RRockyocky GreatGreat MountainsMountains Southwest PlainsPlains Research Note RM-RN-533 April 11995' 995 USDA Forest!st Serviice ce ~ockyRocky Mountain Forest and Range Experiment Station

Larch Dwarf Mistletoe Not Found on Alpine Robert L. Mathiasen'.Mathiasen1, Brian W.W. Geilsl,Geils'. Clinton E. Carlson2,Carlson'. and Frank G. HawksworthlHawksworth'

ReportsReports of larch dwarf mistletoe parasitizing alpine larch are based on two collections of this hostlparasitehosVparasite combination made by J.R.J .R. Weir in Montana during the early 1900s.t 900s. Examination of host material from these cocollectionsllections indicates thatthat the host is western larch, not alpine larlarchch as previously reported. Attempts to locate larch dwarf mistletoemistletoe on alpine larch were unsuccessful,unsuccessful, lealeavingvi ng no valid reportsreports of larch dwarf mistletoemistletoe on alpine larch.

Keywords: Arceuthobium laricis,lariet's. LarixLarix lyallii,/yallii, LarixLarix occidentalis, hosts

Larch dwarf mistletoe (Arceuthobium iaricislaricis (Piper) Alpine larch (Larix(LArix lyallii Parl.)ParI.) occurs at upper St. John) is a common parasite of western larch (LArix(Larix timberline in the NorthNorth Cascades of and occidentalis Nutt.) throughout thethe range of this com-com~ extreme southern British Columbia, inin the Northern mercially valuablevaluable (Hawksworth and Wiens of westernwestern Montana and northern 1972). SeveSeverely rely infectedinfected trees exhibit reduced growth , and in the southern Canadian Rocky Moun-Moun~ and are eventually killed by the parasitepara site (Weir 1916, tains of southeastern British Columbia and south-south­ Pierce 1960, Baranyay and SmitSmithh 1972). Surveys con-con~ western Alberta (Aro(Arnoandand Habeck 1972). According ducted during the latelate 1950s found that over 60% of toto Arno and Habeck (1972), the species ranges from western larch stands in eastern Washington, north-north­ approximatelyapproximately 1500 m (5,000 ft)ft) to 3000 m (9900 ft). ern IdahoIdaho and western Montana were infested with Alpine larch generallygenerally inhabits cold,cold, rocky sites and larch dwarf mistletoe (Graham 1960). AlthoughlarchAlthough larch is seldom sympatric with western larch.larch. Although dwarf mistletoe parasitizes severalseveral otherother conifer spe­spe- the two larchlarch species frequently occur inin thethe same cies, parasitism of these secondary hosts is usually mountain ranges, they are usually separatedseparated by 150- neither severe nor damaging (Hawks (Hawksworth worth and 300 m (500-1000 ft) of elevation.elevation. The different larch Wiens 1972). species, however, are only rarely found together,together, for exampleexample in areas where alpinealpine larchlarch descends below lr Robert L. Mathiasen, volunteer; Brian W. Geils, Research its normal rangerange by colonizingcolonizing avalanche chutes,chutes, Pathologist; Clinton E. Carlson, Project LeaderLeader;; Frank G. talus slopes,slopes, or burned areas. CarlsonCarlson and Blake Hawksworth,Hawkswotth, Research Plant Pathologist (deceased)(deceased).. Rocky Mountain Forest and Range Experiment Station. Headquarters (1969) and Carlson et al. (1990) identified several is in Fort Collins, in cooperation with Colorado State University. natural hybrid populations in thethe Bitterroot Moun-Moun­ *11 Forestry Sciences Laboratory, Intermountain Forest and tainstains of Montana where these species are sympatric. Range Experiment Station, Missoula, in cooperation with the University of Montana.Montana. This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain. 1 Alpine larch has been reported as a secondary host (somatic mutation) or other (unknown) causes as of larch dwarf mistletoe (Gi1l1935, Hawksworth and described by Buckland and Kuijt (1957) for alpine Wiens 1972). These reports were based on only two larch and other . collections from Montana. These collectio.ns· were We further examined several sites on Carlton Ridge made by J.R. Weir in the early 1900s (Hawksworth where western and alpine larch are sympatric and and Wiens 1972), and the associated label informa­ hybridize (Carlson et al. 1990). No infection of either tion is very brief. Weir only described the collection host by larch dwarf mistletoe occurred at