Sappy Bark

Sappy bark, also called papery bark, is a minor fungal disease of apple that occurs on older trees. The pathogen can also occur on numerous other woody broadleaves, some of which are listed in Pest Notes: Wood Decay Fungi in Landscape Trees.

Identification

Where bark and wood becomes infected with the fungus, during damp weather the affected bark appears spongy. When the canker is dry the bark appears papery and peels off. Dark sap sometimes oozes from the diseased areas.

Bracketlike spore-forming structures of the fungus may grow along the edges of affected bark and wood. Each bracket is about 1 to 4 inches wide and occurs in a group overlapping. The bracts appear as concentric rings that are dark to pale brown alternating with pale colored bands of tan to whitish and sometimes other colors. These fruiting bodies resemble the tail of a strutting turkey with its tail feathers spread. The wood decay pathogen is sometimes called turkey tail fungus.

Life Cycle

The sappy bark fungus infects limbs and sometimes trunks, commonly at the site of pruning cuts or sunburned bark. Infected bark and wood decay and become discolored and spongy. Affected bark commonly peels away, exposing the dark, decayed wood underneath.

Damage

Sappy bark commonly develops in the Central Coast and North Coast on older trees that were improperly pruned. McIntosh, Red Delicious, and to a lesser extent Fuji are most commonly affected. In interior locations sunburned bark is a common site of infections.

Sappy bark cankers girdle branches. When a lesion grows to entirely circle a limb the branch is killed outward or upward from the site of the lesion. If infection occurs on the trunk, this can girdle and kill the tree. If limbs that shade lower bark are removed, this can lead to sunburn of bark and a canker susceptible to infection by T. versicolor.

Solutions

To reduce the incidence of sappy bark, provide trees with a good growing environment and proper cultural care to keep them growing vigorously. Appropriate irrigation and proper pruning are especially important.

Consider pruning off diseased wood and dispose of it away from desirable trees. Because the cankers grow only a few inches per year, it may be possible to remove the cankered bark before limbs become completely girdled.

To avoid creating the type of wounds commonly infected by the fungus, make pruning cuts that leave no stubs. When pruning, do so with a sharp tool and make each cut just outside the branch collar and branch bark ridge. Avoid excessive pruning during a single year. If upper limbs are removed and formerly shaded bark is exposed to direct sunlight, whitewash the bark by painting it with white, interior, latex paint diluted with an equal amount of water.

Adapted from Trametes versicolor, Mushroomexpert.com and Integrated Pest Management for Apples and Pears, University of California Statewide Integrated Pest Management Program (UC IPM).