Healthy pear trees have attractive foliage, but several different diseases can blacken and damage their leaves. The symptoms and treatment options vary depending upon the infection.
The Erwinia amylovora bacterium causes fire blight, a destructive disease that attacks the foliage and fruit of pear trees. Pears are also susceptible to sooty mould disease, which is a fungal infection caused by insects.
Fire blight affects the blossoms and foliage of pear trees. The leaves and flowers turn black and cling to the tree, giving the plant a burnt or scorched appearance. Sucking insects such as mealybugs, scale, and whiteflies suck juices from pear leaves and excrete a watery, sticky substance called honeydew that falls on the foliage. Thick, velvety-black mould forms on the honeydew deposits.
Fire blight is controlled by pruning and destroying infected branches. Timed applications of copper fungicides will reduce the effects of new infections, according to the University of California Statewide Integrated Pest Management Program, but will not cure existing infections. Sooty mould infections are controlled by eradicating the insects that are depositing honeydew. Insecticides are commonly used to manage insect infestations.