any of these from the Bitterroot Mountains as "near Lolo, Mon­ sites. Lodgepole pine dwarf mistletoe (Arceuthobium tana" and the collection from the Cabinet Mountains americanum Nutt.) was present on lodgepole pine as "region Scotchmans Peak." Because he provided (Pinus contorta Dougl. ex Loud.) at one site, but no no data on the abundance of infection at the collec­ . crossover infection to alpine larch was observed. tion sites, the susceptibility of alpine larch to larch Because western larch is thought to be immune to dwarf mistletoe could only be tentatively assigned lodgepole pine dwarf mistletoe (Hawksworth and by Hawksworth and Wiens (1972). Wiens 1972), it is unlikely that lodgepole pine dwarf To assess the natural susceptibility of alpine larch mistletoe would parasitize alpine larch. to larch dwarf mistletoe, we surveyed larch stands in In addition to these field surveys, we re-examined the general locations where Weir reported making Weir's collections to confirm host identifica tion. These his collections: a large population of alpine larch on specimens (Weir 8366, Lolo, MT, 1914 and Weir 3250, Carlton Ridge in the Bitterroot Mountains (7 km Scotchman Peak, n.d.) are deposited at the Univer­ southwest of Lolo, MT), and a small population on sity of Illinois Herbarium, Urbana, Illinois (ILL) and the north-facing slopes of Savage Mountain and East at the USDA Forest Service Forest Pathology Her­ Fork Peak in the Cabinet Range (3 km north of barium, Fort Collins, Colorado (FPF). Specimens from Scotchman Peak and 13 km northeast of Clark Fork, these two collections were examined by the first ID). Our extensive surveys of the Carlton Ridge and three authors and Steven Arno, USDA Forest Service, Savage Mountain locations during 1992 and 1993 Missoula, MT. failed, however, to locate any dwarf mistletoe infect­ Host material from Weir's specimens was com­ ing alpine larch. Larch dwarf mistletoe populations pared with herbarium specimens of both western infecting western larch were located at 1720 m (5500 and alpine larchdepositedatthe USDA Forest Service ft) near Carlton Ridge and at 1590 m (5200 ft) near Herbarium, Missoula, MT (MRC). Larch characters Savage Mountain. No alpine were found near examined included pubescence and bark color of dwarf mistletoe-infected western larches on Carlton young twigs, and pubescence and color of short Ridge or at the Savage Mountain location. shoots (Hitchcock et al. 1973). The collections con­ Although we found no alpine larches.that were tained only a few 1- or 2-year-old twigs; those present infected by dwarf mistletoe, the Carlton Ridge popu­ were glabrous to lightly pubescent rather than to­ lation did include a few isolated alpine larch trees mentose. The several short shoots present were not with one or two large witches' brooms in the middle tomentose but rather resembled those of western or top of the crown. These brooms were, however, larch. Bark color also matched that of western larch of not caused by dwarf mistletoe. The general appear­ similar age. No ovulate cones were available with ance of mistletoe-caused brooms is usually deter­ Weir's specimens. Because of the lack of tomentose mined by the parasite rather than the host pubescence on this host material and other similari­ (Hawksworth and Wiens 1972); these brooms did ties of the material to western larch (short shoot not resemble typical mistletoe brooms on western pubescence and bark color), we concluded that both larch. Because dwarf mistletoe spreads primarily by specimens collected by Weir were western larch. an explosive fruit, infections (and eventually brooms) Thus, these specimens do not represent collections of tend to occur in clusters and more often in the lower larch dwarf mistletoe on alpine larch. crown; these brooms were isolated and high in the Even though this identification leaves no valid crown. Finally, most dwarf mistletoe infections pro­ report of larch dwarf mistletoe parasitizing alpine duce distinctive, aerial shoots; no mistletoe shoots larch, the species is probably susceptible to larch were associated with these brooms. We therefore dwarf mistletoe. Closely related conifer species are concluded these brooms were induced by genetic frequently parasitized by the same dwarf mistletoe

