Green mold on dogwood branches
We have noticed green mold on our dogwood branches for many years which eventually kills the tree. Now we are noticing it on the maple in our yard as well as around Baltimore city. Should we be worried about our maples? Is there anything we can do to prevent further damage?
The green patches you are seeing are called lichens. Lichens are harmless to trees and do not need any treatment. They are interesting organisms (and some would say beautiful) that can also be a sign of good air quality.
They grow most readily on still objects-- dead wood, benches, rocks, etc.
Younger trees tend to grow more quickly and so are less likely to have them.
Here is more information about lichens: http://extension.umd.edu/hgic/topics/lichens