Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Datasheet

Arceuthobium americanum
(lodgepole pine dwarf mistletoe)

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Datasheet

Arceuthobium americanum (lodgepole pine dwarf mistletoe)

Summary

  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Host Plant
  • Preferred Scientific Name
  • Arceuthobium americanum
  • Preferred Common Name
  • lodgepole pine dwarf mistletoe
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • A. americanum does not spread rapidly and cannot be considered highly invasive. It does, however, constitute a serious threat as a result of its ability to build up gradually over the life of a forest and cause severe damaging effects on a number of...

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Pictures

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PictureTitleCaptionCopyright
Male shoot of A. americanum on Pinus contorta in California, USA.
TitleMale shoot
CaptionMale shoot of A. americanum on Pinus contorta in California, USA.
Copyright©Chris Parker/Bristol, UK
Male shoot of A. americanum on Pinus contorta in California, USA.
Male shootMale shoot of A. americanum on Pinus contorta in California, USA.©Chris Parker/Bristol, UK
Female shoot of A. americanum on Pinus contorta in California, USA.
TitleFemale shoot
CaptionFemale shoot of A. americanum on Pinus contorta in California, USA.
Copyright©Chris Parker/Bristol, UK
Female shoot of A. americanum on Pinus contorta in California, USA.
Female shootFemale shoot of A. americanum on Pinus contorta in California, USA.©Chris Parker/Bristol, UK
Pinus contorta with dense brooms (arrowed) caused by A. americanum in California, USA.
TitleDamage symptom
CaptionPinus contorta with dense brooms (arrowed) caused by A. americanum in California, USA.
Copyright©Chris Parker/Bristol, UK
Pinus contorta with dense brooms (arrowed) caused by A. americanum in California, USA.
Damage symptomPinus contorta with dense brooms (arrowed) caused by A. americanum in California, USA.©Chris Parker/Bristol, UK

Identity

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Preferred Scientific Name

  • Arceuthobium americanum Nutt. Ex Engelm. (1950)

Preferred Common Name

  • lodgepole pine dwarf mistletoe

Other Scientific Names

  • Razoumofskya americana (Nutt. ex Engelm.) Kuntze (1891)

International Common Names

  • English: Jack pine dwarf mistletoe

EPPO code

  • AREAM (Arceuthobium americanum)

Summary of Invasiveness

Top of page A. americanum does not spread rapidly and cannot be considered highly invasive. It does, however, constitute a serious threat as a result of its ability to build up gradually over the life of a forest and cause severe damaging effects on a number of important forest species. Its potential to establish in other areas is limited by the need for the living parasite to survive on the pathway and reproduce after entry. Nevertheless, the risk of economic impact is considerable if host species are available. The conifers at greatest risk would be the known hosts, planted as exotics in other countries, but there is also a possibility of spread to related species that are not known to be hosts.

Taxonomic Tree

Top of page
  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Santalales
  •                         Family: Viscaceae
  •                             Genus: Arceuthobium
  •                                 Species: Arceuthobium americanum

Notes on Taxonomy and Nomenclature

Top of page A detailed discussion of the taxonomy and taxonomic history of the genus Arceuthobium is provided by Hawksworth and Wiens (1996). The genus Arceuthobium is a member of the plant family Viscaceae and is a clearly defined group of small (generally less than 20 cm high), variously coloured flowering plants that are aerial parasites on conifers of the families Pinaceae and Cupressaceae. They are considered to be the most evolutionary specialized genus of the family Viscaceae. Arceuthobium has been previously included in the subfamily Viscoideae of the family Loranthaceae, however, the subfamilies Loranthoideae and Viscoideae are now generally considered to have family status (Loranthaceae and Viscaceae).

It has recently been confirmed that, although indistinguishable morphologically, three races of A. americanum can be distinguished by molecular studies. These correspond to the forms attacking Pinus banksiana, P. contorta var. murrayana and P. contorta var. latifolia (Jerome and Ford, 2002a, b).

