Eline Melton

Callery pear trees between the Berg Instructional Center (BIC) and northern parking lots, where the trees are three rows deep.

Every year, multitudes of people across the United States venture out into the springtime air only to be accosted by the smell of musk and lightly rotting sewage. The culprit – the Callery pear tree – seems impossible to escape, growing along roads, downtown areas, backyards, forests and right here at the College of DuPage (COD).

This April was no different, but Illinois residents can breathe a little easier with the knowledge that the tree’s days are numbered. In October 2025, the Illinois Department of Natural Resources (IDNR) added the Callery pear to the Illinois Exotic Weed Act, along with several other invasive species. The Exotic Weed Act aims to create a decline in populations of invasive species that threaten the native ecosystem. This change in legal status bans the buying, selling, planting or distributing of Callery pear or any of its cultivars (varieties) such as Bradford pear in the state.

Unlike other species added, the ban on Callery pear won’t take effect until January 2028, giving distributors time to adjust their stock. College of DuPage students may recognize these trees, as they are still commonly used as ornamental trees. Dirk Heid, buildings and grounds manager at COD, was able to confirm the presence of Callery pear trees on COD’s campus. In fact, some areas of campus are three rows deep in Callery pear, such as the path between the Berg Instructional Center (BIC) and the northern parking lots.

Callery pears are shorter trees, standing at 30-40 feet tall with waxy, rounded and serrated leaves. Their bark is smooth when they are young and cracks as they mature, sometimes sprouting thorny spines. The flowers are white and five-petaled, growing in clumps around the tree.

The smell — which the tree uses to attract flies for pollination — comes from the chemical compounds trimethylamine and dimethyl sulfide, which are also found in rotting fish and bodily fluids. This is, for those who aren’t fans, the least of its issues. 

Austin Gimondo, assistant horticulture professor at COD, said the tree’s odor is less concerning than its effect on native ecosystems. 

 “Callery pears are among the more aggressive invasives we deal with in our area,” Gimondo said.

The Callery pear, which is native to East Asia, was introduced to the United States in 1908 as an answer to fire blight — a contagious disease that had been decimating the edible pear population. The Callery pear provided fire blight-resistant rootstock for edible pear species to be grafted onto. In the 1960s, a variant of the Callery pear — called the Bradford pear — was developed and released to the American public as an ornamental tree, prized for its beautiful blossoms along with its neat branch layout. Despite the best of intentions, the Bradford variant spearheaded the invasive spread from urban areas into native ecosystems.

Sharon Yiesla, plant knowledge specialist at the Morton Arboretum, explained the evolution of the Callery pear from ornamentation to naturalized into the landscape and invasive.

“Originally, this tree did not produce fruit. Over time, it was able to cross-pollinate with edible pears and is now able to produce abundant fruit,” Yiesla said. This proved to be a universal issue with Callery pears in the United States. 

While its small brown fruit is eaten by some birds and mammals, the seeds that they carry can remain viable in soil for over a decade.

Yiesla shares that the naturalized populations of Callery pear “can out-compete native plants that provide food and shelter for animals and insects.”

She also shared that Callery pear is a relatively short-lived tree species, having “the potential to live for around 25 years” or less, as some cultivars are particularly susceptible to storm damage. Despite its short lifespan and weakness, Illinoisans will be fighting an uphill battle. While some other states — such as Ohio, South Carolina and Pennsylvania — have passed similar bans or restrictions, most states have not. This includes those neighboring states of Illinois, where birds can carry the seeds over long distances back into our soil.

The Illinois Exotic Weeds Act does not require the removal of trees that are already in place, so seeds will continue to spread ahead of and into the ban. Yiesla shares that conscientious citizens and organizations have already begun removing trees from their property, including the Morton Arboretum. 

Heid said COD’s building and grounds department are not working to remove the Callery trees already on campus at this time. However, the department has refrained from planting more Callery trees for the past several years due to claims of environmental concerns. 

“The current plan is to remove the Callery trees as they show signs of decline or become a safety concern,” he said. 

In the classroom, horticulture professors like Gimondo focus on “educating practitioners in our classrooms to remove/replace invasives with better alternatives.”

Yiesla said locals with any questions concerning the Callery pear or other invasive plants can reach out to the Morton Arboretum’s Plant Clinic, which aims to help inform people on invasive species. The Plant Clinic can be reached in person at their Visitor Center, by phone at (630) 719-2424 or by email at [email protected].

As Illinois prepares for the 2028 ban, residents may continue to see — and smell — the Callery pear for years to come, even as efforts to remove the invasive tree expand statewide.