Association of Pine Wood Nematode with Stressed Treesin Minnesota, Iowa, and Wisconsin

M. J. WINGFIELD and R. A. BLANCHETTE, Department of Plant Pathology, University of Minnesota, St. Paul55108, T. H. NICHOLLS, North Central Forest Experiment Station, and K. ROBBINS, State and Private Forestry,U.S. Forest Service, St. Paul 55108

ABSTRACTWingfield, M. J., B!anchette, R. A., Nicholls, T. H., and Robbins. K. 1982. Association of pinewood nematode with stressed trees in Minnesota, Iowa, and Wisconsin. Plant Disease 66:934-937.

Trees infected with the pine wood nematode BursapheJenchus xylophiJusin Minnesota, Iowa, andWisconsin were stressed by various forest diseases and insects. Nematodes were only found in treesalready colonized by secondary insects such as bark beetles (Scolytidae) and borers(Cerambycidae). B. xylophilus was also found in dead tops or dead branches of otherwise healthytrees that appeared to have died as a result of fungal infection or insect attack. Typical wiltsymptoms associated with B. xylophilus infection in Japan were not observed.

The pine wood nematode Bursaphelen.chus xylophilus (Steiner and Buhrer):Nickle (formerly B. lignicolus Mamiyaand Kiyohara [13]) causes a wilt diseaseof pines in Japan. Extensive losses toJapanese black pine (Pinus thunberghiiParI.) and Japanese red pine (P,densiflora Sieb. et Zucc.) have occurredin southwestern Japan (17). B. xylophilusis vectored primarily by longhorn beetles(Coleoptera: Cerambycidae) that emergefrom dead trees carrying the dauer larvaeto healthy trees where they enter feedingwounds caused by the beetle (9,1 I). Thenematodes mature and reproduce rapidly

Paper 11,969, Scientific Journal Series, MinnesotaAgricultural Experiment Station, St. Paul 55108.

Accepted for publication 3 Fo:bruary !982.

The publication costs of this article were defrayed in partby page charge payment. Thisarticle must therefore behereby marked "adverlisement"' in accordance with 18U.S.C. §1734 solely to indicate this fact

0191-2917/82/10093404/$03.00/0c1982 American Phytopathological Society

934 Plant Disease/Vo1. 66 No. 10

in the resin canals, resulting in reducedoleoresin flow, arrest of transpiration,chlorosis, and death within 3 mo afterinitial infection (7). Cerambycid beetlesoviposit in dying trees, and the life cycleof the nematode, closely coordinatedwith the beetle vector (I8), is repeated.

B. xylophilus was reported from theUnited States in 1979(4) where it was firstfound on Austrian (P. nigra Arnold) andScots (P. sylvestris L.) pines in Columbia,MO. The nematode has now beenreported in 33 states on 20 pine species,atlas cedar (Cedrus atlamica Manetti),deodar cedar (c. deodara (Roxb.)Loud.), European larch (Larix deciduaMilL), tamarack (L. laricina (Du Roi) K.Koch), and white spruce (Picea glauca(Moench) Voss) (18). Since the firstreport, concern has been expressed thatB. xylophilus poses a threat to forests ofthe United States similar to that apparentin Japan (I8). This report documents theresults of a 2-yr field investigation madeto establish the relative importance of thepine wood nematode in a number of

study sites in Minnesota, Iowa. andWisconsin.

MA TERIALS AND METHODSAreas in which B. xylophilus was

found in a preliminary survey to beassociated with a considerable number ofdead or dying trees were chosen forfurther examination. The following areaswere examined during the summers of1980 and 1981: Zimmerman, M?'\(Sherburne County), 18-yr-old Austrianand red pine (P. resinosa Ait.) in an oldChristmas tree plantation; Cloquet. M?\(Carlton County), 30-yr-old easternwhite pine (P. strobus L.), CloquetForestry Center, University of Minnesota;Durand, WI (Pepin County), I5-yr-oldAustrian and red pine in an old Christmastree plantation; Black River FalJs, WI(Jackson County), 20-yr-oldjack pine (P.banksiana Lamb.), Gordon plantation;Btack River Falls, WI (Jackson County),15-yr-old red pine, Shamrock plantation;Farmington, IA (Lee and Van Burencounties), 20-yr-old Scots and red pine,Shimek State Forest.

Healthy as well as dead or dying treeswere examined for root, stem, branch,and needle disease symptoms. Isolationsfor fungi from diseased portions of thetree were made on 2% malt extract agar(20 g of Difco malt extract and 20 g ofDifco Bacto agar per 1,000 ml of water).Samples for nematode extractions weretaken from roots; bottom, middle, andtop thirds of the bole; lower branches;upper branches; and small twigs of eachtree sampled. Disks of wood about 15em

Number of trees infested with

Trees sampled Bark beetles Borers Other diseasesTree health (no.) (Scolltidae) (Cerambyddae) B. xylophilus and insects.

