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Summer 2015

Central Coast

Vineyard News

AssessingGrapevineleafrollandRedBlotchDiseaseImpactsinLocalVineyards

LarryBettiga,ViticultureFarmAdvisor

UniversityofCaliforniaCooperativeExtensionGrapevineleafrollandredblotchdiseasearetwovirus‐associateddiseasesthatshouldbeontheradarof all grape growers.The following articlewill hopefullyprovide you anupdateon thesevirusdiseasesbaseonourcurrentknowledge.Surveyingvineyardsduringharvestisagreattimetoassessvineyardblocksforthepresenceofdiseasesymptoms.GrapevineLeafrollDiseaseLeafrollisoneofthemoreimportantvirusdiseasesofgrapevines.Itoccursineverymajorgrapegrowingareaoftheworld.Therearefivegrapevineleafrollassociatedviruses(GLRaVs)thatareserologically distinct. These single stranded RNA viruses are placed in a family calledClosteroviridae.ThemajorityofthesearegroupedinthegenusAmpelovirus(GLRaV‐1,‐3,and‐4),mostofthevirusesinthisgenushavebeendemonstratedtobevectoredbymealybugsandscaleinsectsinvineyards.GLRav‐2isinthegenusClosterovirus,andGLRaV‐7isinthegenusVelarivirus,thereisnoknownvectorofthesetwogenera.These viruses can cause similar symptoms in infected grapevines. All the GLRaVs can betransmitted by vegetative propagation and grafting; GLRaVs in Ampelovirus can also betransmitted by themealybugs and soft‐scale insects in vineyards. GLRaV‐3 is the predominantspeciesfoundinmostvineyardsworldwide.Recentsurveysinthenorthcoasthaveshown80%ofsymptomaticvinessampledwereinfectedwithGLRaV‐3.To further complicate matters there are variants that have been identified for given GLRaVspecies.ForGLRaV‐3thereareseveraldistinctvariantsknowntoexist.WhatneedstobebetterunderstoodisthesignificanceoftheseGLRaV‐3variantsandtheirinteractionswithotherviruseswhenmultiple infectionsexist inavine.ForGLRaV‐2the“RedGlobe”variant isknowntocausegraftincompatibilitywhengraftedontocertainrootstocks(5BB,5C,3309Cand1103P)resultinginthedeclineanddeathofvines.Inthepost‐phylloxerainfestationplantingsthathaveoccurredonthecentralcoastduringthepast20 years there has been an increased incidence of grapevine leafroll disease. The use of non‐certifiedscionmaterialhasbeenamajorcontributortothisdiseaseincrease.Theotherissuehasbeen the spread of leafroll (primarily GLRaV‐3) from infected vineyards to adjacent vineyardsplantedwithCalifornia‐certifiedstock.UCresearchdocumentedtherapidspreadofleafrollintoa

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certifiedplanting fromanadjacent infectedblock.During the5yearsofobservation theannualrateofincreaseinleafrollsymptomaticvineswasmorethan10%inaNapaValleysite.RecognizingLeafrollLeaf symptoms become visually apparent by early summer and generally intensify intomidsummerandfall.Physicalstressesto thevinemayincreasesymptomseverityandtherearesimilarsymptomscausedbyotherabioticandbioticinjuries.Onaffectedvines,themarginsoftheleafbladesrolldownward,startingwiththebasalleafonthecane.Areasbetweenthemajorveinsturn yellow or red, depending on whether the cultivar produces white or red fruit. In somecultivars,theareaadjacenttothemajorveinsremainsgreenuntillatefall.Themost importanteffectof leafrolldisease isareduction intheyieldandqualityof fruit frominfected vines. Yield losses of 10 to 20%are fairly typical. Because leafroll viruses damage thephloemofinfectedvines,sugaraccumulationisdelayedandcolorpigmentproductionisreduced.Fruitfrominfectedvinescanbelowinsugar,poorlycolored,andlateinripening.Itisimportanttorememberthatthelackofsymptomsinagrapevinedoesnotguaranteefreedomfrominfectionbythevirusesthatarethecausalagentsofleafrolldisease.

