Unit 24 (024)

1. Prunus or Cherries

Cyanide poisoning can be a problem in wilted foliage.

The leaves, twigs, and bark of black cherry contain cyanide in bound form as the

cyanogenic glycoside, prunasin. During foliage wilting, cyanide is released and

domestic livestock that eat wilted foliage may get sick or die. Native deer can eat

unwilted foliage without harm.

Most Prunus leaves have glands on the petiole or leaf stalk. Viburnum opulus and

Viburnum trilobum also have glands on the petiole (see Unit 022).

2. Pyrus calleryana or Bradford Pear

Fire blight bacteria disease is an often fatal problem in Pears. The Bradford Pear

Pyrus calleryana cv. Bradford and related cultivars were selected for fire blight


They have been widely used as street trees, but there is one problem. The trees main

branches develop narrow crotch angles and these narrow branch angles split more

easily in storms. The narrow crotch angles contain bark inside the angle instead

of solid wood like in a wide branch angle on an oak tree.