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Pear Fungus

By Theresa Leschmann ; Updated September 21, 2017
Fungus disease is easily spread from one pear tree to another.
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Ornamental and fruit-bearing pear trees are susceptible to a variety of fungus diseases which can ruin the appearance of the tree, damage the fruit or even kill the tree if left untended. Recognizing the symptoms of fungus diseases is the first step in slowing their progression. Understanding how they grow and spread is the next step. Several options are available for treating pear tree fungus.


There are several fungus diseases that can affect pear trees. Some affect fruit, such as pear scab, sometimes called brown rot, sooty blotch or gray mold. Others affect the tree itself, such as cankers, which can be caused by a variety of fungi, and Armillaria Root and crown rot, which starts in the soil and attacks roots before spreading to the crown.


Fungus diseases that appear on the fruit are recognized by olive green to dull black smudges for sooty blotch, gray mold spots for gray mold, or as dark brown scabs and lesions on fruit that becomes increasingly misshapen for pear scab. Pear scab also appears as small brown spots on leaves and petioles before appearing on fruit. Cankers are patches of dead or peeling bark. Armillaria root and crown rot begins as a slow decline of the tree’s overall health over several years before progressing to a sudden wilting that can kill the tree in a matter of weeks.


Several fungus diseases are spread by the splashing of water carrying spores of that fungus. Pear scab overwinters in leaves on the ground and in twigs on the tree. Spring rains and wind splash it to other tissue. Sooty blotch occurs in late summer and thrives in extended warm, humid conditions. Fruit is susceptible two to three weeks after fall by spores in splashing rainwater. The fungus that causes cankers enters the tree through wounds caused by environmental stress or by mechanical means. The fungus that causes Armillaria root and crown rot lives in the soil for years and enters the tree through the roots when soil is cool and moist. Gray mold also enters during cool moist weather through wounds in the fruit skin.


No effective chemical treatment exists for Armillaria root and crown rot. Exposure of the roots and crown by removing the top 9 to 12 inches of soil for the remainder of the growing season allows the roots system to dry out and slows the growth of the disease. If pear scab is present use of a fungicide when green shoots begin to appear is effective in treating it the following spring. Fungicide and cultural practices used as prevention are how sooty blotch is treated. Adequate watering may slow the growth of cankers though cultural practices are the only way to avoid cankers.


With the exception of Armillaria root and crown rot, most fungus diseases can be avoided by protecting the health of the tree. Trees should be watered during dry periods early in the morning to allow ample time for water to dry. Supply fertilizer when necessary to maintain soil nutrients. A sound practice of annual pruning which keeps the tree open to sunlight and air circulation helps eliminate conditions which foster fungus infection. Pruning cuts should be clean and not jagged; jagged cuts invite infestation. Cut limbs, fallen fruit and leaves and other debris should be removed from under the tree to eliminate overwintering opportunities. In locations where winter scald causes trees to split, a white latex-based paint should be applied to the trunk to reflect sunlight away.