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).