Ligustrum spp. Oleaceae

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Present on Pacific Islands?  yes

Threat only at high elevations?  no

Risk assessment results: 
Reject, score: 11 (Go to the risk assessment for Ligustrum lucidum (Australia))
Evaluate, score: 6 (Go to the risk assessment for Ligustrum lucidum (Pacific))
Evaluate, Score: 6 (Go to the risk assessment for Ligustrum japonicum)
High risk, Score: 11 (Go to the risk assessment for Ligustrum sinense)

Common name(s): [more details]

English: privet

French: troène de Californie, troène de Ceylan, troène des haies

Habit:  shrub/tree

Description:  "Small trees or erect shrubs, sometimes deciduous; leaves simple, short-petiolate, the blades entire, often glandular beneath; inflorescences terminal, thyrsoid or paniculiform, bracteate, the flowers small, 4-merous, subsessile or short-pedicellate; calyx campanulate, truncate or shortly 4-dentate; corolla infundibular or campanulate, the tube equal to or longer than calyx tube, the lobes induplicate-valvate in bud, becoming spreading, slightly shorter than or longer than corolla tube; stamens 2, inserted on corolla tube, the filaments slender, short, the anthers basifixed, ellipsoid or oblong, usually exserted; ovary subglobose, the ovules 2 per locule, pendulous, the style often filiform, the stigma 2-lobed; fruit a carnose berry or somewhat drupaceous, the endocarp chartaceous or membranous, the seeds usually solitary, sometimes 2-4"  (Smith, 1988; pp. 135-136).

Habitat/ecology:  Privets are extremely aggressive and can form dense, impenetrable thickets that crowd out desirable plants. They are prolific seed producers.

Dry, moist, and wet forests, open areas, roadsides, up to at least 6,000 ft. elevation in Hawai‘i. In Australia, Ligustrum lucidum is an invasive species in coastal rainforest and L. sinense naturalizes along fencelines and on the margins of rainforest (Csurhes & Edwards, 1998; p. 174).

Propagation:  Seeds distributed by frugiferous birds (Carr et al., 1992, cited in Csurhes & Edwards, Smith, 1991; pp. 238-239). 

'Under shaded conditions [L. robustum var. walkeri] does not bear fruit.  The juvenile period is shortest in open areas and longest under forest canopy.  It is possible to delay sexual maturity by preserving a dense forest cover"   (Kueffer & Lavergne, 2004, p. 25).

Native range:  Eurasia to Malaysia and tropical Australia. Commonly used as hedges and ornamentals.

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
American Samoa Tutuila Islands	Tutuila Island	introduced invasive cultivated	Space, James C./Flynn, Tim (2000) (pp. 5, 11) L. sinense?
Australia (Pacific offshore islands) Lord Howe Island	Lord Howe Island	introduced invasive	Csurhes, S./Edwards, R. (1998) (p. 174) L. sinense
Australia (Pacific offshore islands) Lord Howe Island	Lord Howe Island	introduced	Pickard, J. (1984) (p. 207) L. sinense
Australia (Pacific offshore islands) Lord Howe Island	Lord Howe Island	introduced invasive	Orchard, Anthony E., ed. (1994) (p. 20) L. sinense Lour. "A native of China which has also escaped from cultivation and is proving a serious weed in places". Vouchers cited: A.C. Beauglehole, 5848 (CANB, MEL), J. Pickard 1411 (NSW), J. Pickard 3458 (NSW), J. Pickard 3462 (NSW)
Australia (Pacific offshore islands) Norfolk Islands	Norfolk Island	introduced invasive	Orchard, Anthony E., ed. (1994) (p. 9) L. lucidum W.T. Aiton "A native of western and southern China which has escaped from cultivation and has proved a serious weed in some places". Voucher cited: W.R. Sykes NI 617 (CHR); L. sinense Lour. "A native of China which has also escaped from cultivation and is proving a serious weed in places". Voucher cited: W.R. Sykes NI 227 (CHR)
Fiji Fiji Islands	Viti Levu Island	introduced cultivated	Smith, Albert C. (1988) (p. 136) Ligustrum sinense. Vouchers cited: DA 9809, DA 12240
Guam Guam Island	Guam Island	introduced	Fosberg, F. R./Sachet, Marie-Hélène/Oliver, Royce (1979) (p. 209) L. japonicum, L. sinense
State of Hawaii Hawaiian Islands	Hawai‘i (Big) Island	introduced invasive	Herbarium Pacificum Staff (1999) (p. 6) L. sinense Lour.; voucher cited: T. Tunison s.n. (BISH 605525)
State of Hawaii Hawaiian Islands	Hawai‘i (Big) Island	introduced invasive	Staples, George W./Imada, Clyde T./Herbst, Derral R. (2003) (p. 16) Ligustrum lucidum Ait., voucher cited: T. Motley, W. Char, B. Pang & C. Imada 1001 (BISH)
State of Hawaii Hawaiian Islands	Kaua‘i Island	introduced invasive	Lorence, David/Flynn, Tim (1999) (p. 5) L. sinense Lour.; vouchers cited: D. Lorence, T. Flynn, S. Joe, F. Kraus, K. Reinard, J. Plews 8149 (BISH, K, MO, PTBG, US), T. Flynn & D. Lorence 6132 (BISH, K, PTBG) Profusely naturalized in Koke‘e State Park.
New Caledonia New Caledonia Archipelago	Île Grande Terre	introduced invasive cultivated	MacKee, H. S. (1994) (p. 108) L. lucidum; voucher cited: MacKee 37698 (cult.); L. sinense; vouchers cited: MacKee 1669 (spontané), MacKee 24853 (cult.) Spontané
Samoa Western Samoa Islands	Upolu Island	introduced cultivated	Space, James C./Flynn, Tim (2002) (p. 10) Ligustrum sp. L. sinense? Single cultivated plant in house yard.
Tonga Tongatapu Group	Tongatapu Island	introduced cultivated	Space, James C./Flynn, Tim (2001) (p. 7) Ligustrum sp.

