Download pdf - Efficacy of Organic Fungicides for Control of Powdery ...€¦ · efficacy of certified organic fungicides against a conventional fungicide program for the control of powdery mildew,

1

EfficacyofOrganicFungicidesforControlofPowderyMildew,DownyMildew,andPlectosporiuminPumpkins

TrevorSimmons

MajorProject/ReportsubmittedtothefacultyofVirginiaPolytechnicInstituteandStateUniversityinpartialfulfillmentoftherequirementsforthedegreeof

MasterofAgriculturalandLifeSciences

In

PlantSciencesandPestManagement

AntonBaudoin,DepartmentofPlantPathology,Physiology,andWeedScience,Chair

DavidLangston,TidewaterAgriculturalResearchandExtensionCenter

GregoryWelbaum,DepartmentofHorticulture

May2,2017

Blacksburg,VA

Keywords:organicpumpkins,organiccucurbits,organicfungicides,powderymildew,plectosporium

2

Contents

Abstract……………………………………………………………………………………………………………..3

Introduction………………………………………………………………………………………………………3

MaterialsandMethods…………………………………………………………………………………….7

ResultsandDiscussion………………………………………………………………………………………9

Conclusion………………………………………………………………………………………………………11

Appendix………………………………………………………………………………………………………...15

3

Abstract:

IncreasedagritourisminthestateofVirginiahasledtoanincreaseinthepumpkinplantingacreageforpick-your-ownoperationsacrossthecommonwealth.Virginiapumpkinproducersfaceyieldlossesfromnumeroussources,includingseveralfungaldiseases.Theobjectiveofthisresearchwastocomparetheefficacyofcertifiedorganicfungicidesagainstaconventionalfungicideprogramforthecontrolofpowderymildew,downymildew,andplectosporium.CultivarWartyGoblinpumpkinsweregrowninRockville,Virginiaduringthe2016cropseason.Fivedifferenttreatments(water,Kaligreen,Nordox75,Regalia,andBravo+Quintec/Proline)wereassessedfortheircontrolofpowderymildew,downymildew,andplectosporium.DiseaseobservationsandtreatmentsweremadeweeklyfromAugust12–September15.Diseaseratingsforpowderymildewshowedthatconventionalfungicidesprovidedthegreatestcontrol,withorganicproductsKaligreenandNordox(thelatterappliedatanabove-labelrate)providingnext-bestcontrol,statisticallyequivalentinsomeanalyses.Regaliadidnotprovidesignificantlybetterdiseasecontrolthanuntreatedwatercontrols.Plectosporiumdiseaseseveritywasreducedthemostinplotsreceivingconventionalfungicides,withNordoxbeingalmostaseffective.Kaligreenprovidednocontrolofplectosporium.Regaliaprovidedmodestcontrol,whichinsomeanalyseswassignificantlybetterthantheuntreatedcontrol.Downymildewpressurewasextremelylimited,andnosignificantdifferencesindiseaseincidencewereseenamongthetreatments.Inconclusion,severalofthetestedorganicmaterialsprovedtobestatisticallyaseffectiveastheconventionalfungicidesincontrollingbothpowderymildewandplectosporium,althoughconventionalfungicidesprovidednumericallysuperiorcontrolforalldiseases.

Introduction:

Commercialproductionofcucurbits,includingpumpkins,reliesheavilyonuseofchemicalinputs,includingsyntheticfungicides.Thesefungicidesareusedtopreventandcontrolthespreadofpathogensthatdecreaseplantvigorandreduceyield.Asmoreislearnedaboutthepotentialnegativeconsequencesofthesechemicalsintheenvironment,producersarelookingtofindlessharmfultreatmentoptionsinresponsetogrowingconsumerpressure.Thefungaldiseasespowderymildew,downymildew,andplectosporiumallmaylimitproductionofcucurbitsintheUnitedStatesandaroundtheworld.Historically,muchoftheacademicresearchforcontroloftheseorganismshasfocusedonsyntheticchemistries,withlessattentiongiventobiologicalornaturallyderivedproducts.Thefocusofthisinvestigationwastocomparediseasecontrolefficacyofseveralorganicallyapprovedtreatmentoptionswiththatofaconventionalfungicideprogram.

PowderyMildew

Powderymildewsimpactseveralimportantvegetablespecies,withcucurbitsbeingsomeofthemostseverelyaffected.Cucurbitpowderymildewcanbecausedbytwomajorcausalorganisms.Thespeciesnowthoughttobemostcommoninthemid-AtlanticUnitedStatesisPodosphaeraxanthii(synonym:SphaerothecafuligineaorS.fusca);asecondspecies(or,accordingtosome,severalspecies),Erysiphecichoracearum,Golovinomycescichoracearum,G.orontii,orE.orontii(Perez-Garciaetal.2009)is

4

presentinotherregionsbutisrarelyfoundintheeasternUSA(McGrath2011;Shishkoff,personalcommunication).Powderymildewincucurbitsisafungaldiseasemarkedbywhitepowderylesionsthatappearontheupperandlowerleafsurfaces,petioles,andstemsoftheplantfamilyCucurbitaceae.Thetypicalwhitelesionsseeninpowderymildewaremostlyduetoreproductiveconidiaproducedbytheinfectingfungus(Glawe2008).

