Does Black Spot Maple Tree Fungus Affect Apple Trees?

Disease Identification

• The black spot fungus on a maple tree is referred to as "tar spot." The disease is caused by the Rystisma group of fungi, primarily R. acerinum and R. punctatum. Other host trees of the fungi include yellow poplar and tulip tree. Apple is not a host for the disease, as cited by the University of California Extension.

Symptoms

• The tar spot disease is characterized by the appearance of light green to yellow green spots on the foliage of infected trees. As the infection progresses, tar-like, shiny, black fruiting bodies start appearing within the spots. These fruiting bodies coalesce to create 1-inch round patches. The areas under the spots, on foliage undersides, turn brown. The black spots retain their texture and color even after the leaf color changes during fall. The fungus spreads most rapidly during the moist weather conditions in spring.

Damage

• The tar spot disease is quite similar to anthracnose but is among the least damaging maple diseases. The disease is more cosmetic in nature, causing aesthetic damage rather than any serious loss of tree vigor. Given the stark symptoms, tar spots are very easy to recognize and identify. Cases of severe infection can lead to premature defoliation or withering foliage.

Control

• Maintain good sanitation around the tree to prevent the fungal spores from overwintering in the fallen leaves and infecting tree again in spring. The use of chemicals is generally not recommended or required for the control of the disorder. In cases of severe infection, recommended products include those that contain copper, mancozeb or triadimefon.