COLUMBUS, Ohio – They line roadways and fill fields with their showy white blossoms in early spring. But don’t be taken in by their beauty. Callery pear trees are aggressively taking over the landscape in many places, crowding out native species. Plus, they can have thorns that will pop a tractor tire or injure livestock.

The Callery pear is an ornamental pear tree native to Asia, which has become an invasive plant. It was introduced to North America in the early 1900s to breed some disease resistance into fruiting pears, which were an agricultural crop but were highly susceptible to a disease called fire blight, said Tom Macy, forest health program manager with the Ohio Department of Natural Resources Division of Forestry.

Fire blight is a bacterial disease, and Callery pear trees seem to show strong resistance to it. They were initially introduced to hybridize with the fruiting pear to develop some resistance to that disease.

“It was noted that it had some potentially nice ornamental traits, the spring flowering, and the compact form,” Macy said. “It seemed tough, and can grow in a lot of difficult situations with poor soil. It was thought maybe this could be a nice urban tree, a yard tree, and so they were used for that purpose.”

Unfortunately, that one variety didn’t seem to produce fruit; it seemed that it wouldn’t self-pollinate. Macy said. But, over time, other varieties of Callery pear were introduced. They could cross with each other and could produce viable fruit.

“So now we have Callery pears that produce lots of viable seeds,” he explained. “Birds and other wildlife help to spread that seed around. In the meantime, we realized that, other than the fact that it is becoming invasive, it has some not-so-good traits for an ornamental tree. It has a dense branching structure that, with snow or ice storms, is susceptible to breakage.”

Callery pear trees are behaving like a lot of other invasive, non-native plants, Macy said. They are spreading aggressively and forming almost a monoculture. They out-compete native plants and there is less diversity. Callery pear trees are less valuable for wildlife.

“So they’re really aggressively spreading, colonizing, these kinds of disturbed areas near roadsides or abandoned fields, really outcompeting native vegetation,” Macy said.

As of 2023, Callery pear trees were banned from sale or propagation within the State of Ohio. Unfortunately, Kentucky hasn’t quite gotten there yet.

“Our Invasive Plant Council of Kentucky has worked hard every year to spread awareness of the issues of invasive plants,” said Alexandra Blevins, forest health program coordinator with the Kentucky Division of Forestry. “Last year, we had a bill (banning the sale and propagation of Callery pear trees) that was passing through, but didn’t quite make it. We are hoping that it will get pushed through in the near future and everyone can agree that we need to ban the sale of this major invasive species through the ornamental industry.”

At the nursery, the plants will not necessarily be labeled Callery pear. Bradford Pear, Cleveland Select, Aristocrat and Chanticleer are all popular varieties, Blevins said. Basically, any kind of flowering pear that is on the market will have the Callery pear rootstock.

“Say one neighbor has a Bradford pear, and the house next-door has one of those Aristocrat cultivars, those two different cultivars can cross-pollinate and the seed that they make that is going to be their rootstock, which is the Callery pear,” Blevins said.

The trees do produce fruit, but the pears are tiny. They are not palatable to humans, but bird species will eat them, and that is how they spread, Blevins said. The birds eat those fruits, and get the seeds on the landscape. So Callery pear trees are taking up old, fallow farm fields.

“If the farmer wanted to convert that field back to a farm field, or use it for conservation purposes, they’re going to have to get rid of the Callery pears,” Blevins said. “They have these wicked thorns on them so they can injure you or your equipment. I have heard horror stories of tractor tires getting punctured.

“It can cost big bucks to remove those invasives once they overtake an area,” she explained. “They can cause damage on multiple levels, and these are the things we are up against every day. Consumers should be hyper-vigilant when looking for a new tree; don’t buy any cultivars of flowering pears.”

Callery pear trees can spread by seeds and roots underground. For small seedlings, mechanical control, just pulling them out, can work if you can get the root system, Macy said. Unfortunately, just cutting them down is not enough as they will sprout aggressively from the roots.

“A lot of times, herbicides are necessary to get control of them,” Macy said. “Different methods and different herbicides can be effective. For smaller seedlings and saplings, foliar application of herbicides, like glyphosate, can be effective.”

For larger trees, a cut-stump treatment will be necessary; you cut the tree down and treat the stump with herbicide to try to prevent root sprouting. These stumps readily sprout if the tree is cut down. That’s the challenge. Chemical herbicides are necessary to successfully control them.

Added Blevins: “If you have them overtaking your landscape, look at the proper ways to remove them, whether mechanical or chemical. And, as with all invasives, follow-up is key.”