Pear trees that develop black, wilted leaves are often infected with a bacterial disease known as fire blight. This disease primarily affects young shoots, twigs and leaves, giving them a scorched appearance.
Bacterial fire blight is a serious disease that commonly affects pears, apples, crabapples and firethorn, according to Ohio State University. Certain types of pears, such as the Callery pear, are less susceptible to the effects of fire blight. Warm, humid weather is favourable for the development of this disease, which is most damaging to the tree during blooming.
Symptoms associated with bacterial fire blight in pear trees include wilted leaves and black, crooked branches. Pustules often form on the tree and ooze a brown substance during warm, humid days. According to the National Gardening Association, this brown substance contains bacteria which is spread by insects or rain to other trees.
Controlling bacterial fire blight in pear trees is best accomplished by pruning infected trees, removing the wilted branch at least 200 mm (8 inches) below the wilt. Pruning shears must be sterilised between the cutting of branches to avoid spreading the infection to healthy portions of the tree or other trees. Removing plants which serve as hosts to fire blight such as wild apples and mountain ash is recommended. Spraying pear trees with insecticidal soap will help eliminate pests and prevent the spread of fire blight.