Living 4 0 0 0 D~BDead top 8 8 8 6 D~B

ZPMDead branches 4 4 4 3 D~B

ZPMDead or dying 4 4 4 4 D:\B

ZP~1

living 2 0 0 0Dead top 6 6 6 4 WPBRDead branches 2 2 0 0 WPBRDead or dying 3 3 3 3 WPBR

ARRVRD

thick were removed \\Iith a chain sawfrom the root and bole samples: branchesand twigs were randomly remO\-ed usingpruning shears. Nematodes were extractedfrom 60- to 90-g(fresh weight) subsamplesusing Baerman funnels. The generalhealth of surrounding trees and thepresence of insects on sample trees weredocumented.

RESULTSZimmerman, MN. Red pine were

healthy, whereas many Austrian pine onthis site were dead and dying (Fig. I).Austrian pine had severe Dothistromaneedle blight caused by DOlhisIromapiniHulb. and held only current-year needles.About half the Austrian pine in the areahad dead tops or dead branches in the topthird of the crown (Fig. 2) associated withsevere infestations of the Zimmermanpine moth, Dioryctria zimmermani(Grote), which results in copious resinexudation at the base of the dead parts(Fig. 3). Four living Austrian pine treeswere sampled and found free of B.xyJophi/us and other disease-causingorganisms. B. xyJophiJus was only foundin dead portions of Austrian pine withdead tops or branches and in all deadtrees or trees with chlorotic needles thatwere infested by bark beetles (Coleoptera:Scolytidae) and wood borers (Coleoptera:Cerambycidae) (Table I).

Cloquet. MN. A large number of thewhite pine had dead branches or deadtops resulting from white pine blister rust(Cronartium ribicoJa J. C. Fischer exRhabh.) infection. In some cases, treesinfected with blister rust were chloroticand dying. These trees had Armillariellamellea(Vahl) ex Karst. and Verticicladiellaprocera Kendrick root infections (6). B.xyJophiJus was not isolated from healthytrees or trees with blister rust infection.The nematode was, however. present indead tOps and in the bole of trees thatwere chlorotic and infested by insects(Table I).

Durand, WI. No mortality occurred in

red pine. whereas about 70% oi theadjacent Austrian pine trees were dead ordying (Fig. 4). Austrian pine needles wereheavily infected with DOlhislroma pini,and branches only held the current-yearneedles. In addition, most of the trees hadadvanced pine root collar weevil(Hylobius radicis Buch.) infestation,resulting in resin exudation in the rootcollar area (Fig. 5). B. xylophilus was notextracted from trees with green needlesbut was present in all dead or dying treescolonized by insects (Table 2).

Black River Falls, WI (Gordonplantation). About 95% of the 2.000 jackpine in the study area were dead or dying(Fig. 6). All living and dead or dying jackpine had pine root weevil(H. rhi;:ophagusM.B.W.) infestation. Red pine insurrounding stands were healthy. Smallertwigs and branches of trees were damagedby hail and insect feeding and wereinfected by Diplodia pinea Kickx. (Fig.7). Dead twigs of otherwise healthy treeswere free of B. xylophilus. Dead or dyingtrees, some with early bark beetle andborer attack, contained B. xylophilus.Otherwise healthy trees with early rootweevil infestation, without crownsymptoms and before bark beetle andborer infestation, did not comain B.xylophilus (Table 2).

Black River Falls, WI (Shamrockplantation). About 50% of the 800 redpine in the study area had dead tops (Fig.8) caused by DipJodia pinea infection. Inthree out of 10 cankered trees sampled,dead tops contained B. xyJophilus andhealthy parts of the same trees were freeof nematodes (Table 2). B. xylophi/us,bark beetles, and borers were notdetected in any of the healthy treeSsampled.

Farmington, IA. Red pine and Scotspine had hail~initiated Diplodia pineacankers on the boles and branches.Cankers on Scots pine were larger andmore numerous, causing death of smallerbranches. About 50% of the 1,200 Scotspine in the area examined were dead or

dying. whereas the red pine appearedhealthy (Fig. 9). Bark beetles and borershad attacked severely cankered trees.These trees contained B. xylophilus(Table 2). Dead twigs and smallerbranches that had not been infested byinsects were free of B. xylophilus. In oneotherwise healthy tree. however. a singledead branch had been colonized byinsects and also contained B. xylophilus.

DISCUSSIONIn Japan, trees infected with B.

x,vlophi/us die within 3 mo after typicalwilt symptoms (8). Trees infected with B.xyJophilus in this investigation did notappear to die ofa wilt disease. Tree deathwas gradual and associated with variousfungal pathogens and insects. Pinespecies in the study areas that are notsusceptible to the forest pathogens andinsects observed did not die. For instance,Austrian pine is highly susceptible toDothistroma needle blight. whereas redpine is resistant to this disease (12) andless susceptible to root collar weevilinfestation. (L. T. Wilson. personalcommunication). In our study, only theAustrian pine had died and contained B.xylophilus. Similarly. the extrememortality of the jack pine in Black RiverFalls has been attributed to the effects ofH. rhizophagus (5,10). Trees with initialroot weevil infestation that still heldgreen needles and had not been infestedwith bark beetles and borers did notcontain nematodes. The observationsimply that the nematodes colonize treesat the same time as bark beetles andborers.

