Abundant recent rain and pleasantly moderate temperatures both promise that it is nearly spring. Temperatures are forecast to reach the lower 20s Saturday morning, reminding us that winter may not be over. A spring highlight is the first emergence of flowers. A few hardy annuals and early daffodils will be on display in landscapes, but in natural landscapes, the flowers of redbuds and dogwoods announce the beginning of the growing season.
One of the earliest and most striking trees to flower is the Bradford Pear. Its complete scientific name is Pyrus calleryana var. “Bradford,” indicating that it is a variety derived from the Callery pear. Callery pears were collected in China and imported into California in the early 1900s. Initial evaluation of the Callery pear were to find trees that offered resistance to fire blight, a disease that was seriously impacting California’s pear crop. Resistance was identified and proved useful in breeding productive varieties of several stone fruits.
Development of ornamental pears came later. The cultivar known as the Bradford was developed in Maryland in the 1960s. Bradford Pears were introduced and expected to be sterile. Bradford trees were propagated clonally so they did not cross pollinate — they produced spectacular flowers, but no fruit. Unfortunately, other sources of pollen have developed and little pears, produced in the fall, contain viable seeds. Bradford specimens often were grafted onto root stock of the Callery pear. If the top growth failed or was broken, root sprouts could survive and often became the source of pollen. If the seeds produce a new plant, it will be a form of the Callery pear, the wild relative of Bradford and other cultivated varieties.
Callery pears are an aggressive invasive species. Thorns occur on stems and branches and can be up to 3 inches long. In addition to spread by seed, assisted by birds eating the fruit, Callery pear rapidly produces root sprouts leading to rapid spread over an old field, vacant lot or pasture. They have also become established in forest understories. Once in place, they are very difficult to control because of thorns, which can easily puncture the skin, wound livestock or pop tires on vehicles or implements. Prescribed fire has not proven to provide a control procedure; research has demonstrated for every stem killed by the fires, four new sprouts will replace it.
An additional liability of the Bradford variety is poor structural features. It was selected for a “lollipop” shape, but the rounded crown results from a branching pattern of many branches originating from a small span of the main trunk. As branches increase in size, they crowd one another off the trunk, seriously weakening branch attachments. As a result, Bradfords tend to split, losing as much as half the trunk diameter in a single event. If such a tree is ignored or abandoned, sprouts originating from the Callery rootstock may replace it.
Proliferation of Callery pears has increased rapidly. The invaders are displacing native trees and plants in the wild, and can form dense colonies. As is common to many invasive plants, the growth rate is faster than native trees, thereby slowing or preventing their growth. Because their growth begins so early, Callery pears leaf out before woodland wildflowers emerge from dormancy, shading them from essential sunlight and preventing their growth. This can also harm certain pollinators that use these plants as their larval host.
A number of historic Bradfords have been influential in our nation’s history. Among others, William Bradford was the first governor of the Plymouth Colony. Unfortunately, the immigrant tree has not been so honorable. If you are considering trees for you landscapes, choose alternative plants, preferably natives such as the redbud or service berry. If you have existing Bradford pears, monitor closely and remove any root sprouts that occur. As the trees age and fail, find other species to replace them.
Roger Gates is the agricultural and natural resources agent for University of Georgia Extension, Whitfield County. Contact him at firstname.lastname@example.org.