Cankers of Japanese Maple

Disease Information


Symptoms and damage

Cankers on trees appear as isolated dead areas on the bark, stems, branches or twigs. Cankers may appear as discolored areas or depressed places on the bark.

A fungus that enters the tree and grows between the bark and the wood killing the bark generally causes cankers. However, cankers can also be caused by damage from weed eaters, lawnmowers, chemicals, insects or environmental conditions.

The canker itself makes the tree highly vulnerable to bacteria, fungus and insects. Young fruit trees have an especially difficult time recovering from cankers. Established shade trees may weaken and become susceptible to wind damage.

COMMENTS on disease

Depending on the region where you live, different cankers on trees are found. Some of the more common types of canker in trees include:

·         Thyronectria canker is caused by a fungus and is most common on the honey locust tree.

·         Nectria canker tends to attack deciduous shade trees, crabapples and pears.

·         Cytospora canker is found most often in fruit trees, hardwood forest trees and shrubs, as well as over 70 species of conifers.

·         Hypoxylon canker is seen in different species of oak including red and white.


Preventing tree cankers is the best method of protection. It is best to plant native or well-adapted species for your growing region. These tree species will suffer less stress and adapt well to the soil type, sun exposure and overall environmental conditions in your area.

The avoidance of stress is the best and most effective protection against canker diseases. Proper tree care including watering, feeding, mulching and pruning will help to keep trees as healthy as possible.

Once a tree has canker, it is essential to remove as much of the canker fungi as possible from the tree to avoid infection and spread. Prune only during dry weather and make cuts with a sterilized cutting tool at least 4 inches below the edge of the canker on trees.


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