Citrus Tree Pruning Principles And Practices

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Citrus Tree Pruning Principles And Practices
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Fact sheet
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Tucker, D.P.H.
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University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS
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"HS-144"

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FactSheetHS-144 June1994CitrusTreePruningPrinciplesandPractices1 D.P.H.Tucker,T.A.WheatonandR.P.Muraro2Pruninghealthy,maturecitrustreesusually Figure1. PruningforCanopyBearingSurfaceofCitrusTrees.reducesyieldinproportiontotheamountoffoliage removedandcandelayfruitingofyoung,nonbearing trees.Pruningshouldthereforebelimitedtothat requiredforfuturecanopybearingsurface developmentandfortheconductofefficientcultural andharvestingoperations(Figure1).Thepruning process1)adjuststreeshapeandtheratioof 1.ThisdocumentisFactSheetHS-144,aseriesoftheHorticulturalSciencesDepartment,FloridaCooperativeExtensionService,Institute ofFoodandAgriculturalSciences,UniversityofFlorida.Publicationdate:June1992.Reviewed:June1994. 2.D.P.H.Tucker,professor,extensionhorticulturist,DepartmentofHorticulturalSciences;T.A.Wheaton,professor,horticulturist, DepartmentofHorticulturalSciences;R.P.Muraro,associateprofessor,extensioneconomist,DepartmentofFoodandResource Economics,CitrusResearchandEducationCenter,LakeAlfred,Florida,abranchoftheUniversityofFlorida,Gainesville,Florida. 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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CitrusTreePruningPrinciplesandPractices Page2frameworktofruitbearingshellofthecanopy,2) altersthetop/rootratio,and3)changesthe carbohydrate(foodstorage)statusofthetree.Proper controlofvegetativegrowthisessentialforthe maintenanceofhealthy,productivecitrusgroves. MostgrovesinFloridamustbeprunedatsometime duringtheirdevelopmenttoavoidproblems associatedwithovercrowded,excessivelytalltrees. Whenpruningshouldbeginwilldependtoalarge degreeontheinitialtreeplantingdensity.Crowded conditionsresultinpoorlightaccessibility,lossof lowerfoliageandbearingwood,relocationoffruiting totheuppertreecanopyareasandreductioninfruit yield,size,andexternalquality.Goodmanagement thereforedictatestheneedtoprunebeforethe occurrenceoftheseundesirableeffects. Theresponsetopruningdependsonseveral factorsincludingvariety,treeageandvigor,fruiting habits,growingconditions,andproductionpractices. Asnoonesystemorsetofrulesisadequateforthe numeroussituationsencounteredinthefield,growers areencouragedtogainaclearunderstandingofthe principlesinvolvedinpruningandtotakeadvantage ofresearchresultsandknowledgeablecolleagueand customoperators'observations.SUNLIGHT,PHOTOSYNTHESIS,ANDFOOD STORAGETheimportanceofsunlightinterceptedbythe treecanopyontheproductionofhighyieldsofgood qualityfruitcannotbeoveremphasized.Light providestheenergyforphotosynthesisinwhich carbondioxidefromtheairandwaterfromthesoil arecombinedintheleavestoformthebasicfoods uponwhichtreeslive,grow,andbearfruit.Light becomesalimitingfactorincrowdedgrovesand pruningimproveslightaccess.Adjustmentsmustbe madeintreeheight,rowmiddlewidth,andhedging angletomaximizesunlightimpingementonthetree canopy.Sunlightnotonlyinfluencesfloweringand fruitsetbutalsoenhancesfruitqualityandcolor development. Incitrus,carbohydratesarestoredinleaves,twigs, andbrancheswithonlyaminoramountgoingtothe rootsystem.Themaximumamountofstoredfoodis reachedinspringjustbeforetheonsetofgrowthflush activity.Thefoliageofcitrustreesthereforeactsas animportantfoodstoragearea,andheavypruning causesthetreetoproducevegetativegrowthatthe expenseoffruitproduction.HORMONALRELATIONSHIPSANDAPICAL DOMINANCEWhilehormonesoccurringinthecitrustreeaffect fruitset,theeffectsofpruningontheiractionisnot wellunderstood.Suppressionoflateralbudgrowth bytheterminalbudisknownasapicaldominance. Apicaldominanceexplainsmanyofthegrowth