Kent Daane, Associate Specialist, University of California Extension,
UC Berkeley; Ed Weber, Napa County Farm Advisor, University
of California Cooperative Extension; & Walt Bentley,
Entomologist, University of California Statewide IPM Project
species of mealybugs are pests of grapevines in many parts of the
world. In California, the grape mealybug, long-tailed mealybug,
and obscure mealybug have long been present in vineyards, but they
are usually minor pests not requiring chemical control. Recently,
the invasive vine mealybug (VMB) has emerged as a serious pest in
many parts of the state. It brings with it the need for aggressive
Distribution and damage
Vine mealybug is found in the Mediterranean regions of Europe and
North and South Africa, as well as grapegrowing regions in the Middle
East, Argentina and Mexico and now in California.
In California, vine mealybug was first discovered in 1994 in table
grape vineyards in the Coachella Valley (Riverside County), although
it probably entered the state a year or two earlier. It spread throughout
the Coachella Valley, and in 1998 was found in the southern San
Joaquin Valley (Kern County).
Its dispersion into new regions has been dramatic: VMB was found
in Fresno County in 1998, Santa Barbara County in 2000, San Luis
Obispo County in 2001, and in El Dorado, Madera, Monterey, Napa,
Sacramento, Sonoma, and Stanislaus counties in 2002. To date (March
2004), VMB has been found in 17 counties in California (Table
I). It is likely that there are more infestations that have
yet to be identified or have not been reported.
Circumstantial evidence suggests this rapid dispersion resulted
from movement of infested vineyard equipment (mechanical harvesters,
bins, tractors, etc.) and through sales of infested nursery stock
(from 1998 to 2003). Other possible factors include spread with
field crews and natural dispersion (such as birds and wind-blown
Mealybugs are phloem feeders. As they feed, they produce a sugary
excretion (honeydew) that supports the growth of sooty mold. Infested
clusters become contaminated with honeydew, sooty mold, egg sacs,
and lots of mealybugs.
In southern California, severe vine mealybug infestations have also
reduced vine growth and resulted in defoliation, bunch rots and
even spur and cane death. In addition, like other mealybugs, vine
mealybugs can spread grapevine virus diseases, such as leafroll
and corky bark.
Several factors make vine mealybug much more damaging and difficult
to control than other mealybug species:
- First, the vine
mealybug reproduces at a higher rate than other species, enabling
small numbers of mealybugs to reach damaging levels in one season.
Females can each deposit up to 700 eggs (average is approximately
San Joaquin Valley, vine mealybug has four to seven generations
per year compared with two for the grape mealybug. This greatly
increases the population size, and it leads to overlapping generations.
The overlap makes chemical control more difficult, since some
insecticides are effective only against the nymphal stages.
- Second, vine mealybug
excretes much more honeydew than other species. This honeydew
can cover leaves, canes, trunks and fruit, making entire clusters
and vines a sticky mess. The honeydew often becomes so thick it
resembles soft candle wax.
Fruit from heavily infested vines is not suitable for harvest.
The stickiness of all the plant parts also facilitates spread
of VMB from vineyard to vineyard on equipment and worker clothes.
- Third, vine mealybug
can feed on all parts of the vine throughout the year. It can
be found on leaves, in clusters, under the bark, and even on the
roots of grapevines. By hiding under bark or on the roots, VMB
is protected from most foliar insecticides, from high summer temperatures,
and from parasitoids and other natural enemies.
- Fourth, vine mealybug
is not native to California, so it has fewer natural enemies than
the grape or longtailed mealybug species. Established populations
will require repeated insecticide treatments to keep them at manageable
- Finally, vine mealybug
has a wide host range. It can feed on subtropical (grapes, figs,
apples, and citrus) and tropical (dates, bananas, avocados, and
mangos) crops as well as a number of common weeds, such as malva,
burclover, black nightshade, sowthistle, and lambsquarter. However,
in California, grapevines appear to be its preferred host throughout
Vine mealybug population cycles and its distribution on vines can
vary dramatically, depending on temperatures and vine condition.
