Dramaticneedlebrowningandcanopydiebackofeasternwhitepine(Pinusstrobus)insouthernNewEngland
NicholasJ.Brazee,Ph.D.ExtensionPlantPathologist Duringthespringof2016,adramaticdeclineofeasternwhitepine(Pinusstrobus)hasbeenobservedthroughoutsouthernNewEngland.Needlesofmaturetreesbecomestraw‐coloredtobrownbeforetheyareprematurelyshedfromthecanopy.Insomecases,onlyafewmainbranchesaresymptomaticwhereasonothertrees,theentirecanopyexhibitsthesymptoms(Fig.1).Onefeatureofthedeclineisthatdespitesignificantneedlebrowningandprematuresheddinginthecanopy,thecurrentseason’sneedlesareelongatingandappearhealthy(Fig.2).
FIGURE1.EASTERNWHITEPINEONTHEUMASSCAMPUSWITHEXTENSIVENEEDLEBROWNINGANDPREMATURE
SHEDDINGTHATDEVELOPEDINSPRINGOF2016.
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FIGURE2.DEVELOPINGCANDLES(BRANCHLETS)WITHCLUSTERSOFMALECONESAREABUNDANTWHILEOLDER
NEEDLESBECAMEBROWNANDWEREPREMATURELYSHED.
Basedonobservationsfromarborists,landscapersandhomeownersmadetotheUMassPlantDiagnosticLaboratory(UMPDL),whitepinedeclineseemstobeespeciallysevereinsoutheasternNewHampshire,easternMassachusettsandeasternConnecticut.Thecauseofthisdramaticdeclineeventisnotentirelyunderstood,asthereareseveralinteractingstressesthatmustaccountedfor.However,needleblightpathogenshavebeenaprimaryissueaffectingwhitepinesinceapproximately2010.RecentstudieshaveidentifiedseveralfungalpathogensareresponsibleforwhitepineneedleblightinNewEngland(Brodersetal.2015,WykaandBroders2016).Fourneedleblightfungiinparticularhavebeenidentifiedastheprincipalpathogensassociatedwithwhitepineneedleblightintheregion(Wykaetal.2016)andinclude:
1. Lecanostictaacicola(formerlyMycosphaerelladearnessii)2. Lophophacidiumdooksii(formerlyCanavirgellabanfieldii)3. Bifusellalinearis4. Septorioidesstrobi
BasedonsamplessubmittedtotheUMPDL,threeofthesefourpathogenshavebeenregularlyfound
onwhitepineswithsymptomsofneedleblight(Lophophacidiumhasbeenuncommontodate).Evidencenowsuggeststhereisastronglinkbetweenclimatechangeandtheincreaseindamagefromneedleblightpathogensofwhitepine.Usingregionalweatherdata,Wykaetal.(2016)determinedthatanincreaseinprecipitationduringthemonthsofMay,JuneandJuly—thetimeperiodwhenwhitepineneedlesareelongating—ispositivelycorrelatedwithdamagefromneedleblightpathogens.However,asisthecasewithmanyconiferneedlepathogens,thateffecthasaoneyeardelay.Forexample,above‐averageprecipitationbetweenMay–Julyin2016wouldcorrelatetohigherdiseasepressurein2017.
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Therefore,wemustgobacktothegrowingseasonof2015tobetterunderstandwhatfactorsmightbeinfluencingthedamagedobservedthisyear.Duringthespringof2015,Maywasextremelydrywithabove‐averagetemperaturesandbelow‐averageprecipitationwasalsorecordedfromJulythroughSeptemberintheareaswherewhitepinedeclineappearstobethemostsevere(Fig.3).June,incontrast,wasverywetandthereweremultiplerainstormswithaccumulations>0.75″(Fig.4).Heavyrainspromotesporulationanddispersesignificantvolumesofneedleblightpathogensporesthroughsplashingandrunningwater.Despitetheabove‐averagerainfallinJune,therestofthegrowingseasonwasfairlydryandmanytreesmayhaveenteredthedormantperiodsufferingfromdroughtstress.
