BY Kent Daane, Associate Specialist,University of California Extension,UC Berkeley;Ed Weber, Napa County Farm Advisor,University of California CooperativeExtension;Walt Bentley, Entomologist, Universityof California Statewide IPM Project

Several species of mealybugs arepests of grapevines in manyparts of the world. In California,the grape mealybug, long-tailed

mealybug, and obscure mealybug havelong been present in vineyards, but theyare usually minor pests not requiringchemical control. Recently, the invasivevine mealybug (VMB) has emerged as aserious pest in many parts of the state. Itbrings with it the need for aggressivechemical management.

Distribution and damageVine mealybug is found in the

Mediterranean regions of Europe andNorth and South Africa, as well asgrapegrowing regions in the MiddleEast, Argentina and Mexico — andnow in California.

In California, vine mealybug was firstdiscovered in 1994 in table grape vine-

yards in the Coachella Valley (RiversideCounty), although it probably enteredthe state a year or two earlier. It spreadthroughout the Coachella Valley, and in1998 was found in the southern SanJoaquin Valley (Kern County).

Its dispersion into new regions hasbeen dramatic: VMB was found inFresno County in 1998, Santa BarbaraCounty in 2000, San Luis ObispoCounty in 2001, and in El Dorado,Madera, Monterey, Napa, Sacramento,Sonoma, and Stanislaus counties in2002. To date (March 2004), VMB hasbeen found in 17 counties in California(Table I). It is likely that there are moreinfestations that have yet to be identi-fied or have not been reported.

Circumstantial evidence suggests thisrapid dispersion resulted from move-ment of infested vineyard equipment(mechanical harvesters, bins, tractors,etc.) and through sales of infested nurs-ery stock (from 1998 to 2003). Other pos-sible factors include spread with fieldcrews and natural dispersion (such asbirds and wind-blown infested leaves).

Mealybugs are phloem feeders. As theyfeed, they produce a sugary excretion(honeydew) that supports the growth ofsooty mold. Infested clusters become con-

taminated with honeydew, sooty mold,egg sacs, and lots of mealybugs.

In southern California, severe vinemealybug infestations have also reducedvine growth and resulted in defoliation,bunch rots and even spur and cane death.In addition, like other mealybugs, vinemealybugs can spread grapevine virusdiseases, such as leafroll and corky bark.

Several factors make vine mealybugmuch more damaging and difficult tocontrol than other mealybug species:• First, the vine mealybug reproducesat a higher rate than other species,enabling small numbers of mealybugsto reach damaging levels in one sea-son. Females can each deposit up to700 eggs (average is approximately300).

In San Joaquin Valley, vine mealy-bug has four to seven generations peryear compared with two for the grapemealybug. This greatly increases thepopulation size, and it leads to over-lapping generations. The overlapmakes chemical control more difficult,since some insecticides are effectiveonly against the nymphal stages.• Second, vine mealybug excretesmuch more honeydew than otherspecies. This honeydew can coverleaves, canes, trunks and fruit, makingentire clusters and vines a sticky mess.The honeydew often becomes so thickit resembles soft candle wax.

Fruit from heavily infested vines isnot suitable for harvest. The stickiness ofall the plant parts also facilitates spreadof VMB from vineyard to vineyard onequipment and worker clothes.

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Cabernet Sauvignon infested with vinemealybug. This degree of honeydewbuildup is typical of the damage that occursin warm areas (San Luis Obispo County, inthis case). [Photo by Mark Battany]

VINE MEALYBUG

Formidable pestspreading throughCalifornia vineyards

Large infestations of vine mealybugs canlead to defoliation, berry damage, and rot.

• Third, vine mealybug can feed on allparts of the vine throughout the year. Itcan be found on leaves, in clusters, underthe bark, and even on the roots ofgrapevines. By hiding under bark or onthe roots, VMB is protected from mostfoliar insecticides, from high summertemperatures, and from parasitoids andother natural enemies.• Fourth, vine mealybug is not native toCalifornia, so it has fewer natural enemiesthan the grape or longtailed mealybugspecies. Established populations willrequire repeated insecticide treatments tokeep them at manageable levels.• Finally, vine mealybug has a wide hostrange. It can feed on subtropical (grapes,figs, apples, and citrus) and tropical(dates, bananas, avocados, and mangos)crops as well as a number of commonweeds, such as malva, burclover, blacknightshade, sowthistle, and lambsquarter.However, in California, grapevinesappear to be its preferred host throughoutthe season.