Leafroll disease on Pinot noir (left) showing burgundy red between green main leaf veinsaccompaniedbydownward rollingof the leafmargins;onChardonnay (right) leaves showamoregeneralizedchlorosisanddownwardrollingoftheleafmarginsinlatefall.LabTestingLeafrollvirusesmaybediagnosedusingELISAandRT‐PCRtests.Virustiterlevelsarevariablenotonly within the year, but also within the vine. Collect petioles in late summer and fall, orshoots/canesforcambiumscrapingsinfallandwinter.PCRandELISAtestsarenotavailableforall GLRaVs. Checkwith the commercial lab for their preferred samplingmethod and collectiontimepriortotakingsamples.MealybugVectorsThemostcommonmealybugfound inCaliforniavineyards is thegrapemealybug(Pseudococcusmaritimus).Obscuremealybug(P.viburni)ispresentincentralcoastvineyardsbutlesscommon

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thanthegrapemealybug.Thevinemealybug(Planococcusficus)wasintroducedintoCaliforniain1994andhasnowbeenfoundinmostproductionareaofthestate.Lesscommonisthelong‐tailedmealybug(P.longispinus)foundprimarilyinthecoolerareasofthesouthcentralcoast.TheGill’smealybug (Ferrisia gilli) is the fifth species found in California but is currently very limited indistributionwithpopulationsfoundintheSierrafoothills,inthenortherncoast(LakeCounty)andinthesouthernSanJoaquinValley.All theabovespeciesarecapableofbeingavector for leafrolldisease.Researchhasshownthatmealybugscanbecomeinfectiveafteronehouroffeedingonaleafrollvirusinfectedvineandcantransmit the virus to a clean host after one hour of feeding. Although all female instars cantransmit thevirusonce infected, the first instar is themosteffectivevectorsof thedisease.Thefirst instaror “crawler”moves to finda feedingspotand is considered tobe themost commondispersalstageofamealybugpopulation.Wind,equipment,workersand infestednurserystockcanalsomovemealybugs.

Movement of leafroll disease into a recently planted vineyard of certified planting stock from aninfectedblockontheoppositesideoftheavenue.Notethevinesshowingsymptomsarenearesttheavenueandarenotpresentonvinesfurtherdowntherows.ManagementofGrapevineLeafrollDisease1.PlantMaterial.Thefirstmanagementstrategyshouldbetoplantcertifiedvinesthathavebeengrown and produced by a nursery participating in the California Grapevine Registration andCertification Program. Once virus infected a vine will remain infected, there is no cure.Commercial nurseries that produce certified grapevines and participate in the CaliforniaGrapevine R&C Program obtain their clean stock from the Foundation Plant Services at theUniversityofCalifornia,Davis.UCDavishasafoundationvineyardformajorgrapecultivarsandclones. Before being planted in the foundation vineyard, all vines are tested across biologicalindicators,andbyELISAandRT‐PCR.Thefoundationvineyardismonitoredbyvisualinspectionsinspringandfall,andaportionofitisretestedeveryyearbyELISAandRT‐PCRforvirusesknownto spread naturally. This provides the highest level of confidence about the virus status of theselections.