Description

Top of page Arceuthobium spp. are obligate parasites with an endophytic 'root' system ramifying within the host branch. This endophyte expands within the cortex and becomes embedded in the xylem for some years before aerial shoots are produced, encircling the infected branch and growing along it. In A. americanum the endophyte may remain relatively localized, causing discrete fusiform swellings in the host branch, or it may become systemic and affect whole branch systems. The shoots of A. americanum, which appear after 2-5 years of 'incubation' are 5-9 (max. 30) cm high. Shoots are glabrous, leafless, yellowish to olive green, with verticillate branching. Basal diameter of dominant shoots is 1-3 (mean 1.5) mm; third internode 5-20 mm long, 1-2 mm wide. The plant is dioecious; staminate flowers are borne on pedicel-like segments, ca. 2 mm long, 2.2 mm across; perianth mostly 3-merous, sometimes 4-merous, the same colour as the shoots; segments ca. 1.1 mm long, 1.0 mm wide. Each segment has a sessile, one-chambered circular anther 0.6 mm in diameter, centered 0.7 mm from the tip of the segment. Pollen polar diameter 19-28 µm; equatorial diameter 23-30 µm; polar/equatorial diameter ratio 1:1.16; spine height (mean 1.8 µm) equal to or slightly greater than wall thickness (mean 1.5 µm). Pistillate flowers are verticillate, ca. 1.5 mm long, 1.0 mm across, 2-merous, epigynous with a single style. Perianth segments are persistent, adnate to the ovary. Mature fruit an ovoid berry 3.5-4.5 mm long, 1.5-2.5 mm wide, the proximal portion ca. 2.5 mm long, differently coloured; mucilaginous; the single seed 2.4 x 1.1 mm. (from Hawksworth and Wiens, 1996; Geils et al., 2002).

Plant Type

Top of page Parasitic
Perennial
Seed propagated

Distribution

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A. americanum has the most extensive distribution of any North American dwarf mistletoe, centred on the range of its principal host Pinus contorta in the Western USA and Canada. It occurs at elevations from 200 to 3350 m asl. The distribution in EPPO (2014) includes Northwest Territory (Canada) and Alaska (USA), but these records are not confirmed from other sources.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

North America

CanadaRestricted distributionEPPO, 2014
-AlbertaPresentNative Invasive Hawksworth and Wiens, 1996; EPPO, 2014
-British ColumbiaPresentNative Invasive Hawksworth and Wiens, 1996; EPPO, 2014
-ManitobaPresentNative Invasive Hawksworth and Wiens, 1996; EPPO, 2014
-Northwest TerritoriesAbsent, reported but not confirmedEPPO, 2014
-OntarioPresentNative Invasive Hawksworth and Wiens, 1996; EPPO, 2014
-SaskatchewanPresentNative Invasive Hawksworth and Wiens, 1996; EPPO, 2014
USARestricted distributionEPPO, 2014
-AlaskaAbsent, reported but not confirmedEPPO, 2014
-CaliforniaPresentNative Invasive Hawksworth and Wiens, 1996; EPPO, 2014
-ColoradoPresentNative Invasive Hawksworth and Wiens, 1996; EPPO, 2014
-IdahoPresentNative Invasive Hawksworth and Wiens, 1996; EPPO, 2014
-MontanaPresentNative Invasive Hawksworth and Wiens, 1996; EPPO, 2014
-OregonPresentNative Invasive Hawksworth and Wiens, 1996; EPPO, 2014
-UtahPresentNative Invasive Hawksworth and Wiens, 1996; EPPO, 2014
-WashingtonPresentNative Invasive Hawksworth and Wiens, 1996; EPPO, 2014
-WyomingPresentNative Invasive Hawksworth and Wiens, 1996; EPPO, 2014

History of Introduction and Spread

Top of page A. americanum is not known to have spread beyond its native origin in western North America.

