What is the black substance on Maple trees?
I have many maple trees with various amounts of a black substance on their trunks. I am assuming it is a fungus, but am not sure. On trees with just a little, it appears circular and is located near the base of the tree. On trees with a lot of fungus, it almost fully covers the trunk and extends upward towards the tree canopy. The leaves of the trees did have some black spots on them in the summer, but it was very minimal. The other thing noticed was that when one of these trees was cut, a white growth appeared on the cut edges of the wood and the outside bark. I have many trees over approximately one acre that have some degree of this fungus. Is it hurting the trees? Is there any organic remedy that I could use to reduce/eliminate this fungus?
Lynne M. Holland, Horticulture and Social Media Professional
First, the wood on the ground has mold and fungi that are growing as the logs decay. This is normal and is not related to the issue on the live maples. Second, the black spots on the leaves in summer are likely tar spot. The amount of tar spot that develops usually depends on whether or not a summer is particularly wet or dry and rarely affects the health of the tree overall.