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Both the fruiting scion and the rootstock need to come from certified mother plants. A verycommonspreadofleafrollistheuseofinfectedbudwoodfromcommercialvineyards.Thelackofsymptoms in the source vineyard cannot be relied upon as a guarantee that there is no virus;many of the major grapevine viruses show no symptoms during some or all of the season.Particularlyifwoodiscollectedduringthedormantseason,itisunlikelythatthesourcevineswillshowdistinctsymptomsofvirusinfection.Selectedgrapevinesshouldalsobepre‐testedforvirusbyacompetentdiagnostic laboratory if thistypeofmaterial isgoingtobeused.Evenwithvinetesting sourcingbudwood fromestablishedvineyards carries a riskof introducing virus into anewplanting.2.Learntorecognizeleafrollsymptoms.Leafrollsymptomsbecomevisuallyapparentbyearlysummerandgenerallyintensifyintomidsummerandfallasnotedabove.Symptomscanvarybyleafroll species,multiplevirus infections, andby cultivarand rootstock combination. Symptomsare generally more apparent in cultivars producing red or black fruit than in white fruitingcultivars.Rememberthatthelackofsymptomsinagrapevinedoesnotguaranteefreedomfrominfectionbythevirusesthatarethecausalagentsofleafrolldisease.3.Recognizeandbeawareofpotential leafrollvectors.As discussed abovemealybugs andscaleinsectsareknownvectorsofsomespeciesofGLRaVs.Monitorandbeawareofwhichinsectvectorsmaybe in your vineyards.More informationon these insects is available inGrapePestManagement UCANR publication 3343 or in the online UC IPM guideline for grapes,http://www.ipm.ucdavis.edu. Knowwhich species ofmealybugs are present in your vineyards,their population dynamics are different and will influence the timing of any needed controlpractices. European fruit lecanium scale (Parthenolecanium corni) is a common insect found inCaliforniavineyards,itandotherscaleinsectshasbeenshowntotransmitsomeGLRaVspecies.4.Beawareofpotentialspreadfromleafrollinfectedblocks.Leafrollinfectedblockscanbeasourceforvectoranddiseasespreadintoadjacentcleanplantings.Considerifplantremovalisaviableoptiontoreducefurtherspreadforboththesourceandcleanblocks.Vectorcontrolmaybeamanagementdecisiontoconsider.RecentresearchsuggeststherateofdiseasespreadofGLRaV‐3isgreaterwhenhighermealybugpopulationlevelsarepresent.Treatmentofvirussourceblocksshouldminimizethe infectivevectors leavingtheblock; thetreatmentofcleanblocksshouldbetargetedtokillinfectivevectorsquicklyuponenteringtheblockandtoreducesecondaryspreadtoadjacentvines.5. Area‐widemanagement.When both mealybug populations and the virus causing leafrolldisease are present in an area, cooperation between neighboring vineyard owners will benecessary to improve on reducing the spread of disease from infected source blocks to non‐infectedvineyards.Grapevine leafroll disease is actively being studied both here in the US and internationally.Improvements in identification techniquesandbetterunderstandingofdiseaseepidemiology invineyardswillhopefullyimproveourabilitytodevelopmanagementpracticestoreduceeconomicimpacts.

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RedBlotchDiseaseGrapevineredblotchdiseasewassuspectedasaconcernonvinesgrowingintheNapaValleyin2008.In2011aDNAviruswasidentifiedinindependentstudiesinCaliforniaandNewYorkandshowntobeassociatedwiththesymptomsoninfectedvines.SincetheinitialidentificationofGrapevineredblotch‐associatedvirus(GRBaV),ithasbeenfoundtobewidespreadinvineyardproducingareasoftheUnitedStatesandCanada.ArecentsurveyofagrapeherbariumcollectionatUCDavishasshownoneplantspecimencollectedbyHaroldOlmoin1940fromaSonomaCountyvineyardtobepositiveforGRBaV.RecognizingRedBlotchInredwinecultivars,irregularredblotchesformontheleafbladesonthebasalpartsofshoots.Veinsonaffectedleavescanturnpinktoredincolor.Symptomscanvarybetweencultivarsandtheseveritymayalsovarybetweenyears.Inwhitecultivarsthesymptomsarenotasdramatic.Interveinalchlorosisismostcommonfollowedbyirregularchloroticblotches.ThesesymptomscanbegintoappearasearlyasJulyandaslateasSeptember.Incomparingredblotchtoleafrolldisease,leafrollsymptomsaregenerallymoreuniformacrosstheleafblade,theveinsremaingreen,andthetherecanbeadownwardrollingoftheleafmargin.Formorepicturesofredblotchsymptomsondifferentcultivarsgotto:GRBaVsymptoms

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LatesummersymptomsonChardonnay,redblotchontheleftandleafrollontheright.

