Bradford Pear Trees and Cyanide
The Bradford pear or callery pear (Pyrus calleryana 'Bradford,' USDA zones 5-9) is a common landscaping tree that many home owners consider a nuisance. Its flowers smell fishy, its branches tend to break, and its tiny fruits fall messily everywhere. Even worse, that unsightly pulp littering your yard and sidewalk can be downright dangerous. The Bradford pear contains seeds, each of which contain a small amount of cyanide.
Bradford Pear Tree Facts
The Arnold Arboretum reports that the Bradford pear tree was commercially released in 1961, and problems with the integrity of its structure began to appear twenty years later. This is a medium-sized ornamental tree grown for its pleasing symmetrical shape, its attractive foliage and its showy white flowers. Its rapid growth and effective disease resistance make it a popular choice in landscaping. Upon maturity, it also has potential as a shade tree.
Rosaceae and Cyanide
Bradford pears, like all pear trees, are members of the rose plant family (Rosaceae). Other members include apples, quinces, loquats, peaches, apricots, nectarines and plums. The fruits of these trees have seeds which are, to varying extents, poisonous. They contain cyanogenic glycoside, a form of cyanide combined with fruit sugars. Digesting this substance releases hydrogen cyanide gas. In sufficient quantity, cyanide kills by prohibiting cells from processing oxygen.
Relative Toxicity of Pear Seeds
Different members of the rose family carry different amounts of cyanogenic glycoside. Though pear and apple seeds aren't at the top of the list, they're easy to swallow accidentally.
Are Bradford pears poisonous to humans? Technically, the answer is yes, but Cornell University notes that pear trees and their fruits are not particularly toxic, and it would take eating a lot of seeds to suffer ill effects of cyanide. Swallowing the seeds from a single pear or apple is typically insufficient to cause harm. Bradford pear tree leaves, as well as other parts of this plant, also contain cyanogenic glycoside.
Toxicity to Human Adults
The seeds of the Bradford pear are no more toxic than any other type of pear seed. However, its seed to pulp ratio is particularly high. But Bradford pear isn't typically grown for its fruit; this is an ornamental tree. Can you eat Bradford pear fruit? You can, but its speckled, green-brown pears are too tiny and too hard (and, of course, too full of seeds) to be worth eating.
Though some home brewers harvest the fruit's pulp for making wine, most people simply rake the pears up and throw them away. The likelihood of an adult eating even one Bradford pear seed, let alone a large quantity, is low.
Toxicity to Children and Pets
The real danger of the Bradford pear is to pets and small children. Their smaller body mass makes them more susceptible to toxins than an adult human. They also tend to consider edible any object that will fit in their mouths, they won't necessarily stop at just one, and they'll find hundreds of them while wandering around the yard under your Bradford pear tree.
If you're in this situation, be vigilant when your tree is fruiting. Clean up every pear you can find. Watch your children and pets when they're out in the yard to prevent them snacking on any fruit you missed. Better still, consider replacing your tree with another ornamental, one that doesn't fruit.