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Tree Bark Fungus

bark image by Nellie Vin from

Trees experience fungus that appear on bark, causing damage to the outer surface of your tree as well as disease that often leads to severe tree injury and decline. The fungus on the bark of your tree is likely a symptom of an underlying disease. Get to know the types of fungus that attack bark as well as how to deal with problems when they arise for a healthy home garden.


Vigorous trees and bark are more likely to resist or fight off fungus-related diseases when compared to plants that are stressed, injured or in decline. Proper maintenance and culture is essential for healthy trees. Grow your selected trees in the proper soil requirements, including moisture level, pH level and porosity. See that your trees receive appropriate sunlight, whether it's full sun exposure or partial shade. Also, alter your maintenance with changes in your local environment; for example, if a drought occurs, your tree will need more water and may benefit from mulch, according to the Iowa State University Extension.


Thyronectria canker is one type of fungus problem that affects tree bark. It is caused by the fungus Thyronectria austro-Americana, and honeylocusts are most often the primary target. Hypoxylon canker is another bark-related disease, caused by different species of the fungus Hypoxylon, according to the Iowa State University Extension. Hypoxylon canker often attacks oak trees.


Thyronectria canker tends to target trees that are already stressed due to environmental problems. Look for cankers or lesions of dying bark tissue on branches and trunks of trees. Leaves often turn yellow and wilt and branches experience dieback. The cankers related to this fungus sink into the tree, killing areas of bark that change color to orange/brown and then to a more vibrant yellow-orange, according to the Iowa State University Extension. The sapwood of the tree also experiences discoloration and damage, leaving the tree in a state of diminished vigor and cosmetic damage. Hypoxylon canker also targets environmentally injured trees, resulting in the presence of leaves that turn yellow and wilt, branch dieback, and the destruction of long pieces of bark that peel away from the tree.


Avoiding highly susceptible trees and selecting resistant species and varieties will increase your likelihood of avoiding fungus problems that cause great damage to the health of your trees. Additionally, if you are re-planting on a site where a tree was removed due to fungal disease, planting a resistant tree is your best bet for avoiding future problems as fungal spores often remain in one area, waiting to re-infect new plants. For example, when dealing with areas commonly affected by thyronectria canker, choose the honeylocust variety Skycole with moderate resistance over Suncole that has poor resistance, according to the Iowa State University Extension.


Chemical controls like fungicides do not provide effective management of tree bark fungus, so cultural control practices are necessary. Remove and destroy affected plant parts by pruning cankers from trees to remove fungus. Prune your trees on a dry day as moisture spreads fungi and promotes germination. Prune approximately 4 inches behind a canker for optimal results, according to the Iowa State University Extension. Choose resistant trees and avoid tree injury and wounds to the bark to prevent fungus invasion. Always sanitize pruning tools between each cut and from one tree to the next to prevent disease spread. Additionally, if your tree experiences severe problems on the trunk or if infection is extreme, remove the entire tree.

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