characteristicsoftreesandtheirresponsestopruning. Branchingisinfluencedbyanauxinproducedinthe terminalbudwhichmovesdownthesystemtoinhibit lateralbudbreak.Removaloftheterminalbud destroysapicaldominancesothatoneorseveral lateralbudswillcommencetogrowandbranching results.Vigorousshootscalledwatersproutsor suckersshowextremeapicaldominancewithno side-branchdevelopment.Apicaldominancevaries somewhatwithvigorandvariety.BEARINGHABITSThebalancebetweentreegrowthandfruitfulness appearstodepend,tosomeextent,upona relationshipbetweencarbohydratesandnitrogenous compoundswithinthetree.Whenbothareadequate, moderategrowthandhighyieldsoccur.Whenboth arelow,citrustreesgrowandfruitpoorly.Atreelow incarbohydratesandhighinnitrogentendsto producevigorousvegetativegrowthattheexpenseof fruitproduction.Sincecarbohydratesare manufacturedandstoredintheleaves,heavypruning whichremovesalargeportionoftheleafareacan resultinthiscondition.Toomuchnitrogenafter severepruningcanaggravatetheproblem,causing thickandpuffyfruitpeel.Nitrogenapplications shouldthereforebeadjustedtotheseverityof pruning.Reducingnitrogenapplicationsavoidsan imbalancewhenheavypruningisdone.Omittinga nitrogenapplicationbeforeheavypruningand possiblyafterwillreducebothcostsandexcessive vegetativegrowth.Thelengthoftimethislimitation shouldcontinuewilldependupontheseverityof pruningandtherateoftoprecovery.Light maintenancepruningshouldnotaffectfertilizer requirements. Somecitrusgrovestendtohaveabearinghabit withalternatinghighandlowyields.Aheavycropof fruittendstodepletecarbohydratesandresultsina smallcropandincreasedvegetativegrowththe followingyear.Pruningafteraheavycrop additionallystimulatesvegetativegrowththefollowing yearbecausethecarbohydratesupplyhasbeen somewhatdepletedandthecapacitytoresupplyhas

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CitrusTreePruningPrinciplesandPractices Page3beenreduced.Poorfruitqualitymayalsoresultfrom thispractice.Pruningafteralightcropandbeforean expectedheavycropshouldhelpreducealternate bearing. Theorientationofbranchesinspacehasa markedeffectongrowthandfruiting.Adecreasein growthrateandanincreaseinfloweringoccurswhen branchesbendtoahorizontalposition.Apossible explanationforthisphenomenonisachangeinthe distributionofgrowthsubstancesandcarbohydrates. Favoringhorizontalbranchesoveruprightones shouldresultinbettergrowthcontrolandmorefruit production.BASICPRUNINGCUTSHeadingbackandthinningoutarethemaintypes ofpruningcutsandareusedforsomewhatopposing objectives.Headingbackremovestheterminal portionofashootorbranch,destroyingapical dominanceandstimulatinglateralbudbreaks.This tendstoproduceamorebushy,compacttree. Mechanicalhedgingandtoppingareformsofmass headingback.Astheindividualtreeorhedgerow increasesinsize,internalwoodmaybecomeless productiveandeventuallydie.Thinningoutinvolves theremovalofcompletebranchestolateralsortothe maintrunkandisdonebyselectivepruningwith hand-heldequipment.Itencourageslongergrowthof theremainingterminalsandcanresultinalarger, moreopentree.Thistypeofpruningmaybedone forbetterlightpenetrationintothetree,butis generallyconsideredtoolaborintensiveandnotmuch practicedinFlorida.RESPONSESTOSEVEREPRUNINGSeverepruningstimulatesvigorousnewvegetative growth,especiallywhendonebeforeamajorgrowth flush.Thishappensbecauseanundisturbedroot systemisprovidingwaterandnutrientstoareduced leafarea.Thelargerthewoodthatiscut,thelarger thesubsequentshoot.Vegetativeresponsetopruning isgreatestwherethemostseverecutsaremade, resultinginastrongtendencyforprunedtreesto resumetheirnaturalshape.Severepruningreduces fruitingandincreasesfruitsizeandjuicecontent, decreasessolublesolidsandacid,withusuallyno changeinthesolublesolids/acidratio.Suchpruning ofaseverelycrowdedgrovetypicallyresultsinacrop reductionthefirstyear,recoveryofpreviousyieldthe secondorthirdyear,andhigheryieldsthereafter, althoughthiscanvarywithtreevigor,grove conditions,andthesizeofthepreviouscrop.SUGGESTEDPRUNINGPRACTICES YoungTreesSeverepruningandtrainingofyoung,nonbearing treestendstodelayfruitproductionandshouldbe avoided.Mosttreesusuallyneednopruningforthe