Introduction

Pyrus calleryana is often called the Bradford Pear after the cultivar that was planted widely in the US in the 1960s and 1970s and still sometimes is today. However, the Bradford Pear itself is an infertile cultivar, hence the more appropriate common name of the Callery Pear. The Bradford Pear cultivar can neither self-pollinate or cross-pollinate with the same cultivar as its seeds are infertile. However, if different cultivars of Pyrus calleryana are grown within 100 m of each other they can cross-pollinate and produce fertile offspring. The resulting Callery Pear is a fast-growing aggressive tree with a broad ecological tolerance, rapid growth, few pests and early sexual maturity. It produces abundant tiny fruits with abundant tiny seeds. The fruits are hard and woody but soften after a hard frost and become appealing to birds which then spread their seeds around. It quickly replaces native vegetation wherever its seeds have a chance to grow. Once established, removing or controlling Callery or Bradford Pear can be challenging.

Do not buy any cultivars of Pyrus calleryana because they may cross-pollinate and spread in the wild. The Bradford / Callery Pear story is a perfect example of why we should not buy supposed “sterile cultivars” of invasive species because we never know how they will behave until they have already escaped into the wild. Supposed sterile cultivars of Scotch Broom and Purple Loosestrife have also done a similar thing. Instead, research plants that are native to your area and plant those. Native plants tend to be naturally resistant to pathogens and insects, require little watering or feeding, and promote biodiversity and wildlife values. Also, there are always lovely native plants everywhere that are just as beautiful as invasive cultivars, if we just look for them we will find them.

Description of Pyrus calleryana

Leaves & Stems

The Callery Pear is a deciduous tree that can grow 5 – 20 m tall and has a trunk that is up to 0.6m in diameter. The trunk, however, often splits into multiple branches that tend to break easily in storms damaging the tree and shortening its usefulness as a landscape tree. Its branches are reddish-brown when young and become grayish-brown with age with vertical grooves in the older bark.

Pyrus calleryana simple leaves are arranged alternately on the stem. They are 4 – 9 cm long and are on 2 – 4.5 cm long petioles. Leaf blades are ovate, broadly ovate or oblong–lanceolate. The surface is shiny green glabrous (hairless) with undulate (wavy) and slightly toothed margins. In fall the leaves turn yellow, orange, and red before falling off for the winter.

Leaf shape can be variable and these indicate the different varieties of Pyrus calleryana. For the purpose of invasive species removal or control, identification to the species level alone is sufficient. There will always be variations in morphology because the wild species are all hybrids of various cultivars and as such will generally exhibit intermediate characteristics between its two parent varieties.

Flowers & Fruits

Callery Pear flowers in April and May just before the leaves appear. The flowers are malodorous smelling somewhat of rotten fish. Flowers are 2.5 cm wide with 5 white obovate petals 6 – 7 (–13) mm long and × 6 – 7 (–13) mm wide.

Pyrus calleryana has numerous stamens with white filaments and topped with reddish or brownish anthers. Its ovaries are 2 – 3 (–4)-locular and they are topped with 2 or 3 styles.

Fruits are small pomes (like an apple), around 1 cm in diameter and globular (round) in shape. They are green when young in late spring and summer but turn brown when ripe in the fall and winter. They contain numerous cyanide-laced seeds inside.

Similar Species Frequently Confused With

There are numerous species of mostly Pyrus and Prunus (plum and cherry) species that Pyrus calleryana could be confused with as well as some other genera. All genera it can be confused with are part of the Rosaceae family. Sometimes people confuse it with Populus species as well but the appearance of the flowers in the spring will easily distinguish it from those.

