By CELIA LLOPIS-JEPSEN
Kansas News Service
Let’s talk about very hungry caterpillars.
In Kansas and Missouri, they face an increasingly difficult time finding things to eat. That’s making it ever harder for butterflies and moths to survive.
Their populations are shrinking, especially in the Midwest, and the birds that eat them are disappearing, too.
The invasive Callery pear trees (also known as Bradford pears, Cleveland pears, etc.) spreading like weeds across Kansas and Missouri don’t get all the blame — not by a longshot.
And yet these ornamental trees with the white springtime blossoms and a pungent smell pose a significant problem. Stopping them from continuing to choke out native flowers, shrubs and trees would bring back food for wildlife.
This month, if you help with the effort, you can get a free native tree.
The ‘desert’ effect
From the outside, a grove of rogue pears looks pretty. In spring, flowers cloak their branches. In fall, red leaves cover the branches.
But when Kansas forester Ryan Armbrust pushes his way into one of those groves, he finds something despairing beneath the dense canopy: neither prairie nor woodland nor much to support the natural food chain.
“You’ll have bare ground,” Armbrust said. “A few straggling bits of grass that are still trying to hang on.”
And as the trademark flowers, shrubs and trees of the Midwest get crowded out, the animals do, too.
“This becomes essentially a desert,” he said. “There’s nothing under there. You’re not going to have any wildlife really. … You’re not going to have many insects.”
Here’s an easy way to measure the scope of the loss when invasive plants win out: Butterflies and moths.
A single oak tree growing in Kansas City offers a tasty meal to more than 400 species of butterflies and moths in their caterpillar phase of life.
A wild plum bush supports more than 300 species. A goldenrod plant, about 100.
They are all native to the region.
But Callery pears, like many ornamental plants that escaped from gardens into the wild, are more or less inedible to the caterpillars of North America.
Scientists who take the time to search these trees for insects don’t find much. Entomologist Doug Tallamy wrote last year that he has found just one caterpillar species on them.
Tallamy and his students at the University of Delaware studied what might at first glance appear to be wild areas, but were actually overgrown with invasives such as Callery pear and bush honeysuckle (another invasive plant taking over parts of Kansas and Missouri). They compared them to natural areas dominated by native plants.
The spaces overrun with invasives had lost more than 90% of their caterpillar populations. That’s a huge hit to butterfly and moth populations. And, to birds.
The vast majority of songbirds have to feed their chicks soft insects — primarily caterpillars. A single nest of chickadees eats several thousand caterpillars, Tallamy says.
That’s just one reason that biologists, foresters and even state and county governments are desperate to kill off the trees.
Photos show the rapid spread
Check out these images compiled by Armbrust, who coordinates rural forestry at the Kansas Forest Service. These show just how fast the pears are spreading across the state and beating out local trees, shrubs and wildflowers.
Yet rural landowners, foresters and conservation agencies can’t use the same techniques they do for fighting other rogue trees: fire and blades. If you burn a field full of Callery pears, they survive it. If you mow down the saplings and chop down the bigger ones, they simply grow back.
The only remedy is to poison the offenders by hand, for example by cutting them down and applying weed killer or tree killer to their stumps.
Johnson County is doing just that.
Workers at Johnson County Park and Recreation District have removed hundreds of Callery pear trees and countless more saplings infesting Shawnee Mission Park.
Their work isn’t done. Each spring, they scour this 1,700-acre park — the most visited park in Kansas — when blooms make the pears more easily visible. They chop the trees down and apply herbicide carefully, to avoid killing nearby native plants.
“It’s really important for people to understand that these ornamental trees don’t stay in your front yard,” said Matt Garrett, the agency’s field biologist. “It’s affecting everything around you.”
Trading good trees for bad ones
This month, nearly 1,000 people in Missouri and Kansas can get a free native tree — about 4 or 5 feet tall — in return for killing a Callery pear on their property.
The program started in parts of Missouri, led by the Missouri Invasive Plant Council, and grew to include the Kansas City metro.
Whether you live in Kansas or Missouri, you can sign up here, then chop down a Callery pear and submit a photo of yourself standing next to it. Those who do can choose among a variety of native trees, such as serviceberry, river birch, green hawthorn and chinkapin oak, and pick it up at a participating site.
In Missouri, Fedex is paying for the replacement trees. In Kansas, Johnson County Park & Recreation District is.
Yes, even 1,000 dead Callery pears are a drop in the bucket compared to the number of these trees that are growing across those two states. But part of the goal is simply to spread the word about the havoc that the trees wreak.
After all, many nurseries and big-box stores such as Lowe’s continue to sell them.
Callery trees (Pyrus calleryana) come from Asia, and the ones sold in the U.S. go by many names: including Bradford, Cleveland and Chanticleer.
Plant breeders never intended for the trees to spread on this continent. In fact, they thought it couldn’t happen. They sold sterile cultivars.
Homeowners snapped up the trees to adorn yards. Cities and developers planted row after row of them for their spring flowers and autumn colors.
Then — cue the “Jurassic Park” music — things went very wrong.
Although each cultivar (Bradford, etc.) couldn’t reproduce among its own kind, it turned out the supposedly sterile trees were mightily prolific once the various cultivars came into contact with each other and cross-pollinated.
Armbrust started spotting saplings in ditches and natural areas more than a decade ago. In 2020, the Kansas Forest Service began mapping out how far the tree has spread in Kansas.
“When you started to look, and you trained your eye to see it,” he said, “you kind of had that moment of, ‘Oh my goodness, this stuff is everywhere! What are we going to do?’”
The trees now grow wild in at least half of Kansas counties, and maybe more. The Kansas Forest Service isn’t done looking.
Ironically, adult birds eat Callery pear fruit in the fall, and this helps spread the very trees that erode the caterpillar populations that the birds need to feed their chicks.
Tips for killing a Callery pear:
- Mowing won’t do the trick. If you mow down a sapling, it just sprouts back with more stems or trunks.
- Option one: Go after the trunk. Cut down the tree and, within 20 minutes, treat it with an herbicide such as Tordon or glyphosate-based weedkillers such as Roundup.
- Option two: Go after the leaves. You can spray herbicide on them and cut down the tree after it dies.
- Read more details on the above options before starting. Or watch this video discussing removal methods and herbicides.
You can also learn about some of the native alternatives to callery pears here.