firstfewyearsinthegroveexceptforremovalof sproutsonthetrunk.Thesecanbeeasilybrushedoff whenyoungandtenderandthewoundswillbesmall. Largersproutsshouldbecutoffflushwiththetrunk. Sproutingonthetrunksofyoung,nonbearingtrees canbegreatlyreducedbyusingacommercialsprout inhibitorcontainingnaphthaleneaceticacid.While protectivewrapsaroundthetrunkwillreduce sprouting,carefulobservationisrequiredtoavoid insectanddiseaseproblemsunderthewraps. Occasionally,avigoroussuckerwilldominateaweak treeorasuckermayarisefromtherootstock.These shouldberemovedearlybeforetheycompetewith moredesirablegrowth.Selectionofpermanent scaffoldbranchesduringthefirstfewyearsisrarely successfulsincethenaturalgrowthhabitofthese treesissounpredictable.Newgrowthmayoccurat unexpectedplacesandbecomedominantover selectedbranches.Whenthetreeis3or4yearsold, dependingonitsgrowth,branchesthataretooclosely spacedorarecrossedandentangledmayberemoved. Thispruningshouldbelight,justsufficientto establishadesirableframeworkwithoutstimulating excessivevegetativegrowth.Optionalpruningduring thenextseveralyearsshouldbelimitedtoremovalof watersprouts,deadwoodandoccasionalbranches whichinterferewiththegrowthofscaffoldlimbs.MatureTreesTheserequirelittlepruninguntiltreesapproach containmentsize.Deadwoodmayberemovedevery 3to5years,dependingontheamountpresentandon thelaborsupply,sinceitcanscarfruitandbea sourceofmelanoseinfection.Thiscanbedoneat anytimewhenlaborisplentifulandparticularly followingfreezes.Growersneedonlyremovedead branchesof1/4in.indiameterorlargersincesmaller deadwoodisoftenbrokenoffinharvestingandother groveoperations.Allcutsshouldbemadeintolive wood,flushwithalargerbranchoratalateral. Whenagroveislaidout,eachtreeisallotteda unitofspaceinwhichtogrow.Whenthisspaceis

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CitrusTreePruningPrinciplesandPractices Page4exceededcrowdingoccursresultingininadequate lightconditions,lossoffoliageandfruitproductionin thelowerportionofthetree.Culturalandharvesting operationsarealsoadverselyaffected.HedgingHedging,whichconsistsofcuttingbackthesides oftreestopreventoralleviatecrowding,isacommon practicesincethedevelopmentofmechanical equipmentforthispurpose.Hedgingleaves numerouscutwoodsurfacesalongthesideofthetree canopyfromwhichnewsproutsariseeventually developingintoawallofnewfoliage.Middles (alleys)betweentreerowsshouldbesufficientlywide toaccommodategroveequipmentandprovide adequatelightaccesstothesidesofthetrees. Middlesareusuallyhedgedtoawidthof7to8ft. Hedgingshouldbestartedbeforecrowding becomesaproblemsothatonlycuttingofsmall branchesisnecessaryandminimalcropreduction results.Thecloserthespacingandthemorevigorous thetrees,thesoonerhedgingisrequiredandthe morefrequentlyitneedstobedone.Removalofa largeportionofthetreemayberequiredwhen pruningisdeferreduntilseverecrowdingoccurs. Excessivevegetativegrowthandadrasticreductionin subsequentyieldmayresult.Hedgingofseverely crowdedgrovesaidsintheeventualrestorationofthe treeskirtsandopensthemupforpassageofgrove equipment.However,heavycuttingismore expensive,aninitialcropreductioncanbeexpected, andbrushdisposalismoretroublesomeandcostly. Hedgingisusuallydoneatanangle,withthe boomtiltedtowardthetreetopssothatthemiddles arewideratthetopthanatthebottom,allowing morelighttoreachtheskirtsofthetree.Hedging anglesbeingusedvaryfrom0to25degreesfrom vertical,with10to15degreesbeingmorecommonly usedandmoresatisfactory.Greaterhedgingangles resultinlongerexposureofthesidestosunlightand delayedovergrowthoftheskirtsbythemore vigorouslygrowingshouldersofthetrees.Withwide angles,toppingcansometimesbedonewithonepass oftheboominsteadoftwoorcanbeeliminated entirelyifthetreescometoapeakatasuitable height.Otheradvantagesofhedgingatwiderangles maybebetterspraycoverage,particularlyaerial,and moreefficientharvestingsinceahigherpercentageof thefruitisaccessibletopickersontheground. Possibledisadvantagesofextremeanglesareagreater initialyieldreductionwhentheyareimposedonolder trees,greaterstimulationoflong,undesirableshoot growthandgreaterexposureoffruittopossiblecold