Pacific Rim
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Australia Australia (continental)	New South Wales	introduced invasive cultivated	Csurhes, S./Edwards, R. (1998) (p. 174) L. lucidum, L. sinense
Australia Australia (continental)	Queensland	introduced invasive cultivated	Csurhes, S./Edwards, R. (1998) (p. 174) L. lucidum, L. sinense
New Zealand New Zealand	New Zealand (country)	introduced invasive	Owen, S. J. (1997) L. lucidum, L. sinense
New Zealand New Zealand	New Zealand (country)	introduced invasive cultivated	Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. (1988) (pp. 878-880) L. lucidum Aiton f., "Naturalised extensively in waste places, margins of remnant forest stands, coastal cliffs, and gardens"; L. ovalifolium Hassk., "Forest remnant margins, roadside banks, and waste places"; L. sinense Lour., "Forest margins, waste places, particularly roadsides and cliffs in and near towns and cities"; L. vulgare L., "Usually on waste land, roadside banks and in and around modified forest remnants".

Indian Ocean
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
La Réunion (France) La Réunion Island	La Réunion Island	introduced invasive	MacDonald, I. A. W./Thebaud, C./Strahm, W. A./Strasberg, D. (1991) (pp. 51-61) L. robustum, L. sinense
La Réunion (France) La Réunion Island	La Réunion Island	introduced invasive	Lavergne, Christophe (2006) Ligustrum robustum (Roxb.) Blume subsp. walkeri (Decne) P.S. Green, "Très envahissant"; Ligustrum ovalifolium Hassk, "Cultivé/naturalisé"
La Réunion (France) La Réunion Island	La Réunion Island	introduced invasive	Kueffer, C./Lavergne, C. (2004) (p. 4) Ligustrum robustum subsp. walkeri
Mauritius Mautitius Islands (Mauritius and Rodrigues)	Mauritius Island	introduced invasive	Lorence, D./Sussman, R. W. (1988) (pp. 187-204) L. robustum var. walkeri (Decne.) Mansfr.).
Mauritius Mautitius Islands (Mauritius and Rodrigues)	Mauritius Island	introduced invasive	Kueffer, C./Mauremootoo, J. (2004) (p. 6) L. robustum var. walkeri (Decne.) Mansfr.).
Mauritius Mautitius Islands (Mauritius and Rodrigues)	Rodrigues Island	introduced invasive	Cronk, Q. C. B./Fuller, J. L. (2001) (p. 166) Ligustrum robustum
Mauritius Mautitius Islands (Mauritius and Rodrigues)	Rodrigues Island	introduced invasive	Kueffer, C./Mauremootoo, J. (2004) (p. 6) L. robustum var. walkeri (Decne.) Mansfr.).

