Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

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Ligustrum vulgare
(common privet)

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Datasheet

Ligustrum vulgare (common privet)

Summary

  • Last modified
  • 16 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Host Plant
  • Preferred Scientific Name
  • Ligustrum vulgare
  • Preferred Common Name
  • common privet
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • L. vulgare is a shrub or small tree depending on climatic conditions, native to Europe, western Asia, and northern Africa. It has been introduced to many countries in different continents for ornamental use or...

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Identity

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Preferred Scientific Name

  • Ligustrum vulgare L.

Preferred Common Name

  • common privet

Other Scientific Names

  • Ligustrum album Gueldenst. ex Ledeb.
  • Ligustrum incipiens Gand.
  • Ligustrum insulare Decne.
  • Ligustrum insulense Decne.
  • Ligustrum italicum Mill.
  • Ligustrum lodense Glogau
  • Ligustrum oviforme Gand.
  • Ligustrum vicinum Gand.

International Common Names

  • English: European privet; golden privet; wild privet
  • Spanish: aligustre; aligustre comun
  • French: troène; troene commun
  • Portuguese: alfeneiro

Local Common Names

  • Brazil: ligustro
  • Germany: Gemeiner Liguster; Rainweide
  • Italy: ligustro comune

EPPO code

  • LIGVU (Ligustrum vulgare)

Summary of Invasiveness

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L. vulgare is a shrub or small tree depending on climatic conditions, native to Europe, western Asia, and northern Africa. It has been introduced to many countries in different continents for ornamental use or for hedgerows. It is highly invasive, and although it prefers direct sunlight it is shade tolerant and will invade forest edges and other shady areas, as well as degraded areas. It is tolerant of most soil types and grows well in humid areas. It flowers abundantly and may produce more than 10,000 fruits per tree, with 1-4 seeds per fruit. Fruits are dispersed by birds and other animals, which facilitate invasion into vegetated areas. Control can be labour intensive as invasions advance and displace native plants. No biological control agents have been successfully identified so far. Pollen may cause allergies or asthma.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Oleales
  •                         Family: Oleaceae
  •                             Genus: Ligustrum
  •                                 Species: Ligustrum vulgare

Notes on Taxonomy and Nomenclature

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The genus Ligustrum contains around 40 species and is found throughout most of the temperate and tropical Old World except Africa and the coldest regions (Green, 1987), and is a member of the Oleaceae, a medium sized family consisting of around 600 species in 25 genera. Recent molecular studies have revealed that Ligustrum and Syringa are closely related and exist in the subtribe Ligustrinae within the tribe Oleeae (Wallander and Albert, 2000). The genus Ligustrum has been the subject of repeated reviews in the past (Green, 1985; Green, 1990; Green, 1995) and the current opinion is that the distinctions between species in Ligustrum are small.

The Plant List (2013) cites 11 synonyms of L. vulgare, 2 of which are invalid and one is illegitimate. There are also 14 varieties, 1 subspecies and 2 forms of L. vulgare listed. Plants from the warmer parts of the range show a stronger tendency to be fully evergreen; these have sometimes been treated as a separate variety, Ligustrum vulgare var. italicum (Bean, 1978) but others do not regard it as distinct.

The common name of ‘European privet’ reflects its native range. The species has been used commercially for hedging, and so a number of cultivars have been selected.

Description

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Semi-evergreen shrub or small tree growing to 3 or 6m height, according to habitat and climatic characteristics. Trunks are formed by multiple stems with many long, leafy branches. Opposite, lanceolate leaves 2.5-6 cm long, 0.5-1.5 cm wide (Invasive.org, 2010). Leaves may be oval or elliptical, dark green, glossy, and waxy in appearance, turning purple in some countries in the autumn (GISD, 2015). The flowers have a strong fragrance and are produced in mid summer in panicles 3–6 cm long, each flower creamy-white, with a tubular base and a four-lobed corolla ('petals') 4–6 mm diameter; stamens 2, attached to the corolla tube; ovary superior, style single, stigmas 2. Spherical fruit, 1 to 1.3 cm in diameter, starting green and ripening to dark purple, almost black colour; contain 1-4 seeds. Smooth, grey-brown bark, spotted with small brown lenticels. Tends to stay evergreen in warmer climates (Natural Medicine Facts, 2015).