Risk of Introduction

Top of page The risk presented by Arceuthobium spp. introductions into other areas of the world is related to the availability of their hosts. The most obvious risk arises from the fact that several North American hosts (Pinus contorta, P. ponderosa, Tsuga spp., Pseudotsuga menziesii) have been more or less widely planted in other continents, in the absence of these mistletoes (curiously, P. radiata, one of the North American pines most widely planted around the world, is hardly reported as an Arceuthobium host, nor is Picea sitchensis, much planted in parts of Europe). Conversely, the European or Asian hosts of Arceuthobium have not been substantially planted outside their natural range. A secondary risk is that, although in their natural range Arceuthobium spp. occur rather rarely on species other than their main hosts, there is limited data suggesting that they may readily infect some exotic species. There is accordingly a certain risk that Arceuthobium spp. may spread to and affect such exotic hosts if they are introduced into other continents, e.g. P. sylvestris in Europe, Juniperus virginiana in North America.

The risk of accidental introduction is already well recognized and trade in conifer plants is correspondingly controlled in many countries. Exotic Arceuthobium species are also specifically listed as prohibited imports in the European Union, other European countries, Australia, New Zealand, Turkey, Tanzania and no doubt many others. North American countries similarly restrict import of conifers.

Habitat

Top of page The habitat of A. americanum is dictated by that of its conifer hosts, especially Pinus contorta and P. banksiana, but within this total habitat range there is evidence of variation in intensity according to different habitat and plant associations. It may for instance be commoner in a drier pine-moss association than in a moister pine-heath association, and more common on slopes and ridges than at the bottom of slopes (Hawksworth and Johnson, 1989).

Habitat List

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CategoryHabitatPresenceStatus
Terrestrial-managed
Managed forests, plantations and orchards Present, no further details Harmful (pest or invasive)
Terrestrial-natural/semi-natural
Natural forests Present, no further details Harmful (pest or invasive)

Hosts/Species Affected

Top of page Principal hosts are Pinus contorta and P. banksiana. P. ponderosa var. scopulorum is also frequently affected, especially when growing with infested P. contorta, but var. ponderosa is less susceptible and only occasionally attacked. Other occasional hosts are P. albicaulis, P. flexilis and P. jeffreyi.

P. aristata, P. attenuata, Picea glauca, Picea mariana, Picea engelmannii, Picea pungens, Pseudotsuga menziesii and Abies lasiocarpa subsp. lasiocarpa have rarely been reported to be infected in the field (Geils et al., 2002).

The exotics P. sylvestris and P. mugo have been found infected in a plantation and by inoculation, respectively.

Host Plants and Other Plants Affected

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Biology and Ecology

Top of page Genetics

Chromosome number 2n = 28. In spite of wide distribution and some variation in morphology, no sub-species have been described, but recent molecular studies have confirmed the existence of three genetic races, corresponding to the forms attacking Pinus banksiana, P. contorta var. murrayana and P. contorta var. latifolia (Jerome and Ford, 2002a, b).

Physiology and Phenology

Arceuthobium spp. are obligate parasites, depending on an endophytic system within the host branch to draw water and nutrients from their hosts. Germination usually occurs in the spring following autumn dispersal and is favoured by light, but the seedling shows negative phototropism, causing it to bore directly into the host shoot, even from below. The seedlings of most Arceuthobium spp. can only penetrate young branches less than 5 years old, but those of A. americanum can establish on branches of P. contorta up to 60 years old, developing a 'penetration wedge' after germination, which enters the cortex and then ramifies throughout the bark, developing sinkers into the xylem. These sinkers, however, do not necessarily contain xylem elements. Furthermore there is no evidence for any direct symplastic connection with the host tissues, and most Arceuthobium spp. including A. americanum have no phloem tissue. Transfer of nutrients, including sugars, may depend on close association of host and parasite parenchyma cells, and apoplastic movement via the walls of these cells. Graniferous tracheary elements could also be involved (see Hawksworth and Wiens, 1996, for detailed discussion on this topic). Photosynthesis is apparently important in supporting the seedling as it germinates and attaches, but for the next 2-7 years (usually 3-4) of its life, the parasite persists only as the endophyte inside the host tissue without any aerial shoot. Even after emergence of the aerial shoots, the established parasite has a relatively low photosynthetic capacity, usually much less than 50% of 'normal'.

Once emerged, the parasite shoots produce fruits annually, for at least 2 years, and often for 5 years or more (Hawksworth and Wiens, 1996).