Comments:  L. robustum Blume var. walkeri (Decne.) Mansfr is reported to be a problem on Mauritius (Lorence and Sussman, 1988) and La Réunion (Kueffer & Lavergne, 2004, p. 24). Some other well-known pest ligustrums are L. lucidum Aiton, L. ovalifolium and L. sinense Lour. All species should be avoided, as several have proven invasive in island ecosystems.

Control:  The Nature Conservancy's Stewardship Abstract contains information on control methods.

Physical: Small plants may be hand pulled; older individuals need to be dug out.

Chemical: Foliar treatment of actively growing plants with glyphosate herbicide. Treat cut stumps to prevent resprouting.

"Foliar applications of glyphosate effective. Katie Cassel (Kōke‘e Museum) reported privet was susceptible to cut-stump applications of triclopyr or glyphosate.  Stems <0.5 inch diameter susceptible to basal bark application of 20% triclopyr ester in oil.  Larger stems must be notched or frilled.  HAVO staff report control with triclopyr amine at 10% of product in water applied to cut stumps  (Chris Zimmer, HAVO).  The manufacturer reported that metsulfuron was highly effective when applied to the foliage of actively growing plants at a rate of 5 grams per 10 liters of water (spray to wet the foliage)"  (Motooka et al., 2003).

For L. robustum var. walkeri in Réunion, "the most effective technique lasts for three years and is applied in natural, fairly undisturbed forests.  In the first year, seedlings are removed by hand and mature plants are cut at the base and then treated with a solution of glyphosate (Missile at 360 g/l).  Further control measures are necessary during the first two years after treatment to eliminate all regrowing plants.  The longevity of the seeds in the soil is rather short (maximum two years).  The systematic elimination of all seedlings and adults over a period of two years guarantees the total eradication of the species in a site.  Additionally, knowing that the minimum juvenile period is two years in open areas and 4-5 years under forest canopy, the control efforts need to be applied only every 2-4 years, according to light conditions"  (Kueffer & Lavergne, 2004, p. 24).

Biological: An investigation of possible biological control agents for L. robustum var. walkeri is under way on La Réunion.  "Among the 30 plant pathogen species collected, only one species, the mitosporic fungus Thedgonia ligustrina, is promising.  Twenty-one insect species were assessed and host specificity testing begin.  The epiplemid moth Epiplema albida seems to be a promising biocontrol agent.  Before releasing E. albida in Réunion, research is currently concentrating on collecting fresh E. albida material from Sri Lanka, eliminating its associated parasitoids, and then conducting complementary tests  in quarantine in Réunion"  (Kueffer & Lavergne, 2004, p. 25).

Additional information:
Information from the book "Weeds of Hawaii‘s Pastures and Natural Areas; An Identification and Management Guide" (Motooka et al., 2003). (PDF format).
Report (PDF format) from US Geological Survey, Biological Resources Division, Haleakala Field Station, Hawaii "Plants of Hawaii".
NRCS Plant Guide for Ligustrum sinense (PDF)
See information on the Environment Bay of Plenty, New Zealand, web site on both L. lucidum and L. sinense.
Fact sheet, including control information, from the Bay of Plenty Regional Council, New Zealand.
Chinese privet (Ligustrum sinense) factsheet (PDF format) from Virginia Department of Conservation & Recreation's invasive plant species list
Photos and additional information on Ligustrum sinense at University of Florida, Center for Aquatic and Invasive Plants.
The Nature Conservancy photos and Stewardship Abstract.
Information from "Invasive plants of Asian origin established in the United States and their natural enemies, volume 1" (PDF format).
Information on Ligustrum lucidum from the Global Invasive Species Database.
Information on Ligustrum robustum from the Global Invasive Species Database.
Information on Ligustrum sinense from the Global Invasive Species Database.
Information on Ligustrum vulgare from the Global Invasive Species Database.
Information on Ligustrum sinense and Ligustrum vulgare from the publication "Nonnative invasive plants of Southern forests: A field guide for identification and control".
Information on Ligustrum japonicum and Ligustrum lucidum from the publication "Nonnative invasive plants of Southern forests: A field guide for identification and control".
Information from the Southeast Exotic Pest Plant Council Invasive Plant Manual.
Information on Ligustrum sinense from the book "Identification and biology of non-native plants in Florida's natural areas" (PDF format).

Additional online information about Ligustrum spp. is available from the Hawaiian Ecosystems at Risk project (HEAR).

Information about Ligustrum spp. as a weed (worldwide references) may be available from the Global Compendium of Weeds (GCW).

Taxonomic information about Ligustrum spp. may be available from the Germplasm Resources Information Network (GRIN).