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Datasheet

Rhododendron ponticum (rhododendron)

Summary

  • Last modified
  • 29 March 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Host Plant
  • Preferred Scientific Name
  • Rhododendron ponticum
  • Preferred Common Name
  • rhododendron
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • R. ponticum has become established in the UK and other parts of Europe where it is threatening natural and semi-native habitats and the associated flora and fauna. In its native range, R. ponticum is also spreading and causing problems in the forests...

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Pictures

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PictureTitleCaptionCopyright
R. ponticum flowering in its natural habitat. Serra de Monchique, Algarve, Portugal.
TitleHabit
CaptionR. ponticum flowering in its natural habitat. Serra de Monchique, Algarve, Portugal.
CopyrightHarry C. Evans/CABI Bioscience
R. ponticum flowering in its natural habitat. Serra de Monchique, Algarve, Portugal.
HabitR. ponticum flowering in its natural habitat. Serra de Monchique, Algarve, Portugal.Harry C. Evans/CABI Bioscience
R. ponticum flowering in its natural habitat. Serra de Monchique, Algarve, Portugal.
TitleHabit
CaptionR. ponticum flowering in its natural habitat. Serra de Monchique, Algarve, Portugal.
CopyrightHarry C. Evans/CABI Bioscience
R. ponticum flowering in its natural habitat. Serra de Monchique, Algarve, Portugal.
HabitR. ponticum flowering in its natural habitat. Serra de Monchique, Algarve, Portugal.Harry C. Evans/CABI Bioscience
Regeneration of R. ponticum from cut stumps in 'cleared' site on steep granite slopes. East coast of Lundy Island, UK.
TitleRegeneration
CaptionRegeneration of R. ponticum from cut stumps in 'cleared' site on steep granite slopes. East coast of Lundy Island, UK.
CopyrightHarry C. Evans/CABI Bioscience
Regeneration of R. ponticum from cut stumps in 'cleared' site on steep granite slopes. East coast of Lundy Island, UK.
RegenerationRegeneration of R. ponticum from cut stumps in 'cleared' site on steep granite slopes. East coast of Lundy Island, UK.Harry C. Evans/CABI Bioscience
Monotypic stand of R. ponticum several years after cutting-out treatment. East coast of Lundy Island, UK.
TitleMonotypic stand
CaptionMonotypic stand of R. ponticum several years after cutting-out treatment. East coast of Lundy Island, UK.
CopyrightHarry C. Evans/CABI Bioscience
Monotypic stand of R. ponticum several years after cutting-out treatment. East coast of Lundy Island, UK.
Monotypic standMonotypic stand of R. ponticum several years after cutting-out treatment. East coast of Lundy Island, UK.Harry C. Evans/CABI Bioscience
Monoculture of R. ponticum on the east coast of Lundy Island, UK. All other species have been shaded out, including the endangered endemic Lundy cabbage (Coincya wrightii).
TitleInvasive monoculture
CaptionMonoculture of R. ponticum on the east coast of Lundy Island, UK. All other species have been shaded out, including the endangered endemic Lundy cabbage (Coincya wrightii).
CopyrightHarry C. Evans/CABI Bioscience
Monoculture of R. ponticum on the east coast of Lundy Island, UK. All other species have been shaded out, including the endangered endemic Lundy cabbage (Coincya wrightii).
Invasive monocultureMonoculture of R. ponticum on the east coast of Lundy Island, UK. All other species have been shaded out, including the endangered endemic Lundy cabbage (Coincya wrightii).Harry C. Evans/CABI Bioscience

Identity

Top of page

Preferred Scientific Name

  • Rhododendron ponticum L.

Preferred Common Name

  • rhododendron

Other Scientific Names

  • Rhododendron lancifolium Moench
  • Rhododendron speciosum Salisb.