2 (Hawksworth and Wiens 1972). Ba sed on artificial toe where alpine and western larch are sympatric inoculations of seedlings, Weir (191 8) demonstrated and to proceed with artificial inoculations of larch that European larch (Larix decidu a Mill.) and Japa­ dwarf mistletoe on alpine larch seedlings and ma­ nese larch (Larix kaempferi (Lamb.) Carr.) are.suscep­ ture trees. tible to larch dwarf mistletoe. Because alpine' and western larch are closely related (Carlson and Blake 1969; Ca rlson et al. 1990, 1991 ; Carlson and Theroux Distinguishing Alpine Larch 1993), alpine larch is also likely susceptible to larch dwarf mistletoe. Furthermore, larch dwarf mistletoe Alpine larch is easily distinguished from has a relatively wide host range. As summarized by western larch based on several morphologi­ tiawksworthand Wiens (1 972). it commonly parasit­ izes lodgepole pine, subalpine fir (A bies /asiocnrpa cal characteristics (Hitchcock et al. 1973, (Hook.), N utt.) a nd mountain hemlock (Ts uga Carlson et al. 1990, Carlson and Theroux mertensiana (Bong.) Carr.). These species are even 1993). The most notable characteristics are less closely related to western larch than alpine larch. that young twigs and short shoots of alpine Artificial inocula tion experiments should be at­ larch are distinctly tomentose, whereas those tempted under fi eld conditions to test the suscepti­ of western larch are glabrous to slightly pu­ bility of alpine larch to larch dwarf mistletoe. Field bescent. The leaves of alpine larch are four­ inocula tions on alpine larch would not only provide information on its susceptibility to larch dwarf mistle­ angled in cross section, about as thick as toe but could also provide information on w hether or broad, and possess two relatively large resin not larch dwarf mistletoe ca n successfully reproduce ducts visible in leaf cross sections magnified at elevations above its known altitudinal limits. 25x. Larch d warf mistletoe specimens deposited at FPF In contrast, leaves of western larch are ha ve seldom been collected above 1520 rn. The only triangular in cross section, the upper surface specimens of larch d warf mistletoe collected above almost flat with only a slight ridge, the lower 1520 m are from the Blue Mountains of eastern Or­ egon at 1980 m (Hawkswortlt 981). The specimens of surface ridged in the middle; and they pos­ larch dwarf mistletoe from other states (Washington, sess small resin ducts visible in cross section Montana, and Idaho) were collected below 1550 m. (Carlson and Blake 1969). Alpine larch foli­ During our fi eld surveys, however, we found larch age is blue-green and not shiny; western dwarf mistletoe as high as 1720 m near Col rlton Ridge larch foliage is olive-green and shiny. Bark and 1590 m near Sewage Mountain. texture and color of 3-year-old branches dif­ Most dwarf mistletoes have elevationallimits be­ fers between the species as well: alpine larch low that of their principal hosts (Hawksworth 1956, Hawksworth and Wiens 1972, Acciavatti and Weiss bark on 3-year-old branches is gray and 1974, Mathiasen a nd Haw ksworth 1980). rough-textured and bark of western larch is Hawksworth (1969) suggested that d warf mistletoe brown and smooth (Carlson et al. 1990). fruits may not mature at elevations above their natu­ Other characters that distinguish these ral limits beca use of short growing seasons. This species are the morphology of ovulate cones situation could certainly influence the distribution of and seed shape (Carlson and Theroux 1993). larch d warf mistletoe. Even if alpine larch were Alpine larch has ovulate cones from 3.5 t04.5 susceptible to larch d warf mistletoe, prevailing cli­ matic conditions in alpine larch stands at high eleva­ em long; shorter western larch cones are tions could still prevent larch d warf mistletoe from from 2.5 to 3 em long. Seeds of western larch reproducing. Nonetheless, if alpine larch were sus­ are narrower, shallower, and have thinner ceptible to larch dwarf mistletoe, then cross-over seedcoats than those of alpine larch. Chemi­ infec tions from western larch should occur where cal differences (foliar terpenes) also occur both species grow in close proximity (within 10 m) , between the two species (CarlsonetaI.1991). We plan to continue searching for larchdwarf mistle-

