Effects Of Cultural Practices On Cold Protection

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Title:
Effects Of Cultural Practices On Cold Protection
Physical Description:
Fact Sheet
Creator:
Jackson, Larry K.
Publisher:
University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS
Place of Publication:
Gainesville, Fla.
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Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Melanie Mercer.
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Published
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"Publication date: June 1992. Reviewed: June 1994."
General Note:
"HS-119"

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University of Florida Institutional Repository
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University of Florida
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IR00003737:00001


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FactSheetHS-119 June1994EffectsofCulturalPracticesonColdProtection1 L.K.Jackson2Therelationofculturalpracticestofreeze damagewillrefertoradiationfreezesunlessotherwise stated.Advectivefreezes,suchasthosethatoccurred inthe1980's,behavedifferently.Mostofthe principlesinthefollowingapplyforallfreezesbutare lesseffectiveduringwindyfreezesbecauseofthe rapidairmovementandtransportofcoldairduring theseevents.SOILMANAGEMENTThetextureandcolorofsoilsaffecttheirability toabsorb,storeandradiateheat;however,such characteristicscannotbemanipulatedinan establishedgrovesotheyarenotconsideredhere.On theotherhand,modifyingthegrovefloorandadding soilmoistureoffersamajormeansofpassivecold protection.Muchmoreheatcanbestoredand conductedbetterinmoistthanindrysoil.Also, compactsoilwithafirmsurfaceisabetterconductor ofheatthanloosesoilwhichhasbeenrecently cultivated.Weeds,sodandlitterareeffectiveheat insulators.Theyreduceboththeheatabsorbedduring thedayandthatemittedatnight.Weeds,particularly highweedsinmiddles,impedetheflowofcoldair downslopesandaredeleterious.Therefore,soil shouldbemanagedsoitisasfreefromweedsand litteraspossible,moistandcompact.Dataastothe degreeofeffectivenessoftheaboveissparsebut observationsconfirmtheimportanceofthese conditions.Temperaturedifferencesbetweensodand otherweedcontrolsystemsweresmallestwhenitwas closelymowedandgreaterwhenheightofweedswas increased.Recentlycultivatedsoilsresultedinlower temperaturesthanthattilledearlyenoughtoletthe soilcompact.MostFloridagrowersherbicidethetree rowbutnotthespacesbetweentrees,whichiseither mowedorcultivated.Also,manygrowershavelow volumeirrigationthatwetsonlypartofthesoil surface.Herbicidingtheentiregrovefloorandusing asystemthatwetsasmuchofthesoilareaaspossible shouldenhanceprotectionfromaradiationfreeze andmayevenprovideassistanceinthecaseof advectivefreezes.Weedsinthegroveduringthe wintermayalsobeaseriousfirehazard,especially aftertheyaredesiccatedfromdroughtorfrost.IMPEDINGAIRDRAINAGEGoodairdrainageisrecognizedasoneofthe majorfactorsdeterminingthewarmthofasiteduring radiationfreezes.ThisisparticularlytrueforFlorida's Ridgeareawhichhasmanyhills,oftenwithlakesat thebottom.Weedsalsohaveharmfuleffects(see "SoilManagement").Also,damsofbrushortreesat thefootofaslopecangreatlychangethe temperatureofatleastaportionofaslopeby blockingtheflowofcoldairtolower-lyingland. Brushandtreedamsaremostlikelytooccuratedges ofswampyareasandlakes.Growersattimesdrag pruningrefusetothebottomoftheslopeandthereby createatemporarydam.Removingthebrushand 1.ThisdocumentisFactSheetHS-119,aseriesoftheHorticulturalSciencesDepartment,FloridaCooperativeExtensionService,Institute ofFoodandAgriculturalSciences,UniversityofFlorida.Publicationdate:June1992.Reviewed:June1994. 2.LarryK.Jackson,professor,extensionhorticulturist,DepartmentofFruitCrops,CitrusResearchandEducationCenter,LakeAlfred, Florida,abranchcampusoftheUniversityofFlorida,GainesvilleFlorida. 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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EffectsofCulturalPracticesonColdProtection Page2treesorthepruningrefuseentirelyorevencuttinga numberofswathsthroughthemwillhelpalleviatethe problem.TREESPACINGANDROWORIENTATIONPlantingswithwidespacesbetweentreesare colderthanthosespacedmorecloselybecausethere ismoretreemassperacre,morecanopytointercept radiantheatfromthesoil,andbecausethereismore transferofradiantheatbetweencloselyspacedtrees. Treesplantedinarectangleonaslopeshouldhave rowsrunupanddowntheslope.Therowsshouldbe keptprunedbyhedgingformaximumairdrainage. Thismayconflictwiththebenefitsofrunningrows northandsouthtoprovidemaximumlightontree sides.Thecoldhazardusuallyoutweighsanybenefits ofaddedlight.Hedgerowingacrosstheslopeserves asadamthatimpedesairdrainagejustasbrush, trees,andhighweedsdo.Iftreesareplantedsoclose inarowthathedgingismandated,thenoccasional linesoftreesrunningdowntheslopeshouldbe removedtoprovideforairdrainage.Somegrowers feel"liftingthetreeskirts"(removingthelower branches)willpermitthecoldairtoflowunderthe trees,anditwill.Thisreducesthebeneficial microclimateeffectofthecanopy.However,"lifting theskirts"benefitssprayapplicationandother culturalpractices.Therefore,thegrowerwillhaveto choosewhichculturalpracticehaspriority. Interestingly,plantingsatveryhighdensitiesare moreeffectiveatblockingthewindintheeventofan advectivefreeze.Withwindyfreezes,minimizationof windmovementmaybebeneficial.PRUNINGAlthoughahedgedandtoppedgroveisprobably slightlycolderthanacompletelycanopiedone, growershavenochoicebuttohedgetreesidesand topinordertofacilitateharvestingandpestcontrol andtomaintainmaximumyield.Severelytopping treesjustpriortoorduringthefreezeseasonisa majormistakebecauseitdestroysthecanopyandits attendantadvantages.Hedgingduringthisperiodis likelytoreducetheeffectivenessofthecanopybut notnearlyasmuchastopping.Ontheotherhand, hedgingandtoppingwellbeforethefreezeseasoncan stimulatethegrowthofathickercanopyandbe advantageous.Therearenoresearchdatatoconfirm theaboveviews,onlyobservationsandlogicbasedon theprinciplesofphysics.PESTANDDISEASECONTROLTheobjectiveofpestanddiseasecontrolin protectingagainstfreezedamageistomaintaina densecanopyandavoiddebilitationofthetree. Virus-damagedtreesarereportedlymoresusceptible tofreezedamage.Theprimarypestsanddiseasesthat causeleafdropandtherebytendtoreducethe warmthofthemicroclimateunderthecanopyare greasyspotandmites.Severeleafdropcouldalso debilitatethetree.Theleveltowhichvaryingdegrees ofleaflossreducethecanopyeffectanddebilitates thetreehasnotbeendocumented.Itisquitepossible thatslightormoderateleaflosshaslittleornoeffect; however,growerswithchronicallycoldareaswouldbe welladvisedtomaintainadensecanopy.MINERALNUTRITIONThebulkofevidenceindicatesfreezedamageis notinfluencedbyanymineralelementassuch. Maximumcoldhardinesscomesfrommaintaininga densecanopyofleavesthatarenotdeficientinany mineralelement.Deficienciesofmagnesium(Mg) causedsevereleaflossseveraldecadesagoandgave risetothesuggestionthatmagnesiumwasdirectly relatedtocoldhardiness;however,itsinfluenceon hardinessappearstobethroughitseffectonleafdrop andnottoagivenlevelofMginleaves.Likewise,it iswelldocumentedthathighlevelsofpotassiumalso donotincreasehardiness.Lateapplicationsof nitrogenthatcauseexcessivegrowthanddelaythe developmentofwinterdormancyreducescold hardinessandshouldbeavoided.IRRIGATIONReducingirrigationinthefallandearlywinter wasshowntoinducedormancyandincreasecold hardiness.However,waterdeficiencysevereenough toweakenthetreeandcauseleafdropreducescold hardiness.Itappearslogicaltowithholdenoughwater infallandearlywintertoinduceearlydormancy,or atleastnotdelayit,butwaterstressshouldnotbe developedtoapointwherearainwouldforcenew growthanddestroydormancy.Laterinthewinter whendormancyandhardinessarecontrolledbythe temperature,irrigationshouldbeusedtoprovidea maximumreservoirofheatandoptimumconduction ofheatintothesoilduringthedayandoutatnight.