Plant Type

Top of page Broadleaved
Perennial
Seed propagated
Shrub
Tree
Vegetatively propagated
Woody

Distribution

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L. vulgare is native to much of Europe, extending as far north as southwest Sweden and southeast Norway (USDA-ARS, 2015). It is also native to northwestern Africa (Morocco), and extends as far east as western Asia (Turkey, northwestern Iran, Armenia, Azerbaijan and Georgia)(Weeds of Australia, 2015). It is now also widely naturalized in south-eastern Australia, and naturalized in southern Africa, the Azores, New Zealand, the USA and southern Canada (Weeds of Australia, 2015). It is reported as invasive in North and South America (Canada, USA, Argentina and Brazil), South Africa, Australia and New Zealand.

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

ArmeniaPresentNative Not invasive USDA-ARS, 2015; Weeds of Australia, 2015
AzerbaijanPresentNative Not invasive USDA-ARS, 2015
Georgia (Republic of)PresentNative Not invasive USDA-ARS, 2015
IranPresentNative Not invasive USDA-ARS, 2015Northwest Iran
TurkeyPresentNative Not invasive USDA-ARS, 2015

Africa

MoroccoPresentNative Not invasive USDA-ARS, 2015
South AfricaPresentIntroduced Invasive Henderson, 2001; USDA-ARS, 2015

North America

CanadaPresentIntroduced Invasive Zhao, 2012Southern region
-British ColumbiaPresentIntroducedUSDA-NRCS, 2015
-OntarioPresentIntroducedUSDA-NRCS, 2015
USAPresentPresent based on regional distribution.
-AlabamaPresentIntroducedUS Forest Service, 2006; Texas Invasives, 2008
-ArkansasPresentIntroducedUS Forest Service, 2006; Texas Invasives, 2008
-ColoradoLocalisedIntroducedUSDA-NRCS, 2015
-ConnecticutPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-DelawarePresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-District of ColumbiaPresentIntroduced Invasive US Forest Service, 2006; USDA-NRCS, 2015
-GeorgiaPresentIntroducedUS Forest Service, 2006; Texas Invasives, 2008
-IllinoisPresentIntroducedUS Forest Service, 2006; Texas Invasives, 2008
-IndianaPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-KentuckyPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-LouisianaPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-MainePresentIntroducedUS Forest Service, 2006; Texas Invasives, 2008
-MarylandPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-MassachusettsPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-MichiganPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-MissouriLocalisedIntroducedUSDA-NRCS, 2015
-MontanaPresentIntroducedUS Forest Service, 2006; Texas Invasives, 2008
-NebraskaPresentIntroducedUS Forest Service, 2006; Texas Invasives, 2008
-New HampshirePresentIntroducedUS Forest Service, 2006; Texas Invasives, 2008
-New JerseyPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-New MexicoPresentIntroducedUSDA-NRCS, 2015
-New YorkPresentIntroducedUS Forest Service, 2006; Texas Invasives, 2008
-North CarolinaPresentIntroducedUS Forest Service, 2006; Texas Invasives, 2008
-OhioPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-OregonPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-PennsylvaniaPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-Rhode IslandPresentIntroducedUS Forest Service, 2006; Texas Invasives, 2008
-South CarolinaPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-TennesseePresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-TexasPresentIntroducedUS Forest Service, 2006; Texas Invasives, 2008
-UtahPresentIntroducedUS Forest Service, 2006; Texas Invasives, 2008
-VermontPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-VirginiaPresentIntroducedUS Forest Service, 2006; Texas Invasives, 2008
-WashingtonPresentIntroduced Invasive US Forest Service, 2006; USDA-NRCS, 2015
-West VirginiaPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008
-WisconsinPresentIntroduced Invasive US Forest Service, 2006; Texas Invasives, 2008