While it can be found on all parts of the vine at any time of the
growing season, there are clear dispersal and abundance patterns
that influence the amount of damage and the effectiveness of chemical
and biological controls.
For example, in the Coachella Valley, most of the vine mealybug
population overwinters on the roots and lower trunk sections. As
temperatures warm, populations rapidly increase reaching a peak
in April and May. Accompanying the increased density is the pests
movement up the vine, from the roots and lower trunk to the leaves
and grape clusters.
Management becomes a race between the table grape harvest (May-June)
and the time when mealybugs reach the clusters. With hot summer
temperatures after harvest, the population decreases and again is
found primarily on the lower trunk and roots. There is another population
increase in fall, before the overwintering period.
In San Joaquin Valley, vine mealybugs also overwinter on the roots
and lower trunk, and as the temperatures warm in spring and summer,
they move up to the leaves and bunches. Unlike in Coachella Valley,
populations continue to increase during summer, and they remain
on leaves until August.
All stages were found throughout the summer, feeding on leaves and
canes in exposed locations, suggesting that San Joaquin Valley temperatures
had little effect on vine mealybug densities. A late-season reduction
was not accompanied by an increase in summer temperatures, but was
associated with increased parasitism levels. Nevertheless, the longer
the mealybugs remain on leaves and clusters, the more damage they
cause to the crop.
In the Central Coast and North Coast, VMB appears to follow a pattern
similar to San Joaquin Valley. However, the populations continue
to increase through September and October. The late season increase
is most likely due to an absence of parasites in these areas. As
in other regions, considerable damage is likely to occur unless
insecticides are used. Because most VMB infestations are still discrete
in these regions, eradication programs are being attempted in some
for further spread
Until recently, little attention was given to vine mealybug, leading
to its rapid spread throughout California. This history shows how
easily it can be moved, both within grapegrowing regions and over
long distances. With more attention now focused on vine mealybug,
its further spread should be slowed, although complete control is
not likely to occur.
The sticky nature of the honeydew produced by vine mealybug greatly
facilitates its spread. All parts of the vine get very sticky
leaves, canes, berries, clusters, cordons, and trunks. Adult insects,
nymphs, and eggs can get stuck to tractors, bins, picking pans,
gloves, etc., and can thereby be transported to other locations.
Machine harvesters pose a significant risk because they operate
in vineyards when populations are high. They have considerable contact
with fruit and foliage, and are frequently moved from vineyard to
vineyard. If operated in an infested block and then moved without
a thorough cleaning, spread could easily result. Operators need
to be made aware of any vine mealybug infestations in blocks they
are harvesting, and growers should discuss equipment sanitation
practices if using a contract harvesting service.
Movement of infested nursery stock has resulted in numerous infestations
throughout California. Some nurseries have recently implemented
prevention measures that should greatly reduce the chances of further
introductions on plant material. In addition, the California Department
of Food and Agriculture (CDFA) has issued a nursery advisory that
requires monitoring and/or sanitation protocols for VMB.
Nursery sanitation practices include hot water treatment of cuttings
and dormant vines, insecticide applications to green-growing plants,
and insecticide applications to nursery mother blocks. CDFA regulations
do not require nurseries to take all of these steps, so it is prudent
for buyers to discuss vine mealybug control practices with their
nursery sources prior to purchasing vines.
Furthermore, while hot water treatments for dormant wood can provide
excellent control, insecticide treatments of green-growing plants
have not yet been thoroughly tested.
Grape clusters harvested from infested vineyards could also lead
to spread of VMB because the stems will likely still contain insects
or eggs after passing through a winery crusher/ destemmer. If spread
directly back into vineyards, new infestations could result.
Composting infested stems (away from any vineyards) should provide
adequate control, as long as the composting process follows state
regulations and proper temperatures are reached within the compost
piles (above 130†F). Further research is needed to confirm the effects
of composting on infested stems.