Reproductive Biology

Arceuthobium spp. are dioecious. In A. americanum the ratio of male to female plants is close to 50:50. Pollination in A. americanum appears to be predominantly due to insects (especially ants and flies) but may also occur by wind (Hawksworth and Wiens, 1996). Anthesis occurs between April and June. Following fertilization of the 'ovule', the fruit matures in August or September of the following year, i.e. after about 16 months. No true seed is formed, as there is no testa, but the embryo is embedded in chlorophyllous endosperm, surrounded by viscin. This will be referred to as a seed for convenience. The embryo is green, a few mm long, and has a meristematic radicular apex without a root cap. Dispersal of the seed is exceptional, involving a hydrostatic, explosive process which expels the seed at least 10 m. Most dispersal occurs as temperatures rise and humidity declines in the morning. The viscin ensures that it is retained by any host shoot that is hit, but if this is a needle, it may slide down with gravity to the base of the needle and germinate there. Although this is the main means of dispersal over a short range, long-distance dispersal also occurs as a result of seeds sticking to birds or mammals. However, any seeds that are ingested by animals are destroyed. Seeds of Arceuthobium spp. do not generally show dormancy and germination normally occurs in the first season after dispersal, though seeds may retain dormancy for 1-4 years when stored in ideal conditions. Germination of A. americanum seeds may be well over 90%.

Environmental Requirements

The main environmental constraint on an Arceuthobium sp. is the presence of its host, which is in turn determined by multiple environmental requirements. The different North American species most obviously differ in the latitude limits of their range, from those which occur in Canada and the northern USA, to those which are confined to Mexico, with all intermediates. Species also differ from those with an essentially coastal distribution to those with a continental distribution. The relevant factors further interact to determine an altitudinal range, reflecting the fact that conifers form a distinctive element of montane vegetation. Soil conditions have practically no importance.

Associations

A. americanum provides a source of food for some bird species, including the chickadee (Parus atricapillus) and grouse species (Dendragapus and Bonasa spp.).

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
0 0 0 0

Air Temperature

Top of page
Parameter Lower limit Upper limit
Mean annual temperature (ºC) 2 15
Mean maximum temperature of hottest month (ºC) 26 32
Mean minimum temperature of coldest month (ºC) -22 -2

Rainfall

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ParameterLower limitUpper limitDescription
Dry season duration212number of consecutive months with <40 mm rainfall
Mean annual rainfall200600mm; lower/upper limits

Rainfall Regime

Top of page Uniform

Natural enemies

Top of page
Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Caliciopsis arceuthobii Pathogen Fruits/pods
Dasypyga alternosquamella Herbivore Leaves/Stems
Glomerella cingulata Pathogen Stems
Mitoura spinetorum Herbivore Stems
Peridermium bethelii Pathogen Stems
Septogloeum gillii Pathogen Leaves/Stems
Tamiasciurus hudsonicus Herbivore Stems

Notes on Natural Enemies

Top of page Although a number of insects and fungal pathogens are widely recorded on A. americanum, damage is generally minor or localized. However, Dasypyga alternosquamella may be 'extremely destructive' in British Columbia, Canada, where larvae are recorded destroying an entire crop of mistletoe shoots by mining larger shoots and consuming smaller ones. The fungus Colletotrichum gloeosporioides [Glomerella cingulata] can also exert significant control of A. americanum; over half the shoots of A. americanum were affected in Alberta, Canada (Hawksworth and Wiens, 1996).

Means of Movement and Dispersal

Top of page Natural Dispersal (Non-Biotic)

Natural dispersal is by the explosive fruits which can expel the seeds at speeds of 2.6 m/s up to a 15-m distance (Hinds and Hawksworth, 1965). In spite of this, the natural spread may not exceed about 1.5 m/annum (Hawksworth, 1958).

Vector Transmission (Biotic)

Seeds falling onto the plumage of birds, or the fur of animals, tend to stick and may be dispersed for long distances. About 7% of birds and mammals trapped carried seeds, this rose to 22% during the 2-week period of maximum seed release (Hawksworth and Johnson, 1989).

