The leaves on my maple tree are covered with a black, sooty material. What is it and is it harming the tree?
The black sooty material is likely sooty mold. Sooty mold is caused by several different fungi. The fungi don’t infect plants, but grow on the sugary honeydew excreted by aphids, scales, mealybugs, and other insects. In Iowa, sooty mold is most common on pine, maple, linden, and elm trees.
While sooty mold can reduce plant vigor by blocking sunlight and interfering with photosynthesis, the damage is mainly aesthetic. Sooty mold does not cause serious harm to healthy, well established trees. Sooty mold does not need to be controlled.
While sooty mold is not a serious problem, the scales, aphids, and mealybugs may need to be controlled. Properly identify the insect pest and follow recommended control measures if their presence threatens the health of the tree.