• Pyrus communis – the Common Pear has very similar flowers and leaves but its mature bark has horizontal and vertical grooves in it making it more of a checkerboard-like pattern than the vertical striations of Pyrus communis. Its leaves are usually smooth-margined rather than undulate. Also, the fruits grow much, much larger, are pear-shaped and edible.
• Crataegus spp – there are multiple Crataegus species in its range in North America that, like many Rosaceae, have very similar flowers. However, Crataegus species always have variously lobed leaves compared to the simple unlobed leaves of Pyrus calleryana.
• Prunus avium – the Wild Cherry has a similar range, similar leaves and flowers. Its bark is smoother and shinier, lacking any longitudinal or horizontal grooving. The smooth bark does, however, possess numerous horizontal lenticels (slightly raised striations). Its fruits are also larger and of varying shades of red or sometimes yellow when ripe. The fruits have a single pit and are edible.
• Prunus mahaleb – the St. Lucia Cherry or American Black Cherry has a similar range, leaves and flowers as well. However, it never grows to more than a large shrub up to 5 m tall. Its bark lacks the grooves of Pyrus calleryana and it has horizontal striations. Its bitter fruits are also black when ripe and possess a single pit.
• Prunus mexicana – the Mexican Plum has a similar range, leaves and flowers as well. However, its filaments on its many stamens are often pink, the flowers are often pinkish-white, and its fruits are larger, plum-like and pinkish to purple when ripe rather than brown.
• Prunus cerasifera – the Myrobalan Plum or Plum-Cherry has similar flowers, leaves and range. However, its flowers are either white or pink and the anthers are typically yellow rather than reddish or brownish. The fruits are yellow to reddish in color when ripe and are edible and larger, to 2-3 cm in diameter.
• Prunus serotina – the Capulin or Black Cherry has a similar range, leaves and flowers too but the flowers grow in elongated racemes instead of umbels. Also, its bark is more smooth and covered with horizontal striations. The somewhat bitter fruits are a bit larger and are reddish-black to black in color with a single pit as opposed to brown with multiple seeds.
• Viburnum prunifolium – this Rosaceae member has similar leaves and range as Pyrus communis. However, its flowers are much smaller, to 0.9 cm in diameter, they only have 5 stamens, and they are arranged in tighter umbels with more flowers.

Native Distribution of Pyrus calleryana

The Callery Pear is native to Asia in China, Japan, Korea, Taiwan and Vietnam.

Habitat Types Where Bradford Pear is Found

Callery Pear can be found growing in empty lots, mixed forests, forest edges, thickets and plains. It can grow from 0 – 800 m in elevation. It prefers full sun but can tolerate part shade. Pyrus calleryana does not grow in full shade.

Pyrus calleryana is tolerant of a very wide range of soil types and pH. It easily tolerates the poor soils and polluted conditions of living in urban environments. It can grow in poor and rich soil alike. Callery Pear tolerates a range of soil conditions and will tolerate temporarily water-logged soils and temporary droughts. However, it will not survive extended periods of flooding or extended periods of drought.

Human Uses of Bradford Pear

Callery Pear Pyrus calleryana as Ornamental or Tools

The Bradford Pear was widely planted in the USA in the 1960s and 1970s as a fast-growing and low-maintenance landscape tree. As a landscape tree, it produces abundant white flowers in spring and has red foliage in the fall making it a desirable ornamental despite the malodorous flowers. Callery Pear is often used as a rootstock to graft fruit cultivars onto.

Callery Pear wood, like all Pyrus wood, is very fine-textured and sometimes used for making musical instruments, veneer, woodcuts, or other fine wooden products.

Distribution of Pyrus calleryana in North America

The species was first brought to North America in 1909. It was later widely planted in the 1960s and 1970s in the USA.

In Canada, Pyrus calleryana has not yet been recorded on Canadensys. However, there have been reports on iNaturalist in southern Ontario, Nova Scotia and possibly in southern BC. It is not clear if those are all planted or wild specimens. Given that it is invasive just south of the border in these locations it seems likely that it may start spreading more into Canada soon.

In the USA, Callery Pear has been introduced in Oklahoma, Texas, Arkansas, Louisiana, Mississippi, Alabama, Georgia, Florida, South Carolina, North Carolina, Tennessee, Kentucky, Illinois, Indiana, Ohio, Pennsylvania, West Virginia, Virginia, Delaware, Washington DC, Maryland, New Jersey, New York, Connecticut, and Massachusetts. On iNaturalist it is also reported in Colorado and all along the west coast but most of these may be intentional plantings of cultivars that may or may not yet have escaped into the wild.

In Mexico Pyrus calleryana so far has only been reported in Tamaulipas. Given its close proximity to the northern Mexican border on the US side, it is likely that it will spread more in the near future.

How Callery Pear Spreads

Callery Pear is primarily spread through long-distance by deliberate human introductions as garden and landscape ornamentals. While the Bradford Pear itself is infertile it can cross-pollinate with other cultivars of Pyrus calleryana and the Asian Pear Pyrus betulifolia which can then produce fertile seeds and spread in the wild. Also, fertile varieties are often used as the rootstock when grafting. If the infertile crown of the tree is damaged sometimes the fertile rootstock will then grow and produce fertile fruits.