Agricultural Practices

Logging and movement of timber which has not been completely de-barked, can result in movement of complete plants of Arceuthobium and possible transfer of seeds and establishment of new infestations.

Accidental Introduction

Accidental introduction of Arceuthobium spp. into new areas or continents does not appear very likely. Seeds are short-lived, and unlikely to reach a host tree under circumstances in which they could develop. Conifer plants could carry living mistletoe plants, especially in the prolonged endophytic stage before the external plant develops, but young plants, as normally traded, are not very likely to be infected. Mistletoes could be carried on cut branches, including Christmas trees, and possibly on logs with bark (though mistletoes normally occur on the branches of trees, not on trunks). But it seems unlikely that mistletoes borne on cut, dead plants present any risk of transmission. Accordingly, introduction can be prevented relatively easily. The prohibition of import of plants for planting of the main host genera (as established, for example, in the phytosanitary regulations of the European Union) blocks the only really dangerous pathway.

Intentional Introduction

Intentional introduction would seem extremely unlikely, other than for research.

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Bark whole plants
Stems (above ground)/Shoots/Trunks/Branches whole plants
Plant parts not known to carry the pest in trade/transport
Flowers/Inflorescences/Cones/Calyx
Fruits (inc. pods)
Growing medium accompanying plants
Leaves
Roots
Seedlings/Micropropagated plants
True seeds (inc. grain)

Impact Summary

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CategoryImpact
Animal/plant collections None
Animal/plant products None
Biodiversity (generally) Positive
Crop production None
Environment (generally) None
Fisheries / aquaculture None
Forestry production Negative
Human health None
Livestock production None
Native fauna Positive
Native flora None
Rare/protected species None
Tourism None
Trade/international relations Negative
Transport/travel None

Impact

Top of page Economic Impact

Arceuthobium species as a whole are regarded as some of the most serious of all pests/diseases of North American forests. Dwarf mistletoes are very much more damaging to their hosts than the 'green' mistletoes in both Loranthaceae and Viscaceae. Having little photosynthetic capacity, they draw more heavily on host carbohydrate, and furthermore interfere with photosynthate translocation to the roots. The mistletoe has a girdling effect, resulting in an accumulation of photosynthate above the site of infection. Apparently carbohydrates are withheld from the roots in quantities sufficient to cause the characteristic decline of the tree (Rediske and Shea, 1961; Hawksworth and Wiens, 1996). There are also severe growth-regulatory effects resulting from cytokinin production at the point of infection and the redirection of host photosynthate into the resulting witches broom growths. These distort and suppress growth of branches and even the main trunk. Wood quality is further affected as a result of swellings, witches' brooms and knots, and structural weakening associated with shortened, distorted tracheids. Hawksworth and Johnson (1989) describe the range of damaging effects from A. americanum on Pinus contorta. The proportion of timber in the stronger vigour classes A and B was 55% in uninfected stands vs. 33% in infected. Diameter growth has been shown to suffer a 5% reduction for every decade since infection. Hence trees infected for 70 years have a diameter only 65% of uninfected trees. A formula has been developed for estimating the radial growth reduction from different levels of infection on the 0-6 scale (Myers et al., 1971). Tree height is also affected; while a mistletoe rating of 2 causes only a 2% height reduction over 10 years, a rating of 4 causes 18% reduction and a rating of 6 causes 60% reduction over the same period. Mistletoe ratings of 4 and above result in about twice the normal mortality rate, and the overall reductions in merchantable timber from heavy infestation (ratings 5-6) approach 50%. In western Canada, estimated losses of Pinus contorta from A. americanum included volume losses of 170,000 m³/year due to growth reduction, 898,000 m³/year due to mortality and 10,726,000 m³/year due to wood decay (Brandt, 1995). In Manitoba, the overall volume reduction in P. banksiana, due to dwarf mistletoe, represented 4-8% of the merchantable volume timber in the surveyed area (Baker et al., 1992). In P. banksiana it has also been shown that moderate or heavy infection by A. americanum reduces viable seed production by at least 75% (Sproule, 1996).