International Common Names

  • English: pontic rhododendron; purple-flowered rhododendron
  • French: rhododendron pontique
  • Portuguese: adelfeira

Local Common Names

  • Germany: Pontische alpenrose
  • Italy: rhododendro pontico
  • Netherlands: pontische rododendron

EPPO code

  • RHOPO (Rhododendron ponticum)

Summary of Invasiveness

Top of page R. ponticum has become established in the UK and other parts of Europe where it is threatening natural and semi-native habitats and the associated flora and fauna. In its native range, R. ponticum is also spreading and causing problems in the forests of Turkey where again it displaces native vegetation. It smothers the forest floor when it becomes established and shades out all other vegetation. Present control methods are expensive and labour-intensive and classical biological control is not really an option due to the many associated species in the genus. A proposed method of biocontrol would be to use a native wood-rotting pathogen formulated as a stump treatment, but more research and work is needed.

Taxonomic Tree

Top of page
  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Ericales
  •                         Family: Ericaceae
  •                             Genus: Rhododendron
  •                                 Species: Rhododendron ponticum

Notes on Taxonomy and Nomenclature

Top of page The genus Rhododendron is the largest in the Ericaceae family with 1200 species. There are two subspecies of Rhododendron ponticum, subsp. baeticum and subsp. ponticum, with a number of varieties recorded, R. ponticum var. album, a form with white flowers, R. ponticum var. cheiranthifolium a compact variety with narrow and wavy leaves, R. ponticum var. lancifolium compact with narrow leaves, R. ponticum var. variegatum has variegated foliage, and R. ponticum var. heterophyllum from Turkey newly recorded in 2000 (Terzioglu et al., 2001).

Description

Top of page R. ponticum is a large evergreen shrub, which can grow 2-8 m high. The shrub can consist of several major axes forming from an irregular base (Cross, 1975). R. ponticum forms a compact shrub in open areas, while in the shade it adopts a larger spread when competing for light and other resources. The leaves are glabrous, dark green glossy above, paler beneath, oblong to elliptic in shape, up to 22 cm long. The wood is hard and light brown with the bark being rough, brown to dark brown. The flowers can vary in color from lilac pink to various light and dark shades of purple, spotted with brown and orange. Flowers occur in compact racemes borne from the glabrous pedicel. The flowers present 10 stamens with curved filaments. The fruit is a woody capsule that can persist for up to three years bearing multiple seeds.

Plant Type

Top of page Broadleaved
Perennial
Seed propagated
Shrub
Vegetatively propagated
Woody

Distribution

Top of page R. ponticum subsp. ponticum has a wide native distribution covering an area south of the Black Sea, including Bulgaria, Turkey (Bean, 1976), Georgia (USDA-ARS, 2003), the Krasnodar region of southern Russia (Czekalski, 1998; USDA-ARS, 2003) and Lebanon (Cross, 1975), and may be or may have been also native to Syria. Small pockets of native habitat are found in south western Spain and central and southern Portugal where R. ponticum subsp. baeticum is found (Milne and Abbott, 2000). R. ponticum has spread to other parts of Europe but not to other continents, is now naturalized in Belgium and France (Tutin et al., 1972; Cross, 1975) and invasive in the UK. It is found throughout Ireland (Kelly, 1981), Scotland, Wales and England (Cross, 1975) but grows best in the damper west of the country.

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 ReportedInvasivePlantedReferenceNotes

Asia

Georgia (Republic of)PresentNative Natural USDA-ARS, 2003; EPPO, 2014
LebanonPresentNative Not invasive Natural Cross, 1975; EPPO, 2014
SyriaAbsent, unreliable recordEPPO, 2014
TurkeyWidespreadNative Invasive Natural Ansin and Terzioglu, 1994; EPPO, 2014