Population cyclesVine mealybug population cycles and

its distribution on vines can vary dra-matically, depending on temperaturesand vine condition. While it can befound on all parts of the vine at any timeof the growing season, there are clear dis-persal and abundance patterns thatinfluence the amount of damage and theeffectiveness of chemical and biologicalcontrols.

For example, in the Coachella Valley,most of the vine mealybug populationoverwinters on the roots and lower trunksections. As temperatures warm, popula-tions rapidly increase reaching a peak inApril and May. Accompanying theincreased density is the pest’s movementup the vine, from the roots and lowertrunk to the leaves and grape clusters.

Management becomes a race betweenthe table grape harvest (May-June) andthe time when mealybugs reach the clus-ters. With hot summer temperaturesafter harvest, the population decreasesand again is found primarily on thelower trunk and roots. There is anotherpopulation increase in fall, before theoverwintering period.

In San Joaquin Valley, vine mealybugsalso overwinter on the roots and lowertrunk, and as the temperatures warm inspring and summer, they move up to theleaves and bunches. Unlike in CoachellaValley, populations continue to increaseduring summer, and they remain onleaves until August.

All stages were found throughoutthe summer, feeding on leaves andcanes in exposed locations, suggestingthat San Joaquin Valley temperatureshad little effect on vine mealybug den-sities. A late-season reduction was notaccompanied by an increase in sum-mer temperatures, but was associatedwith increased parasitism levels.Nevertheless, the longer the mealy-bugs remain on leaves and clusters, themore damage they cause to the crop.

In the Central Coast and NorthCoast, VMB appears to follow a patternsimilar to San Joaquin Valley. However,the populations continue to increasethrough September and October. Thelate season increase is most likely dueto an absence of parasites in theseareas. As in other regions, considerabledamage is likely to occur unless insec-ticides are used. Because most VMBinfestations are still discrete in theseregions, eradication programs arebeing attempted in some counties.

Potential for further spreadUntil recently, little attention was

given to vine mealybug, leading to itsrapid spread throughout California.This history shows how easily it can bemoved, both within grapegrowingregions and over long distances. Withmore attention now focused on vinemealybug, its further spread should beslowed, although complete control isnot likely to occur.

The sticky nature of the honeydewproduced by vine mealybug greatlyfacilitates its spread. All parts of thevine get very sticky — leaves, canes,berries, clusters, cordons, and trunks.Adult insects, nymphs, and eggs canget stuck to tractors, bins, picking

pans, gloves, etc., and can thereby betransported to other locations.

Machine harvesters pose a signifi-cant risk because they operate invineyards when populations arehigh. They have considerable contactwith fruit and foliage, and are fre-quently moved from vineyard tovineyard. If operated in an infestedblock and then moved without athorough cleaning, spread could eas-ily result. Operators need to be madeaware of any vine mealybug infesta-tions in blocks they are harvesting,and growers should discuss equip-ment sanitation practices if using acontract harvesting service.

Movement of infested nurserystock has resulted in numerous infes-tations throughout California. Somenurseries have recently implementedprevention measures that shouldgreatly reduce the chances of furtherintroductions on plant material. Inaddition, the California Departmentof Food and Agriculture (CDFA) hasissued a nursery advisory thatrequires monitoring and/or sanita-tion protocols for VMB.

Nursery sanitation practices includehot water treatment of cuttings anddormant vines, insecticide applicationsto green-growing plants, and insecti-cide applications to nursery motherblocks. CDFA regulations do notrequire nurseries to take all of thesesteps, so it is prudent for buyers to dis-cuss vine mealybug control practiceswith their nursery sources prior to pur-chasing vines.

Furthermore, while hot water treat-ments for dormant wood can provideexcellent control, insecticide treatmentsof green-growing plants have not yetbeen thoroughly tested.

Grape clusters harvested frominfested vineyards could also lead tospread of VMB because the stems willlikely still contain insects or eggs afterpassing through a winery crusher/

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Sex-pheromone baited traps are beingused to monitor male vine mealybug flighttimes and densities.

Table I. Counties with VMB infestations

AlamedaEl DoradoFresnoKernMaderaMontereyNapaRiversideSacramento

San JoaquinSan Luis ObispoSanta BarbaraSanta ClaraSonomaStanislausTulareYolo

destemmer. If spread directly back intovineyards, new infestations could result.

Composting infested stems (awayfrom any vineyards) should provide ade-quate control, as long as the compostingprocess follows state regulations andproper temperatures are reached withinthe compost piles (above 130ºF). Furtherresearch is needed to confirm the effects ofcomposting on infested stems.