To prevent damage from vine mealybug, the best way is to keep the
pest out of vineyards or to chemically treat populations when an
infestation just begins. However, mealybugs are difficult to detect
in the early stages because they are often hidden under bark or
underground. Visible signs of an infestation include the presence
of foraging ants, honeydew or sooty mold on leaves or trunks, bark
that appears wet, and white wax protruding from underneath the bark.
Until recently, visual sampling methods were the only way to spot
new infestations, and they were far too labor-intensive to be practical.
In 2001, a faster, more effective method to monitor VMB was developed,
based on a sex pheromone that female VMBs use to attract winged
This pheromone has now been synthetically produced. In field tests,
traps baited with synthetic pheromone were attractive for two months,
had an effective range of about 300 feet, and had counts that could
be correlated with VMB densities in the vineyard. Using this sex
pheromone to attract winged males is a far more efficient method
of detecting new infestations than trying to search thousands of
vines for hidden females.
Unfortunately, the males are extremely small (less than 1/64 of
an inch) and difficult to identify without considerable training
and experience. Many growers are establishing their own trapping
programs and are working with their local agricultural commissioners
office for help in identification of insects in their traps.
Male vine mealybugs are tiny (a bit smaller than adult thrips) and
brown-to-black in color. They have a single pair of wings, a small
V tail, and long antennae. In sticky traps, they quickly
lose their coating of white wax and become even more difficult to
identify. For this reason, examine traps as soon as suspicious insects
are observed. Remember that close up photographs make
the insects look larger and easier to identify.
In California, free traps and lures may be available in 2004 from
county agricultural commissioners. The preferred trap is the tent-shaped
trap loaded with a vine
mealybug pheromone lure. These three-dimensional traps provide
better adult male VMB catch and lower unwanted insect
catch as compared with flat traps.
Traps should be hung at or above the cordon and near the center
of the vine. Trellis wires make a good attachment point. Traps can
be placed in the canopy to get some protection from wind and equipment,
but the open ends should be exposed so that VMB males can easily
fly, rather than walk, into the trap. The trap position may have
to be changed during the season to avoid interference with vineyard
Two traps are suggested for each 20- to 40-acre block monitored.
Put one trap near the center of the block and the other in a high
traffic area (near roads or intersections, equipment storage
areas, field shops, or packing houses).
There is no reason to place traps deep inside the vine or well within
a vineyard block such that crews cannot easily find and monitor
them. If more traps are used, they should be placed at least 30
rows apart (about 200 to 300 feet) and at least 10 vines from the
edge of each block. Make sure the triangular entrance to the trap
is not blocked by leaves. This will reduce the number of males caught.
Traps should be checked every two weeks during the male flight period
(see below). Lures should be changed at least every six to eight
weeks. Traps need to be changed only when they are old and dirty,
or when male VMB are detected (so they can be confirmed microscopically
and counted). If no male mealybugs are found and the sticky surface
is still functioning, new lures can be placed into old traps.
In heavily infested vineyards, we have found over 2,000 males weekly
per trap. Typically, an infested vineyard will have between 20 to
300 males per trap per week. If fewer than 10 VMB males are found
weekly in a trap, then the infestation may be in another block.
Trapped males may be from neighboring or even distant blocks, as
the males can be wind-blown from one-half mile or more away.
In those counties where vine mealybug does not commonly occur, vineyard
managers should contact the county agricultural commissioners
office and the UC Cooperative Extension farm advisor to get a positive
identification of trapped mealybugs, and to discuss management decisions
and compliance agreements as necessary.
Male flight periods
In Coachella Valley, the male flight period extends from about March
through August. In San Joaquin Valley, the flight will run from
May through October. On the North Coast, males have been trapped
from May to November, with the largest numbers occurring late in
the season. Females often mate in the fall, so the first male flight
in the following spring may be after vine mealybug activity begins.