Europe

BelgiumPresentIntroduced Not invasive Planted Cross, 1975; EPPO, 2014
BulgariaWidespreadNative Not invasive Natural Bean, 1976; EPPO, 2014
FrancePresentIntroduced Not invasive Planted Cross, 1975; EPPO, 2014
GibraltarPresentNative Not invasive Natural Cross, 1975
IrelandWidespreadIntroduced Invasive Planted Kelly, 1981; EPPO, 2014
NorwayRestricted distributionIntroduced Invasive Planted Cross, 1975; EPPO, 2014
PolandPresentIntroduced Not invasive Planted Czekalski, 1996; EPPO, 2014
PortugalRestricted distributionNative Not invasive Natural Cross, 1975; EPPO, 2014
Russian FederationRestricted distributionEPPO, 2014
-Southern RussiaRestricted distributionNative Not invasive Natural Czekalski, 1996; EPPO, 2014
SlovakiaRestricted distributionIntroduced Not invasive Planted Czekalski, 1996; EPPO, 2014
SpainRestricted distributionNative Not invasive Natural Cross, 1975; EPPO, 2014
UKWidespreadIntroduced1763 Invasive Planted Elton, 1958; EPPO, 2014

History of Introduction and Spread

Top of page R. ponticum was first introduced to the UK, via Gibraltar in 1763 by the nurseryman Conrad Lodiges (Cronk and Fuller, 1995). By 1803, R. ponticum was being sold on London markets as a flowering pot-plant and was established throughout England as an ornamental in stately homes. Recent molecular studies support Iberia as the origin of UK material (Milne and Abbott, 2000). Ireland saw the introduction of R. ponticum around 1800 (Doyle et al., 1999) though fossil records of Irish peat deposits show R. ponticum was a native to Ireland during the Gortian Interglacial period 428,000-302,000 years ago. It is unclear when R. ponticum was first introduced into Wales, UK, though the invasiveness of the species was being documented in 1943 (Gritten, 1995; Thomson et al., 1993). It is now naturalized in Belgium and France (Tutin et al., 1972; Cross, 1975). Further spread of this shrub is possible due to its invasive characteristics, though further spread is unlikely if adequate control and management is applied in its introduced range.

Risk of Introduction

Top of page Further introduction of R. ponticum by man is likely for ornamental purposes for large gardens and as a cover for game. R. ponticum is widely available in garden centers as pot-plants and via mail order seed companies and via the Internet.

Habitat

Top of page R. ponticum is a large evergreen shrub, which can grow in a variety of different habitats. The species is well suited to a wide range of temperatures and grows best in damp conditions, being intolerant of drought. In its native range, R. ponticum is present from sea level to over 2000 m altitude, occurring in deciduous and evergreen forests in the Pontic Mountain ranges of Turkey, pine woods in Lebanon and on granite slopes in Spain and Portugal. In its introduced range, R. ponticum has colonized an array of habitats from managed and ancient woodlands to moorland and urban areas in the UK, also invading peatlands, scrub woods, heathlands and woodlands (Foley, 1990; Doyle et al., 1999), and has spread from gardens to invade woodland and national parks (Thomson et al., 1993).

Habitat List

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CategoryHabitatPresenceStatus
Littoral
Coastal areas Present, no further details
Terrestrial-managed
Cultivated / agricultural land Present, no further details Harmful (pest or invasive)
Disturbed areas Present, no further details
Managed forests, plantations and orchards Present, no further details Harmful (pest or invasive)
Managed grasslands (grazing systems) Present, no further details
Rail / roadsides Present, no further details
Urban / peri-urban areas Present, no further details
Terrestrial-natural/semi-natural
Natural forests Present, no further details Harmful (pest or invasive)
Natural grasslands Present, no further details

Hosts/Species Affected

Top of page R. ponticum does not pose a significant threat to plants in agricultural systems. Nevertheless, R. ponticum has become a serious pest in commercial land management (Rotherham, 1990) and has proved to have dramatic effects on habitat structure and native biodiversity in the areas where it has been introduced. Where R. ponticum is introduced in an area all plant species are threatened.

Host Plants and Other Plants Affected

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Plant nameFamilyContext
Calluna vulgaris (heather)EricaceaeWild host
Fagus sylvatica (common beech)FagaceaeWild host
Ilex aquifolium (holly)AquifoliaceaeWild host
Pteridium aquilinum (bracken)DennstaedtiaceaeWild host

Growth Stages

Top of page Pre-emergence, Seedling stage, Vegetative growing stage

Biology and Ecology

Top of page Genetics

The chromosome number of R. ponticum is 2n=26.