Environmental Impact

Top of page Severe infestation by A. americanum can result in significant mortality and the opening up of forest stands, but no major change in the plant community.

Impact: Biodiversity

Top of page The opening of the canopy, and the creation of witches' brooms may result in some increase in biodiversity, as a number of bird species have been noted to favour the witches' brooms as nesting sites.

Social Impact

Top of page No serious social impact has been recorded.

Risk and Impact Factors

Top of page Invasiveness
  • Invasive in its native range
  • Highly mobile locally
  • Has high reproductive potential
Impact outcomes
  • Negatively impacts agriculture
Impact mechanisms
  • Competition - monopolizing resources
Likelihood of entry/control
  • Difficult/costly to control

Uses

Top of page No uses of this species are known.

Similarities to Other Species/Conditions

Top of page Arceuthobium species are all superficially similar in their morphology and difficult to separate. A. americanum is, however, distinguished from most others in N. America by its verticillate (whorled), rather than flabellate (fan-like) branching. The only other species with similar branching are A. abietis-religiosae, which only occurs on Picea spp. in Mexico, and A. verticilliflorum, with much larger fruits 10 mm long, on Pinus spp. also in Mexico; also the most widespread Old-World species, A. oxy-cedri, but this is greener in colour and occurs mainly on Juniperus species, and never on Pinus spp. Detailed keys are provided in Hawksworth and Wiens (1996), and Geils et. al. (2002).

Prevention and Control

Top of page Cultural Control

In the absence of any simple direct means of control of dwarf mistletoes, and the vast areas of forest involved, cultural management is virtually the only approach to the problem, the techniques varying according to the type of stand in which the problem occurs. Management options listed by Hawksworth and Johnson (1989) include:

- Survey

- Use RMYLD model to predict yields (Edminster, 1978; Hawksworth, 1978)

- Favour or plant resistant tree species

- Prune infected branches and witches' brooms

- Destroy the whole stand (including the use of fire) and regenerate

- Fell non-merchantable infected trees

- Sanitation thin

- Harvest and regenerate the stand

- Do nothing.

Hawksworth and Johnson (1989) also refer to mechanisms to help prevent infection, including the use of natural or man-made barriers (roads, streams, strips of non-susceptible forest) to reduce (re)invasion from adjacent infested stands; and removing infected trees before re-planting/regeneration.

Detailed surveys are an essential ingredient of successful control programmes and the 6-class rating system (Hawksworth, 1977) is widely accepted as a standard. This involves a 0-6 score based on 0, 1 or 2 for each third (lower, middle, upper) of the tree; 0 for no infection, 1 for light infection (less than half the branches affected) or 2 for heavy infection (more than half infected).

In recently harvested, regenerating stands, the emphasis is on the complete removal of any infected trees over 2 m, regardless of commercial value, both within the stand, and along borders to a distance of 18 m, before the regeneration is 1 m high.

In pre-commercial stands in which surveys show less than 40% infected trees, it should be economic to do selective thinning to remove all those infected. Above 40% this is unlikely to be economic. Severely infested stands may best be harvested early and regenerated, but decisions may require use of available models to help devise the most economic option. Some of the available models are described by Muir and Geils (2002).

Dwarf mistletoes may contribute in various ways to biodiversity - by creating openings in the forest following tree death, by providing nesting sites in the 'brooms' and by providing food for a range of vertebrates and invertebrates. There can therefore be some conflict between the requirements of forest exploitation, and environmental concerns.

Mechanical Control

Pruning may be appropriate as a means of reducing damage to individual trees, but more generally to reduce the source of infection for surrounding trees. The practicality, however, is that it will only be feasible in particular amenity and recreation areas.

Clear-felling (with or without fire) is appropriate where a stand is so severely infested that it needs to be abandoned and regenerated or re-planted.

Chemical Control

The only chemical approved for use against dwarf mistletoes is the ethylene-releasing growth regulator, ethephon, which can cause abscission of the shoots of A. americanum and delay fresh seeding for 2-4 years, but there is eventual re-growth from the endophyte. It is difficult to achieve good coverage in larger trees from the ground, while applications from the air fail to penetrate the canopy adequately. The treatment is therefore of interest mainly for high-value amenity trees.