Powderymildewsareobligateparasitesthatrequirehosttissuetoevolvethroughtheirlifecycle.Unfortunatelyforresearchers,thischaracteristicmakesresearchdifficultasstudiescannotbeconductedinartificialmedia.Furtherdifficultiesinpowderymildewresearchresultfromexistenceofbothsexual(teleomorph)andasexual(anamorph)reproductivemethods(Glawe2008).

Infectionbypowderymildewoccursastheresultofascosporesorconidialandingonasuitablehost.Thesestructuresthengerminatetoformagermtubethatexpandstoformahypha,withstructurescalledhaustoria,thatpenetrateintothehostcells.Thepenetrationintohostcelltissueisenabledbyturgorpressureandenzymaticactivity(Glawe2008).Infectionmaybetheresultofeitherlocalorlongrangesporedispersal.

Onacommerciallevel,powderymildewisoftencontrolledand/orpreventedwithmultipleapplicationsofsyntheticfungicidesand/orplantbreedingtechniquesthatproduceresistantcultivars.Mostextensionservicesrecommendaprogramrotatingfungicideclasseswitha7-10-daysprayscheduleoncediseasedetectionhasoccurred(McGrath2011),(Mid-AtlanticCommercialVegetableProductionGuide2016).Unfortunately,severalinstancesoffungicideresistancehavebeendocumentedincucurbitpowderymildew,includingresistancetothestrobilurinfungicides(Ishiietal.2001).

Furtherissueswithcontrolofpowderymildewresultfromfavoredinfectionlocationofabaxialleafsurfacesvsadaxialleafsurfaces(McGrath2001).Hyphalgrowthontheabaxialleafsurfacesishardertocontrolasnon-systemicfungicidesmayhavelessappliedcoverageonundersideofleafsurfaces.Higherapplicationratesandblower-stylesprayersareoftenrecommendedforcompleteplantcoverage.Duetothefactthatmostoftheplantinfectionbypowderymildewoccursontheexteriorofleafsurfaces,contactfungicidesprovideexcellentcontrolofpowderymildewprovidedgoodcoverageisachieved.Numerousbiological/organiccontactcontrolsexist,makingcontrolofpowderymildewinpumpkinspotentiallypossiblewithouttheuseofsyntheticfungicides(Keinath&Dubose2012)

Resistancetosyntheticfungicidesandincreasingdemandforlimitedpesticideresiduesonfoodcrops/organicproductionhavecausedanincreasedinterestinorganicallyapprovedfungicides.(Reuvenietal1996).

Plectosporium

Plectosporiumblightisarelativelynewdiseaseofthecucurbitfamily,causedbytheorganismPlectosporiumtabacinum(formerlyalsoknownasMicrodochiumtabacinumandFusariumtabacinum).DamagetonumerouscucurbitspeciesbythisorganismhavebeenobservedinEuropeandAsia,

5

howeverthestrainfoundintheUnitedStatesmostlyimpactsgourds,pumpkins,summersquash,andzucchini(Boucher2012).PlectosporiumblightwasfirstfoundintheUnitedStatesin1988inTennesseeandhasspreadrapidlythroughouttheeasternUnitedStates(Boucher2012).PlectosporiumblightwasfirstdocumentedinVirginiain1994whenitappearedinzucchiniandpumpkinfields(Hansen2009).

Plectosporiumblightinfectsthefruit,leaves,andstemsofthepumpkinplantwithsmall,diamond-shapedwhitelesions.Theselesionsmayfirstappearonpetiolesorleafveins.Thelesionsmayenlargeandsevereinfestationmaycausecompletedefoliationand/orturnthepumpkinvines/stemscompletelywhite.Whitelesionsmayalsoappearonfruit,withthefruitstempossiblyturningcompletelywhite.(Hansen2009).Lesionsonthefruitandhandlespecificallyinpumpkinscanrenderfruitunmarketableandalsoallowforsecondaryinfectionbyfruitrotsthatresultinfurthercroplossesandreducedshelflife.Yieldlossescanbeashighas100%inyearsthatfavordiseasedevelopment(Boucher2012).

