Pyrus calleryana Dcne.
Rose family (Rosaceae)
Origin: China and Vietnam
Callery pear was imported multiple times to the U.S., including the first introduction in 1909 to the Arnold Arboretum and an introduction in 1916 by the U.S. Department of Agriculture for development of fire blight resistance in the common pear (Pyrus communis), which was devastating the commercial pear industry. It was widely planted as a rootstock for common pear long before it gained interest as an ornamental. Around 1950, the ornamental value and hardiness of Callery pear were recognized, leading to the development of a number of cultivars, including ‘Bradford.’ Cultivars in the U.S. originated from China and represent different genotypes. While some genotypes are self-incompatible, meaning they require cross pollination from another genotype in order to set seed, others can pollinate themselves. Different genotypes growing near each other (e.g., within about 300 ft.) can cross-pollinate and produce fruit with viable seed. Also, cultivars are often grafted onto seed-grown rootstocks with varying genotypes; if the plant produces shoots from the rootstock (which it often does), then these shoots and the graft can pollinate one another. Thus, the Bradford pear cultivar is one of several cultivars (varieties) of Callery pear capable of spreading and being invasive. Pyrus calleryana ‘Bradford’ is one genotype. It is propagated asexually (by grafting and cuttings) and does not change over time. Any plant resulting from a seed produced by Pyrus calleryana ‘Bradford’ is a different genotype of Pyrus calleryana and not a member of any cultivar (unless somebody propagates that seedling and names it as a new cultivar). The plants that spread in natural areas are not cultivars. They are sexually reproducing populations consisting of multiple genotypes that recombine every generation.
Distribution and Habitat
Callery pear occurs throughout the eastern U.S. from New Jersey to Illinois and south to Texas. It grows best in full sun but will tolerate some shading and drought.
Once established Callery pear forms dense thickets that push out other plants including native species that can’t tolerate the deep shade or compete with pear for water, soil and space. A single tree can spread rapidly by seed and vegetative means forming a sizeable patch within several years. Its success as an invader results from its capacity to produce copious amounts of seed that is dispersed by birds and possibly small mammals, seedlings that germinate and grow rapidly in disturbed areas and a general lack of natural controls like insects and diseases, with the exception of fire blight.
Description and Biology
Prevention and Control
Do not plant Callery pear or any cultivars including the well known Bradford pear. Seedlings and shallow-rooted plants can be pulled when soil is moist. Medium to large trees should be cut down and stumps treated with a systemic glyphosate or triclopyr-based herbicide (see Control Options).
Several native trees would make excellent substitutes for Callery pear, including common serviceberry (Amelanchier arborea), Allegheny serviceberry (Amelanchier laevis), cockspur hawthorne (Crataegus crus-galli), green hawthorne (C. viridis) and the native sweet crabapple (Malus coronaria), although its availability may be limited currently.
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