This plant is also available in many cultivars, including the more well-known Bradford pear tree. By 1966, this tree’s status was upgraded as they were planted in downtown Washington, D.C.
There are plenty of advantages and positive attributes that made Bradford pears a common landscape plant. These trees adapted well to poor soils, inconsistent water, acidity, and a host of other adverse conditions that made them a “go-to” plant for roadsides and other poor conditions.
Their ability to survive in small soil volumes made them a common choice for parking lots and other paved areas. These trees also exhibited a fair amount of disease and insect resistance while being tolerant to full sun and shade. Other attributes included a showy spring flower and a dense, somewhat symmetrical almost, elegant canopy.
It was, in fact, named an “almost ideal tree” by The New York Times in 1964. All of this was before the discovery that they certainly were not ideal and there is where the advantages came to an abrupt halt.
The prolific flowering can be very showy in the spring. However, they attract many more pollinators than just bees and also can be a huge food source for flies. Additionally, these white blossoms give off a very offensive, rancid odor, making them not-so-pleasant if you’re downwind in the spring. This becomes more problematic around restaurants and in outdoor living situations.
Secondly, as they mature some will grow thick woody thorns, making maintenance and pruning more difficult. While tens, if not hundreds, of thousands or more of these trees have been planted around the U.S., it is unusual to see a fully matured specimen. The primary reason is their branching structure. The trunk gives rise to branches in a more vertical or upright growth pattern, making the angle between the branch and the trunk more acute or far less than 90 degrees. It is this type of growth that makes the branches fairly weak appendages. In many cases a strong wind, especially if paired with snow or ice accumulation, spells disaster for these trees as they are very prone to branch breakage. This makes them a danger to be planted around structures, parking areas or anywhere else where something of value could be in that strike zone.
Finally, the biggest issue and greatest reason why this tree is deemed invasive in many areas is that they can reproduce and spread to the point of crowding out other plants. In the past, some species were bred to bear sterile fruit which was thought to be able to thwart the spread. If the sterile varieties are grown in pollination range of other varieties, then viable seeds can be produced through cross-pollination. These seeds are encapsulated in the small fruit that tends to be plentiful on most trees. These tiny pears are a food source for birds that can disperse the seeds in their droppings. In addition to seed spread, established trees can send up new shoots from their shallow root system which over time can create a thicket type of scenario and out-compete other native plants.
This holds true even for removed trees. Roots and below grade structures and root fragments can live on, producing more suckering or shoot growth. It has been reported that Callery pear has become established outside of cultivation in 152 counties in 25 states.
Five Guidelines for Curbing Invasion
For all of these reasons, Ohio has led the charge on reducing the proliferation. As of 2023, the state of Ohio has banned the production, sales, and installation of Callery pear trees. Pennsylvania, along with South Carolina, will follow suit. This is just the first step in curbing their invasive pressure. Penn State Extension has issued some existing plant guidelines that I have summarized below.
- Cutting or mowing of sucker growth will help, but should be paired with a herbicide application to the cut stems in order to resist regrowth.
- Herbicides can and should be applied to cut stumps. Oil-based products can be used any time, while water-based materials should be used on a fresh cut.
- Foliar herbicide treatments are feasible for trees up to 10 feet. The common mixture is glyphosate with a water-based formulation of triclopyr.
- Basal bark applications of triclopyr ester in basal oil can be effective on trees with less than a 6-inch-diameter trunk and performed any time of the year except when snow or water is not covering the lower portion of the tree.
- Larger trees will require the “hack and squirt” method where a gash or notch is made with a hatchet and filled with glyphosate or triclopyr. Dormant season hack patterns should completely girdle the stem, but during the growing season they can be spaced about 1 inch apart.
Want to Learn More About Proper Eradication? Lean on Us
Callery pear is very persistent and without employing the proper eradication techniques, you risk reinvasion. For more complete recommendations, feel free to contact myself or Pat Gross, Ewing’s Tech Team. Email me at firstname.lastname@example.org or call/text 480-669-8791. Email Pat at email@example.com or call/text 714-321-6101.