Assessing the Invasive Potential of 12 Ligustrum Sinense, Ligustrum Lucidum and Ligustrum Japonicum Cultivars Grown in Northern and Southern Florida

Chinese privet (Ligustrum sinense) and glossy privet (Ligustrum lucidum) have widely naturalized throughout the southeast United States, dominating the understory of mesic forests and displacing native plant communities.  Both are serious environmental weeds in Australia and New Zealand.  In Florida, chinese privet and glossy privet have escaped cultivation in x and x counties, respectively and are listed by the Florida Exotic Pest Plant Council as Category I invasives and are not recommended for planting by the University of Florida IFAS status assessment protocol.  A third privet, japanese privet (Ligustrum japonicum) has escaped cultivation but is not listed as invasive in Florida.  All three species have ornamental value, with numerous cultivars commercially available.  Seedlings of chinese privet, glossy privet and japanese privet (wildtype selections) and clonally propagated cultivars, including one hybrid (L. lucidum x L. japonicum), were obtained in finished 1 gal pots.  Field plantings of nine uniform plants of each were installed under full sun conditions in south FL (Fort Pierce, USDA Cold Hardiness 9b) and north FL (Quincy, USDA Cold Hardiness, 8b).  Plants were evaluated monthly for flowering and fruiting, and tri-monthly for visual quality.  Visual quality was based on a scale from 1 to 5 where 1=poor, and 5=excellent. 

 

 

Visual quality and flowering varied by cultivar and site.  Regardless of cultivar, after 72 weeks (Nov. 2009), north FL plants received higher visual quality ratings than south FL plants. However, ‘Howard’ japanese privet, ‘Jack Frost’ japanese privet, and ‘Variegatum’ chinese privet had very good to excellent landscape performance at both sites.  After 72 weeks, north FL plants were 1.2 to 2.8 times larger and produced 31 times more fruit than south FL plants.

 

Seed viability and germination experiments were conducted from larger, independent populations of chinese privet, glossy privet and japanese privet.  Pre-germination viability was 77% (chinese privet), 96% (glossy privet), and 37% (japanese privet) correlating to 68%, 90%, and 21% germination in the greenhouse, respectively.  Germination varied by temperature and light.  Under a 12 hr photoperiod, chinese privet had the greatest germination (79%) at 20/10 °C, followed by glossy privet (76%) at 20/10 °C, followed by japanese privet (71%) at 25/10 °C.  Field trials will continue to determine stability of variegation.