Physiology and Phenology

The growth rate of seedlings is slow and can take up to two years for a seedling to become a juvenile bearing adult sized leaves. The growth of R. ponticum can occur throughout the growing season with defined periods of growth occurring between May and June, July-August and a third period of growth in September. The initial shoot extension takes place in early May, though under favorable conditions this may be bought forward to as early as February. In Mediterranean populations, the plant flowers over two months in late spring, though flowers can still be seen during the autumn-winter period (Mejias, et al., 2002). Flowers appear from late spring to late summer in the introduced range, though the influence of increased latitude and altitude will delay this process. The plant can extend both laterally and vertically, though the main growth form is the former as the stems lacks the strength to support large vertically growth unless supported by other vegetation or man-made structures. The root system consists of an extensive root mat laid down in the top 2-15 cm of the soil. This characteristic root system allows the shrub to exhaust the available soil oxygen thus exerting an indirect competition effect on surrounding plant species (Esen, 2000). The competitiveness of the root system is enhanced by mycorrhizal symbionts, which enhance mineral and nutrient acquisition.

Reproductive Biology

Reproduction is mainly by seed with vegetative spread being limited to air layering, with branches rooting if buried in damp soil. R. ponticum flowers from the age of 12 years and pollination is assisted by insect species of the families Hymenoptera and Syrphidae. Rhododendron bushes 2 m high can produce over one million light small seeds each per annum (Shaw, 1984). The average weight of the seed varies from 0.02 to 0.19 mg depending upon location (Esen, 2000). Light is an essential prerequisite for the germination of seeds as is a temperature range of about 10-15°C.

Environmental Requirements

R. ponticum is tolerant of a range of climatic conditions from as cold as -17°C to 25.9°C in its native range in Turkey to a much narrower climate in its introduced range. The species is intolerant of drought and grows best in areas of uniform damp climates. High humidity, mild winters and acidic soils are favoured for the growth of R. ponticum. The ability to tolerate dense shade gives R. ponticum a great advantage over its competitors. Even almost closed canopy conditions do not prevent this species from growing. A well drained humus soil type is the preferred conditions for optimum growth and R. ponticum will grow on other types of soils in its introduced range though not so vigorously.

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
48 30 0 2000

Air Temperature

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Parameter Lower limit Upper limit
Absolute minimum temperature (ºC) -20 0
Mean annual temperature (ºC) -17 40
Mean maximum temperature of hottest month (ºC) 16 40
Mean minimum temperature of coldest month (ºC) -17 6

Rainfall

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ParameterLower limitUpper limitDescription
Dry season duration00number of consecutive months with <40 mm rainfall
Mean annual rainfall5251300mm; lower/upper limits

Rainfall Regime

Top of page Uniform

Soil Tolerances

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Soil drainage

  • free

Soil reaction

  • acid
  • neutral
  • very acid

Soil texture

  • heavy
  • medium

Special soil tolerances

  • shallow

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Chondrostereum purpureum Pathogen Stems
Chrysomyxa rhododendri Herbivore Leaves
Ditula angustiorana Herbivore Stems
Illinoia lambersi Herbivore Growing point/Leaves
Stephanitis rhododendri Herbivore Growing point/Leaves