injury.Althoughmoreyieldreductionmayoccurif considerablefoliageisremovedwhenagreater hedgingangleisfirstimposed,yieldstendtodiffer little,ifany,betweenanglesinsubsequentyears. Fewgrovesarenowcrosshedgedtomaintain spacebetweentreesinbothdirectionsasthis operationisdifficultorimpossibleinbeddedgroves. Crosshedgingprovidednoincreaseinyieldorfruit qualityinseveralexperimentsinbothridgeand flatwoodgroves.Inolder,widelyspacedgroves,cross hedgingfacilitatedmovementofpickersbetweentrees andplacementoffruitcontainers.Italsomaintained fruit-bearingsurfacesonallsidesofthetrees,but doesnotnecessarilyincreasecanopybearingvolume peracre.Itisnotrecommendedincloselyspaced grovesandforbeddedplantingsystems.A15ftinrowspacingseemstobethelowerlimitforcross hedging.Wheretreesarecloselyplantedintherow, crosshedgingbetweeneverytwoormoretreesis morepracticalthancrosshedgingtomaintain individualtrees.Thisallowsthosebetweentogrow togetherasunitsoffoliage.Thedistancesbetween crosshedgingcutsshouldbeconsistentwith harvestingneeds.Perhapsamorepractical alternativewouldbetheremovalofeverythirdor moretrees,dependingontreespacingsandother considerations.Thisallowsgroupsoftwoormore treestogrowtogetherasunitsoffoliagewhile providingthedesiredspacingandreducingpruning requirements.Treestoberemovedcouldbe progressivelycutbacktoallownormalgrowthofthe permanenttreesandtakenoutwhentheywillno longerreturnaprofit.Treesmayberemovedby pullingwithafront-endloadercuttingthemoffat groundlevel.Crosshedgingortreeremovalresults inresumptionofvigorousweedgrowthinpreviously shadedgrovefloorareasandadisruptionofirrigation systems. Mostgrovesarehedgedinonedirectionsothat hedgerowsaremaintained.Wherepickerscomplain becauseofdifficultyinmovingbetweentreesand insufficientspaceforfruitcontainerplacement,a changeinharvestingpracticesmaybejustifiedfor hedgerowplantings.However,thegreatmajorityof newplantingswhicharedesignedtoprovidea continuoushedgerowasrapidlyaspossible,are apparentlybeingsuccessfullymanagedandharvested.

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CitrusTreePruningPrinciplesandPractices Page5ToppingToppingshouldbedonebeforetreeshave becomeexcessivelytallandshouldbeanintegralpart ofamaintenanceprogram.Longintervalsbetween toppingwillincreasecostsoftheoperationdueto heavycuttingandmorebrushdisposal.Excessively talltreesaremoredifficultandexpensivetoharvest andspray.Toppingtreeswillincreaselight penetrationintotreestherebystimulatingintense growthandflush.Itwillalsoreduceharvestingcosts, enhancepestanddiseasecontrolduetobetterspray coverage,andincreasefruitqualityandsize.Yield reductionduetolighttoppingisusuallynotgreatif treesstillhavetheirlowerskirtareas,especiallysince fruitdensityisgenerallygreaterinshortertrees. However,ifthetreeshavelosttheirlowercanopy bearingwood,alargereductioninyieldwilloccurin thefirstyearsincemuchofthefruit-producingwood andfoliagewouldberemoved.Toppingthesetrees wouldstillbebeneficialinthelongrunsinceitwould helpthemregaintheirskirtareasandbringthemto amoremanageableheight.Sincetoppingusually increasesfruitsize(byreducingcropload), fresh-marketfruitfromtoppedtreesmayhavea higherpackout. Sometreesareflat-topped,especiallyiftheyare smallornarroworhavebeenhedgedatawideangle. Closely-spacedrowsandthosewithasufficient hedginganglecanbeflat-toppedwithasinglepassof theboom.However,morearetoppedatangles whichmayvaryfrom15to30degreesfrom horizontal,resultinginapeakwhichis2ormoreft higherthantheshoulders.Anglesbetweenthese extremesarecommonlyused.Theslopeaids machinesinsweepingbrushfromthetops. Optimumtreeheightdependsonthedistance betweentrees,thehedgingangleandtreewidth. Toppingheightmayvaryfromabout10to20ft,but isusuallyabouthalfwaybetween.Somecommon toppingheightsare12to14ftattheshoulderand15 to16ftatthepeak.Lowerheightsaresometimes usedfortrainingtrees,increasingfruitsizeor rejuvenatingdecliningtrees.Tallertreesare sometimesmaintainedwhentheyarevigorousand widelyspaced.Treesintheflatwoodareasare generallytoppedlowerthanthoseontheridge