Black Spots on the Bark of a Sugar Maple

Identification

• Red maple trees are susceptible to Steganosporium canker, which is caused by Steganosponum ovatum fungus. The disease is common on trees stressed by drought or winter damage. Canker-causing fungi usually enter trees through wounds.

Damage

• The disease is characterized by the appearance of small, black fungal spots or pustules on infected tree bark. As the disease progresses, the spots grow larger and merge to create a black, crust-like coating on bark. In cases of severe infection, cankers girdle and kill branches. The foliage on infected trees browns and wilts.

Management

• Trees should be pruned during late dormancy, just prior to budding, with clean cutting and pruning tools. Trees in dry soil should be watered every week in summer. All infected tree parts should be removed and discarded.