Nathan Johnson, Director of Public Lands, May 14, 2018
The aggressive non-native callery pear is dominating roadsides and recently disturbed areas throughout Central Ohio. Often known as “Bradford” or “Cleveland Select” ornamental pear, this foreign invader is one of the greatest scourges of the NNIS (non-native invasive species) world.
Native to China, the tree was first brought to America in the early 20th century as an alternative roostock for commercial pear trees. The species ornamental value was recognized in the 1950s, and the first “Bradford” clones hit the market in 1962. The tree has since become one of the most widely planted urban street trees in Central Ohio and the nation.
Not good. Callery pear is no longer restricted to strip malls, city sidewalks, and manicured suburban lawns. Although, it still heavily present in all these places – as its explosions of white flowers in early spring will attest. Not content with its honored status in domesticated environs, this dangerous spawn has invaded natural areas far and wide across the U.S.
This weed is aggressive in the extreme. Callery pear grows so thickly that it pushes out and shades out native vegetation and native tree seedlings. Take a look at most any major roadside running through Columbus in early spring. All of those beautiful white flowers are callery pear.
This tree is extremely fast growing. Callery starts flowering and reproducing from seed as early as three years of age. It flowers and fruits profusely, and birds spread its small fruits and seeds everywhere. It also banks its seeds, meaning that several years-worth of seeds can rest in the soil, waiting for an opportune time to germinate and shoot for the sky.
Along with one of its main partners in crime – invasive bush honeysuckle – callery is one of the first species to leaf in spring and one of the last to drop leaf in fall. This gives callery pear an energy advantage over the competition. The tree is also tolerant of most soil types and a wide range of growing conditions. Many seed-grown individuals develop thorns that deter herbivores (and humans!) from eliminating them.
If all this weren’t enough, the tree is known for the unpleasant smell of its flowers, which has been described as smelling like rotting fish.
Ohio has a prominent role in this unfortunate story. One of the most popular and widely planted domestic cultivars – “Chanticleer” a.k.a. “Cleveland Select” – was cloned from a street tree found in Cleveland, Ohio. It was named the 2005 Urban Tree of the Year by the Society of Municipal Arborists.
Thankfully, awareness is starting to catch up. This January, callery pear was officially placed on Ohio’s list of invasive species. The regulation allows nurseries and landscapers to continue selling the tree for five years, after which the sale of callery pear in Ohio will be unlawful.
This tree is everywhere. You likely see many of them every day without even realizing it. By far the easiest time to recognize them is in early spring, when they are in full bloom with pretty white flowers. The fact that they bloom before most anything else makes them all the more conspicuous in the landscape.
Callery pears are fairly small trees. They tend to grow to 15 to 30 feet in height. They often have a narrow, conical growing habit. In summer, they have dark green leaves. They bear tiny fruits in later summer and early fall. Late fall colors are highly ornamental, with good reds, pinks, purples, and bronzes.
The most effective method is complete removal. Cut down trees and immediately apply an appropriate systemic herbicide, such as concentrated glyphosate (typically between 20 to 50%) to the freshly cut stump. Untreated stumps often sprout profusely.
Small seedlings and saplings can be hand pulled when the soil is moist. Mowing and cutting small stems is ineffective, due to sprouting.
Follow-up treatments will typically be required for several years in heavily infested areas. Stump sprouts and the persistent seed bank will see to that.