Notes on Natural Enemies

Top of page There are few natural enemies associated with R. ponticum even in its native range. Judd and Rotherham (1992) found a total of 31 phytophagous insects associated with the shrub throughout its introduced range. The most closely associated insects include Stephanitis rhododendri, Illinoia lambersi (syn. Masonaphis lambersi) (Hemiptera) and Melolontha melolontha (Coleoptera). Farr et al. (1996) have identified a number of fungi associated with the shrub including a rust fungus from its native range in Portugal. Others include Colletotrichum spp. (leaf spot), Phytophthora cactorum (stem-rot), Armillaria mellea, and Chondrostereum purpureum has been associated with die back of Rhododendron in the UK (Strouts and Winter, 2000). Phytophthora ramorum, the fungus causing sudden oak death in the USA, was found on R. ponticum shrubs in 2003 in the UK (Anon., 2003). A disease outbreak in Windsor Great Park, Berkshire, UK showed signs of a virulent dieback, with cross sections of the diseased stems revealing cankered sections of the wood. An unusual Cryptosporiopsis sp. (Deuteromycotina: Coelomycetes) appeared to be associated with the disease symptoms.

Means of Movement and Dispersal

Top of page Natural Dispersal (Non-Biotic)

Natural dispersal is effective with the aid of wind and seeds can travel considerable distances, estimated at up to 1000 m, though this is considerably reduced to as little as 10 m in wooded areas (Shaw, 1984). Seeds are mature after 6 months and dispersal generally occurs 2 months after this time when the capsules open (Cross, 1981).

Vector Transmission (Biotic)

There are no known incidences of animals, other than man, acting as disseminators of seed.

Agricultural Practices

There is no agricultural use for R. ponticum and therefore no agricultural practices associated with the species, but seed may be transferred by machinery involved in controlling R. ponticum infestations.

Accidental Introduction

R. ponticum has only been introduced deliberately as an ornamental and then escaped accidentally from the enclosed areas. Accidental introduction may have occurred via the disposal of R. ponticum pot-plants or plant parts in landfill sites or rubbish collection sites.

Intentional Introduction

R. ponticum was intentionally introduced into the UK where it was planted as an ornamental in gardens of large houses and in estates, where it provided cover for game animals. For many years, R. ponticum was more or less restricted to these artificial habitats but with the gradual erosion of large estates and the attendant workforces, the plant was allowed to spread unchecked. The warmer winters and wetter climates of the western UK appear to favor the fecundity, spread and establishment of the plant and it is in these areas where R. ponticum, within the past 40-50 years, has changed from a naturalized, prized garden plant to an invasive category 4 species (Cronk and Fuller, 1995).

Impact Summary

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

Impact

Top of page The economic impact of eradicating R. ponticum in a local area can run to many millions. The cost of clearing the weed in Snowdonia National Park, Wales, UK has been estimated at over £30 million (over US$50 million) (Mabberley, 1998). R. ponticum on the small island of Hebridean, Colonsay, Scotland, UK is spreading at a rate of 1 km² every 5 years and the cost of prevention and eradication of the weed is estimated to be £120,000 (approximately US$200,000) per year for a planned 16 year programme. On the small island of Lundy, Devon, UK, 105 days work and £26,880 (approximately US$50,000) is required per year to clear R. ponticum from cliffs (Compton and Key, 1998). Toxins in the leaves of R. ponticum have been known to poison sheep, cattle (Black, 1991), goats (Humpherys, et al., 1983) and dogs (Frape and Ward, 1993) and the nectar of R. ponticum is poisonous to bees, though there are no reported costs associated with this.

Environmental Impact

Top of page R. ponticum is widely recognized as being very environmentally and ecologically damaging to semi-natural habitats, woodlands, heathlands and managed plantations. R. ponticum threatens forests throughout the UK and in its native range in Turkey (Colak et al., 1998) and where conditions are suitable for R. ponticum to grow, it will out-compete most native plant species. Once the native plants have disappeared then the associated fauna will disappear too. R. ponticum will cover the ground preventing saplings from becoming established and therefore eventually producing a monocultural stand.