becausethemorelimitedrootsystemswillusuallynot supportasmuchtopgrowth.Toppingshouldbe startedbeforeheavycuttingisrequired.Ifheavy cuttingisrequired,inoldergrovestheinitialcuts shouldbelowenoughtoavoidcuttingheavywoodin subsequenttoppingoperations.Retoppingis generallydonejustabovetheoldcut.PRUNINGPROGRAMSApruningprogramshouldbeginbeforeanyheavy cuttingisnecessaryandshouldbecontinuedat appropriateintervalssothatdesiredtree(hedgerow) sizeandshapecanbemaintainedatlowcostandwith minimumlossofcanopy.Regularmaintenance hedgingandtoppingremovesonlysmallportionsof thecanopy.Aregularpruningprogrameliminates thenecessityforlargecuts,avoidsexcessivevegetative growth,maintainsgoodfruitproduction,and simplifiesbrushdisposal.Maintenancehedging betweenrowsshouldbeginassoonastreesbeginto encroachonthedesigned7to8ftmiddlewidthso thatnotmorethanafootoffoliageisremovedfrom eachside.Byavoidingthestimulationofexcessive vegetativegrowthon Alternaria fungussusceptible varieties,suchas'Dancy','Minneola',and'Orlando', theseverityofthisdiseaseislessened. Hedgingprogramscanvaryconsiderablywith variety,treevigor,spacing,andgrowerpreference. Grovesona2-yearprogramarehedgedinone middleoneyearandtheothermiddlethenext.A3yearprogrammightconsistofhedgingonemiddlethe firstyear,theotherthesecondandtoppinginthe thirdyear.A4-yearprogrammaybequiteadequate forlessvigoroustreesorthoseplantedatawide spacing.Thepossibilitiesforhedgingandtopping schedulesarenumerousandshouldbedecidedonan individualbasis.Asoldergrovesarereplacedusing morecloselyspacedtreeswithpermanentlowvolume irrigationsystems,crosshedgingisnolongerfeasible. However,whereolderwidelyspacedgrovesstillexist withoutabovegroundirrigationlines,crosshedging maybeincorporatedintotheschedule.Grovesin whichtreesaremaintainedashedgerowsmayalsobe ona1-,2-,3-,or4-yearpruningprogram.Here,the growercanhedgeeverymiddleeveryyear;hedge alternatemiddleseveryyear;hedgeeverymiddle everyotheryear;hedgealternatemiddlesfor2years andtopthethirdyear;hedgealternatemiddlesevery otheryear;orhedgeallmiddlesevery4thyear. Annualorbiennialmaintenancehedgingispreferred formostgrovesofaveragetohighvigorinorderto reduceexcessiveencroachmentintomiddles,shading oftreeskirts,andbrushdisposalproblems. Thebesttimeofyeartohedgedependson variety,location,severityofpruning,andavailability ofequipment.Sincehedgingisusuallydoneafter

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CitrusTreePruningPrinciplesandPractices Page6removalofthecrop,earlymaturingvarietiesare generallyhedgedbeforethosewhichmaturelaterin theseason.Manyprefertohedgeearlybefore bloom,buttheymayalsogetmoreregrowthwhich mayormaynotbedesirable.Hedgingcouldbeginas earlyasDecemberinwarmerareas.Forcolder locations,itisbesttowaituntilthedangeroffreezing temperaturesispast.January,February,andMarch arethepreferredpruningmonthsformanygrowers. ModeratehedgingcanbedoneuntilJulywithlittleor nocroplossandperhapslessregrowth.Light maintenancepruningcanbedonethroughoutthe summeranduntilearlyfallwithlittleornolossin fruitproduction.Hedgingshouldnotcontinueinto thefallinfreeze-proneareasastreeswithtender regrowtharemoresusceptibletocoldinjury. Hedging`Valencia'orangeorlateharvested grapefruitpresentsaspecialproblembecauseof overlappingcrops.Hedginghasusuallybeendonein latespringaftertheoldcropisharvestedandthenew cropisset.Fruitharvestshouldbescheduledearlyin theseasonfor`Valencia'grovesthataretobe hedged.Goodresultshavebeenobtainedwhen annualhedginghasbeendoneinlatewinterwiththe oldcropstillonthetreeandbeforebloom.Thefirst cutisusuallydoneafterharvestandthenthegroveis rehedgedannuallyinJanuaryorFebruary.Whenthis isdoneannuallyatthesamewidth,thewoodand foliageremovedcontainsfewfruitandthereislittle ornoreductioninyield.Thekeytothisprogramis consistency. Toppingshouldnotbestartedincoldareasuntil afterthethreatoffreezingtemperaturesispastto avoidpossiblecoldinjury.Heavytoppingshouldbe completedintimeforexposedlimbstobecovered withnewgrowthbeforetheadventofhot,dry weatherinthelatespringandsummer.Adequate soilmoistureatthetimeoftoppingaidsrecovery. ToppinginAprilorMaywithoutgoodsoilmoisture