Ligustrum japonicum
(Japanese privet)

Ligustrum japonicum is a shrub to small tree listed as invasive in the USA, Chile and Brazil. In the USA, it is listed as naturalized in 12 of the southeastern states, being considered as invasive in some states including Tennessee, Alabama and South Carolina. L. japonicum is not considered as invasive in Texas but as an F3 species, defined as ‘being repeatedly introduced or long-persisting in some areas, or as an incipient invasive’. In Georgia, it is listed as a Category 2 species which is defined as 'a moderate exotic plant problem in natural areas, invading native plant communities and displacing native species, but to a lesser degree than Category 1 species’. L. japonicum is listed as potentially invasive in Cuba, being categorized as a species that is naturalized with a tendency to proliferate. This species invades lowlands and uplands, fence rows, abandoned pastures, intermittent streambeds and woodlands. It colonizes areas by root sprouting and through animal dispersal. It forms dense thickets in fields and forest understoreys, shading and displacing many native species in the process. It is difficult to eradicate once established.

Ligustrum japonicum is a shrub to small tree native to Japan and South Korea and used as an ornamental throughout its distribution range (Flora of China Editorial Committee, 2020). It is reported from Asia, North America, the Caribbean, South America, Europe and Oceania (See Distribution Table for details: Maccioni, 1929; Hsieh et al., 1998; Sobrino et al., 2002; Jalili et al., 2010; Acevedo-Rodríguez and Strong, 2012; Uzzell, 2017;PIER, 2018; ; Barcham Trees, 2020; Flora of China Editorial Committee, 2020; I3N-Brasil, 2020; Missouri Botanical Garden, 2020; USDA-NRCS, 2020).

Ligustrum japonicum is a species with a high risk of introduction into subtropical and temperate areas with mild winter temperatures. It is available for sale at nurseries and various internet sites worldwide (Gilman and Watson, 1993; Dave’s Garden, 2020). L. japonicum is reported as escaping from cultivation and forming dense thickets in fields and forests understoreys where it outcompetes native species. It is also considered difficult to eradicate (Swearingen and Bargeron, 2020).

Ligustrum japonicum is a shrub to small tree reported from thickets, forest edges, damp forests, gallery forests, disturbed sites and as cultivated in urban areas (Sobrino et al., 2002; I3N-Brasil, 2020; North Carolina Invasive Plant Council, 2021; Texas Invasives, 2020).

Genetics

Germplasm collections of L. japonicum are available at USDA facilities (USDA-ARS, 2020). Various cultivars have been developed and are available as ornamentals (Gilman and Watson, 1993). Research for developing sterile or seedless tetraploids have been made by Fetouh et al. (2016), to reduce or eliminate the species invasive potential. The chromosome number reported for this species is 2n = 22, 44, 46 (Sugiura, 1936; Hsu, 1967; Somego, 1974; Kumar, 1987). Many cultivars are available (Gilman et al. 2018).

Reproductive Biology

Ligustrum japonicum is mainly propagated by cuttings and seeds (Dave’s Garden, 2020). Pollinators reported for this species are butterflies [Lepidoptera] and honeybees (Camillo and Garófalo, 1989; Dave’s Garden, 2020). Birds are reported as seed dispersers (Gilman and Watson, 1993; Witmer, 1996). Nearly all seed germination occurs during the next year’s growing season (Uzzell, 2017). L. japonicum usually produces numerous volunteers in gardens and will resprout from the roots (Dave’s Garden, 2020; Swearingen and Bargeron, 2020).

Physiology and Phenology

Ligustrum japonicum grows fast when young but then slows down with age (Gilman and Watson, 1993). Flowering is reported from July to October and fruiting in autumn (Gilman and Watson, 1993). In Korea, flowering occurs from June to July and fruiting from October to November (Jang et al., 2020). This species is not adapted to hot weather and the foliage will scorch at high temperatures (Missouri Botanical Garden, 2018). Munger (2003) reports that L. japonicum will resprout after fires. No allelopathic effects are known for this species (HEAR, 2017).

Longevity

Ligustrum japonicum is a perennial shrub to small tree (Maddox et al., 2010).

Environmental Requirements

Ligustrum japonicum is a perennial shrub to small tree that grows best in temperate climates, in full sun to partial shade and in a wide range of well-drained soils with a pH from 6.1 to 7.8 (Gilman and Watson, 1993; Maddox et al., 2010; Dave’s Garden, 2020). Although this species is reported as surviving temperatures down to -17°C (Dave’s Garden, 2020), there are also reports that L. japonicum will not survive freezing temperatures (Jalili et al., 2010). It  is reported as being salt intolerant and unable to grow when exposed to direct salt spray (Gilman and Watson, 1993). It is also listed as growing in coastal coral sands of the Pacific (PIER, 2018). L. japonicum is drought tolerant (Gilman and Watson, 1993) and pollution resistant (North Carolina State Extension, 2020).