Impact: Biodiversity

Top of page R. ponticum has a dramatic effect on native biodiversity in areas where the plant has been introduced. Due to the spreading and competitive nature of the plant, R. ponticum can cast a dense shade in the understorey and no other plant is able to grow. Almost all plants and animals in a forest are under threat when R. ponticum is present and left to spread. Firstly the ground vegetation disappears, such as wild forest flowers, ferns and mosses. R. ponticum is posing a significant threat to the rare endemic Lundy cabbage, Conincya wrightii (Brassicaceae), and a flea beetle (Psylliodes luridipennis) associated with this plant on the island of Lundy, UK (Compton and Key, 1958). C. wrightii is restricted to the east coast of Lundy due to grazing pressure from livestock and R. ponticum is encroaching on the habitat of this rare cabbage and is threatening its existence.

Social Impact

Top of page The eradication of R. ponticum is an expensive and time-consuming process. Footpaths and parks can become besieged by this shrub, restricting public access and reducing the natural composition of the site. The nectar of R. ponticum is poisonous to man, bees, mice and cats (Abrahams, 1998).

Risk and Impact Factors

Top of page Invasiveness
  • Invasive in its native range
  • Proved invasive outside its native range
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Highly mobile locally
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
Impact outcomes
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Negatively impacts animal health
  • Reduced native biodiversity
Likelihood of entry/control
  • Difficult/costly to control

Uses

Top of page R. ponticum was used as cover for game animals in the UK and as an ornamental species. Nowadays R. ponticum has no real use in its native or introduced range except for nesting sites for birds and animal species. It continues to be, however, a very popular ornamental species with numerous varieties and cultivars selected and sold for the colourful, abundant and showy flowers.

Uses List

Top of page

Environmental

  • Agroforestry
  • Graft stock

General

  • Ornamental

Medicinal, pharmaceutical

  • Traditional/folklore

Similarities to Other Species/Conditions

Top of page Common Rhododendron species found in R. ponticum's introduced range and with which it mat be confused include R. annae, R. arboreum, R. campanulatum, R. niveum, R. oreodoxa and R. wallichii, though differentiation is generally possible with available keys.

Prevention and Control

Top of page Cultural Control

Grazing is not a method for control. R. ponticum is unpalatable to most herbivores due to the large amounts of toxic chemicals, particularly 'free' phenols and diterpenes in the leaves (Esen, 2000). The diterpenes, known as grayanotoxins, are not found in all species of Rhododendron but occur in the leaves, flowers and nectar of R. ponticum. Phenols are mostly concentrated in the young tissues, such as young emergent leaves and buds providing a primary defense against herbivores before the tissues have acquired the added deterrent of physical toughness found in older tissues. Young emergent leaf buds have the additional protection of a sticky exudate, which also contains phenols. This also gives protection to the buds against attack by invertebrates.

Mechanical Control

Heavy machinery with long hydraulic arms is best for digging up the root material and crushing the branches. However, heavy machinery in certain habitats such as ancient woodlands compacts the forest floor causing problems such as increased erosion (Esen, 2000). Operator knowledge of the structural growth of the plant is essential to enable full eradication of the plant without leaving underground suckers. The surface rooting characteristics of R. ponticum should allow for the shrub to be lifted entirely from a site with most of the main rooting structure intact. R. ponticum removal is best suited to autumn and winter in order to make, and take advantage of, a clean uncontaminated seedbed in the spring. Due to the spread of the shrub, a systematic approach is best suited to the removal of the weed at each stage. If R. ponticum is just cut back, this will be followed by vigorous growth from the stumps during the next growing season. An approach of methodical cutting, mechanical removal and burning of root material and stumps is the preferred means to achieve a R. ponticum-free site.

Chemical Control

Spraying cut stems with ammonium sulfamate is effective in controlling the growth of R. ponticum though surrounding vegetation may be effected. Glyphosate is commonly used to control R. ponticum in the UK after the bulk of the biomass has been removed by burning or mechanical removal, and triclopyr and imazapyr at differing concentrations have also been used with varying success (Lawrie and Clay, 1989).