MonitoringTo prevent damage from vine mealy-

bug, the best way is to keep the pest outof vineyards or to chemically treat popu-lations when an infestation just begins.However, mealybugs are difficult todetect in the early stages because they areoften hidden under bark or under-ground. Visible signs of an infestationinclude the presence of foraging ants,honeydew or sooty mold on leaves ortrunks, bark that appears wet, and whitewax protruding from underneath thebark.

Until recently, visual sampling meth-ods were the only way to spot new infes-tations, and they were far too labor-inten-sive to be practical. In 2001, a faster, moreeffective method to monitor VMB wasdeveloped, based on a sex pheromonethat female VMBs use to attract wingedadult males.

This pheromone has now been syn-thetically produced. In field tests, trapsbaited with synthetic pheromone wereattractive for two months, had an effec-tive range of about 300 feet, and hadcounts that could be correlated with VMBdensities in the vineyard. Using this sexpheromone to attract winged males is afar more efficient method of detecting

new infestations than trying to searchthousands of vines for hidden females.

Unfortunately, the males areextremely small (less than 1⁄64 of aninch) and difficult to identify withoutconsiderable training and experience.Many growers are establishing theirown trapping programs and are work-ing with their local agricultural com-missioner’s office for help in identifica-tion of insects in their traps.

Male vine mealybugs are tiny (a bitsmaller than adult thrips) and brown-to-black in color. They have a single pair ofwings, a small “V” tail, and long anten-nae. In sticky traps, they quickly losetheir coating of white wax and becomeeven more difficult to identify. For thisreason, examine traps as soon as suspi-cious insects are observed. Rememberthat “close up” photographs make theinsects look larger and easier to identify.

Trapping programsIn California, free traps and lures

may be available in 2004 from countyagricultural commissioners. The pre-ferred trap is the tent-shaped Pherocon®

IIID trap (www.trece.com) loaded with avine mealybug pheromone lure(www.suterra.com). These three-dimen-sional traps provide better adult maleVMB catch and lower “unwanted”insect catch as compared with flat traps.

Traps should be hung at or above thecordon and near the center of the vine.Trellis wires make a good attachmentpoint. Traps can be placed in the canopyto get some protection from wind andequipment, but the open ends should beexposed so that VMB males can easilyfly, rather than walk, into the trap. Thetrap position may have to be changedduring the season to avoid interferencewith vineyard management operations.

Two traps are suggested for each 20-to 40-acre block monitored. Put one trapnear the center of the block and the otherin a “high traffic” area (near roads orintersections, equipment storage areas,field shops, or packing houses).

There is no reason to place traps deepinside the vine or well within a vineyardblock such that crews cannot easily findand monitor them. If more traps areused, they should be placed at least 30rows apart (about 200 to 300 feet) and atleast 10 vines from the edge of eachblock. Make sure the triangular entranceto the trap is not blocked by leaves. Thiswill reduce the number of males caught.

Traps should be checked every twoweeks during the male flight period(see below). Lures should be changedat least every six to eight weeks. Trapsneed to be changed only when they areold and dirty, or when male VMB aredetected (so they can be confirmedmicroscopically and counted). If nomale mealybugs are found and thesticky surface is still functioning, newlures can be placed into old traps.

In heavily infested vineyards, wehave found over 2,000 males weeklyper trap. Typically, an infested vine-yard will have between 20 to 300 malesper trap per week. If fewer than 10VMB males are found weekly in a trap,then the infestation may be in anotherblock. Trapped males may be fromneighboring or even distant blocks, asthe males can be wind-blown fromone-half mile or more away.

In those counties where vine mealy-bug does not commonly occur, vineyardmanagers should contact the countyagricultural commissioner’s office andthe UC Cooperative Extension farmadvisor to get a positive identification oftrapped mealybugs, and to discussmanagement decisions and complianceagreements as necessary.

Male flight periodsIn Coachella Valley, the male flight

period extends from about Marchthrough August. In San Joaquin Valley,the flight will run from May throughOctober. On the North Coast, maleshave been trapped from May toNovember, with the largest numbersoccurring late in the season. Femalesoften mate in the fall, so the first maleflight in the following spring may beafter vine mealybug activity begins.

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An adult male vine mealybug (the onlystage that has wings), near an adult femalewhich is beginning to deposit a waxy“ovisac” that contains the eggs.

An adult female vine mealybug just beforeshe begins to produce eggs. Note the short“tail” filaments that help to distinguish thevine mealybug from other vineyard mealy-bugs.

