Mistletoe

Dwarf Mistletoes

Arceuthobium

Status: Native

 

Hosts (in California):  Many native conifer species, particularly prevalent on white and red fir, various pine species and Douglas fir.  Most species of dwarf mistletoe are relatively host specific attacking only one or a few host tree species.

 

Management: Dwarf mistletoes are obligate parasites therefore if the host tree is killed the mistletoe will die.  The main forms of management are to remove infected trees during thinning operations and clearcutting of highly infested stands.  Maintaining mixed species stands can reduce the amount of infection since the dwarf mistletoes are very host specific and the chances of infection of new hosts is significantly reduced.  Regeneration of non-host species below infected trees will reduce the chance of infection pf the new, developing stand.  Pruning out infected branches from high value trees is an option if the infection has not reached the main bole.  Infection on pruned branches must be further out than a foot from the trunk or it has already reached and infected the main stem.

 

Significance: Dwarf mistletoes very host specific, however most native California conifer species are attacked by a mistletoe.  Dwarf mistletoes exist from sea level to the high alpine forest of the Sierra Nevada Range at over 10,000 ft. elevation.  The plants are dioecious, meaning they have separate male and female plants.  The plants are largely leafless and yellow to light green in color and are obligate parasites receiving nearly all their water and most nutrients from the host tree.  

 

Sticky seeds are spread by explosive discharge from the female plant.  They can be shot up to 100 feet in distance.  If they land on a susceptible host, they can germinate and send a root-like structure into the host tissue.  In one to four years a new dwarf mistletoe plant will emerge from the host tree.

 

Dwarf mistletoe are considered among the most damaging forest disease agents.  The parasitic plants cause deformation of the host wood, growth loss, reduced host vigor, poor wood quality and branch and whole tree mortality.  They can create hazard tree conditions, ladder fuels during fires and act as disease courts for other pest organisms.  Some can also cause witches brooms when causing the host to form many small branches around the point of infection.  However, they are important for various wildlife species as a source of food, nesting sites and roosting opportunities.

Dwarf mistletoe plants on a white fir branch.  Photo by William Jacobi.
Dwarf mistletoe plants on a white fir branch. Photo by William Jacobi.

Dwarf mistletoe plants on a white fir branch.

White fir dwarf mistletoe (Arceuthobium abietinum f.sp. concoloris) seed on needles.  Photo from the
White fir dwarf mistletoe (Arceuthobium abietinum f.sp. concoloris) seed on needles. Photo from the

White fir dwarf mistletoe (Arceuthobium abietinum f.sp. concoloris) seed on needles.

Dwarf mistletoe
Dwarf mistletoe

Dwarf mistletoe

Dwarf mistletoe plants on a white fir branch.  Photo by William Jacobi.
Dwarf mistletoe plants on a white fir branch. Photo by William Jacobi.

Dwarf mistletoe plants on a white fir branch.

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Recommended Literature

Beatty, J.S., and R.L. Mathiasen.  2003. Dwarf mistletoes of ponderosa pine. Forest Insect and Disease Leaflet 40. USDA Forest Service. 8pp.

 

Filip, G.M., J.S. Beatty and R.L. Mathiasen. 2000. Fir dwarf mistletoe. Forest Insect and Disease Leaflet 89. USDA Forest Service. 7pp.

 

Hadfield, J.S., R.L. Mathiasen and F.G. Hawksworth. 2000. Douglas-fir dwarf mistletoe. Forest Insect and Disease Leaflet 54.  USDA Forest Service. 9pp.

 

Mathiasen, R.L., J. Pronos and J.S. Beatty. 2005. Sugar pine and western white pine dwarf mistletoes. Forest Insect and Disease Leaflet 113. USDA Forest Service. 11pp.

 

Pronos, J., R.L. Mathiasen and J.S. Beatty. 2004. Gray pine dwarf mistletoe. Forest Insect and Disease Leaflet 173. USDA Forest Service. 7pp.

Beatty, J.S., and R.L. Mathiasen.  2003. Dwarf mistletoes of ponderosa pine. Forest Insect and Disease Leaflet 40. USDA Forest Service. 8pp.

 

Filip, G.M., J.S. Beatty and R.L. Mathiasen. 2000. Fir dwarf mistletoe. Forest Insect and Disease Leaflet 89. USDA Forest Service. 7pp.

 

Hadfield, J.S., R.L. Mathiasen and F.G. Hawksworth. 2000. Douglas-fir dwarf mistletoe. Forest Insect and Disease Leaflet 54.  USDA Forest Service. 9pp.

 

Mathiasen, R.L., J. Pronos and J.S. Beatty. 2005. Sugar pine and western white pine dwarf mistletoes. Forest Insect and Disease Leaflet 113. USDA Forest Service. 11pp.