Fungal diseases (eg, Diplodia pineacanker and Dothistroma needle blight)and insects (eg, pine root collar and pineroot weevils) may stress trees, predispos-ing them to nematode infestation.Stresses such as poor site conditions anddrought have previously been associatedwith B. xylophi/us~killed trees in Japan(14-16). In other parts of the UnitedStates, such as Missouri (y, H. Dropkin,

Table 1. Insects and diseases associated with Bursaphelenchus xy/ophi/us infection of trees from two locations in Minnesota during the summers of 1980and 1981

Tree speciesand location

Austrian pine.Zimmerman

White pine,Cloquet

"ARR = Armillaria root rot. D:\B = Dothistroma needle blight, VRD = Verticicladiella root disease, WPBR = white pine blister rust, ZP~t =Zimmerman pine moth.

Plant Disease/October 1982 935

\

Figs. }-9. Trees stressed by various forest diseases and insects. (1) Dead Austrian pine (arrow) infested with Bursaphelenchus xylophi/us. with healthy

red pine in the background. (2) Dead top of Austrian pine containing B. xyfophilus. (3) Resin exudation resulting from Zimmerman pine mothinfestation associated with dead top of Austrian pine. (4) Dead Austrian pine infested with B. xylophilus next to healthy red pine. (5) Resin associatedwith pine root eoUar weevil infestation (arrow) on Austrian pine infested with B. xylophilus. (6) Stand of dead jack pine infested with B. xy/ophilus.(7) DipJodia pineo infection of hail wounds (arrow) on jack pine. (8) D. pineo canker (arrow) at the base of a red pine top infested with B. xylophi/us.(9) Dyinf Scots pine (arrow) surrounded by healthy red pine.

936 Plant DiseaseNol. 66 No. 10

Number of trees infested with

Tree species Trees sampled Bark beetles Borers Other diseasesand location Tree health (no.) (Scolytidae) (Cerambycidae) B. xylophilus and insects.

Austrian pine, Living 2 0 0 0 ONBDurand, WI Dead or dying 5 5 5 5 ONB

PRCW

Jack pine, Living 4 0 0 0 OPTBBlack River Falls. PRWWI Dead or dying 5 5 5 5 OPTB

PRW

Red pine Living 2 0 0 0Black River Falls, Dead top 10 10 10 ] OPCWI

,

.Table 2. Insects and diseases associated with Bursaphelenchus xylophi/us infection of trees from four locations in Wisconsin and Iowa during thesummers of 1980 and 1981

'

Scots pine, Living 3 0 0 0 DPCFarmington, IA Dead or dying 4 4 4 4 DPC.DNB = Dothistroma needle blight, DPC = Diplodia pinea canker, OPTB = D. pinea tip blight, PRCW = pine root collar weevil, PRW = pine root

weevil. ~

personal communication) and Delaware(1), however, Scots pine and Japaneseblack pine are thought to be dyingprimarily of B. xylophi/us infection. Thisapparent difference may be explained bythe fact that Japanese black pine isextremely sensitive to nematode infection(7), whereas both species are exotic to theUnited States and may be stressed.

B. xylophilus has been reported insingle dead branches of otherwise healthvtrees in Louisiana (V. H. Dropki~,personal communication). In this study,B. xylophilus was found in dead tops andbranches. Mortality of branches or topswas, however, associated with an insector pathogen (blister rust on white pine,Zimmerman pine moth on Austrian pine,D. pinea cankers on red pine) with thecapacity to kill portions of a tree (2.3;Nicholls, unpublished). It is possible thatB. xylophilus is only able to establishitself on stressed parts ofa tree. However,cerambycid vectors of B. xylophilus mayalso transmit nematodes to dead anddying trees or parts of trees duringoviposition. Further studies, includingfield inoculations with B. xylophilus andsampling of trees over an extended timeperiod, are necessary to elucidate thesignificance of the pine wood nematode

in Minnesota, Iowa, and Wisconsin.

ACK:'oIOWLEDG:\1E:"ITSWe thank Kathy Zuzek, Jane Hess. Frank Morse,

Wayne Fuhlbrugge, Roger Conklin, and VictorDropkin for assistance. This research was supportedby funds provided by the USDA Forest Service,North Central Forest Experiment Station,R WU-:'oiC-2205.

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(Co]eoptera: Cerambycidae). Nematologica]8:159-162.

10. :vIillers, I., Benjamin, D. :vi., and Warner. R. E.]963. A new Hylobius weevil associated with jackpine stand deterioration (Co]eoptera:Curculionidae). Can. Entomol. 95:18-22.

[I. Morimoto, K., and Iwasaki, A. ]972. Role ofMonochamus alternatus (Co]eoptera:Cerambycidae) as a vector of Bursaphefenchuslignicolus (:"Jematoda:Aphelenchoididae). J.Jpn. For. Soc. 54:177-/83.

]2. \'icholls. T. H., and Hud]er, G. W. ]971.DOlhistroma pini on Pinus nigra in Minnesota.Plant Dis. Rep. 55:1040.

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Plant Disease/October 1982 937