Short-distance dispersal occurs primarily through birds and humans. The hard fruits become soft after a frost and are a popular winter food source for winter birds in North America. The birds eat the winter fruits and spread the abundant fertile seeds in their feces. Even without fruits Callery Pear also reproduces short distances vegetatively through suckers.

Humans can also spread the seeds short distances unintentionally on their shoes or clothes. Often the disposal of unwanted trees or branches removed from pruning while in fruit results in infestations from yard waste piles when they are not burned or properly disposed of.

Habitats at Risk of Invasion in North America

Callery Pear often forms dense patches in abandoned fields, empty lots, disturbed areas and on roadsides. It can invade any riparian area, open mixed forests, meadows, thickets, mountain slopes and anywhere else its fertile seeds land and grow. Since it is tolerant of such a wide range of soil conditions this means that many habitats are at risk.

It generally will not invade dense forests, particularly coniferous ones. Also, it typically does not invade permanent wetlands except where drier conditions exist. It does not tolerate severe drought so will not invade desert areas.

Impacts of Invasion by Pyrus calleryana

Pyrus calleryana often creates dense near monoculture stands, particularly in disturbed areas, roadsides and old fields. It can also gain a significant foothold in open mixed forests. They out-compete the native vegetation and significantly reduce the biodiversity in the area upon infestation. Once a dense stand is created it can be difficult to remove.

Potential Benefits of Invasion

Birds enjoy Callery Pears abundant fruits throughout the winter, including many native birds. However, the birds are the primary dispersal method and would likely have eaten native fruits left on trees that were displaced by the Callery Pear.

Methods to Remove Bradford or Callery Pear

As always prevention is the preferred method of control. It, like most invasive species, is still widely sold online and in most local garden stores. Do not buy or transport any Pyrus calleryana cultivars. Even though Bradford Pear themselves may be infertile they can cross-pollinate with other cultivars and escape into the wild. Do not plant it in your yard. Instead, research native species to your region. Native species require little or no maintenance, are very beautiful and provide wildlife and biodiversity values.

If you see them being sold online or in your local garden stores please inform them of their invasive status and ask them to do their part and cease selling them. Inform them that though supposedly infertile they are still able to cross-pollinate with other cultivars and they are spreading in the wild. Ask them to instead sell more native species as ecologically friendly garden alternatives to invasive species.

Physical Control of Bradford or Callery Pear

Once already established physical control is always the most effective means to remove Callery Pear. Physical control is labor-intensive and time-consuming but it causes the least amount of environmental damage.

The best time to remove Callery Pear is in the early spring either before or during flowering but before the plant sets fruit to avoid dispersing the seeds around.

Physical methods to remove Callery Pear depend on the size. Young seedlings or trees can simply be pulled out. When the ground is moist it makes removal easy as the roots cling less tightly to the soil when it is moist. Young trees can be pulled out with a weed-puller like the one shown in the affiliate ads below.

Mature trees on the other hand will need to be cut down and then the root pulled out by digging it with a shovel or machine, depending on the size. If it is too difficult to remove the root then you can deal with it one of three ways. First, you can solarize the stump with a plastic tarp by laying the tarp over the stump and weighing it down with rocks. Leave it like that at least until the following year. The second method is to return to the site every year and cut any sprouts that try to grow. Eventually, it will starve out the root. The final method is to chemically treat the stump with a herbicide.

Another method to control large trees in areas that make them difficult to remove is to ring the bark. Using a very sharp knife cut into the bark and remove a horizontal patch at least 5 cm wide all the way around the tree. Be sure to remove all bark in this patch down to the heartwood. This prevents the tree from transporting nutrients and water up and the products of photosynthesis down. This effectively starves the tree so that it will eventually die. It would still need monitoring however to be sure that no new sprouts try to start from its stump.

Disposal of the Trees Once Removed

If you have plants that have seeds on them they must either be burned or solarized. Do not dispose of them in yard waste if they have mature fruits. Large trees can also be cut into firewood. If you do not have a fireplace and are not allowed yard burning in your area then you will need to solarize them before disposal. To solarize put the trees under a thick black tarp and leave them in the full sun for a good 6 – 10 weeks at least to be sure that all seeds are no longer viable. If there are no fruits on the trees you can dispose of them in yard waste.