FIGURE3.BELOW‐AVERAGEPRECIPITATIONDURINGMAY(LEFT)ANDFROMJULYTHROUGHSEPTEMBER(RIGHT)IN2015.
FIGURE4.ABOVE‐AVERAGEPRECIPITATIONDURINGJUNEOF2015.
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BeginninginJulyof2015,theUMPDLbegantoreceivewhitepinesampleswithanuncharacteristicsymptom:blightedtipsoncurrentseason’sneedles.Symptomsofinfectionfromneedleblightfungitypicallydeveloponolderneedleswhilethecurrentseason’sneedlesappeargreenandhealthy.TheconditionwasreportedfromWestVirginiatoMainebutaffectedtreeswerescatteredonthelandscapeandinmanycasesweredirectlyadjacenttohealthytrees.Onamajorityofthesamples,anunknownfungalpathogenwaspresentthatwaslateridentifiedasSeptorioidesstrobi.WhilethisspecieswasonlyrecentlydescribedithasbeenfoundtobeassociatedwithwhitepineneedleblightthroughoutnortheasternNorthAmerica(WykaandBroders2016,Wykaetal.2016).Mostoften,needletipswerestraw‐coloredtobrownwhilethebaseoftheneedleremainedgreenandhealthy.Needlelesions,sporemassesandcolorless,asexualsporesareshownbelow(Figs.5&6).
FIGURE5:BLACK‐COLORED,CIRCULARLESIONSEXTRUDINGCLEARMASSESOFSPORESONBLIGHTEDNEEDLETIPS.
FIGURE6:ASEXUALSPORESPRODUCEDBYSeptorioidesstrobi.
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Asweenteredthelastmonthsofthe2015calendaryear,temperaturesthroughouttheregionwereabove‐average,especiallyinDecember(Fig.7).Thesewarm,lateseasontemperaturesmayhaveadverselyaffectedtheabilityofwhitepinestoacclimateforcoldwintertemperatures.Droughtstressisalsoknowntoreducewinterhardiness.OncetemperaturesbecamemoreseasonableinJanuaryandFebruary,coldinjurymayhavebeeninflicted.However,theeffectofwarm,lateseasontemperaturesisspeculativeandmaynotbeacurrentfactorinwhitepinedecline.
FIGURE7:ABOVE‐AVERAGETEMPERATURESFROMOCTOBERTHROUGHDECEMBER(LEFT)THATWERE
PARTICULARLYPRONOUNCEDINTHEMONTHOFDECEMBERALONE(RIGHT).
Tosummarize,thecurrentdeclineofeasternwhitepineisnotfullyunderstoodandwilltakemanymoremonthstobetterunderstand.However,thefollowingfactorsshouldbeconsideredinthedecline:
1. Multipleneedleblightpathogensthatmayormaynotco‐occuronthesametree.2. IncreasedprecipitationinthemonthsofMay,JuneandJulythatwouldpromoteneedleblight
infectionsondevelopingwhitepineneedles.3. Environmentalstresssuchasdrought.4. Branchcankering?CankeringbythefungalpathogenCaliciopsishasemergedasasignificantthreat
toforestwhitepines(seeMuncketal.2015)butmaynotbeasimportantinlandscapesettings.LiteratureCited:
1. Brodersetal.,2015.Characterizationoffungalpathogensassociatedwithwhitepineneedledamage(WPND)innortheasternNorthAmerica.Forests6:4088–4104.
2. Muncketal.,2015.ExtentandseverityofCaliciopsiscankerinNewEngland,USA:anemergingdiseaseofeasternwhitepine(PinusstrobusL.).Forests6:4360–4373.
3. WykaandBroders,2016.ThenewfamilySeptorioideaceae,withintheBotryosphaerialesandSeptorioidesstrobiasanewspeciesassociatedwithneedledefoliationofPinusstrobusintheUnitedStates.FungalBiology(Inpress).
4. Wykaetal.,2016.EmergenceofWhitePineNeedleDamage(WPND)inthenortheasternU.S.isassociatedwithchangesinpathogenpressureinresponsetoclimatechange.GlobalChangeBiology(Inpress).