canker with fruiting bodies (17783 bytes)

Canker Diseases of Trees

By Laura Pottorff, Colorado State University Cooperative Extension agent, horticulture, plant pathology

Canker diseases are common on Colorado trees. Cankers appear as sunken areas on branches or the trunk. A cankered area also will be of a different color than surrounding bark.

The fungi that causes canker diseases are weak pathogens and attack only trees under environmental stress. Symptoms appear at any time during the growing season, but usually show up during hot weather. Branches and associated leaves wilt. Several branches on one side of the tree might be affected, or a branch here and there might show symptoms. If symptoms are present, look for cankers on branches or the trunk on the side of the tree that's affected.

To check for cankers, run your fingers along the bark to check for little orange or black bumps or pimple-like structures. These are the fruiting structures of the fungus that is responsible for the disease. In the spring of the year, many of these "pimples" will ooze an orange coiled thread-like spore tendril.

To control canker diseases, affected limbs must be pruned. Chemical control is not effective.

If you don't feel or see any of the pimples or orange tendrils, the wilting may be from a different cause.

Photo: Judy Sedbrook

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Date last revised: 01/05/2010