South America

ArgentinaWidespreadIntroduced Invasive I3N-Argentina, 2014
BrazilPresentIntroduced Invasive I3N-Brasil, 2015In Mixed Ombrophilous Forest with Araucaria angustifolia
-ParanaWidespreadIntroduced Invasive I3N-Brasil, 2015
-Rio Grande do SulWidespreadIntroduced Invasive I3N-Brasil, 2015
-Santa CatarinaWidespreadIntroduced Invasive I3N-Brasil, 2015

Europe

AlbaniaPresentNativeUSDA-ARS, 2015
AustriaPresentNativeUSDA-ARS, 2015
BelgiumPresentNativeUSDA-ARS, 2015
BulgariaPresentNativeUSDA-ARS, 2015
Czechoslovakia (former)PresentNativeUSDA-ARS, 2015
FrancePresentNativeUSDA-ARS, 2015
GermanyPresentNativeUSDA-ARS, 2015
GreecePresentNative Natural USDA-ARS, 2015
HungaryPresentNativeUSDA-ARS, 2015
IrelandPresentNativeUSDA-ARS, 2015
ItalyPresentNativeUSDA-ARS, 2015
MoldovaPresentNativeUSDA-ARS, 2015
NetherlandsPresentNativeUSDA-ARS, 2015
NorwayPresentNativeUSDA-ARS, 2015Southeast
PolandPresentNativeUSDA-ARS, 2015
PortugalPresentNativeUSDA-ARS, 2015
-AzoresPresentIntroducedUSDA-ARS, 2015
RomaniaPresentNativeUSDA-ARS, 2015
Russian FederationPresent Natural
-Southern RussiaPresentNativeUSDA-ARS, 2015
SpainPresentNativeUSDA-ARS, 2015
SwedenPresentNativeUSDA-ARS, 2015Southwest
SwitzerlandPresentNativeUSDA-ARS, 2015
UKPresentNativeUSDA-ARS, 2015
UkrainePresentNativeUSDA-ARS, 2015
Yugoslavia (former)PresentNativeUSDA-ARS, 2015

Oceania

AustraliaWidespreadIntroduced Invasive Weeds of Australia, 2015
-New South WalesPresentIntroduced Invasive Weeds of Australia, 2015Tablelands
-QueenslandPresentIntroduced Invasive Weeds of Australia, 2015Southeast, cooler areas
-South AustraliaWidespreadIntroduced Invasive Weeds of Australia, 2015
-TasmaniaWidespreadIntroduced Invasive Weeds of Australia, 2015
-VictoriaWidespreadIntroduced Invasive Weeds of Australia, 2015
New ZealandWidespreadIntroduced Invasive McGregor, 2000; Weeds of Australia, 2015South and North Islands, particularly in Tauranga, Wellington, Canterbury and central Otago; in the colder parts of South Island

History of Introduction and Spread

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L. vulgare has been introduced and widely established in southern Africa (Henderson, 2001), the Azores, Australia, New Zealand, the USA and southern Canada (Weeds of Australia, 2015). In New Zealand L. vulgare, along with other Ligustrum species, is found in both islands, particularly in Tauranga, Wellington, Canterbury and central Otago. L. vulgare is less important as an invasive in New Zealand than other species in the genus (L. sinense and L. lucidum), although it is considered the most abundant species in colder parts of the South Island (McGregor, 2000).

L. vulgare is widely established in southeastern Australia, more commonly in Victoria, Tasmania, and southeastern South Australia. Also present in New South Wales tablelands and in the cooler parts of southeastern Queensland. It is nvasive in Victoria, Tasmania, and South Australia and is considered a potential sleeper weed in other parts of southern Australia (Weeds of Australia, 2015).

In the USA, L. vulgare was introduced in the colonial period as a hedge plant (Cothran, 2003), and has since escaped from cultivation and is becoming naturalized in eastern North American (Zhao et al., 2013; USDA-NRCS, 2015). Haragan (1996) put the date of introduction to the USA as the early to mid-1800s. Its range is still expanding in the eastern and southern USA (Wang and Grant, 2012). Having escaped from cultivation in gardens and along highways, it is invasive mostly in temperate and eastern states and in southern Canada (Zhao, 2012).

