Invasive Species Awareness Week- Callery Pear

By: Cody Wright

March 1, 2022

Photo Credit: Ohio Environmental Council

This iconic suburban tree has come to be known by many different trade names throughout the years: Bradford Pear, Cleveland Select, Metropolitan Pear. Yet they all derive from one species native to China—the Callery Pear (Pyrus calleryana). This NNIS was introduced to the U.S. in the mid-1900s as an ornamental street and yard tree and quickly gained popularity for its bright white, early spring blooms and colorful fall foliage. Through selective cultivation, multiple sterile cultivar types were created and mass produced for public purchase. According to Dr. Theresa Culley, Professor and Head of the Department of Biological Sciences at the University of Cincinnati, “It is not the cultivar itself that is invasive, per se, but rather the problem arises when two different cultivars cross-pollinate.” Dr. Culley has an ongoing research project at UC using DNA examination and tracking of the various cultivar crosses and invasive trends. More on Dr. Culley’s research can be found at www.culleylab.com.
The premise behind these sterile cultivars is that when a cultivar is pollinated by another individual of the same cultivar, Cleveland Select x Cleveland Select, for example, the cross is unsuccessful in producing viable seed since the two were genetically the same. However, since multiple types of cultivars were created and grafted, it is possible for the different cultivars to cross-pollinate with each other because they are of the same species but genetically different. Importantly, this cross-pollination has led to an abundance of viable seed production and has allowed the Callery Pear to gain a foothold across much of the eastern United States.

Photo Credit: Ohio Environmental Council

Although Pyrus calleryana is a pear tree, it does not bear the large, juicy fruit that one would typically expect from such a plant. Instead, it produces thousands of small, hard, grape-sized fruits . While unpalatable to humans, these berries are the perfect snack for a hungry songbird. Does this dispersal tactic sound familiar to you?

This mass production of seed is the driving force behind the Callery Pear invasion. Since escaping cultivation, this tree has established itself across many habitats and disturbed areas, most notably lining highway corridors and old fields throughout the state. Next time you are out for a sunny spring drive, be on the lookout for a wall of white , and know that it is more than likely this nasty invader.

Luckily, there is hope for dealing with this nuisance tree. Pyrus calleryana was officially banned for nursery sale in the state of Ohio on January 7th, 2023. This measure alone will help combat the spread to a small degree, but further intervention is crucial to successfully eliminating Callery Pear from the native landscape. Our trained staff at MAD utilize integrated pest management techniques to complete projects dealing with Callery Pear, and the results can be astonishing . Like many other invasive plants, herbicides are effective when used in combination with mechanical methods and has proven itself time and time again.
When looking to replace this tree with a native species, Flowering Dogwood (Cornus florida), Black Tupelo (Nyssa sylvatica), and Serviceberry (Amelanchier spp.) are all great candidates! Just remember to research the desired species’ needs and responsibly source your new natives.

…we’ll continue tomorrow with the tale of Narrow-leaved and Hybrid Cattail.