AsPlectosporiumisarelativelynewthreattocucurbits,verylittleisknownaboutitsreproductivecycle.WhatisknownisthatPlectosporiumproducestwo-celledsporesthatappearcylindricaltoellipsoidalinshapeandareslightlycurved(Babadoost2012).Publishedliteraturehasconflictingopinionsonfavorableweatherconditionsforthisfungus.Certainsourcessaythatdiseaseisfavoredundercool,wetweather(Boucher2012),whereothersclaimthatPlectosporiumisfavoredunderwarm,wetweather(UniversityofMassachusettsExtension2013).ThePlectosporiumfunguscanpersistoncropresidueforseveralyearsandmayalsobedispersedlongdistancesthroughaerialspores(Boucher2012).Diseasemayalsospreadthroughrainsplash(UniversityofMassachusettsExtension2013).

NumerousextensionservicesrecommendtheuseofcroprotationandchemicalfungicidesforcontrollingPlectosporium(UniversityofMassachusettsExtension2013),(Babadoost2012),(Hansen2009).Thepracticeofno-tillplantingintoacovercrophasalsobeenshowntodecreasetheincidenceofPlectosporiumblightanddecreaseneedforfungicideapplications(Everts2002)

DownyMildew

DownymildewofcucurbitsiscausedbytheorganismPseudoperonosporacubensis(Berkeley&Curtis)Rostovtsev.Thisorganismcausesdownymildewincucumber,pumpkin,watermelon,andsquash(Savoryetal.2011).Theorganismwasdiscoveredin1868inCubaanddescribedbyresearchersBerkeleyandCurtis.Downymildewisoneofthemajoreconomicpestsofcucurbitsaroundtheworld(Lebeda&Cohen2011).P.cubensisisanobligateparasiteandcannotsurvivewithouthostplantmaterialexceptasoospores(Lebeda&Cohen2011).Downymildewutilizesbothasexualandsexualreproductionfordiseaseproliferation.Althoughbothtypesofreproductionexist,sexualreproductionisextremelyrareandnotseenasamajorsourceofinfectionintheUnitedStates(Lebeda&Cohen2011).Asexualspores,orsporangia,arethemainsourceofinfection.Sporangiaaredistributedbywindorwatersplash(Lebeda&Cohen2011).Inthepresenceoffreewater,sporangiareleasezoosporesthatpossesslocomotiveappendages,calledflagella,thatareusedtomovetowardsstomatalopeningsinleaftissue.Onceastomatalopeningisfound,azoosporeformsagermtubethatisabletopenetrateinto

6

newhosttissue.Afterinitialinfection,thepathogendevelopsinsideoftheplanttissue(Colucci&Holmes2010).

Althoughthesamecausalorganisminfectsdifferentmembersofthecucurbitfamily,symptomscanvarybasedontheenvironmentandcropspecies.Inpumpkins,downymildewformsyellowlesionsonleavesthatmayeventuallyturnbrown(Egel,2008).Theleaflesionsresultinlossofphotosyntheticabilityoftheplant,withacorrespondinglossinyield.Unlikepowderymildew,nodownymildew-resistantcultivarsofpumpkinsarecommerciallyavailable.Agronomicpracticesthatlimittheamountoffreewateronleaftissue,suchasirrigatinginthemorning,mayhelpsloworpreventtheprogressionofdownymildew.Ifinoculumispresentandconditionsareidealforinfection,thelackofresistantcultivarsmakeschemicalcontroltheprimarycontrolmethodforgrowers.

Downymildewfavorswarm,humidweathermakingthesoutheastUnitedStatesanidealenvironment.Eachyear,downymildewmigratesnorthwardfrommoresouthernregionslikeFloridaandGeorgiaallthewaytotheNewEnglandandGreatLakeStates.Downymildewisnotabletosurviveoutsideofahostandrequiresthecontinuousproductionareasofthesoutheastandgreenhousecultivationtoproduceinoculumthatmigratesnorthwardasseasonaltemperatureswarm(Colucci&Holmes2010).

Aforecastingmodelmanagedbyseverallandgrantuniversitiesisavailableathttp://cdm.ipmpipe.org/.Thetooltracksreportedcucurbitdownymildewinfectionssothatgrowerscanmakepreventativefungicideapplicationsandincreasescoutingeffortswheninoculumismostlikelytobepresent.Althoughthistrackerisavaluabletool,downymildewsporesareveryeasilydispersedintheairandcantravelgreatdistancesbetweeninfectionsites,withdocumentedspreadofgreaterthan800kmbetweeninfectedfields(Ojiambo&Holmes2011).Forthatreason,extensionrecommendationsgenerallysuggestfrequentscoutingandpreventativefungicideapplications.Afterdiseaseisobserved,suggestedsprayprogramsrotatefungicidechemistriesona7-dayorshorterschedule(Wyenandt2016);(MidAtlanticcommercialvegetableproductionguide2016).

KnownEfficacyofTestedMaterials

Plectosporium:

Comparedtodownymildewandpowderymildew,Plectosporiumhasbeenthesubjectoflimitedresearchinvestigatingorganiccontrolmethods.Thelimiteddataavailabilityisunderstandablegiventhemore-recentdiscoveryofthediseasecomparedtopowderyanddownymildew.Noneoftheorganicagentstested(Kaligreen,Nordox,Regalia)claimanyefficacyagainstPlectosporiumontheirlabels.Bravo(chlorothalonil)hasshownpartialcontrolofPlectosporiuminprevioustrialsandisrecommendedbyseveraluniversityextensionprogramsaspartofafungicideprogram(Miller,Mera,&Baysal-Gurel,2012),(MidAtlanticcommercialvegetableproductionguide2016).QuintecandProlineconventionalfungicidesusedinthisexperimentarenotlabeledforcontrolofPlectosporium.OnestudyhaslimiteddatashowingeffectivenessinreducingPlectosporiumincidencewithacombinedsprayofQuintecandPristine,neitherofwhicharelabeledforPlectosporium(Egel,&Hoke,2010).

7

PowderyMildew

Alltestedmaterialsinthisexperimentarelabeledforcontrolofpowderymildew.KaligreenandRegaliahaveproveneffectivenessincontrollingpowderymildewincucurbits(Everts&Newark,2013),(McGrath&Shishkoff,1999),(Reuveni,Agapov,&Reuveni,1995).TheliteratureprovidedseveralexamplessupportingtheefficacyofKaligreen.NofieldtrialdatacouldbefoundforNordoxcontrolofpowderymildewincucurbits;however,otherOMRI-listedcopper-basedproductshaveshownefficacy(Marineetal.2016).TheconventionalfungicidesBravo,Quintec,andProlinearealllabeledforpowderymildewandextensivedataareavailableshowingtheirefficacyandtheyarerecommendedbyseveraluniversityextensionprograms.

DownyMildew:

TestedmaterialsRegaliaandNordoxarebothlabeledforcontrolofdownymildewincucurbits.NodatawerefoundtosupportRegaliashavinganyefficacyinreducingdownypressure.NofieldtrialdatacouldbefoundforNordoxcontrolofdownymildewincucurbits,however,otherOMRI-listedcopper-basedproductshaveshownefficacy(Everts&Newark,2013).Coppercontainingcompoundsareeffectivetreatmentsforseveralfungalfoliardiseasesandhavebeenusedtotreatthemforalongtime.TheconventionalfungicideBravoisrecommendedaspartofasprayprogramforcontrolofdownymildewbyseveraluniversityextensionprograms(MidAtlanticcommercialvegetableproductionguide2016).QuintecandProlinearenotlabeledfordownymildewcontrolincucurbits.

MaterialsandMethods

Thefieldexperimentwasconductedduringthe2016growingseasonatLloydFamilyFarmsinRockville,Virginia.ThesoilattheexperimentalsitewasaCecilFineSandyLoam.Topreparetheexperimentalfield,herbicideandfertilizerwereappliedaccordingtoVirginiaCooperativeExtensionrecommendations.Additionalhandremovalofweedswasperformedweeklyasneeded.FiverowsofcultivarWartyGoblinwereplantedwithintra-rowspacingof4feetandinter-rowspacingof9feetonJuly1st,2016.

Toensure100%stand,plotswereplantedatahigher-than-normalpopulationdensity.Finalplotdensitywashigherthandesiredduetoresearchertimeconstraintsregardingthinning.Every4’withineachrowtherewere2pumpkinplants,insteadof1asisthecommerciallyrecommendedpractice.Althoughdifferentfromcommercialrecommendations,thismethodofover-seedingtoensure100%standiscommonpracticeforthefarmonwhichresearchwasperformed.

Arandomizedblockdesignwasusedtoassign4replicatesofthe5treatmentswithintheexperimentalfield.Chemicalapplicationsweremadeusingabackpacksprayerwithahandheld4-nozzlesprayboomconfigurationwithTeejet8002VStipsspacedat18”.Allchemicalswereappliedusingacarrierrateof20gallonsofwaterperacre(GPA)at35PSI.Sprayvolumeaccuracywasensuredbyapressuregaugeontheboomandsprayvolumecatchtest.Diseaseobservationsandtreatmentsweremadeweeklyfrom

8

August5–September15.

VisualdiseaseratingsweremadeweeklyfromAugust5thtoSeptember15th.Diseaseratingsrepresentpercentofplantfoliage/stemsshowingsymptomsofdisease;thisincludestheundersidesofleaves,stemsandappearanceoflesionsonfruit.Diseaseratingsweremadeforthe4centrallylocatedpumpkinplantsintheresearchplots,tooffsetpotentialimpactsfromover-sprayinadjacentplots.Diseaseratingsweremadebasedon%ofplanttissuesshowinglesions.Thecropwasscoutedweeklytomonitorfordiseasepressure.ChemicalapplicationsweremadeaccordingtoTable1.

JMP13wasusedforstatisticalanalysis.Individualdiseaseratingsshoweddistinctrelationshipsbetweenmeansandstandarddeviations,andnosingletransformationperformedbestwithrespecttohomogenizingvariances.Areasunderthediseaseprogresscurve(AUDPC)werecalculatedforthelast3weeks;diseaseratingsforeachplotweresummedoverthethreeweeks,andequalityofvariancewastested.Threeanalysesapproacheswerecompared.OneusedJMP’sFitYbyXplatformforaone-wayANOVAoflog-transformedAUDPCvalues,followedbymeansseparationusingTukey’sHSData=0.05.ThesecondapproachalsousedtheFitYbyXplatform,andfittedageneralizedlinearmodelusingaPoissondistribution.Thedataweresomewhatover-dispersed,andtheoverdispersionfactorwasusedtoadjusttheteststatistics.IndividualcontrastswerecomparedusingtheHolm-Bonferronicorrectiontoadjusttheoverallerrorrate.ThethirdapproachusedJMP’sFitModelplatform,andfittedamixedmodel,analyzingtheindividualratingsofweeks4through6asrepeatedmeasures,andconsideringTreatment,Block,andWeekasfixedandWeek*Blockasrandomvariables.

9

Table1.(ApplicationDatesincludingProductsandRates)

Date

Water(control)

Kaligreen(PotassiumBicarbonate)ArystaLifeScienceNorthAmericaLLC

**Nordox75WG(83.9%CuprousOxide)MontereyAgResources

Regalia(5%ExtractofReynoutriasachalinensis)MarroneBioInnovations

ConventionalFungicidesBravoWeatherStik(chlorothalonil54%)

SyngentaProline(prothioconazole,41%)BayerCrop

ScienceQuintec(quinoxyfen22.58%)Dow

AgroSciencesPresidio(fluopicolide39.5%)Valent

8/5/2016 20GPAcarriervolumeonly

2.5lbs/acre 1.5lbs/acre 32oz/acre 32oz/acreBravo,4oz/acreQuintec



*8/19/2016 20GPAcarriervolumeonly

2.5lbs/acre 1.5lbs/acre 32oz/acre 32oz/acreBravo,5.7oz/acreProline




2.5lbs/acre 1.5lbs/acre 32oz/acre 32oz/acreBravo,5.7oz/acreProline



*Presidioappliedtoalltreatments(includingwatercontrol)atrateof4oz/acreon8/19/2016tocontroldownymildew.Downymildewwascontrolledtomaintainresearchfocusonpowderymildew.SubsequenttreatmentsofPresidiotocontroldownymildewwerenotmadeasthediseasedidnotprogressfurther.

**Nordox75WGwasmistakenlyappliedatahigherthanlabeledrate(1.5lb/Aratherthan1.25lb/A)duetoamisunderstandingabouttheformulationinvolved.

ResultsandDiscussion:

Weeklymeansofdiseaseseverityforweeks4through6areshowninTable2,alongwiththeresultsofthethreedifferentstatisticalanalyses.

DownyMildew:

Downymildewpressurewasextremelylimitedduetodryweatherandjudgingfromlackofdiseasedevelopmentelsewhereonthefarm.Presidiowasappliedtoalltreatments,includingwatercontrol,on8/19/2016(week2)tocontroldownymildew,inordertomaintainresearchfocusonpowderymildew/plectosporiumwhichappearedtohavegreaterpotentialfordiseasedevelopment.Nosignificantdifferencesindownymildewseveritywereseenbetweendifferentresearchplots.SubsequenttreatmentsofPresidiotocontroldownymildewwerenotmadeasthediseasedidnotprogressfurther.

10

Table2:MeanDiseaseSeverity(%planttissueshowingdiseasesymptoms)Mean

separation*

Disease Treatment Week4 Week5 Week6 AUDPC 1 2 3PowderyMildew Water** 8 11 14 33 a a a Kaligreen,2.5lbs/acre 2 3 6 11 ab b b Regalia,32oz/acre 4 8 14 25 ab a a Nordox75,1.5lbs/acre 0 3 4 8 b b b Conventional*** 0 0 0 0 c c b DownyMildew Water** 2 6 6 Kaligreen,2.5lbs/acre 1 4 4 Regalia,32oz/acre 0 3 4 Nordox75,1.5lbs/acre 0 1 1 Conventional*** 0 1 1 Plectosporium Water** 21 33 54 108 a a a Kaligreen,2.5lbs/acre 26 36 45 108 a a a Regalia,32oz/acre 16 24 29 69 a b b Nordox75,1.5lbs/acre 9 9 11 28 b c c Conventional*** 6 6 6 19 b c d *Analysismethodandmeanseparation:1:AUDPC(log-transformed);2:AUDPCGLMwithHolm-

Bonferronicorrection;3:Repeatedmeasures,mixedmodel.Meansinsamecolumnwithsimilarlettersarenotsignificantlydifferentusingsignificancelevelofα=0.05(Tukey'sHSDMethod)

**alltreatmentsappliedusing20gallonswater/acre***Bravo32oz/A+Quintec4oz/A(Week1,2,4,6),Bravo32oz/A+Proline5.7oz/A(week3,5)

PowderyMildew:

Plantstreatedwiththeconventionalfungicidetreatments(Bravo+QuintecrotatedwithBravo+Proline)showedthemosteffectivepowderymildewcontrol.Regaliaprovidednosignificantcontrol.PlotstreatedwiththeorganictreatmentsNordoxandKaligreenplotsshowedsignificantlylessdiseasethanwatercontrolbutwerelesseffectivethanconventionalfungicidesintwoofthethreeanalyses.NostatisticallyobservabledifferencesindiseasedevelopmentwereseenbetweenplantstreatedwithwaterandRegalia.

Plectosporium:

Plantstreatedwithconventionalfungicidetreatmentshadtheleastamountofdisease.DiseasedevelopmentinplotstreatedwithNordoxshowednostatisticaldifferencefromthosetreatedwithconventionalfungicidesintwoofthethreeanalyses,andwerebetterthanRegaliainallanalyses.

11

Regaliaprovidedslightdiseasecontrol,significantlydifferentfromwaterintwoofthethreeanalyses.Kaligreenprovidednodiseasecontrol.

ForbothpowderymildewandPlectosporium,theconventionalfungiciderotationofferedthegreatestprotectionfromdisease,butseveralorganicproductsoftenprovidedasignificantlevelofcontrolthatsometimes(NordoxagainstPlectosporium)wasstatisticallyequivalent.Thesedataarevaluableasitshowseffectivecontrolofbothdiseasescanbeaccomplishedwithpesticidesthatmaybelessharmfultohumanandenvironmentalhealth.

AbnormalchlorosisandnecrosiswerenoticedintheplotstreatedwithNordox.Thismayhavebeenduetoover-application;themaximumrateforNordox75is1.25lb/A,but1.5lb/Awasapplied.Thesymptomsresembledthoseofcoppertoxicityincucurbits:marginalchlorosisandsubsequentfoliarnecrosis.Chemicalanalysisofleaftissuewasnotperformedtoconfirmincreasedcopperconcentrationswithinleaftissue,butbasedonfieldobservationsitisbelievedthatNordoxcausedpartialdamagetoallplantsreceivingtreatment.TheobserveddamagecanbeseeninTable3,andAppendixFigures2and3.

CostsofdifferentmaterialsarecomparedinTable4.Thecostoftheorganicmaterialsissimilartotheconventionalproductsused.ThecostoftheNordoxtreatmentatthemaximumlabelrate(1.25lb/A)wouldhavebeen$63.75fortheseasoninsteadof$76.50,butitsefficacyatthatratemighthavebeensomewhatlower.Thetotalcostoftheconventionaltreatmentperacreishigherduetotheuseof2productstankmixedperapplicationintheconventionaltrialplotsvsonly1productperapplicationintheotherplots.

Table3.NordoxDamage(%leafareashowingchlorosisorchemicalinjury)**

Nordoxplot1 Nordoxplot2 Nordoxplot3 Nordoxplot42-Sep* 20 20 40 259-Sep 20 25 20 2515-Sep 20 25 30 25*NordoxdamagewasnotratedonAugust12,August19,August26

**Nordox75WGwasmistakenlyappliedatahigherthanlabeledrate(1.5lb/Aratherthan1.25lb/A)duetoamisunderstandingabouttheformulationinvolved.

ProjectLimitationsandFutureRecommendations

Improvementstothisresearchcouldbemadeinseveralareas.Increasedplotsizecouldprovidemorestatisticalrobustness,whilealsolimitingthepossibilityofspraydrift.ChemicalanalysisofplanttissuestodeterminecoppertoxicityfromNordoxwouldbebeneficialtothefutureuseofthisproductincucurbits,whilealsoexploringtheefficacyoflowerapplicationrates.Futureplotdesignmightincorporatelargerplotareasthatincluderoomfordesignatedwalkways/pathstoavoidplant

12

destructionasfungicideapplicationsaremadeanddiseaseobservationsaremade.Additionalefficacymaybegainedbycombiningmultipleorganicproductssimilarlytothestandardpracticeof“tank-mixing”multipleconventionalfungicides.

Table4.Costcomparisonoftreatments

Product Unit Costperunit* rateapplied Costperacre SeasonCost(acre)**BravoWeatherStik gallon $47.00 32oz/acre $11.75

Proline gallon $587.00 5.7oz/acre $26.14Quintec ounce $3.25 4oz/acre $13.00ConventionalTotal 174.78*** Regalia gallon $65.00 32oz/acre $16.25 97.50Nordox lb $8.50 1.5lbs/acre $12.75 76.50Kaligreen lb $10.87 2.5lbs/acre $27.18 70.50*PricesareMSRPprovidedbymanufacturers/distributors.**Costof6applications/acre***Conventionalsprayprogramconsistingof6applicationsofBravo,2applicationsofProline,4applicationsofQuintec

Conclusion:

Fungicideefficacyincontrollingpowderymildewandplectosporiumblightwasobservedin2016.Severalorganicfungicidesshowedstatisticallysimilarabilitytocontrolbothdiseasesforseveralweeksduringthisstudy,althoughnotallorganiccontrolsprovidedstatisticallysignificantprotection.FarmerslookingtoutilizeorganicproductsorproductionmethodstoproducepumpkinsinVirginiashouldfindthatseveralofthetestedmaterialsmaybesuitableintheirfungicideprograms.Thecostsoftheorganicmaterialsshouldbecomparabletothecostsassociatedwithconventionalfungicides.

References

Babadoost,M.2012.“PlectosporiumBlightofCucurbits”.UniversityofIllinoisExtensionRPDNo.946.UniversityofIllinois.http://extension.cropsciences.illinois.edu/fruitveg/pdfs/946_cmplt.pdf

Boucher,T.J.2012.“PlectosporiumBlightandNewSprayRecommendationsfor2005.”UniversityofConnecticutCooperativeExtensionSystem.UniversityofConnecticut.http://ipm.uconn.edu/documents/raw2/Plectosporium%20Blight%20and%20New%20Spray%20Recom

13

mendations%20for%202005/Plectosporium%20Blight.php

Colucci,S.J.andG.J.Holmes.2010.DownyMildewofCucurbits.ThePlantHealthInstructor.DOI:10.1094/PHI-I-2010-0825-01.http://www.apsnet.org/edcenter/intropp/lessons/fungi/Oomycetes/Pages/Cucurbits.aspx

Egel,D.2008.“DownyMildewofPumpkin”.PurdueUniversityExtensionBP-140-W.PurdueUniversity.https://www.extension.purdue.edu/extmedia/BP/BP-140-W.pdf

Egel,D.S.,andS.Hoke.2011."EvaluationofFungicidesfortheControlofPowderyMildewandPlectosporiumBlightonPumpkin,2010."PlantDiseaseManagementReports5:V023Onlinepublication.doi:10.1094/PDMR05.

Everts,K.L.2002."ReducedFungicideApplicationsandHostResistanceforManagingThreeDiseasesinPumpkinGrownonaNo-TillCoverCrop."PlantDisease86:1134-1141.

Everts,K.L.,andM.J.Newark.2014."EvaluationofFungicidesforManagementofMildewDiseasesinOrganicSquashandPumpkin,2013."PlantDiseaseManagementReports8:V211.https://www.plantmanagementnetwork.org/pub/trial/pdmr/volume8/abstracts/v211.asp

Hansen,M.A.2009.“PlectosporiumBlightofCucurbits.”VirginiaCooperativeExtensionPublication450-709.VirginiaTech.https://vtechworks.lib.vt.edu/bitstream/handle/10919/55180/450-709.pdf

Glawe,D.A.2008."ThePowderyMildews:AReviewoftheWorld'sMostFamiliar(YetPoorlyKnown)PlantPathogens."AnnualReviewofPhytopathology46:27-51.http://annualreviews.org/doi/abs/10.1146/annurev.phyto.46.081407.104740

Ishii,H.,B.A.Fraaije,T.Sugiyama,K.Noguchi,K.Nishimura,T.Takeda,T.Amano,andD.W.Hollomon."OccurrenceandMolecularCharacterizationofStrobilurinResistanceinCucumberPowderyMildewandDownyMildew”Phytopathology91.12(2001):1166-1171.https://www.ncbi.nlm.nih.gov/pubmed/18943331

Jasinski,J.R.,S.A.Miller,M.L.LewisIvey,L.H.Rhodes,R.M.Riedel,andR.J.Precheur,2011."EfficacyofConventionalandBio-rationalFungicidesonCucurbitPowderyMildewonPumpkininOH,2010."PlantDiseaseManagementReports5.V170.https://www.plantmanagementnetwork.org/pub/trial/pdmr/volume5/abstracts/v170.asp

Keinath,A.P.,andV.B.Dubose.2012."ControllingPowderyMildewonCucurbitRootstockSeedlingsintheGreenhousewithFungicidesandBiofungicides."CropProtection42:338-344.http://www.vegetablegrafting.org/wp/wp-content/uploads/2013/12/1-s2.0-S0261219412001871-main-keinath.pdf

Lebeda,A.,andY.Cohen2011."CucurbitDownyMildew(PseudoperonosporaCubensis)-biology,Ecology,Epidemiology,Host-pathogenInteractionandControl."EuropeanJournalofPlant

14

Pathology129:157-192.https://www.researchgate.net/publication/226432381_Cucurbit_downy_mildew_Pseudoperonospora_cubensis-biology_ecology_epidemiology_host-pathogen_interaction_and_control

Marine,S.C.,M.J.Newark,R.C.Korir,andK.L.Everts.2016."EvaluationofRotationalBiopesticideProgramsforDiseaseManagementinOrganicCucurbitProduction."PlantDisease100.11:2226-2233.http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-02-16-0252-RE

McGrath,M.T.2001."FungicideResistanceinCucurbitPowderyMildew:ExperiencesandChallenges."PlantDisease85.3:236-45.http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS.2001.85.3.236

McGrath,M.T.2011."PowderyMildewofCucurbits."PowderyMildewofCucurbitsFactSheet.CornellUniversity.http://vegetablemdonline.ppath.cornell.edu/factsheets/Cucurbits_PM.htm

McGrath,M.T.,andN.Shishkoff.1999."EvaluationofBiocompatibleProductsforManagingCucurbitPowderyMildew."CropProtection18.7:471-478.http://agris.fao.org/agris-search/search.do?recordID=US201302944143

Miller,S.A.,J.R.Mera,andF.Baysal-Gurel.2013."EvaluationofFungicidesfortheControlofPlectosporiumBlightandPowderyMildewofPumpkin,2012."PlantDiseaseManagementReports7.V091).https://www.plantmanagementnetwork.org/pub/trial/pdmr/volume7/abstracts/v091.asp

Ojiambo,P.S.,andG.J.Holmes.2011."SpatiotemporalSpreadofCucurbitDownyMildewintheEasternUnitedStates."Phytopathology101.4:451-461.https://www.ncbi.nlm.nih.gov/pubmed/21117875

Perez-Garcia,A.,D.Romero,D.Fernandez-Ortuno,F.Lopez-Ruiz,A.deVicente,andJ.A.Tores.2009.“ThePowderyMildewFungusPodosphaerafusca(synonymPodosphaeraxanthii),aConstantThreattoCucurbits.”MolecularPlantPathology,10:153–160.doi:10.1111/j.1364-3703.2008.00527.x

Reuveni,M.,V.Agapov,andR.Reuveni.1996."ControllingPowderyMildewCausedbySphaerothecaFuligineainCucumberbyFoliarSpraysofPhosphateandPotassiumSalts."CropProtection15.1:49-53.https://www.researchgate.net/publication/248416002_Controlling_powdery_mildew_by_Sphaerotheca_fuliginea_in_cucumber_by_foliar_spray_of_phosphate_and_potassium_salts

Reuveni,M.,V.Agapov,andR.Reuveni.1995."SuppressionofCucumberPowderyMildew(SphaerothecaFuliginea)byFoliarSpraysofPhosphateandPotassiumSalts."PlantPathology44.1:31-39.http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3059.1995.tb02713.x/full

Savory,E.A.,L.Granke,L.,L.M.Quesada-Ocampo,M.Varbanova,M.K.Hausbeck,andB.Day.2011.

15

"TheCucurbitDownyMildewPathogenPseudoperonosporaCubensis."MolecularPlantPathology12.3:217-226.http://onlinelibrary.wiley.com/doi/10.1111/j.1364-3703.2010.00670.x/abstract

UniversityofMassachusettsExtension.2013.“Cucurbits,Plectosporium”.UniversityofMassachusettsExtension.UniversityofMassachusetts.https://ag.umass.edu/vegetable/fact-sheets/cucurbits-plectosporium

Wyenandt,A.(editor).2016.PumpkinsandWinterSquash.PagesF142-F154in:2016Mid-AtlanticCommercialVegetableProductionGuide.VirginiaCooperativeExtension.https://pubs.ext.vt.edu/456/456-420/456-420.html

16

Appendix:

AppendixFigure1:Plotlayoutusingrandomizedblockdesign.

Eachcellaboverepresents1“plot”.Each“plot”contained4setsof2plants,with4feetspacingbetweeneachsetof2plants.Each“plot”contained8plants.Each“row”consistedof32plants

17

Figure2:SuspectedcoppertoxicityfromNordoxapplications.Noticemarginalchlorosis(8-26-2016)

18

Figure3:SuspectedcoppertoxicityfromNordoxapplications.Rustcoloreddepositsareresiduesfromchemicalapplications(8-26-2016)

19

Figure4:Plectosporiumlesionsonpumpkinvine(9-2-2016)

20

Figure5:Researchplotsbeforemajordiseasepressure(8-19-2016)

21

Figure6:Near-completedeathofvineduetoPlectosporium(9-9-2016)

22

Figure7:Seedvarietyandlotusedinresearch