Chemical Control of Bradford or Callery Pear

Chemical applications are almost never an ideal method of control for any invasive species. That is because chemical alteration of the environment often makes the environment more suitable for invasive species than native species. It is often difficult to keep the chemical control method contained so that it does not directly affect any native species that are there during the application process itself. Furthermore, there are no chemical control methods that effectively target only Pyrus calleryana. As a result, plots where chemical control is used usually show a decrease in species richness. On the other hand, in plots where only physical control is used species riches significantly increases.

However, the one suitable exception is the chemical treatment of large root stocks that you are unable to dig out mechanically or by hand. Ideally solarize or return to the area as part of an ongoing monitoring process. If you are unable to do either then chemical control of Callery Pear stumps can be a good alternative as you are only treating the stump to prevent re-sprouting. Research herbicides safe for use in your area and treat only the stump. If it is in a riparian area you may not be able to use this method due to proximity to water. Ideally you should still return the following year to be sure that nothing survived.

Biological Control of Callery Pear

Biological control involves the use of a predator, herbivore, disease, or some other agent to control an invasive species once it is established in the environment. The problem with biological control is that the agent used must be entirely specific to only the target organism before releasing it into the environment. This is often difficult to determine since the agent of control is also not native to the environment and could behave differently when released there. Take the example of the mongoose and the rat. The mongoose was released in Hawaii in the late 1800s to help control the rat. To this day there are still rats in Hawaii but the mongoose has helped to decimate many native bird populations.

Biological control methods are extremely risky and should only be carried out by professionals after years of rigorous study. The use of biological control methods can never be used alone. They must be part of an integrated pest management approach. This is because the control agent would need to effectively destroy over 99% of plants and their seeds to actually control the Callery Pear on their own.

Unfortunately, Pyrus calleryana seems resistant to pests of all kinds. It is part of what made it desirable as a landscape plant. Also, finding suitable pathogens is tricky because if they could be found even testing them in the field could put commercial Pyrus and Prunus crops at risk. While insects and grazers alike will feed on the pear, particularly when young, they are ineffective as a control measure on their own. And once Pyrus calleryana reaches a significant size large herbivores will no longer be able to reach the foliage.

However, young stands of Callery Pears could be controlled with the use of goats which are known to eat anything. Provided that all the trees are young and can be reached by the goats they can be penned in. They will continuously feed on the young trees and over time will destroy any sprouts or seedlings that emerge. This is only suitable in dense young stands, however, as the goats will also eat any native species in their vicinity. The goats would need to remain in the patch for a couple of seasons.

Integrated Pest Management & Ongoing Monitoring

Integrated management is always the best approach. In its simplest and least impactful form this involves physical removal methods, possibly biological control methods, replanting and ongoing monitoring.

Replanting With Native Species is Crucial

In most cases of removal, the site would ideally be replanted with native species to prevent invasive species from re-establishing in the bare soil that was left behind. A replanting program should already be planned and ready to implement immediately upon the removal of Callery Pear. You would need to research plants native to your area and study the site to determine which species would be most suitable. Ideally, gather seed stock from the surrounding area to ensure you have local ecotypes suitable to the area. If this is not possible then buy from a nursery specializing in native species to ensure that you are not planting cultivars of native species.

Ongoing Monitoring is Essential

In all cases of invasive Callery Pear removal, ongoing monitoring is absolutely essential. Yearly monitoring programs should be put in place to ensure that any surviving individuals are removed. This is required whether the area is replanted or not. Callery Pear is aggressive and prolific and can out-compete planted vegetation. Yearly monitoring to remove young plants before they have a chance to become established can prevent this. Yearly monitoring in late spring followed by removal of all sprouts and seedlings will be sufficient for a monitoring program.

References and Resources

Canadensys Plant Search https://data.canadensys.net/vascan/search

Dictionary of Botanical Terms – Lyrae’s Nature Blog Dictionary of Botanical Terms

Eflora of North America http://www.efloras.org/browse.aspx?flora_id=1

iNaturalist Plant Search https://www.inaturalist.org/home

USDA Plants Database https://plants.sc.egov.usda.gov/home

Wikipedia on Pyrus calleryana https://en.wikipedia.org/wiki/Pyrus_calleryana

Willis, Lyrae (2022).  Plant Families of North America. Not yet published.

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