isnotrecommended.Timingoflighttoppingisnot ascriticaliflittlefruitisremoved,butinfreeze-prone areasitisbestnottotopinthefalltoavoidpossible coldinjurytonewgrowthandexposedinternal scaffoldwood.Regrowthismorevigorouswhen toppingisdonebeforeamajorgrowthflush.Topping beforethespringflushresultsinnewgrowththatis moreleggythanwhenitisdoneatothertimes. Maintenancetoppingmaybedoneinthelatesummer whenregrowthshouldbelessvigorous.Closely-spacedGrovesManycitrusgrowershaveturnedtoclosertree spacingsasawayofachievinghigherearlyand sustainedfruityields.Favorableresultshaveusually beenobtainedinearlyyearsbutproblemsof over-crowding,excessiveregrowthfollowingpruning, andreducedyieldswilldevelopifhedgingand toppingarenotstartedassoonastreesreach containmentsize.Pruningvigoroustreesina closely-spacedplantingcanleadtoaperpetual problemofexcessivevegetativegrowthattheexpense offruitproductionunlessproperlycarriedout. Severecuttingshouldbeavoidedasmuchaspossible. Themorevigorousthetreesandthecloserthe spacing,thesoonerpruningshouldbestartedandthe morefrequentlyitshouldbedone.Thus,onlylight cuttingisnecessaryandcropreductionisminimized. Slow-growingtreesrespondmorefavorablytopruning andareeasiertomaintainatagivensizeandshape withoutsacrificingyield.Treevigorcanbecontrolled tosomeextentbyproperselectionofrootstockand scionandbymoderatingnutritionlevels,especially nitrogen.Growerswithclosely-spacedrowsof relativelyvigoroustreesoftenhaveaproblemwith multipleexposedcutsurfacesfromhedging.Pickers dislikethemandtheyareoftenstruckbyequipment withmutualdamage.Thismaybeavoidedbymore frequenthedgingoflessmaturewood.PruningEffectsonCropLoad,FruitSize,and QualityFruitsizeisveryimportantinfreshfruit operations,withsmallsizesoftenresultingina reducedpack-outandlowerprices.Insomecases largerfruitarespot-pickedandtherestofthecropis neverharvestedunlessitsizesupsufficiently.In moreseverecaseswithsomemandarinvarieties,an entirecropmaybeleftonthetreebecauseitisnot economicallyfeasibletoharvest.Somecultivars grownforfreshfruittendtosetveryheavycropsof smallfruitinsomeyearsandverylightcropsthenext year.Pruningafteraheavycropcanincrease alternatebearingandresultinasmallyieldofpoor qualityfruitthenextyear.Hedgingand/ortopping afteralightcropandbeforeanexpectedheavycrop canreducethenumberoffruitwithacorresponding increaseinfruitsizeandalsoreducealternate bearing.Thegrowermayelecttospeculateand prunebeforeanexpectedlargecropissetorwait

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CitrusTreePruningPrinciplesandPractices Page7untilafterfruit-setsothattheamountoffruit-setcan bemoreaccuratelydetermined.Thelattershouldbe donebeforethefruithasattainedappreciablesize sincelaterfruitremovalcouldresultinacrop reductionwithoutacompensatingfruitsizeincrease.SkirtPruningPruningtoraisetreeskirtshasbecomeamore widelyacceptedpractice.Untilrelativelyrecently littlesuchpruningwasdonebecauseofpossibleyield reductionandaddedexpense.Withlowtreeskirts themovementofherbicideboomsandother equipmentisimpeded,andtheinspectionof irrigationsystemsismoredifficult.Fruitandlimbs nearthegroundareoftendamagedbythepassageof suchequipmentbyherbicidesprayandfertilizer contact.Lowtreeskirtsmayalsoincreasethe incidenceof Phytophthoraparasitica ,thecausalagent offootrot,becauseofpooraircirculationunderthe treecanopy.Lowercanopyfruitisalsomore susceptibletobrownrot,theresultof Phytophthora citrophthora infectionundercertainenvironmental conditions.PruningafterFreezeDamageCorrectivepruningshouldbedelayeduntilthe fullextentoffreezedamagecanbedetermined. Sufficienttimeshouldbeallowedfornewgrowthto takeplaceandfordiebacktocease.Premature pruningcanresultinremovalofsomesoundwood andnotremovingsomewhichwillcontinuetodie back,bothofwhichcanslowtreerecovery.Injuryto foliageandtendershootsusuallybecomesvisible withinafewdaysbuttwigsandsmalllimbsmayshow littleornosignofcolddamagefor4to8weeksor more.Itmaybeseveralmonthsbeforesevereinjury tolargerlimbscanbefullydetermined.Therefore, pruningofmaturetreesshouldnotbedonefora