Callery pear

Callery pear has been reported occasionally outside of cultivation in the southern portion of the Great Lakes Basin. It is not known to occur outside of cultivations Minnesota, northern Michigan, northern New York State, or Ontario. It is most frequently reported as invasive in the Central, Southeastern and Mid-Atlantic United States. USDA reports Callery pear as being hardy to a minimum temperature of -28^oF (Zone 4a), though it does not appear to be able to grow from seed in Zones colder than 5a. This species may become more prevalent in the Great Lakes region over time due to the impacts of climate change. Particularly dense populations of Callery pear can be expected in areas where the species and its various cultivars have been or still are popular as ornamental trees.

Additional invasive species distribution data for specific Great Lakes jurisdictions is available via:

• Midwest Invasive Species Information Network (Michigan)
• iMapInvasives (New York and Pennsylvania)
• EDDMapS Ontario

Fruits are produced when genetically different varieties are cross-pollinated by generalist insect pollinators (Hardiman et al. 2010).  Seed is spread over distance by birds, which eat the fruit. Different bird species may be involved in spreading Callery pear to disturbed edge habitats and more intact ecosystems (Culley 2019). Uneaten fruit falls by gravity, leading to thicket-like growth among invasive populations. It can also spread locally by suckering from the root system, especially following damage to the main trunk.

Callery pear occurs most frequently in forest edges, open and disturbed woodlands, roadsides, and fallow fields. However, its tolerance of partial shade allows it the species to move into forest interiors over time (Culley 2019).

Callery pear can quickly establish dense thickets by self-seeding. The trees leaf out early in the spring relative to other species and the thickets shade out native understory plants. The density and thorniness of the thickets can also impact wildlife movement in invaded areas.

The first use of Callery pear in North America was in the early part of the 20th century as rootstock for fruit pears (P. communis) with the goal of improving fire blight resistance. The first ornamental variety of Callery pear, Bradford, was developed and marketed in the middle of the century. Subsequently many more varieties were developed to address structural and breakage problems observed with Bradford. Callery pear varieties continue to be used as landscape trees due to their compact size and shape, fall color, early spring blossoms and high degree of adaptability (Culley 2017; Dirr 1998; Dirr and Warren 2019). Varieties are still sometimes included on municipal street tree lists in the Midwest (author’s personal observation, 2019). Some state and local governments and environmental groups have recently run awareness campaigns about its invasive potential.

Cultivated Callery pear varieties are self-sterile, meaning that a tree cannot be pollinated by another tree of the same variety. However, the varieties are not cross-sterile, and many varieties have been commonly planted, resulting in cross-pollination and seed production. When wild type rootstocks of cultivated varieties are able to sprout and flower, this can also facilitate reproduction (Culley et al. 2011).

A team at North Carolina State University has developed a triploid hybrid of Callery pear called ‘Chastity.’ Triploid plants have three sets of chromosomes and generally produce little to no viable seed. The researchers observed the reproductive success of thirteen different triploids and further developed the least fertile type (Phillips et al. 2016). Seed production in this variety is reduced 99.14% compared to the species (Dirr and Warren 2019). The long-term viability of any seedlings that are generated by a triploid mother plant has not been studied.

Please see our Landscape Alternatives pages for more information about how the WIGL Collaborative selected alternatives.

^a  Feature is considered improved in the listed cultivar(s). However, straight species native plants may provide greater pollinator benefits.
^b  Lindens have attractive, fragrant flowers, but flower several weeks after Callery pear (late spring to early summer)

Green = native to part of the Great Lakes Basin
Yellow = native to the United States
Blue = not native but not invasive

The WIGL Collaborative’s decision trees are designed to help site users, who are perhaps newly discovering that plants that are part of their home landscaping are invasive, prioritize which species should be removed first based on risk to the surrounding environment, economy, and occasionally, to human health. In a perfect world, everybody would remove all invasive plants from their landscaping right away, but in reality, removing mature woody plants involve a hefty investment of time and/or money. These diagrams can help people with multiple woody invasives in their landscaping prioritize to get the most benefit for their efforts.

To learn more about the methodology and information used to develop the decision trees and for helpful hints on how to answer the questions, please see the full report here (PDF).

The following is a brief overview of management techniques shown to be effective on Callery pear. For more detailed information on how to use these techniques, visit our Management and Control page. For local assistance managing woody invasive species, please get in touch with a cooperative invasive species management group or a university extension program.

Timing and spread concerns: Early detection is an advantage in managing any invasive species. Whenever possible, individual plants should be controlled before they are able to fruit in order to prevent spread. If control is undertaken after plants have fruited, it is best not to remove the plants from the site to avoid spreading seed. 

Physical control: Callery pear plants can be pulled or dug up as long as the roots are completely removed. Incomplete removal leads to regrowth. Callery pear regrows vigorously from cut stems and stumps after injury, so methods that top-kill plants, such as prescribed fire, grazing, and stem cutting, are unlikely to provide effective long-term control as stand-alone practices and could potentially increase the density of infestation.

Chemical control and combined approaches: Foliar, basal bark and cut stump herbicide treatments are effective. Foliar spray is the most feasible method for a large, dense infestation of smaller trees and is effective anytime plants are actively growing and fully leafed out. Foliar application can be done as a stand-alone practice or can be used as a follow-up to top-killing physical control methods by applying herbicide to regrowth. Cut stump and basal bark herbicide treatments are effective and can be applied during most of the year, avoiding early spring. In all cases, herbicide should be selected carefully based on site conditions, and label directions read and followed carefully.

With any treatment, it will be necessary to monitor for and treat regrowth and new seedlings in subsequent years. Seeds can remain viable for at least 11 years under optimal storage conditions, so development of a seed bank in highly infested areas is likely (Serota and Culley 2019).

Resources on Management of Callery Pear:

• Missouri Department of Conservation
• Dow Agrosciences

• Culley, TM. 2019. Protecting the future of our forests: Limiting the impact of the introduced ornamental Callery pear tree. Proceedings of the 60th Annual Meeting of the Society for Economic Botany. Cincinnati, OH.
• Culley, TM. 2017. The rise and fall of the ornamental Callery pear tree. Arnoldia 74(3): 1-11.
• Culley, TM, Hardiman, NA, and J Hawks. 2011. The role of horticulture in plant invasions: how grafting in cultivars of Callery pear (Pyrus calleryana) can facilitate spread into natural areas. Biological Invasions 13(3): 739-746.
• Dirr, MA. 1998. Pyrus calleryana. In: Manual of Woody Landscape Plants, Fifth Edition. Champlain, IL: Stipes Publishing. 806-810.
• Dirr, MA and KS Warren. 2019. Pyrus calleryana In: The Tree Book: Superior Selections for Landscapes, Streetscapes, and Gardens. Portland, OR: Timber Press. 705-713.
• Hardiman, NA and TM Culley. 2010. Reproductive success of cultivated Pyrus calleryana (Rosaceae) and establishment ability of invasive, hybrid progeny. American Journal of Botany 97(10): 1698-1706.
• Higgins, A. 2018. Scientists thought they had created the perfect tree, but it became a nightmare. The Washington Post. 5/29/2019.
• Phillips, WD, Ranney, TG, Touchell, DH, and TA Eaker. 2016. Fertility and reproductive pathways of triploid flowering pears. HortScience. 51(8): 968-971.
• Serota, T and TM Culley. 2019. Seed germination and seedling survival of invasive Callery pear (Pyrus calleryana Decene.) 11 years after fruit collection. Castanea 84(1): 47-52.