LabTestingTheidentificationofGRBaVcanbedifficulttodeterminebyvisualobservationduetothesimilarityofthesymptomstoleafrolldiseaseandothernutrientdeficiencies.Thisisespeciallytrueinthecaseofwhitecultivars.Co‐infectionswithothervirusescanalsoaffectsymptomexpression.SuspectedinfectionsshouldbeconfirmedbyhavingsamplesassayedbyaPCRtestbyacommercialdiagnosticlab.Checkwiththecommerciallabfortheirpreferredsamplingmethodandcollectiontimepriortotakingsamples.

DiseaseSpreadGRBaVisspreadbythepropagationofplantingstockorgraftingnon‐infectedvinesusinginfectedbudwood.Thewidespreadoccurrenceofredblotchdiseasewouldsuggestthistypeofspreadhasoccurred.SincetheidentificationofthevirusandtheavailabilityofthePCRtestingin2012,grapevinenurserieshavebeentestingtheirincreaseblocksandremovinginfectedvinestoeliminatethistypeofspread.TherecentlyestablishedRussellRanchFoundationVineyardatUCDavishasbeentestedandallvinesarefreefromGRBaV.EachvineplantedattheRussellRanchhasundergoneextensivevirustestingfollowingaprocessknownasProtocol2010.FornurseriesparticipatingintheCDFAR&CProgramthiswillprovideasourceforfutureincreaseblockstosupplycertifiedvinesforvineyardplantings.GRBaVisaDNAvirusandiscloselyrelatedtoafamilyofvirusescalledGeminiviridae.Insectsuchasleafhoppersandwhitefliescanvectorothervirusdiseaseswithinthisfamily.ResearchersarecurrentlytestingpotentialinsectvectorsofGRBaV.AlthoughtherewasareportofVirginiacreeperleafhopperbeingavectorinagreenhousestudyotherresearchershavebeenunabletoduplicatethatstudy.Theevaluationsofotherpotentialinsectvectorshavenotyetidentifiedonethatcansuccessfullyacquireandtransmitthevirusinthefield.Althoughthereisanecdotalinformationthatthereisspreadwithinsomevineyardstodatethereisinsufficientdatatosupportthatclaim.VineEffectsResearchhasshownthatwhencomparingGRBaVinfectedvinestoonesthathavenoknownGRBaV,leafroll‐associatedviruses,vitiviruses,orNepovirusesthatBrixwerelowerandmalicacidinthejuicewerehigheratharvestforCabernetSauvignonandChardonnaybutnotZinfandel.ForChardonnay,yieldwasalsoreducedforinfectedvines.Astudylookingattheeffectofdroppingcroptoimprovequalityoninfectedvinessawlittlebeneficialeffectfromthatpractice.Formost

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cultivars,thereisadecreaseintotalphenols,tannins,andanthocyanins(forredwinecultivars)forvinesinfectedwithGRBaV.ManagementofRedBlotchDiseaseAswithleafrolldiseasethefirstmanagementstrategyshouldbetousepropagationmaterialthatisfreefromknownviruseswhenestablishingnewvineyardsorgraftingexistingsites.MeetingsoftheGrapevineRegulationsWorkingGrouphavebeenrecentlyconductedtodiscussproposedchangestotheGrapevineRegistration&CertificationProgramwithregardstoredblotchdisease.UntilbudwoodincreasedfromtheRussellRanchFoundationvineyardisavailableforuseitisimportantthatpropagationmaterialistestedtoavoidvirusdisease.Ifyouhaveblocksthathaveleafsymptomsandhavehaddelayedmaturityorlowcropyieldhaveaviruspanelrunbyacommerciallabtoconfirmwhichvirusesarepresent.Remembersymptomsaregoingtobemorenoticeableinredwinecultivarsandlesssowithwhitecultivars.ForconfirmedGRBaVinfectedvineyardsthemanagementresponsemayvarydependingonthevineeffectsthatarebeingobserved.Thedifferenceinsugaraccumulationbetweeninfectedandnon‐infectedvinesinsomevineyardshasbeenasmuchas5Brix.Invineyardswithacombinationofinfectedandnon‐infectedvinesthiswidevariationinmaturityhasresultedinselectiveharveststoimprovefruituniformity.Forinfectedsitesthatfailtomeetyieldandqualityexpectationsvineyardremovalisthebestsolution.Ifonlyalowpercentofvinesinablockareinfected,thenrogueingandreplantingisanoption.Ifvineremovalandreplantingisanoptionthereiscurrentlyassistanceavailable(seebelow).FinancialAssistanceAvailabletoReplantRedblotch‐affectedGrapevines:TheAgriculturalActof2014(the2014FarmBill)authorizedtheTreeAssistanceProgram(TAP)toprovidefinancialassistancetoqualifyingorchardistsandnurserytreegrowerstoreplantorrehabilitateeligibletrees,bushesandvinesdamagedbynaturaldisasters.The2014FarmBillmakesTAPapermanentdisasterprogramandprovidesretroactiveauthoritytocovereligiblelossesbacktoOct.1,2011.InCalifornia,producerswhoarereplantingvinesaffectedbygrapevineredblotchdiseasemaybeeligibleforassistanceandshouldcontacttheirlocalFarmServiceAgencyOfficetoscheduleanappointmentfortherequiredvisualinspection.Formoreinformationgoto:FactSheetReferencesAlRwahnih,M.,etal.2013.AssociationofaDNAviruswithGrapevinesaffectedbyRedBlotchdiseaseinCalifornia.Phytopathology103:1069‐1076.