In South America, it is widely distributed and invasive in Argentina (I3N-Argentina, 2014), while in Brazil it invades Mixed Ombrophilous Forest (Araucaria angustifolia formations) on the southern high plains (around 900 m altitude) (I3N-Brasil, 2015). 

Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
USA Europe Early 1800s Landscape improvement (pathway cause) Yes Cothran (2003)

Risk of Introduction

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This species is not likely to be accidentally introduced over very long distances, as the seeds do not have structures that adhere to physical vectors or are carried by wind. Deliberate introductions are more likely, as the species is part of the ornamental plant trade along with other species in the genus. Once introduced to a region, the seeds can be dispersed by birds.

Habitat

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L. vulgare grows on sandy, loamy and clay soils, on disturbed and ruderal sites, as well as in scrub and shrublands, under shade or exposed to direct sunlight, on dry or moist soils. It tolerates drought and maritime exposure (GISD, 2015).

Zhao (2012) says that in North America it grows well in full sunlight and along stream banks but tolerates shade and drought, also tolerating almost any soil type. It is a frequent invader in riparian areas, forest edges, old fields, floodplains, mature and disturbed woodlands. The US Forest Service (2006) lists it in habitats including bottomlands, mesic and riparian forests, old fields, primary woodlands, closed canopy forests, calcareous glades and barrens, deciduous cove forests, grassland, roadsides, fence rows, windbreaks and other areas with disturbed soil. It grows well in high light, low nutrient soils, but will tolerate lower light levels if nutrients are increased.

The species is extremely tolerant to atmospheric pollution. It also tolerates drought, limey or chalky soils (Irish Gardeners, 2015).

Habitat List

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CategoryHabitatPresenceStatus
Terrestrial-managed
Cultivated / agricultural land Principal habitat Harmful (pest or invasive)
Disturbed areas Principal habitat Harmful (pest or invasive)
Managed forests, plantations and orchards Secondary/tolerated habitat Harmful (pest or invasive)
Protected agriculture (e.g. glasshouse production) Secondary/tolerated habitat Harmful (pest or invasive)
Rail / roadsides Principal habitat Harmful (pest or invasive)
Rail / roadsides Principal habitat Productive/non-natural
Urban / peri-urban areas Principal habitat Harmful (pest or invasive)
Urban / peri-urban areas Principal habitat Productive/non-natural
Terrestrial-natural/semi-natural
Natural forests Secondary/tolerated habitat Harmful (pest or invasive)
Natural forests Secondary/tolerated habitat Natural
Riverbanks Principal habitat Harmful (pest or invasive)
Riverbanks Principal habitat Natural
Scrub / shrublands Secondary/tolerated habitat Harmful (pest or invasive)
Scrub / shrublands Secondary/tolerated habitat Natural
Wetlands Secondary/tolerated habitat Harmful (pest or invasive)

Biology and Ecology

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Genetics

The chromosome number is reported as 2n=46 in Bulgaria (Petrova et al., 2007).

A study in Ohio, USA, found ten haplotypes identified at cpDNA marker trnH and 11 haplotypes identified at trnS, while 16 haplotypes were identified at the combined cpDNA marker. Two haplotypes were dominant at trnH. High levels of genetic diversity were recorded between invasive plants in natural areas and cultivars in nurseries, so interspecific hybridization was considered as a possible explanation (Zhao, 2012).

Reproductive Biology

Flowers are hermaphroditic and pollinated by insects (GISD, 2015). Mature plants can produce hundreds of fruits per plant per year. Seeds are dispersed by birds and other wildlife that eat the fruits and excrete seeds undamaged (US Forest Service, 2006). The species also reproduces from root sprouts (Invasive.org, 2010).

While the species can produce more than 10,000 fruits per plant with 1-4 seeds per fruit, neither fruit nor seed production are significantly affected by defoliation on flowering branches. Plants can regenerate from roots and stump sprouts (Zhao, 2012).

