The Bradford pear or Callery Pear (Pyrus calleryana) 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.
Developed in 1963, Pyrus calleryana 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 makes it a popular choice in landscaping. Upon maturity, it also has potential as a shade tree.
Rosaceae and Cyanide
Bradford pears, like all pears, are members of the rose 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. The UC Davis Toxic Plants database flags both apple and pear seeds as "Major Toxicity: These plants may cause serious illness or death. If ingested, immediately call the Poison Control Center or your doctor." But it takes about a cup (8 ounces by volume) to fatally poison a human being. Swallowing the seeds from a single pear or apple is typically insufficient to cause harm.
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. Theoretically, it's fairly easy to eat enough Bradford pears to poison yourself. But Pyrus calleryana isn't typically grown for its fruit. 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 cupful, 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.