3 Acknowledgments Carlson, C.E.; Theroux, L.J. 1993. Cone and seed morphology of western larch (LArix occidentalis), We gratefully acknowledge the assistance of Steven alpine larch (LArix lyallii), and their hybrids. Cana­ Arno and Peter Stickney with the species deterlrrlna­ dian Journal Forest Research. 23: 1264-1269. tion of host material for the larch dwarf nustletoe Gill, L.S. 1935. Arceuthobium in the United States. specimens collected by J.R. Weir. The late Frank G. Connecticut Academy of Arts and Science Trans­ Hawksworth assisted with most of the initiai work actions. 32: 111-245. involved with this study, so we acknowledge his Graham, D.P. 1960. Surveys expose dwarf mistletoes contributions by including him as an author. Frank problem in Inland Empire. Western Conservation initiated this work and was a constant source of ideas Journal. 17: 56-58. and encouragement until his death in January 1993. Hawksworth, F.G. 1956. Upper altitudinal limits of dwarf mistletoe on lodgepole pine in the central Rocky Mountains. Phytopathology. 46: 561-562. Literature Cited Hawksworth, F.G. 1969. Ecological aspects of dwarf mistletoe distribution. In: Proceedings, 16th West­ Acciavatti,R.E.; Weiss, M.J. 1974. Evaluation of dwarf ern International Forest Disease Work Confer­ mistletoe on Engelmann spruce. Fort Apache In­ ence.l%80ctober28-November I;Coeurd'Alene, dian Reservation, Arizona. Plant Disease Reporter. ID: 74-82. 58: 418-419. Hawksworth, F .G.; Wiens, D. 1972. Biology and clas­ Arno, S.F.; Habeck, J.R. 1972. Ecology of alpine larch sification of dwarf mistletoes (Arceuthobium). Ag­ (LArix lyallii Part) in the Pacific Northwest. Eco­ riculture Handbook 401. Washington, DC: U.S. logical Monographs. 42: 417-450. Department of Agriculture, Forest Service. 234 p. Baranyay, J .A.; Smith, R.B. 1972. Dwarf mistletoes in Hitchcock, c.L.; Cronquist, A.; Ownbey, M. 1973. British Columbia and recommendations for their Flora of the Pacific Northwest. Part 1: Vascular control. Information Report BC-X-72. Victoria, BC: cryptograms, gymnosperms, and monocotyledons. Canadian Forestry Service, Pacific Forest Research Seattle, W A: University ofWashingtonPress.914 p. Centre. 18 p. Mathiasen, R.L.; Hawksworth, F.G. 1980. Buckland, D.C.; Kuijt,J.1957. Unexplained brooming and effects of dwarf mistletoe on bristlecone pine of Douglas-fir and other conifers in British Colum­ on the San Francisco Peaks, Arizona. Research bia and Alberta. Forest Science. 3(3): 236-242. Paper RM-224. Fort Collins, CO: U.S. Department Carlson, C.E.; Arno, S.F.; Menakis, J. 1990. Hybrid of Agriculture, Forest Service, Rocky Mountain larch of Carlton Ridge Research Natural Area in Forest and Range Experiment Station. 10 p. western Montana. Natural Areas Journal. 10:134-139. Pierce, W.R. 1960. Dwarf mistletoe and its effect Carlson, C.E.; BlaKe, G.M. 1969. Hybridization of upon the larch and Douglas-fir of western Mon­ western and alpine larch. Montana Forest and tana. Bulletin 10. Missoula, MT: Montana State Conservation Experiment Station Bulletin 37. University, School of Forestry. 38 p. Missoula, MT: University of Montana, School of Weir,J.R. 1916. Larch mistletoe: Some economic con­ Forestry. siderations of its injurious effects. Agriculture Bul­ Carlson, C.E.; Cates, R.G.; Spencer, S.c. 1991. Foliar letin 317. Washington, DC: U.S. Department of terpenes of a putative hybrid swarm (Larix Agriculture. 25 p. occidentalis x LArix lyallii) in western Montana. Weir, J.R. 1918. Experimental investigations on the Canadian Journal Forest Research. 21: 876-881. genus Razoumofskya. Botanical Gazette. 56: 1-31.

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