Biological Control

Colletotrichum gloeosporioides [Glomerella cingulata] is being developed as a biocontrol agent for use on A. americanum and A. tsugense (Geils et al., 2002) and has shown promise in field trials. Work is also in progress on two other pathogens, Caliciopsis arceuthobii and Nectria neomacrospora.


Integrated Control

Hawksworth and Johnson (1989) emphasise the importance of integrating dwarf mistletoe control, with measures to reduce damage from the mountain pine beetle (Dendroctonus ponderosae).

References

Top of page

Baker FA; Slivitsky M; Knowles K, 1992. Impact of dwarf mistletoe on jack pine forests in Manitoba. Plant Disease, 76(12):1256-1259

Brandt JP, 1995. Forest insect- and disease-caused impacts to timber resources of west-central Canada: 1988-1992. Information Report - Northern Forestry Centre, Canadian Forest Service, No. NOR-X-341:28 pp.; 3 pp. of ref.

Edminster CB, 1978. RMYLD: computation of yield tables for even-aged and two-storied stands. Research Paper RM-199, Fort Collins, USA: United States Department of Agriculture Forest Service.

EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm

Geils BW; Tovar JC; Moody B; (technical coordinators), 2002. Mistletoes of North American Conifers. General Technical Report RMRS-GTR-98. Ogden, USA: United States Department of Agriculture Forest Service.

Hawksworth FG, 1958. Rate of spread and intensification of dwarf mistletoe in young Lodgepole Pine stands. Journal of Forestry, 56:404-407.

Hawksworth FG, 1977. The 6-class dwarf mistletoe rating system. USDA Forest Service General Technical Report, Rocky Mountain Forest and Range Experiment Station, No. RM-48:7 pp.

Hawksworth FG, 1978. Intermediate cuttings in mistletoe-infested lodgepole pine and southwestern ponderosa pine stands. General Technical Report, Pacific Southwest Forest and Range Experiment Station, No. PSW-31:86-92

Hawksworth FG; Johnson DW, 1989. Biology and management of dwarf mistletoe in lodgepole pine in the Rocky Mountains. General Technical Report - Rocky Mountain Forest and Range Experiment Station, USDA Forest Service, No. RM-169:ii + 38 pp.

Hawksworth FG; Wiens D, 1996. Dwarf Mistletoes: Biology, Pathology, and Systematics. Agriculture Handbook 709. Washington DC, USA: United States Department of Agriculture Forest Service.

Hinds TE; Hawksworth FG, 1965. Seed dispersal velocity in four dwarf mistletoes. Science, 148:517-519.

Jerome CA; Ford BA, 2002. Comparative population structure and genetic diversity of Arceuthobium americanum (Viscaceae) and its Pinus host species: insight into host-parasite evolution in parasitic angiosperms. Molecular Ecology, 11(3):407-420; 50 ref.

Jerome CA; Ford BA, 2002. The discovery of three genetic races of the dwarf mistletoe Arceuthobium americanum (Viscaceae) provides insight into the evolution of parasitic angiosperms. Molecular Ecology, 11(3):387-405; many ref.

Muir JA; Geils BW, 2002. Management strategies for dwarf mistletoe: silviculture. General Technical Report - Rocky Mountain Research Station, USDA Forest Service, No. RMRS-GTR-98:83-94.

Myers CA; Hawksworth FG; Stewart JL, 1971. Simulating yields of managed, dwarf mistletoe-infested lodgepole pine stands. Research Paper RM-72. Fort Collins, USA: U.S. Department of Agriculture Forest Service, Rocky Mountain Forest and Range Experiment Station.

Rediske JH; Shea KR, 1961. The production and translocation of photosynthate in dwarf mistletoe and Lodgepole Pine. American Journal of Botany, 48:447-452.

Sproule A, 1996. Impact of dwarf mistletoe on some aspects of the reproductive biology of jack pine. Forestry Chronicle, 72(3):303-306; 11 ref.

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