Grape Berry Moth,
Paralobesia
viteana Clemens
Description and Life Cycle
This is the major insect pest of
grape berries in the eastern United States and Canada. When vineyards are
left unmanaged up to 90 percent of the fruit often is destroyed by the
larvae and the diseases facilitated by the damage inflicted upon the fruit.
Infestations vary greatly from vineyard to vineyard, from year to year, and
within a vineyard. However, vineyards bordering wooded areas are most
vulnerable.
The adult is a
mottled-brown-colored moth with some bluish-gray on the inner halves of the
front wings. The larvae of this small moth are active, greenish to purplish
caterpillars about 3/8 inch long when fully grown. Grape berry moths
overwinter in cocoons within folded leaves in debris on the
vineyard floor and within adjacent woodlots. After emerging in the spring,
the adults mate, and females lay eggs on or near flowers or berry clusters.
Newly hatched larvae feed upon the flowers and young fruit clusters. Larvae
that hatch in June make up the first generation of grape berry moth and
will mature from mid to late-July or August. After mating, females lay eggs
on developing berries, and this second generation matures in August or
September. Larvae of the second generation, after completing their
development, form cocoons in which they overwinter. A third generation
occurs commonly in the southern range of the pest and occasionally in the
northern tier of states.
Damage Symptoms
First-generation larvae web small
flower buds or berries together in early June and feed externally on them or
on tender stems. Larvae that attack grape bunches during this time are
difficult to see.
Second generation larvae tunnel
directly into the green berries and feed internally. Conspicuous reddish
spots develop on the berries at the point of larval entry. Berries affected
in this manner are known as "stung" berries. The second generation is
potentially more damaging than the first. A single larva may destroy 2 to 6
berries in a cluster, depending on berry size, and several larvae frequently
inhabit a single cluster.
At harvest, severely infected
bunches may contain severa
l
larvae, and many of the berries may be completely hollowed. In many cases,
bunches are covered with bunch rot fungi and infested with Drosophila
spp. fruitflies, and often having an unhealthy appearance.
Management
(How to survey vineyard to determine percentage of clusters damaged.)
A protectant insecticide may be
needed to prevent damage in areas heavily infested by grape berry moth. The
number of spray applications depends on the amount of infested berries the
grower is willing to accept. Table grapes require more attention than
grapes grown for juice. Corrective measures are usually suggested if more
than 5% of the clusters are injured. To determine the percentage of
clusters damaged you should randomly inspect 100 clusters along the
perimeter of the vineyard and 100 clusters toward the center of the
vineyard. This method will tell you if treatment of the entire vineyard is
necessary. Treatment of perimeter rows maybe all that is necessary to
control this pest. Control of maturing larvae in mid-to late-July is
particularly important.
Cultural controls can be used to
kill the overwintering pupae in leaves. Leaves can be gathered and
destroyed in the fall, or leaves can be buried within the soil in the
spring, 2 weeks before bloom, by rototilling or cultivating.
An alternate method of control
using pheromone rope ties to disrupt the males of the grape berry moth was
approved by the EPA in 1990. This method prevents mating, thus reducing the
number of fertile grape berry moth females in a treated vineyard. This
method is most effective in vineyards at least 5 acres in size. Ties are
dispensed manually at a rate of 400 ties per acre. When a vineyard is under
heavy pressure from berry moth, it may require spot treatment with an
effective insecticide at the source of the infestation. Studies indicate
that vineyards in close proximity to external berry moth sources such as
woodlots, may require an application of insecticide in addition to the ties
for control of this pest. Vineyards utilizing these ties should continue to
scout their plantings in the same manner as previously mentioned. If
thresholds are reached the decision to apply an insecticide should be
considered.
Monitoring Male Moths
Pheromone traps are available to
monitor the emergence of male grape berry moths during the season. This
information may be useful for optimal spray timing; sprays should target egg
hatch and young larval activity, which occurs several weeks after the first
moths are trapped. A minimum of 3 traps for monitoring a single block of
approximately 10 to 15 acres is recommended. Traps hung from the top wire
of the trellis should be placed around the perimeter of the vineyard before
bloom and should be at least 100 feet apart. Sticky trap bottoms should be
checked weekly for moths, and pheromone caps should be changed monthly to
obtain accurate flight information. Every vineyard location is unique, and
growers should not rely on pheromone trap data from other vineyards for
timing insecticide sprays.
Control
Pheromone traps should be
utilized in vineyards with a history of grape berry moth problems. Trapping
of adult male moths indicates the beginning of flight activity. Mating and
egg laying will occur over a 2 to 3 week period following the first
detection of flight activity. A protective cover spray may be required
during this period to prevent egg laying and hatch. Early season control of
this pest may prevent it from becoming well established within the vineyard,
and may eliminate the need for control later in the season. It should be
noted that the second flight activity period occurring in late July and
August is the most important. These adult moths in late summer produce the
eggs which hatch into larvae capable of causing major damage to the maturing
fruit. One should not solely depend upon a pheromone trap for detecting
this late season threat. Scouting should be implemented on a weekly basis
after bloom. If berry cluster damage reaches 6% in grapes used for
processing or 3% in those grown for fresh market, a protective cover spray
should be applied.
Current
pesticide recommendations may be found HERE
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