Biological Control

Until now, biological control has not been taken into consideration as part of the management strategy for R. ponticum. However, this may offer a potentially simpler, cheaper and safer alternative approach to chemical and mechanical control, or an additional tool in the battle against this weed in the UK. Due to the horticultural importance of the genus Rhododendron, with over 500 spp. currently in cultivation in the UK alone (Mabberley, 1998) the risk associated with the classical approach using coevolved, exotic natural enemies from the native range is considered to be too high (Evans, 2000). However, a number of natural enemies have already been identified in the native range, including a rust fungus from Portugal (Farr et al., 1996). Instead, the proposed strategy is based on the evaluation of natural enemies associated with the weed in the UK, focusing on fungal pathogens for use in an inundative approach. This will involve the mass production and formulation of a selected pathogen and, in the case of R. ponticum, application of such a proposed fungal product or mycoherbicide as a site-selective stump treatment. Potential pathogens include a species of Cryptosporiopsis which was associated with dieback in Berkshire, UK (Shaw, 2003). This strategy has been implemented safely and successfully against woody invasives in the Netherlands, where BioChon, a product based on local strains of the wood-rotting basidiomycete Chondrostereum purpureum, has been marketed for the control of alien Prunus spp. as well as Populus spp. (Jong, 2000). Evaluation of this strategy against similar woody targets is also underway in both Canada and New Zealand.

References

Top of page

Abrahams A, 1998. Rhododendron nectar- poisonous to both bees and man. Scottish Beekeeping, 75:19-20.

Anon., 2003. Dieback hits parks and gardens - the garden. Journal of the Royal Horticultural Society, 128:9.

Ansin R; Terzioglu S, 1994. New botanical variety of Rhododendron ponticum L. (R. ponticum L. subsp. Ponticum var. heterophyllum Ansin var. nova). Turkish Journal of Agriculture and Forestry, 18:137-140.

Bean WJ, 1976. Trees and Shrubs Hardy in the British Isles (8th Edition). London, UK: J. Murray.

Black DH, 1991. Rhododendron poisoning in sheep. Veterinary Record, 128(15):363-364; 4 ref.

Colak AH; Cross JR; Rotherham ID, 1998. Rhododendron ponticum in native and exotic environments, with particular reference to Turkey and the British Isles. Practical Ecology and Conservation, 2:34-41.

Compton SG; Key RS, 1998. Species action plan: Lundy Cabbage (Coincya wrightii) and its associated insects. Peterborough, UK: English Nature.

Cronk QCB; Fuller JL, 1995. Plant invaders: the threat to natural ecosystems. London, UK; Chapman & Hall Ltd, xiv + 241 pp.

Cross JR, 1975. Biological flora of the British Isles, Rhododendron ponticum L. Journal of Ecology, 63:345-364.

Cross JR, 1981. The establishment of Rhododendron ponticum in the Killarney oakwoods, S.W. Ireland. Journal of Ecology, 69(3):807-824

Czekalski M, 1998. Rhododendrons in the former Soviet Union. Caucasian species. American Rhododendron Society Journal, 52(2):81-89; [3 col. pl.]; 50 ref.

Doyle G; Klotzli F; Walther GR, 1999. Conference on recent shifts in vegetation boundaries of deciduous forests, especially due to general global warming. Birkhauser Verlag AG, Basel, Switzerland, 237-251.

Elton CS, 1958. The Ecology of Invasions by Animal and Plants. London, UK: Methuen.

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

Esen D, 2000. Ecology and control of Rhododendron (Rhododendron ponticum L.) in Turkish Eastern Beech (Fagus orientalis Lipsky) forests. Thesis. Virginia Polytechnic Institute and State University.

Evans HC, 2000. Evaluating plant pathogens for biological control of weeds: an alternative view of pest risk assessment. Australasian Plant Pathology, 29(1):1-14; 4 pp. of ref.

Farr DF; Esteban HB; Palm ME, 1996. Fungi on Rhododendron: a World Reference. Boone, North Carolina, USA: Parkway Publication Co.

Foley C, 1990. Rhododendron ponticum at Killarney National Park. Biology and control of invasive plants Ruthin, Clwyd, UK; Richards, Moorhead & Laing Ltd, 62-63

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