, the larvae pupate within the trunk and emerge as adults. Emergence holes of the adults may be seen in the dead wood.

A common method of dealing with this insect is to cut off the old trunk and start a renewal trunk from the roots; nevertheless, the grape trunk borer appears not to be of economic importance.