Pear Disease Fact Sheets
Fire blight is the most serious pear disease in the eastern United States. Caused by the bacterium Erwinia amylovora, the disease can attack some 75 species of plants of the rose family. Fire blight also occurs frequently on pyracantha, spirea, hawthorn, and mountain ash. In fruit trees, the disease can kill blossoms, fruit, shoots, limbs, and tree trunks.
This disease should not be confused with the fire blight or leaf spot diseases of pears. Leaf blight and fruit spot is caused by the fungus Fabraea maculata, which infects the leaves, fruit, and shoots of pear and quince trees and the leaves of apple trees.
The pear leaf spot fungus, Mycosphaerella pyri, infects the leaves of pear, quince, and occasionally apple trees. Numerous leaf spots can produce defoliation. Fortunately, this does not often occur before fall, except in nurseries.
Pear scab resembles apple scab in nearly all respects and is caused by the closely related fungus Venturia pirina.
Sooty mold fungi of the genus Capnodium cause an unsightly blackening over the surface of fruit and leaves. Sooty mold attacks many plants and is most common on pear, although it can affect all tree fruits and tree nuts.
Stony pit of pear is presumed to be caused by a destructive virus, but the virus has not been isolated. Affected fruit are unsightly and unmarketable. This disease is sometimes referred to as "dimpling" because of the symptoms observed on fruit.