Physiology and Phenology

In North America, fruits ripen in the autumn, persist into spring, then seeds are dispersed by animals in winter (Zhao, 2012).

Flowering occurs in the summer, from June to July in Ireland. Fruits are ripe in September - October (Irish Gardeners, 2015).

Environmental Requirements

L. vulgare tolerates a wide range of soil types, and can grow in both sun and shade. It also tolerates drought and maritime exposure (GISD, 2015). Irish Gardeners (2015) states that it can tolerate “most locations and harsh treatments”.

Climate

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ClimateStatusDescriptionRemark
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cw - Warm temperate climate with dry winter Tolerated Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
55 45

Rainfall Regime

Top of page Bimodal
Winter

Soil Tolerances

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Soil drainage

  • free
  • impeded

Soil reaction

  • acid
  • neutral

Soil texture

  • heavy
  • light
  • medium

Special soil tolerances

  • infertile

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Glomerella cingulata Pathogen Leaves McGregor, 2000

Notes on Natural Enemies

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Deer browse on sprouts (Miller, 2003).

In the United States, the species has been affected by twig blight anthracnose (Glomerella cingulata), which causes leaf yellowing (Zhao, 2012).

McGregor (2000) investigated pests and diseases associated with Ligastrum spp. in New Zealand to examine their potential for biological control. The fungus Colletotrichum gloeosporioides [Glomerella cingulata] was recorded as attacking L. vulgare. Both McGregor (2000) and Winks et al. (2012), however, found that while Ligastrum is attacked by a wide range of native and introduced invertebrates in New Zealand, overall damage appears to be minimal with none of the herbivore niches well utilized. Invertebrates reported are not specific to Ligastrum, and Winks et al. (2012) also report that no specialised plant pathogens were recovered from Ligastrum spp.

Means of Movement and Dispersal

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L. vulgare produces large numbers of seeds, which can be dispersed by berry-eating birds and other animals in winter (Zhao et al., 2013). It has been intentionally introduced outside its native range for use as a hedging and ornamental plant.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Escape from confinement or garden escapeFrequent accidental escape Yes Henderson, 2001; I3N-Brasil, 2015; Zhao, 2012
Landscape improvement Yes Zhao, 2012
Ornamental purposesIntroduced mainly as a hedge and ornamental plant Yes Yes Zhao, 2012
People sharing resourcesOrnamental use, shade Yes

Impact Summary

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CategoryImpact
Economic/livelihood Negative
Environment (generally) Negative
Human health Negative

Economic Impact

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In New Zealand, control costs of Ligastrum spp. can be high as control is labour intensive, especially because many of the preferred habitats are humid and preclude blanket spraying, making individual plants difficult to find (McGregor, 2000).

When flowering, Ligastrum spp. compete for bees; extensive infestations may reduce pollination of other crops like kiwifruit or honey production, as privet honey is not valued by beekeepers because it has a strong smell, and is too sweet. Privets may host pests and diseases such as the mite Brevipalpus odoratus, which is a potential pest for kiwifruit production, tomato spotted wilt virus Pythium debaryanum and Rosellinia necatrix, and tobacco mosaic virus (McGregor, 2000). The report by McGregor, however, suggests that Ligastrum lucidum and L. sinense are more important as pests and invasive species in New Zealand than L. vulgare.

Environmental Impact

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The species forms dense thickets, therefore displacing native vegetation (GISD, 2015). It shades out and excludes native understory species, and might reduce tree recruitment (Invasives.org, 2010). Shannon et al. (2014) report that in Eastern Deciduous Forest, L. vulgare reduces arbuscular mycorrhizal fungi colonization of native forest understorey species. Shannon-Firestone et al. (2015), in the Eastern Deciduous Forest of Indiana, suggest that allelopathy of L. vulgare and Lonicera maakii could contribute to the decline of susceptible native species.

Social Impact

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Pollen may cause allergic reactions in people (Batanero et al., 1996; Invasive.org, 2010). Berries can be poisonous to humans, although they are consumed by birds (Natural Medicine Facts, 2015).