 

Pronos, J., R.L. Mathiasen and J.S. Beatty. 2004. Gray pine dwarf mistletoe. Forest Insect and Disease Leaflet 173. USDA Forest Service. 7pp.

European Leafy Mistletoe

Viscum album

Status: Non-native

Location: Sonoma County

Hosts in California: Seven native hardwood tree species and over twenty non-native hardwood tree and shrub species

Management: Infected branches can be pruned or entire infected trees destroyed to kill this parasite. One option attempted in some parts of Sonoma County to slow the spread and limit impacts to trees involves excising the living mistletoe shoots from the infected branches and then wrapping the infection site with plastic to try to prevent mistletoe re-emergence. 

Highlights: European leafy mistletoe--which can be recognized by its large, strap-like, yellowish-green leaves, waxy, white berries, and globular plant shape when mature--was intentionally introduced to California ca. 1900 by horticulturist Luther Burbank as a potential cash crop for use as Christmas decorations and medicinal tinctures. It was introduced at Burbank’s farm in Sebastopol and since then has spread slowly in all directions, but primarily to the north and south. This north-south axis generally coincides with the heavily populated Highway 101 corridor, perhaps because European leafy mistletoe’s main hosts in Sonoma County are ornamental and street trees (not native vegetation or the extensive stands of eucalyptus found in the county). The farthest infestation from the introduction point is in Petaluma, around 15 miles (24 km) away.

This mistletoe’s effects on the host plant may vary by host species. It proliferates to an exceptional degree in apple trees (Malus spp.), black locust (Robinia pseudoacacia), and ornamental poplar (Populus) species, but damaging effects manifest only gradually, if at all. In some long-infested black locust trees in the Graton area, it has apparently caused some branch dieback; once an infected branch dies, the entire mistletoe plant dies with it. In wild environments, European leafy mistletoe appears to reproduce and spread most readily in riparian environments on species such as Oregon ash (Fraxinus latifolia).

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European mistletoe (Viscum album) plant
European mistletoe (Viscum album) plant

European mistletoe (Viscum album) plant

Close-up of European mistletoe plant
Close-up of European mistletoe plant

Close-up of European mistletoe plant

Branches and trunks of callery pear (Pyrus communis) trees from which European mistletoe plants have
Branches and trunks of callery pear (Pyrus communis) trees from which European mistletoe plants have

Branches and trunks of callery pear (Pyrus communis) trees from which European mistletoe plants have been removed and where the infection sites have been wrapped in plastic.

European mistletoe (Viscum album) plant
European mistletoe (Viscum album) plant

European mistletoe (Viscum album) plant

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Recommended Literature

Hawksworth, F.G. and Scharpf, R.F. 1986. Spread of European mistletoe (Viscum album) in California, U.S.A. European Journal of Forest Pathology 16, pp. 1-5.

Hawksworth, F.G., Scharpf, R.F., and Marosy, M. 1991. European mistletoe continues to spread in Sonoma County. California Agriculture 45(6), 39-40.

Lim, Y.C., Rajabalaya, R., Lee, S.H.F., Tennakoon,K.U., Le, Q.-V., Idris, A., Zulkipli, I.N., Keasberry, N., and David, S.R. 2016.

Parasitic mistletoes of the genera Scurrula and Viscum: from bench to bedside. Molecules 21(8), 1048.

McCartney, W.O. 1968. European mistletoe, Viscum album, an unusual phanerogamic parasite in California. Plant Disease Reporter 52, pp. 198-201.

McCartney, W.O., Scharpf, R.F., and Hawksworth, F.G. 1973. Additional hosts of Viscum album, European mistletoe, in California. Plant Disease Reporter 57, p. 904.

Scharpf, R.F. and Hawksworth, F.G. 1976. Luther Burbank introduced European mistletoe into California. Plant Disease Reporter 60, pp. 740-742.

Scharpf, R.F. and McCartney, W.O. 1975. Viscum album in California—its introduction, establishment and spread. Plant Disease Reporter 59, p. 257-262.

Shaw, D.C. and Mathiasen, R.L. 2013. Management of higher parasitic plants—mistletoes. In Infectious Forest Diseases. Edited by G. Nicolotti and P. Gonthier. CABI Press, Oxfordshire, UK, pp. 97-114. 

Shaw, D.C. and Lee, C.A. 2020. Expansion of the invasive European mistletoe in California, USA. Botany 98(9), https://doi.org/10.1139/cjb-2019-0215 

True Mistletoe

Phoradendron

Status: Native

Location: Throughout California

Hosts in California: Various conifers and hardwood trees

Management: Infected branches can be pruned or entire infected trees destroyed to kill this parasite. One option sometimes attempted involves excising the living mistletoe shoots from the infected branches and then wrapping the infection site with plastic to try to prevent mistletoe re-emergence. However, before attempting management it is worth assessing whether the parasite causes enough damage to justify extensive intervention. True mistletoes are only hemiparasitic—they obtain water and minerals from their host plants, but they conduct their own photosynthesis—and although they can cause some stress to their host strees, the primary damage they cause comes from the heavy weight of older mistletoe plants, which can occasionally break the host branches they infest.