Daane,K.M.etal.2012.Biologyandmanagementofmealybugsinvineyards.p.271‐307.In:N.J.Bostanianetal.(eds.),ArthropodManagementinVineyards:Pests,ApproachesandFutureDirections.Springer.505p

Golino,D.A.,etal.2002.GrapevineleafrolldiseasecanbespreadbyCaliforniamealybugs.CaliforniaAgriculture56:196‐201.

Golino,D.A.,etal.1992.Grapevinevirusdiseases.In:Bettiga,L,(ed.),GrapePestManagement,3rded.Oakland:UniversityofCaliforniaDivisionofAgricultureandNaturalResources,Publication3343,157‐173.

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Golino,D.A.,etal.2008.LeafrolldiseaseisspreadingrapidlyinaNapaValleyvineyard.Calif.Agric.62:156‐160.

Krenz,B.,Thompson,J.,etal.2012.CompleteGenomeSequenceofaNewCircularDNAVirusfromGrapevine.J.Virol.86:7715.

Krenz,B.,etal.2014.Grapevineredblotch‐associatedvirusiswidespreadintheUnitedStates.Phytopathology.FirstLook.

Oberholster,A.,etal.2015.Impactofredblotchdiseaseongrapeandwinecompositionandquality.AmericanSocietyofEnologyandViticultureNationalConferenceTechnicalAbstracts,p.75.(2015).

Poojari,S.,etal.2013.AleafhoppertransmissibleDNAviruswithnovelevolutionarylineageinthefamilyGeminiviridaeimplicatedingrapevineredleafdiseasebynextgenerationsequencing.PlosOne8:e64194.

Sharma,A.M.etal.2011.Occurrenceofgrapevineleafroll‐associatedviruscomplexinNapaValley.PLoSOne6(10):e26227.

Smith,R.,etal.2015.Effectofcropreductionofvinesinfectedwithgrapevineredblotch‐associatedvirusonfruitmaturity.AmericanSocietyofEnologyandViticultureNationalConferenceTechnicalAbstracts,p.136‐137.

Sudarshana,M.andM.Fuchs.2015.GrapevineredblotchIn:Wilcox,W.,etal,(eds.),CompendiumofGrapeDiseases,DisordersandPests,2nded.TheAmericanPhytopathologicalSociety.122‐123.

Tsai,C.W.,etal.2010.Mealybugtransmissionofgrapevineleafrollviruses:Analysisofvirus–vectorspecificity.Phytopathology100:830‐834.

LarryBettiga

ViticultureFarmAdvisorforMonterey,SanBenitoandSantaCruzCounties.lbettiga@ucanr.edu1432AbbottStreetSalinas,CA93901831‐759‐7361phone831‐758‐3018faxCentralCoastVineyardNewsisproducedbyLarryBettiga.

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