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Highly adaptable to different environments
  • Tolerant of shade
  • Highly mobile locally
  • Benefits from human association (i.e. it is a human commensal)
  • Has high reproductive potential
  • Reproduces asexually
Impact outcomes
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Modification of successional patterns
  • Monoculture formation
  • Negatively impacts agriculture
  • Negatively impacts human health
  • Reduced amenity values
  • Reduced native biodiversity
  • Threat to/ loss of endangered species
  • Threat to/ loss of native species
Impact mechanisms
  • Allelopathic
  • Causes allergic responses
  • Competition - monopolizing resources
  • Competition - shading
  • Competition - smothering
  • Pest and disease transmission
  • Hybridization
  • Poisoning
  • Pollen swamping
Likelihood of entry/control
  • Highly likely to be transported internationally deliberately
  • Highly likely to be transported internationally illegally
  • Difficult to identify/detect as a commodity contaminant
  • Difficult to identify/detect in the field
  • Difficult/costly to control

Uses

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Widely planted as hedges (Brickel, 1996; US Forest Service, 2006). Was planted by homeowners in home landscapes in North America from at least 1920, and by state transportation departments along highways, until it lost favour to other species because of the leaf yellowing caused by infection from Glomerella cingulata (Dirr, 2009).

L. vulgare has been used in folk medicine in southern Europe, particularly as an anti-inflammatory agent (Czerwin´ska et al, 2013).

Uses List

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Environmental

  • Agroforestry
  • Amenity
  • Boundary, barrier or support
  • Graft stock

General

  • Ornamental

Materials

  • Poisonous to mammals

Medicinal, pharmaceutical

  • Traditional/folklore

Ornamental

  • Seed trade

Detection and Inspection

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Plants are often found dispersed in the landscape in native vegetation that can be woody, which makes them difficult to detect, especially in early stages (Zhao, 2012). This is a common problem with forest invaders. Zhao et al. (2013) suggest that identifying favourable habitats for initial patches can assist in early detection of plants such as privet before the population undergoes rapid expansion, but acknowledges that small populations during this phase can be hard to detect. It is suggested that scouting edge habitats where bird dispersed seeds may be initially introduced is probably the most effective means for detecting early invasion.

Similarities to Other Species/Conditions

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Other species in the genus are invasive and quite similar to L. vulgare. Related species include Ligustrum japonicum, Ligustrum lucidum, Ligustrum obtusifolium, Ligastrum ovalifolium, and Ligastrum sinense. It is difficult to separate Ligustrum species once they escape into the wild, as identification depends on flowers. Even then identification can be questionable, as there are many lower taxa (Invasive Plant Atlas of New England, 2015). Maddox et al. (2010) give a key to Ligustrum spp. present in the middle southern USA.

L. japonicum is similar but has larger leaves (Miller, 2003). L. vulgare also resembles Forestiera ligustrina which occurs mainly on rocky sites and has sparse twigs, flowers, and fruit (Miller, 2003).

Symphoricarpos orbiculatus has similar leaves (Bugwood, 2014). S. orbiculatus is distinguished by its very slender twigs, deciduous leaves, red berries borne in axillary clusters, and the lack of a terminal bud.

Prevention and Control

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Physical/Mechanical Control

While plants are small they may be pulled or dug out and uprooted. As this causes soil disturbance, a new invasion may be facilitated, and requires follow up, as it is difficult to remove 100% of roots. Stems must be cut once per growing season or more as close to the ground as possible to contain spread (US Forest Service, 2006).

Biological Control

McGregor (2000) reports a survey of pests and pathogens associated with Ligastrum spp. in New Zealand, and discusses the potential for biological control. While McGregor says that none of the invertebrates listed in published literature as being associated with Ligustrum spp. appear promising as potential biological control agents for privet, some fungal pathogens, particularly rusts, deserve further investigations. It is also suggested that preliminary surveys in southeast Asia found a lepidopteran caterpillar and some fungi that may be useful for biological control of privet in New Zealand. Subsequent work by Winks et al. (2012) in New Zealand found the larvae of a moth, thought to be Trichophysetis cretacea, feeding within privet berries. Recommendations for further studies on this moth, and for proceeding with a classical biological control programme for privet in New Zealand, are made.

