Insect Note #G-3
Prepared by:
K. A. Sorensen, Extension Entomologist
Dated 6/94
Placed o the Web 4/95 by the Department of Entomology, NCSU
Grape Root Borer
Vitacea polistiformis (Harris) Lepidoptera: Aegeriidae
The grape root borer is a native species belonging to a family of
insects known as the clear-winged moths. Other members of this
family which are well known are the peach tree borer and squash
vine borer.
Damage
The larva or borer, once finding a root, first eats its way through
the outer bark and then begins to excavate an irregular burrow.
This burrow may encircle the root several times or run with the
grain of wood. In larger roots this excavation is most likely to
be found extending along the underside of the root. As the borer
advances in its feeding, it packs the burrow behind full of its
coarse, reddish-brown castings. Severe pruning and girdling of
roots lessens the feeding area of the vine and weakens it
correspondingly. Large numbers of borers in the crown and
adjoining root system cause discoloration, loss of vigor and
production and eventual death of the vine. The effect of borer
feeding may not be immediately apparent and depends on various
factors, such as high temperatures plus lack of plant moisture and
winter injury.
Detection
Grape root borer injury first appears as discolored leaves.
Wilting, loss of production and eventual death follows over a
period of years. On examination of weakened, wilting and dead
vines, either previous damage by borers, or actual feeding of
borers in progress will indicate positive identifications. When
full grown, borers are whitish in
color with brown heads, sparsely
covered with stiff hairs and attain a length of one and three-
fourths inches. Shed pupal skins near the base of vines in August
will reveal positive infestations.
Adults fly only by day and bear
a striking resemblance to wasps. However, grape root borer adults
are more sluggish than wasps. Also, their hind pair of wings are
clear and in flight have less rapid wing vibrations. Adult borers
are dark brown in color with two orange and yellow bands on the
abdomen. They also possess characteristic orange-colored tufts on
the tips of the abdomen.
The grape root borer being a native species has adapted to wild
cultivated grapevines. This insect has been reported damaging
grape vines in West Virginia, Virginia, Pennsylvania, South
Carolina, Kentucky, Arkansas, Missouri, Georgia and North Carolina.
In NC the grape root borer has been reported on bunch grapes in
Rutherford, Cleveland, Mecklenburg, Johnston, Henderson, Stokes and
Onslow counties to date. Reports on Muscadine grapes have been
verified in Onslow, Anson, Richmond, Moore, Robeson, Lenoir, Jones,
Pender and Bladen counties. Additional counties will be verified
as growers and extension personnel become acquainted with the
insect and closely examine vineyards. The grape root borer
overwinters in the larval stage, pupation occurs near the soil
surface in June and July. The pupal stage requires about 39 days.
Adults emerge from the pupal case at the soil line during July and
August. After mating, female moths lay some 500 eggs
indiscriminately on weeds, leaves and base of grape vines during
their 7 day life. Flight activity occurs during the day and is
most abundant from 12 p.m. to 4 p.m. Eggs hatch in about 15 days
and larvae enter the soil in search of roots. The cycle is
repeated in 2 years.
Control
Natural enemies consist of barn swallows, mockingbirds, crested fly
catchers, larvae of fireflies, a number of fungi and a species of
nematodes. A number of other parasites and predators undoubtedly
exist. However, these along with unfavorable weather conditions,
fail to offer control.
Resistant root stocks show some promise, but this approach is many
years away.
The female releases a strong sex attractant that attracts males for
mating. Studies are in progress using a mass trapping and mating
confusion technique. Identification and commercial availability of
the pheromone exists. Females, once engaged in
egg laying, can very readily be approached and killed. A periodic
and constant surveillance of vineyards during July and August could
conceivably result in a reduced infestation through elimination of
adult females.
Grape root borers can be controlled. The preventative control
consists of applying Lorsban 4E at the rate of 4 1/2 pints in 100
gallons of water. Apply a quart dilute mixture of spray to the
soil at the base of the vine. A single application with a
herbicide low pressure sprayer 35 days before harvest is suggested.
Spray should not contact the fruit or foliage.
Results of tests in North Carolina indicate that plastic, bark mulch, Leno cloth, or ridges
of soil placed around the base of vines give control. This method
is effective as a physical barrier preventing adult emergence.
Around young vines, plastic also functions in weed control. Proper
timing (about August 1) is critical with this procedure and needs
to be determined for areas and individual vineyards.
Such cultural methods as weed control, fertilization, irrigation,
clean cultivation and weekly cultivation (disturbance of top 1 inch
of soil) are helpful in reducing injury. Hence, the condition of
the vine, whether it is a healthy, good producer, or a weakened,
poor producer because of the lack of good cultural practices, is a
deciding factor in the decline of a vine as a result of injury by
borers.