A number of insecticides can be used to kill exposed vine mealybug,
especially the small nymphal stages. The hidden portion of the population
is harder to control. For this reason, vine mealybug is difficult
to eradicate once it has become well established in a vineyard.
Systemic insecticides (such as Admire®) that reach all parts
of the vine have been the most effective. A control program attempting
to eradicate vine mealybug should include:
- Delayed dormant
application of Lorsban (February or March),
- Spring application
of Applaud or Sevin (Sevin may cause mite outbreaks),
- Systemic application
of Admire in spring,
- Summer to fall foliar
treatments (Applaud, Dimethoate, Imidan, Malathion),
- Post-harvest application
to follow all instructions on the manufacturers labels,
and check for restrictions on use and proper safety considerations
for your area. For more information on chemical controls, contact
your local University of California Cooperative Extension farm
advisor or county agricultural commissioner, and also check out
of California guidelines and a list of registered materials.
A number of predators and parasitoids have been recorded attacking
vine mealybug in California. Many common general predators will
feed on all vineyard mealybug species, including vine mealybug.
Vine mealybug is closely related to the citrus mealybug, sharing
a number of parasitoid species that are already present in California.
Additionally, recent foreign explorations for new parasitoids
have added to the parasitoid complex.
Anagyrus pseudococci is the most common parasitoid attacking vine
mealybug. It is well established in the San Joaquin Valley. The
adult female is about 1/32 of an inch (2 mm) in length, golden
brown in color with long antennae that are black at the base and
then white to the ends. The male is smaller, dark-colored with
In the laboratory, Anagyrus pseudococci attacked second, third,
and adult stage vine mealybugs at rates of 19%, 33%, and 48%,
respectively, indicating that it prefers larger mealybugs. Parasitoid
development time is about 18 days during the summer.
In field trials, this parasitoid attacked 70% to 95% of the exposed
vine mealybugs in August and September in San Joaquin Valley.
However, considerable damage to fruit still occurred. Parasitism
in Coachella Valley was lower, never exceeding 20% (unless parasitoids
were released). The difference in parasitism levels between these
two regions is largely attributed to the greater period of mealybug
exposure to parasitoids in San Joaquin Valley.
Parasitism rates can be improved by releasing Anagyrus pseudococci
early in the season. Studies suggest that an early season release
of 20,000 parasitoids per acre has increased parasitism and reduced
crop damage, although this research is still in progress and may
vary greatly among vineyard regions.
Leptomastidea abnormis was recently released in Coachella and
San Joaquin valleys. The adult is slender, about 1/32 of an inch
(2 mm), and patterned white and black, including the antennae.
Leptomastidea abnormis is not as common as Anagyrus pseudococci,
and it currently accounts for less than 10% of the parasitism.
In the laboratory, Leptomastidea abnormis attacked second, third,
and adult stage vine mealybug at rates of 61%, 32%, and 7%, respectively,
indicating that it preferred smaller mealybugs.
While predators and parasitoids may help reduce the overall number
of vine mealybugs present, they alone will not provide sufficient
control to keep populations below damaging levels.
Vine mealybug is a pest that no one wanted. Along with its potential
for damaging vines and reducing marketable yields, it brings with
it the need for considerable insecticide use. This runs directly
counter to the industrys move towards sustainable farming
methods and reductions in pesticide use.
Continued vigilance is needed to reduce vine mealybug populations
and to limit its further spread, both within vineyards that are
currently infested, and from infested vineyards to non-infested
ones. Growers should train all workers in mealybug identification
and react quickly to any new finds.
Managers of infested blocks should follow all recommended treatment
protocols and manage their equipment and workforce to minimize
Wineries need to be aware of the status of vineyards delivering
fruit to them, and they must take steps to properly dispose of
stems coming from infested blocks. Grapevine nurseries should
implement quality assurance measures to prevent further spread
on plant materials.
Unfortunately, vine mealybug is a pest that is here to stay in
California. However, if everyone takes appropriate steps, its
overall impact should be reduced.
Additional sources of information: