Nursery Site Selection And Citrus Tree Production

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Nursery Site Selection And Citrus Tree Production
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Fact sheet
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Tucker, D.P.H.
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Gainesville, Fla.
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"Publication date: June 1993. Revised: November 1993."
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"HS-167"

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FactSheetHS-167 November1993NurserySiteSelectionandCitrusTreeProduction1 D.P.H.TuckerandC.O.Youtsey2SITESELECTIONFORFIELDNURSERIESNurserysiteselectionisofgreatimportance.A nurserysiteisbestlocatedawayfromdeveloped areasinaplacewherethefrosthazardisminimal, Welldrained,virginsoilispreferredandanadequate supplyofgoodqualitywaterisessential.Goodaccess roadstothesiteandwithinitaredesirablefor inspection,culturaloperations,diggingand transportation.Thesiteshouldalsobefreeof parasiticnematodes,burrowingnematodeandthe citrusnematode.Citrusnurserysitesmustbe approvedbytheDivisionofPlantIndustry, DepartmentofAgricultureandConsumerServices beforeplanting.NURSERYSITEHYGIENEItisimportanttounderstandtherolethat sanitationplaysintheoverallcontrolofdisease problems.Thesinglemostdestructivedisease encounteredinthenurseryis Phytophthoraparasitica. Thisfungalorganismisoneofagroupof"water molds,"so-calledbecausetheyspreadandgrow rapidlyunderhighmoistureconditions.Phytophthora isacommonsoilinhabitantwidelydistributedeven wherenotproducingvisiblesymptoms. Rhizoctoniaisanotherfungusthatfrequently causes"damping-off"inseedbedsinwarmweather. Underfavorableconditionstheseorganismscause damagetotherootsandlowerstemsofseedlings, renderingthemunfitforfurtheruse.Theyarespread bythemovementofinfestedsoil,splashingofrain andirrigationwater,orbyheavyrunofffrominfested areas. Sanitationpracticesincorporatedintothedaily workscheduleassuggestedbelowcangreatlyreduce diseaseincidenceinthenursery: Cleanequipmentbeforebringingitintothe nurseryandconfineittonurseryuse. Donotmovecontaminatedsoilorequipmentinto fumigatedareas. Removediseasedplantsandisolatethearea beforediseasecanbespread. Removeplantresiduesassoonaspossibleafter diggingtrees. Useonlyhealthyseedlingsforlining-out, discardinganyplantswithevidenceofrootor stemrot. Keepstorageorholdingareasfreeofdebrisand periodicallytreatwithfungicidestoreduce diseasespread. 1.ThisdocumentisFactSheetHS-167,aseriesoftheHorticulturalSciencesDepartment,FloridaCooperativeExtensionService,Institute ofFoodandAgriculturalSciences,UniversityofFlorida.Publicationdate:June1993.Revised:November1993. 2.D.P.H.Tucker,professorandExtensionHorticulturist,CitrusResearchandEducationCenter,LakeAlfredFL33850,Cooperative ExtensionService,InstituteofFoodandAgriculturalSciences,UniversityofFlorida,GainesvilleFL32611;C.O.Youtsey,Divisionof PlantIndustry,FloridaDepartmentofAgricultureandConsumerServices,WinterHavenFL33880. Theuseoftradenamesinthispublicationissolelyforthepurposeofprovidingspecificinformation.Itisnotaguaranteeorwarrantyofthe productsnamed,anddoesnotsignifythattheyareapprovedtotheexclusionofothersofsuitablecomposition. TheInstituteofFoodandAgriculturalSciencesisanequalopportunity/affirmativeactionemployerauthorizedtoprovideresearch,educational informationandotherservicesonlytoindividualsandinstitutionsthatfunctionwithoutregardtorace,color,sex,age,handicap,ornational origin.Forinformationonobtainingotherextensionpublications,contactyourcountyCooperativeExtensionServiceoffice. FloridaCooperativeExtensionService/InstituteofFoodandAgriculturalSciences/UniversityofFlorida/ChristineTaylorStephens,Dean

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NurserySiteSelectionandCitrusTreeProduction Page2Inadditiontosoilfungi,theexocortisviroid presentsaspecialsanitationproblem.Thedisease, whenpresentinaplant,canbespreadtootherplants onbuddingknives,clippersandhedgingshears.To preventthis,eachbuddershouldbesuppliedwitha smallcontainerofsterilant(tenpercenthousehold bleach,theactiveingredientofwhichissodium hypochlorite),todisinfectknivesandclipperswhen propagatingorpruning.Thisshouldbecomeaclosely supervisedprocedureasthisdiseaseaffectsmany scionrootstockcombinationsthatcanresultin unproductivegrovetrees.LOCATIONTheseedbedshouldbelocatedinanarea separatedfromthemainnursery.Thiswillavoid run-offfromirrigationorheavyrainthatmay introducediseaseorganismsintotheseededareaand ingreatercontrolofwaterrelations.Seedlingsfor liningoutcanoftenbeproducedinseedflatson raisedbenchesinthegreenhouseareasinashort time,withbetterandhealthierrootsystemsthan thosegrownintheground.BEDPREPARATIONPreviouslycroppedareasmayrequirefumigation forthecontrolofnematodes,diseasesandweeds.Soil acidityshouldbeaadjustedtopH6.5-7.0duringland preparation.Seedbedfumigantshaveattimesresulted inirregularseedlinggrowthfollowinggermination whichmaybecharacterizedbystuntingandnutrient deficiencysymptoms,particularlythoseof phosphorus.Theproblemhasbeenassociatedwith thelackofmycorrhizalfungiinfumigatednurseries asthesefungiareverysensitivetomethylbromide. Experimentalinoculationofcitrusseedlingswithsuch fungiinfumigatedsoilhasvirtuallyeliminatedthe problemandactuallyresultedinspectaculargrowth increasesinCalifornia.Whilesomeinoculationwork hasbeenconductedinFlorida,largescalefieldtrials havenotbeenconclusive.Seedbedaerationby cultivationfollowingfumigationandheavypreplant applicationsofphosphatehavebeenfoundtoreduce theoccurrenceofthisproblem.Seedlingsshouldbe closelyobservedforpoorgrowthandbronzedleaves. Bronzeleavesareasymptomofphosphorus deficiency.SEEDSELECTIONThecarefulselectionofseedforplantingisavery importantfactorintheultimateperformanceofthe tree.CarrizoandTroyercitrangesarecapableof transmittingblindpocketandconcavegumvirusesto seedlingsthroughtheseedfrominfectedmother trees.Seedlingsfromoff-typetreesdonotreactto diseasesandgrowingconditionsinthesamewayas standardtrue-to-typeselections.Forthesereasons, seedshouldbeselectedfromestablishedseedsource plantingschosenforuniformityandfreedomfrom viruses.SEEDPREPARATIONWhilethebestseedgerminationmaybeexpected whenseedsareplantedimmediatelyafterextraction, storageisoftennecessaryinordertoplantcertain speciesatthedesiredtime.Seedsshouldbeextracted andwashedwithcleanwaterandsurface-driedina cool,shadyplaceonacleanwoodorscreensurface. Sometreatmentneedstobemadetoreduce allimismandBluegreenMoldinstorage.Seedsmay bestoredforseveralweeksintherefrigeratorat40F packagedinplasticrefrigeratorbags.Thereare sourcesoftrue-to-typevirusindexedseedinFlorida andCalifornia,thelocationsofwhichmaybe obtainedfromtheCitrusBudwoodRegistration Bureau.PLANTINGTIMEWhilecitrusseedmaybeplantedatanytimeof theyear,latewinterandspringaremostsuitable. Strongwindsduringthisperiodmaycausedamageto youngseedlingsfromblowingsand;therefore,the plantingofcovercropssuchasoatsandryebetween rowsiscommonlypracticedtoreducethiseffect. SeedsplantedafterMay15-30willemergeunder weatherconditionsmostfavorableforthe developmentof"damping-off"diseases,possibly resultinginapoorsurvivaloftheyoungseedlings.PLANTINGSeedmaybeplantedbyhandinopenfurrows approximately1inchdeep,scatteredevenlyinthe bottomofthefurrow,oraplantingboardmaybe usedtoensurethatseedisspacedevenlyatauniform

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NurserySiteSelectionandCitrusTreeProduction Page3depth.Whilethismethodtakesmuchtime,itresults instraighter,moreuniformseedlingswithless benchedrootformationandmakesmaximumuseof availableseed.Broadleaftypessuchassourorange, roughlemonand Citrusmacrophylla shouldbe plantedfurtherapartthanvarietieswithsmallleaves suchasCarrizocitrange, Poncirustrifoliata or Cleopatramandarin.Widthofrowsshouldbe adaptedtoequipmentusedfornurseryoperations. Commercialseedplantersareavailablebutmustbe adaptedforuseincitrusseedbeds.GREENHOUSEPRODUCTIONAproductionsystemforcitrusnurserytreeshas beendevelopedbasedonreusableplastictubesor traysforraisingrootstockseedlings,acommercial growingmedium,plasticcontainersforthebudded treesandoperationwithinanenclosedheatedand cooledplasticcoveredgreenhouse.Plantssuitablefor microbuddingcanbeproducedin3monthswitha finishedplantavailableinabout12months.The systemisflexibleandoffersadvantagesinthe conservationoftimeandspaceandbettercontrol overwaterapplicationthusbetterdiseasecontrol.IRRIGATIONMostcommercialcitrusnurseriesareirrigatedby permanentoverheadsprinklersystems.Thedesignof suchsystemsisimportanttoensuretheeven distributionofwater.Suchevendistributionassumes additionalimportanceifthesystemistobeusedfor theapplicationoffertilizers.Unevendistributionwill leadtoconsiderabledifferencesinamountsapplied, withconsequentinjurytoordeficiencyinplants receivingthehigherorloweramounts.However, utilizationofirrigationsystemsforfrostprotection and"fertigation"shouldnotbeattemptedwithoutthe benefitofsoundengineering.Acarefullymanaged watersystemisessentialfortheproductionofhealthy seedlings.Theuseofexcessiveirrigationhasbeen foundtobethecauseofmanynurseryproblems.The frequencyofseedbedirrigationdependsuponsoil type,temperature,rainfallandsizeofseedlings. Frequentlightwateringisrequiredfornewlyplanted seedbeds.Asseedlingsbecomewellestablished,less frequentheavierapplicationsshouldbemadeto maintainmaximumgrowth.Prolongedwetsoil conditions,highhumidityandcrowdedseedbed conditionsareconducivetothedevelopmentof soilbornPhytophthoraandRhizoctoniafungiwith resultingsevereseedlinglosses.Certaincitrusspecies suchassweetorange,roughlemon,Milam,Carrizo citrange,andCleopatramandarinaremore susceptibletorootdiseasesthanothersanddemand carefulattention.Afterseedlingshaveemerged, irrigationshouldsupplementrainfalltomaintainsoil moisture. Newsystemicfungicidesshowgreatpromisefor thecontrolofPhytophthorarootrotincitrus nurseries.TwooftheseproductsRidomilandAliette, havebeenapprovedforuseinnurseries. Fungicidesshouldbeappliedjudiciouslyand accordingtolabeldirection,withmorefrequent applicationsrequiredduringperiodsofactivegrowth andfrequentrainfall,particularlyduringthesummer months.OveruseofRidomilhasresultedinresistant strainsofPhytophthoraandlackofdiseasecontrol. Controloffungusdiseasescanbemosteffective whenspraysareappliedonaregularbasisbefore infectionisapparent.FERTILIZATIONFertilizerprogramsaredifficultincitrusnurseries becauseoftherapidlychanginggrowthstages.Rates givenrepresentguidelinesonlyandindividual nurserymenwillformulatetheirindividualprograms. Sinceexcessivefertilizerapplicationshavebeen theruleratherthantheexception,itisprudentto notethatcontinualluxuryconsumptionofnutrients andresultingvigorousvegetativegrowthwillenhance theincidenceofdiseases,especiallyinseedbeds. Excessivefertilizingmayresultinleachingofnitrogen intothesubsoilsandcontaminatewellfields.Soil testsshouldbemadeatleastonceayearto determinethestatusofPh,calcium,phosphorus, copperandtotalsolublesalts. Whentheseedlingsare11/2incheshigh,the firstlightapplicationofalowanalysismixedfertilizer shouldbemadetotheseedbed.Useapproximately 200poundsoffertilizerperacre,dependingupon naturalsoilfertility.Fertilizerisbestappliedpriorto orfollowinganirrigationorgoodrain. Foliageshouldbethoroughlydrybefore applicationtopreventleafburn.Fertilizershouldbe appliedat3weekintervals,withagradualincrease toamaximum12monthsold.Aratioof1:1:1,with 15percentofthenitrogenderivedfromorganic sources,isrecommended.Liquidfertilizationsmaybe appliedthroughtheirrigationsystem.

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NurserySiteSelectionandCitrusTreeProduction Page4PREPARINGSITEANDSEEDLINGSTheareatobeusedforgrowingthenurserytrees shouldbethoroughlytilled,leveledandclearedofall rootsandperennialweedresidues.Necessarysoil amendmentsshouldbeaddedatthistimetoadjust thepH6.5.0.Aswiththeseedbed,thissiteshould beinacarefullyselectedlocation. Whenseedlingshavereached3/16/4inchin diameter,theyarereadytobetransplantedor"lined out"inrowsforbudding.Seedlingsheldinthe seedbedforaslongasayeararemorelikelytobe infectedwithrootdiseasesandscaleinsectsdueto crowding.Largeseedlings,especiallythoseof trifoliatehybrids,arehardertotransplantsuccessfully, withtheresultantexpenseofresetting. Seedlingsshouldbedugfromtherowwith spadesormechanicalequipment.Careshouldbe takentoleaveasmanyrootsundamagedaspossible. Topsshouldbeprunedtomanageablepropagation andextremelylongordamagedrootsremoved. Whendigging,"off-type"seedlingsshouldbe discarded,andplantsshowinganydegreeofdiseased rootsorstemsculledatthispoint.Useofdiseased seedlingscanonlyresultinproductionofdiseased treesandspreadthediseasetootherareasofthe nursery.Seedlingsshouldbegradedinto2or3sizes andplantedinthenurseryrowsbysizegroups.This procedureresultsinahighpercentageofuniformity forabudline.Thispracticewillrequirelesslaborand yieldahigherpercentageofsalabletreesmaking moreefficientuseofnurserygrowingarea.SETTINGOUTLINERSThesizeofthenurseryareaandtypeof cultivationwilldictatetoalargeextenttherow spacinganddistanceintherowthatseedlingsshould beset.Currentpracticeistoplantseedlingsasclose as4inchesapartintherowsasopposedtothe formerpracticeof12inches.Whilecloseplanting makesmaximumuseofavailableland,treesthatare tobeheldmorethanoneseasoninthenurserymay bemoresusceptibletoscaleinsectsanddiseasesasa resultofshadingandpooraircirculationnearthesoil surface.Effectivespraycoverageisalsolesslikelyto beachievedundercrowdedconditions. Linersmaybesetatanytimeoftheyear; however,smallseedlingssetinMarchorAprilare oftenlargeenoughtobudbyfall.Dormantbudscan beforcedtogrowinthespringtoasizelarge enoughtobemovedbymidtolatesummer.Seedlings aslargeas1/4/8inchsetinthelatesummerorfall canbewellestablishedbymarchoraprilofthe followingyear,sothattreesbuddedatthattimewill bereadyformovementbyfall. Thesoilshouldcontainadequatemoisturebefore liningoutforplantingfurrowstoremainopen. Linersmaybesetmechanicallyorbyhand;however; witheithermethoditisimportantnottoplantliners anydeeperthantheygrewintheseedbed.Thesoil shouldbepackedfirmlyaroundtherootsleavingno airpockets.Frequentlightirrigations,3/8/2inch perapplication,shouldbeapplieduntilseedlings becomeestablished.Thisisespeciallyimportant duringthewarmsummermonths.Irrigationcanbe scheduledat1/2inchperweekasneededto supplementrainfall. Seedlingsshouldbefertilizedwithin2weeks afterliningout,withaninitialapplicationofabout50 poundsper1000seedlingsofan8-2-8mixtureor approximateequivalentanalysis.Theseedlingsshould befertilizedevery3weeksandwhenapproximately 3monthsold,mayreceive75poundsoffertilizer per1000trees.Highanalysisfertilizersshouldbeused withcautionasplantdamagecanoccur.WEEDCONTROLInthepast,weedcontrolhasundoubtedlybeen themostcostlyproductionpracticeinthenursery operation.Althoughfumigationoffersexcellentweed controlforsomeweeksaftertheoperation,severe weedreinfestationwillfollow.Suchweedgrowthwill quicklygetoutofhand,competewithseedlings,and hindernurseryoperations.Althoughcostly,hand weedingoperationsaresometimesnecessary. Cultivationispracticedwithequipmentmodifiedfor nurseryuse;however,caremustbetakennotto damagetheplantsandtillagedepthshouldbekeptto aminimum. Whileherbicidesarenowcommonlyusedin commercialnurseries,itshouldberememberedthat citrusinyoungstagesofgrowthinthenurseryisvery susceptibletothesematerials. Pesticidemanufacturersarehesitanttoseek herbicideregistrationsfornurseryuseduetothelow volumeusagecomparedwiththehighperacredollar valueofthecrop.Itisessentialthatweedgrowthbe controlledpreferablyatgermination,sincelower

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NurserySiteSelectionandCitrusTreeProduction Page5herbicidedosageratesarelikelytobemore satisfactory. Spottreatmentofisolateddenseareasofweed growthmaybedoneusingcontactorsystemic-type herbicidesprovidedyoungseedlingsandbudlinesare adequatelyshieldedfromthespray.Theapplication ofherbicidesthroughthesprinklersystemisnotan approvedmethodofapplicationfornurseries.WEEDANDSPROUTCONTROLDuringthegrowthofthebuddedtree,weed growthshouldbekeptundercontrolwithlabeled herbicides,usingextremecarenottoinjurethebud. Intheabsenceofrainfall,11/2inchesof supplementalirrigationshouldbeappliedeach7 days.Irrigationshouldbeappliedmorefrequentlybut atalighterrateduringthehotsummerdays. Rootstocksproutsshouldbebrokenorcutroutinely, sincetheyretardthevigoroftheyoungbud.Rough removaloflargesproutswillresultinopenwounds throughwhichdiseaseorganismsmaygainentrance orleavescars.Awhitelatexbaseformulationof naphthaleneaceticacid(NAA)atconcentrationsof 1/2percenthasshownsomepromiseincontrolling rootstocksproutgrowthonestablishedbudlines,and non-bearingcitrustrees.Thematerialshouldnotbe appliedtoareasofthetrunkwithgreenbarkorto foliage.Whilegoodcoverageoftheareatobetreated isrequired,sprayapplicationtothepointofrunoff mayresultintreegrowthinhibitionand/orinjury.NUTRITIONWhenthebudis3-5inchesinlength,fertilizer maybeappliedattherateof50poundsofa 6:6:6:4:0.5:0.5(N:P:K:MgO:MnO:CuO)orequivalent analysismixtureper1000trees.Bythetimethebud reachesthetopofthestake,asimilarfertilizermay beappliedattherateof100poundsper1000trees every4-6weeksuntilaboutSeptember15.Fromtime totimeduringthegrowthofthenurserytree, nutritionalspraysmaybeappliedifsoiltests(for copper)andvisualsymptoms(zincandmanganese)so indicate.COLDPROTECTIONMostcommercialnurserymenincentralFlorida withfieldnurseriesemploycoldprotectionpractices, withbothirrigationandheatbeingusedastheneed arisesdependingonenvironmentalconditions.Cold protectionforfieldgrownnurserystockiscommonly providedwithoverheadirrigation.Onequarterofan inchtoonethirdofaninchperhourisusually adequateforprotectionfromfreezingweather.Good waterdistributionespeciallyonthenorthandwest sidesofthenurseryisveryimportant. Powersuppliesofgasordieselenginesare preferredoverelectricduetotheuncertaintyof electricpowerduringpeakloadsthatoccurduring coldweather. Sprinklersthatarenotaffectedbyiceformation areessentialforcontinuousoperation.Useoflarge volumesofwaterforextendedperiods(2days) makeitessentialthatthesitebewelldrained.PROPERHANDLINGQuiteoften,prioritiesandequipmentusewill dictatethetimeofgroveplanting.Thetimeofcutting backanddiggingthetreesinrelationtothegrowth cycleshouldbeconsidered.Treescutbackanddug justbeforethenewgrowthcycleusuallyrespondbest aftertransplantinginthegrove.Thosedugduringor immediatelyafterthegrowthflushmayresultin weakergrowth.Thisdifferenceingrowthperformance ofthetreemaybeexplainedbyamaximumstorage ofcarbohydratesintherootsinthefirstcaseanda depletioninthelatter.Theuseofantitranspirants (materialswhichreducewaterlossfromtrees) sprayedontreesaftercuttingback,beforedigging, hasshownsomepromiseforimprovingthe performanceoftreesaftertransplantingintothefield. Shortlybeforediggingtrees,topsshouldbecutback tothescaffoldbranches(hat-racking)preferably leavingsomefoliageintact.Treesarethendug mechanicallywithatractordrawnsubsoilbladein mostlargercommercialnurseries,orwitha straight-edgednurseryshovel. Treesshouldthenbestoredinaclosedtruck bodyorintheshadeundercoverandsubjectedto continualsprinklingwithwatertoinsurethatroot systemsarenotallowedtodryout. Spring,summerandfallplantingshouldbe associatedwithcertainproblems,includingextended periodsofdrought,intenseheatstressandtheadvent ofcoldweather,respectively.Instancesoftreeloss duringthemonthsofJuly,August,andSeptember havebeenattributedtoheatstress,associatedwith insufficientrainfallorsupplementalirrigation.

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NurserySiteSelectionandCitrusTreeProduction Page6COMMONCAUSESOFTREELOSSInmanyinstances,thedeathorunsatisfactory growthofrecentlyplantedyounggrovetreeshasbeen attributedtonegligenceinhandlingatsomestage betweenthenurseryoperationandtreeplanting. Desiccationofthefeederrootsystemdueto inadequatewatering,exposuretowindandheatafter digging,duringtransportandbeforeplantingwill resultinrootdeathandconsequentinabilityofthe youngtreetorecoverfromtheshockofmoving. Greatcareshouldbetakentoensurethattreesare deliveredtotheplantingsiteinahealthycondition, andthatthegrowerisadoptingsoundplantingand post-plantingcareprocedures.This,ofcourse, includestheverycriticalwateringphaseofthe operation.Whentreemortalityoccurssomeweeks afterplanting,itisalwaysdifficulttodetermine whetherthegrowerorthenurserymanshouldaccept responsibility.Thegrowerorsomeother knowledgeableindividualshouldbepresentatthe plantingsitetoinspectthetreesonarrivaland determinewhethertheyareinsatisfactorycondition andmeetthetermsofthecontract.