least6monthsafterseverecolddamagehasoccurred. Wheremelanosefungusproducedondeadwoodis expectedtobeaproblemonnewgrowth,andthe cold-damagedcanopyareasareclearlydefined,earlier pruningmaybeadvised.Allpruningcutsshouldbe madeintolivingwoodbelowallseriousbarkdamage andatcrotches,ortoapointwherevigorousnew shootsaregrowing.Furtherlightpruningmay subsequentlybedonewhenneededtoaidinforming anewframework.RejuvenationLossoftreevigorinoldergrovesresultsin thinningofthefoliageandlowyieldsofsmallfruit, andisusuallyaccompaniedbydiebackoftwigsand smallbranches.Thisdeclinemaybeduetoage, disease,soilpests,waterinducedrootdamage,and othercauses.Thecauseofdeclineshouldbe determinedandcorrectedifpossible;otherwise, responsetorejuvenationpruningwillbetemporary. Ifthetrunkandbasicscaffoldlimbsoftreesarenot structurallysoundduetodisease,heartrot,andcold cankers,suchrejuvenationproceduresarenot justified.Alimitedrootsystemduetoahighwater table,ahardpanorpoorsubsoilcanresultinearly treedeclinewithtreesbeingmorereadilystressedby drought.Whenthisoccurs,thetopbecomesoutof balancewiththemorelimitedrootsystemwith consequentinsufficientuptakeofwaterandnutrients bytheroots.Toppingthesetreesshouldtemporarily restorethemtoamorefavorabletoptorootratio, butnotalleviatethelong-termproblem.Theseverity ofpruningforrejuvenationwilldependonthecause anddegreeofdecline.Skeletonization,theremoval ofallfoliageandwoodsmallerthan1-1/2in.in diameterinvigoratesthetreeandresultsin productionoffruitingwoodthroughouttheremainder ofthetree.However,itiscostlyandthecropislost forayear.Buckhorning,cuttingbackthescaffold limbstoaheightof5to6ftabovetheground,isthe mostsevereformofrejuvenationpruning.Itgreatly reducestreesizeandresultsinvigorousregrowth. Largewoundsremainandproductionislostforabout 3years. Itisadvisabletopaintlargecutsurfacesonor nearthetrunkbutitistoocostlyandunnecessaryto coverwoundshigherinthetreewhichresultfrom hedgingandtopping.Awhitelatexpaintthatis non-phytotoxicappearstobequitesatisfactory. Severetoppingforrejuvenationorfollowinga freezewhichexposeslargelimbsandtrunksthathave grownintheshademayresultinseveresunburnwhen doneduringorshortlybeforehot,dryweather.An applicationofwhitelatexpaintusingapowersprayer ismoreefficientwherelargenumbersoftreesare involved.PRUNINGEQUIPMENTPruningequipmentisavailableforpurchaseor usethroughcustomoperators.Whilesmall equipmentmaybemoreeconomicalforlightpruning andintightareas,forlargeequipmentheaviercutting willdobetteratalowercost.Nomatterwhat

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CitrusTreePruningPrinciplesandPractices Page8equipmentisused,bladesshouldalwaysbekeptsharp astheydoabetterjobandrequirelesspower.Hand-HeldPrunersHand-heldequipmentmaybeusedforselective pruningwhererelativelyfewtreesareinvolved.The simplestandleastexpensivepruningtoolsare poweredbyhand,andincludehandshears, long-handledloppersandpruningsaws.Thesaw bladesaregenerallycurved,cutwhenpulled,andfold foreasycarrying.Handpruninghasbeenmade easierwithloppersorsawspoweredbyair,electricity, orhydraulics.Itisimportantthatthepowersource isadequatetomeetthedemandsplaceduponit; otherwise,theoperationmaybeslowerandrepairs morefrequent.Thecuttingbladesareusuallyatthe endsofpolesofvariouslengthswhichextendthe reachoftheoperator.Platformsforreachinghigher inthetreeincludeladdersformanually-poweredtools andmobileplatformsforsmallpowertools.Special one-manmachinesaremarketedbyseveral companies,andothertreefruitgrowershavemounted platformsontrucksandtractors. Withallthis equipment,goodsafetymechanismsandoperator trainingareabsolutelyessential. Hedgingmachinesvaryconsiderablyinsizeand design,rangingfromatractor-mountedverticalboom witharowofbelt-drivencircularsawstoratherlarge machineswithtwoboomsmountedona self-propelledortractor-pulledchassis.Somehave straightboomswitharowofsawsoneachboom. Othershaveboomswithrotatingcrossarmswitha sawattheendofeach.Thelargermachinescando heavycuttingmoreeasilyandrapidly.Theboomson manymachinescanbeadjustedtothedesiredwidth andangle.Toppingmachinesalsovaryfrom