Thrips and mites can cause discolouration of the leaves of L. japonicum and nematodes can be a problem in sandy soils (Gilman et al., 2018).

Pests reported as affecting L. japonicum include Atta texana (Waller, 1989), Macrodactylus sp. (Aragón-García et al., 2010), Ochyromera ligustri (Wray, 1961; Johnson and Lyon, 1991), Palpita quadristigmalis (Villegas-Luján et al., 2019), Asphondylia sphaera (Ohsako et al., 1981; Uechi and Yukawa, 2006), Hishimonus hamatus (Seljak, 2013) and Tuckerella pavoniformis (De Leon, 1955), as well as various scale species such as Phalacrococcus howertoni and Fiorinia phantasma (Wray, 1961; McDaniel, 1974; Hodges and Hodgson, 2010; Ahmed et al., 2021). Pathogens causing disease in L. japonicum include Colletotrichum gloeosporioides [Glomerella cingulata] (Shen et al., 2017), Pseudomonas savastanoi (Bottalico and Ercolani, 1971), Puccinia klugkistiana (Lee et al., 2019), Pseudocercospora lilacis (Andrianova and Minter, 2014), Macrophomina phaseolina (Alfieri and Stokes, 1971), Meloidogyne javanica (Alfieri and Stokes, 1971) and Microsphaera syringae [Erysiphe syringae] (Falacy and Glawe, 2003).

Ligustrum japonicum is reported to be a novel food plant of the southern green stink bug Nezara viridula in Parana, Brazil (Panizzi et al., 1996).

Animal feed, fodder, forage

• Forage

Environmental

• Agroforestry
• Amenity
• Boundary, barrier or support
• Wildlife habitat
• Windbreak

General

• Botanical garden/zoo
• Sociocultural value

Human food and beverage

• Beverage base
• Emergency (famine) food
• Seeds

Medicinal, pharmaceutical

• Traditional/folklore

Ornamental

• Christmas tree
• Cut flower
• garden plant
• Potted plant
• Propagation material
• Seed trade

Ligustrum japonicum is distinguished from other Ligustrum species by its large leaves and usually glabrous stems. The leaves of L. japonicum snap when bent while those of L. lucidum are more flexible and will not break. The corolla tube is shorter than the corolla lobes in L. lucidum while in L. japonicum the corolla tube is longer than the lobes (Carolina Nature, 2015).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

SPS Measures

Since species of Ligustrum are prolific seed producers and dispersed by birds, the recommendation is to not plant any of the species as ornamentals, especially to prevent re-infestation of treated sites (Maddox et al., 2010).

Public Awareness

There are various publications available on L. japonicum, its invasiveness and how to manage, control and eradicate the species (Smith, 2008; Miller et al., 2015; Alabama Forestry Commission, 2020).

Eradication

Smith (2008) proposes the eradication of the species in areas invaded using  a combination of mechanical removal with chemical treatments, and followed up the next year to control re-infestation.

Cultural Control and Sanitary Measures

It is important to manage and frequently monitor recently treated areas for the eradication of the species to prevent the resprouting of L. japonicum (Munger, 2003). Planting native species to accelerate the recuperation of the habitats is also recommended (I3N-Brasil, 2020).

Physical/Mechanical Control

Physical controls such as shading are ineffective in the removal of Ligustrum species. Hand pulling the young seedlings is recommended, combined with chemical control or when herbicides are not permitted (Maddox et al., 2010).

Biological Control

There are no biological methods used to control or eradicate L. japonicum. Munger (2003) suggests the use of goats to provide some control in areas colonized by the species. Fetouh et al. (2016) showed that tetraploids can be readily induced in L. japonicum which could then be used for producing new selections or cultivars with reduced invasive potential.

Chemical Control

The chemicals used to control Ligustrum species include 2,4-D + 2,4-DP, imazapyr + metsulfuron methyl, metsulfuron methyl, fosamine ammonium, glyphosate, imazapyr, imazapyr + glyphosate, metsulfuron methyl and triclopyr (Maddox et al., 2010).

Detailed information on the effects of L. japonicum on habitats or native species is needed. More information on the possible use of tetraploids to control seed production is also needed.

19/03/2020 Original text by:

Jeanine Vélez-Gavilán, University of Puerto Rico at Mayagüez, Puerto Rico