Highlights: Recent treatments of Phoradendron in California disagree as to proper classification for members of the genus. In some cases, existing phylogenetic data based on DNA analysis seems to contradict differences between species based on host plant affinities, morphology, phenology (e.g., time of flowering), and other traits. Species of Phoradendron have relatively large, well-developed plants with either wide leaves or leaves that are reduced to scale-like appendages. This list of Phoradendron species in California follows Mathiasen and Kenaly (2016).

  • Phoradendron californicum: Grows primarily on Prosopis, Parkinsonia, Acacia, Olneya, and leguminous species in the Mojave Desert in California and Sonoran Desert in northern Mexico. Leaves are reduced to scales ~1 mm long.

  • Phoradendron densum: Grows on various species of Juniperus (juniper) and Cupressus (cypress) throughout many parts of California. Has rounded, well-developed leaves that are densely crowded.

  • Phoradendron juniperinum: Also grows on juniper, but leaves are reduced to scales.

  • Phoradendron libocedri: Grows only on Calocedrus decurrens (incense-cedar); plants are very large and pendulous, with leaves that are reduced to scales ~1 mm long.

  • Phoradendron macrophyllum: Grows on over 70 species of hardwood trees throughout California, but attains its greatest prominence on riparian species, including willows, maples, and cottonwoods. Plants are large and pendulous. Its internodes and inflorescences are much longer than that of the other common hardwood-infecting true mistletoes in California.

  • Phoradendron pauciflorum: This mistletoe has well-developed, rounded leaves. It only infects Abies concolor (white fir).

  • Phoradendron villosum: Infects primarily oak, but also some other species of hardwoods. Unlike Phoradendron macrophyllum, this one has densely hairy stems and leaves. Its plants are typically somewhat more compact than those of Phoradendron macrophyllum, but old plants can be quite large.

True mistletoes produce fruits that are whitish, pinkish, or reddish berries. These fruits are consumed and spread by birds, which defecate their seeds onto new trees. Some landscape trees can be recognized as particularly favorable perches by the large numbers of true mistletoe plants infesting them.

Phoradendron villosum in Oregon white oak
Phoradendron villosum in Oregon white oak

Phoradendron villosum in Oregon white oak

Phoradendron densum in Sargent cypress (Hesperocyparis sargentii). Note the yellowish-green color of
Phoradendron densum in Sargent cypress (Hesperocyparis sargentii). Note the yellowish-green color of

Phoradendron densum in Sargent cypress (Hesperocyparis sargentii). Note the yellowish-green color of the mistletoe against the blue-green cypress foliage and the densely foliated habit of this mistletoe

True mistletoe
True mistletoe

True mistletoe

Phoradendron villosum in Oregon white oak
Phoradendron villosum in Oregon white oak

Phoradendron villosum in Oregon white oak

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Recommended Literature

Barbosa, J.M., Sebastián-González, E., Asner, G.P., Knapp, D.E., Anderson, C., Martin, R.E., and Dirzo, R. 2016. Hemiparasite-host plant interactions in a fragmented landscape assessed via imaging spectroscopy and LiDAR. Ecological Applications 26(1), pp. 55-66.

Hollinger, D.Y. 1983. Photosynthesis and water relations of the mistletoe, Phoradendron villosum, and its host, the California valley oak, Quercus lobata. Oecologia 60, 396-400.

Koenig, W.D., Knops, J.M.H., Carmen, W.J., Pesendorfer, M.B., and Dickinson, J.L. 2018. Effects of mistletoe (Phoradendron villosum) on California oaks. Biology Letters 14: 20180240.

Kuijt,J. 2003. Monograph of Phoradendron (Viscaceae). Systematic Botany Monographs Volume 66, The American Society of Plant Taxonomists.

Mathiasen, R.L. and Kenaley, S.C. 2016. The classification of California Viscaceae: an alternative perspective. Madroño 63(1), pp. 8-33.

Mathiasen, R.L., Nickrent, D.L., Shaw, D.C., and Watson, D.M. 2008. Mistletoes: pathology, systematics, ecology, and management. Plant Disease 92, pp. 988-1006.

Shaw, D.C. and Mathiasen, R.L. 2013. Management of higher parasitic plants—mistletoes. In Infectious Forest Diseases. Edited by G. Nicolotti and P. Gonthier. CABI Press, Oxfordshire, UK, pp. 97-114.

Wilson, E.A., Sullivan, P.J., and Dickinson, J.L. 2014. Spatial distribution of oak mistletoe as it relates to habits of oak woodland frugivores. PLoS One 9(11), e111947.