Chemical controlsA number of insecticides can be

used to kill exposed vine mealybug,especially the small nymphal stages.The hidden portion of the populationis harder to control. For this reason,vine mealybug is difficult to eradicateonce it has become well established ina vineyard. Systemic insecticides (suchas Admire®) that reach all parts of thevine have been the most effective. Acontrol program attempting to eradi-cate vine mealybug should include:• Delayed dormant application ofLorsban (February or March),• Spring application of Applaud orSevin (Sevin may cause mite outbreaks),• Systemic application of Admire inspring,• Summer to fall foliar treatments(Applaud, Dimethoate, Imidan, Mala-thion),• Post-harvest application of Lorsban.

Be sure to follow all instructions onthe manufacturers’ labels, and checkfor restrictions on use and propersafety considerations for your area. Formore information on chemical controls,contact your local University ofCalifornia Cooperative Extension farmadvisor or county agricultural commis-sioner. For University of Californiaguidelines and a list of registered mate-rials, see http://www.ipm.ucdavis.edu/PMG/r302301911.html.

Biological controlsA number of predators and para-

sitoids have been recorded attackingvine mealybug in California. Many com-mon general predators will feed on allvineyard mealybug species, includingvine mealybug.

Vine mealybug is closely related tothe citrus mealybug, sharing a number ofparasitoid species that are already pre-sent in California. Additionally, recentforeign explorations for new parasitoidshave added to the parasitoid complex.

Anagyrus pseudococci is the mostcommon parasitoid attacking vinemealybug. It is well established in theSan Joaquin Valley. The adult female isabout 1⁄32 of an inch (2 mm) in length,golden brown in color with long anten-nae that are black at the base and thenwhite to the ends. The male is smaller,dark-colored with hairy antennae.

In the laboratory, Anagyrus pseudo-cocci attacked second, third, and adultstage vine mealybugs at rates of 19%,33%, and 48%, respectively, indicatingthat it prefers larger mealybugs.Parasitoid development time is about18 days during the summer.

In field trials, this parasitoidattacked 70% to 95% of the exposedvine mealybugs in August andSeptember in San Joaquin Valley.However, considerable damage tofruit still occurred. Parasitism inCoachella Valley was lower, neverexceeding 20% (unless parasitoidswere released). The difference in par-asitism levels between these tworegions is largely attributed to thegreater period of mealybug exposureto parasitoids in San Joaquin Valley.

Parasitism rates can be improved byreleasing Anagyrus pseudococci early inthe season. Studies suggest that an earlyseason release of 20,000 parasitoids peracre has increased parasitism andreduced crop damage, although thisresearch is still in progress and may varygreatly among vineyard regions.

Leptomastidea abnormis was recentlyreleased in Coachella and San Joaquinvalleys. The adult is slender, about 1⁄32

of an inch (2 mm), and patternedwhite and black, including the anten-nae. Leptomastidea abnormis is not ascommon as Anagyrus pseudococci, andit currently accounts for less than 10%of the parasitism. In the laboratory,Leptomastidea abnormis attacked sec-ond, third, and adult stage vinemealybug at rates of 61%, 32%, and

7%, respectively, indicating that it pre-ferred smaller mealybugs.

While predators and parasitoidsmay help reduce the overall numberof vine mealybugs present, they alonewill not provide sufficient control tokeep populations below damaginglevels.

Future prospectsVine mealybug is a pest that no one

wanted. Along with its potential for dam-aging vines and reducing marketableyields, it brings with it the need for con-siderable insecticide use. This runsdirectly counter to the industry’s movetowards sustainable farming methodsand reductions in pesticide use.

Continued vigilance is needed toreduce vine mealybug populations andto limit its further spread, both withinvineyards that are currently infested,and from infested vineyards to non-infested ones. Growers should train allworkers in mealybug identificationand react quickly to any new finds.

Managers of infested blocks shouldfollow all recommended treatmentprotocols and manage their equipmentand workforce to minimize spread.

Wineries need to be aware of the sta-tus of vineyards delivering fruit tothem, and they must take steps toproperly dispose of stems coming frominfested blocks. Grapevine nurseriesshould implement quality assurancemeasures to prevent further spread onplant materials.

Unfortunately, vine mealybug is apest that is here to stay in California.However, if everyone takes appropri-ate steps, its overall impact should bereduced. ■

Additional sources of information:http://www.vinemealybug.uckac.edu/http://cenapa.ucdavis.edu/Viticulture/Vine_Mealybug.htm

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