tractor-mountedboomstolargermachinesthatare self-propelledortractor-drawn.Theyalsohave straightorrotatingboomswhichcanbeadjustedto thedesiredtoppingangle. Preparationforhedgingortoppingshouldinclude havingthegroundaslevelaspracticalsothatthe machinewillnotbeslowedbyrutsorother impediments,andadequateturnareasshouldalsobe provided.Beforetopping,risersofoverhead sprinklersmustbetakendownandpriorhedgingis sometimesneededtofacilitatemovementofthe machinethroughthegroveandtoallowthebrushto fallintothemiddles.Whilemachineswillworkin beddedplantingstheiroperationismoredifficult, timeconsuming,andhazardous.Hazardstobe consideredincludeguywires,fences,ditchesand roadways.SpreadofDiseasebyPruningCertainvirusdiseasescanbespreadbypruning equipment,particularlyhand-heldequipment. Cautionshouldthereforebeexercisedwhenmoving equipmentfromasuspectedvirusinfectedblockto oneassumedtobeclean.Aswithanygrove equipment,goodsanitationprocedureswillreducethe incidenceofpestanddiseasemovement.BRUSHDISPOSALThebrushthatresultsfromheavypruningoften presentsthegreatestproblemandexpense.Brush disposalcanbehandledinseveralwaysdependingon amountandsize.Nospecialoperationisnecessary whenbrushisrathersmallsinceitwilldecaywhereit fallsorbeshreddedinroutinemowingoperations. Goodweedcontrolinrowmiddlesissuggestedbefore pruningasremovalofbrushentangledwithheavy weedgrowthcompoundstheproblem.Rotary mowerswhichhavebeenwidelyusedformanyyears arequiteadequatewhenneithertheamountnorsize ofthebrushisgreat.Themowersbeingusedare designedforheavycuttingandareoftenfurther reinforcedforaddedstrength.Safetyprecautions mustbetakentoavoidinjurybyflyingdebris.This typeofequipmenthasbeenusedoncitrusbrushup to3or4in.indiameter,butlargerwoodshouldbe removedfromitspath.Themowershouldgoover thebrushonthedayitiscutortheoperationshould bedelayeduntilthebrushisbrittle.Large, self-propelledbrushshreddersweredevelopedwhich couldshredwooduptoseveralinchesindiameterby meansofheavysteelhammersorteeth.These machineswereusefulinheavybrushsituations,but arenolongerusedinFloridaduetothehigh operationalcosts.SUGGESTEDREADINGBoswell,S.B.andD.R.Atkin.1978.Comparisonof two'Washington'navelplantingsatseveral densities:Avigorousscion-rootstockcombination vs.aslessvigorouscombination.Proc.Fla.State Hort.Soc.91:40-43. Cary,P.R.1981.Citrustreedensityandpruning practicesforthe21stcentury.Proc.Int.Soc. Citriculture1:165-168.

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CitrusTreePruningPrinciplesandPractices Page9Castle,W.S.1978.Controllingcitrustreesizewith rootstocksandvirusesforhigherdensity plantings.Proc.Fla.StateHort.Soc.91:46-50. Koo,R.C.J.andR.P.Muraro.1982.Effectoftree spacingonfruitproductionandnetreturnsof 'Pineapple'oranges.Proc.Fla.StateHort.Soc. 95:29-33. Phillips,R.L.1972.Hedginganglesfor'Hamlin' oranges.Proc.Fla.StateHort.Soc.85:48-50. Phillips,R.L.1974.Performanceof'Pineapple' orangeatthreetreespacings.Proc.Fla.State Hort.Soc.87:81-84. Phillips,R.L.1978.Hedgingandtoppingcitrusin high-densityplantings.Proc.Fla.StateHort.Soc. 91:43-46. Tucker,D.P.H.andT.A.Wheaton.1978.Trendsin highercitrusplantingdensities.Proc.Fla.State Hort.Soc.91:36-40. Wheaton,T.A.,W.S.Castle,D.P.H.TuckerandJ.D. Whitney.1978.Higherdensityplantingsfor Floridacitrus-concepts.Proc.Fla.StateHort. Soc.91:27-33. Wheaton,T.A.,W.S.Castle,J.D.Whitney,D.P.H. TuckerandR.P.Muraro.1990.Ahighdensity citrusplanting.Proc.Fla.StateHort.Soc.103:5559. Wheaton,T.A.,J.D.Whitney,W.S.CastleandD.P.H. Tucker.1986.Treespacingandrootstockaffect growth,yield,fruitquality,andfreezedamageof young'Hamlin'and'Valencia'orangetrees.Proc. Fla.StateHort.Soc.99:29-32. Wheaton,T.A.,J.D.Whitney,D.P.H.Tuckerand W.S.Castle.1984.Crosshedging,treeremoval, andtoppingaffectfruityieldandqualityofcitrus hedgerows.Proc.Int.Soc.Citriculture1:109-114. Whitney,J.D.andS.L.Hedden.1978.Equipmentand methodsforproducingandharvestingcitrusin higherdensityplantings.Proc.Fla.StateHort. Soc.91:52-55. Whitney,J.D.andT.A.Wheaton.1984.Treespacing affectscitrusfruitdistributionandyield.Proc. Fla.StateHort.Soc.97:44-47.