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EffectsofCulturalPracticesonColdProtection Page3MANAGINGFREEZE-DAMAGEDPLANTINGSWheretheextentofdamageissufficientlylimited thataneffectivecanopydevelopsbythefollowing winter,emphasisshouldbeplacedonrepairingthe canopythroughoptimumwater,fertilizerandpest anddiseasecontrolduringthesummer,enhancing developmentofdormancythroughwithholdinglate applicationsoffertilizerandbyrestrictingwateruse asmuchasisfeasibleinthefall.Weed-control, maintenanceofadequatesoilmoistureandavoidance ofdamsofbrushorpruningrefuseatthefootof slopesshouldbeemphasizedduringthewinter. Killingbacktoframeworkbranchescreatesdifferent demandsandoptions.Lackofcanopyreducestree massandthecanopy'sroleasacoverorshieldis destroyed.Somegrowersleavelongframework brancheswhenpruningfreeze-damagedtrees.It wouldhavebeenbettertocutbackmoreseverelyto forceoutaprotectivecanopysooner;however,no pruningpracticeswilldevelopanadequatecanopyby thewinterfollowingthefreeze.Largelimbswith sparsefoliageabsorbmuchheatduringthedayand thebarkisprobablymoreactiveandsusceptibleto colddamagethanshadedones.Littleattentionhas beengiventothissituationforcitrus.Spraying whitewashorwhitepaintoncitrustreeshasbeen usedtopreventsundamagetobarecitrusbranchesin thespringandsummerbutnotinduceormaintain dormancyandcoldhardinessinthefallandwinter followingafreeze.InFlorida,wheresundamageis notlikely,whitewashingdelaysnewgrowthand canopydevelopmentasmuchastwoweekswhen appliedinthespring.Applyingwhitewashspraysto barelimbsinfallandwintershouldenhance dormancy.Whitelatexpaintappliedtothetrunksof peachtreesduringthewinterhavebothlowered trunktemperaturesgreatlyandreducedseverefreeze damagetothem.Modificationofculturalpracticesto maximizetreewarmthandcoldhardinessmayrun contrarytoothermanagementobjectivesattimes.For example,smallorevenmodest-sizedtreesmightbe subjecttoblowingsandifsoiliscompletelybarefrom treetotree,makingitnecessarytoleavestripsof mowedcoverperiodically.Suchfactorsmustbetaken intoaccountandacompromisereached.