Chemical Control

The US Forest Service (2006) suggests that control can be carried out with general use herbicides such as glyphosate or triclopyr. GISD (2015) says that larger L. vulgare plants need to be cut and glyphosate applied to the stump. Metsulphuron methyl (Maddox et al., 2010) has also been suggested for application both to foliage and to cut stumps. Other herbicides listed by Maddox et al. (2010) for Ligastrum  spp. include 2,4-D + 2,4-DP, and imazapyr. Stem injections can also be used for trees that are difficult to cut down.

Ward et al. (1999) suggested that gel pruning might also be an effective method for killing privet in New Zealand. In this method, a gel containing herbicide is applied to the cut surface as stems are pruned.

Sources cited by McGregor et al. (2000) list chemical control methods for Ligustrum spp. including spraying with glyphosate with an adjuvant in spring, and application of picloram mixed with 2,4-D, and picloram mixed with triclopyr ester to cut stumps.

Gaps in Knowledge/Research Needs

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Further research on biological control is highly desirable, especially given that the species is difficult to trace in shrubland or forests in the initial stages of invasion.

References

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Batanero Gonzalez Peña E;MAde la; Villalba M; Monsalve RI; Martin-Esteban M; Rodriguez R, 1996. Isolation, cDNA cloning and expression of Lig v 1, the major allergen from privet pollen. Clinical and Experimental Allergy, 26(12):1401-1410.

Bean WJ, 1978. Trees and Shrubs Hardy in the British Isles, vol 2.

Brickel C, 1996. The Royal Horticultural Society A-Z Encyclopedia of Garden Plants. London, UK: Dorling-Kindersley.

Bugwood, 2014. Ligustrum vulgare. http://wiki.bugwood.org/Ligustrum_vulgare

Cothran JR, 2003. Gardens and Historic Plants of the Antebellum South., USA: The University of South Carolina Press, 217 pp.

Czerwinska ME; Granica S; Kiss AK, 2013. Effects of an aqueous extract from leaves of Ligustrum vulgare on mediators of inflammation in a human neutrophils model. Planta Medica, 79(11):924-932. https://www.thieme-connect.com/ejournals/abstract/10.1055/s-0032-1328718

Dirr MA, 2009. Manual of Woody Landscape Plants: Their Identification, Ornamental Characteristics, Culture, Propagation and Uses [ed. by 6th]. Champaign, IL, USA: Stipes, 641 pp.

GISD, 2015. Global Invasive Species Database (GISD). IUCN. http://www.issg.org/database/welcome/

Green PS, 1985. Ligustrum robustum subsp. walkeri (Oleaceae). Kew Bulletin, 40:130.

Green PS, 1987. The Oleaceae. In: Dassanayake MDF, ed. Flora of Ceylon, Vol VI. New Delhi, India: Amerind Publishing.

Green PS, 1990. Ligustrum (Oleaceae) in Southern India. Kew Bulletin, 45:693-696.

Green PS, 1995. Taxonomic notes relating to Ligustrum (Oleaceae). Kew Bulletin, 50:379-386.

Haragan PD, 1996. Privet (Ligustrum vulgare, L. sinense, L. japonicum). In: Invasive Plants: Weeds of the Global Garden [ed. by Randall, J. M. \Marinelli, J.]. Brooklyn, NY, USA: Brooklyn Botanic Garden, 58-59.

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Links to Websites

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WebsiteURLComment
GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gatewayhttps://doi.org/10.5061/dryad.m93f6Data source for updated system data added to species habitat list.
Global register of Introduced and Invasive species (GRIIS)http://griis.org/Data source for updated system data added to species habitat list.

Contributors

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10/06/15 Original text by:

Dr Silvia Ziller, Society for Wildlife Research and Environmental Education, Curitiba, PR, Brazil

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