Pear trees are susceptible to several diseases caused by fungi, viruses and bacteria. The National Gardening Association reports that fire blight is the most devastating to both commercial and home pear trees in the United States. A bacterial infection spread by rain and insects, fire blight can wipe out every susceptible tree in an orchard in one season.
Pear trees are most susceptible during bloom, so the National Gardening Association recommends anti-bacterial spraying during bloom and slightly after to prevent the disease. The bacteria enters the tree through the blooms, and once established, the infection appears as a reddish or tan ooze on the leaves, stems and branches. Tips of branches wilt, curl and turn black, giving the tree an appearance of having been scorched by fire. Aggressive pruning is necessary, where all infected branches are cut off at least 8 inches down from the infection site. Pruning shears or clippers must be dipped in bleach after every cut to prevent the bacteria from spreading.
To control pear diseases, the insects that spread disease must also be controlled, explains the National Gardening Association. These insects include the pear psylla and aphid. Avoid pesticides and concentrate on oil or soap sprays that make the environment inhospitable to pests. Penn State College of Agricultural Science explains that other pear diseases are primarily fungal infections such as leaf blight and fruit spot, leaf spot and pear scab.