Blackness on Tree Bark - Ask Extension
Our two trees in our backyard have a black layer on their bark. We are unsure what it is and what the best solution is to remove it. They have continu...
Knowledgebase
Blackness on Tree Bark #930396
Asked May 02, 2026, 4:24 PM EDT
Our two trees in our backyard have a black layer on their bark. We are unsure what it is and what the best solution is to remove it. They have continued to grow last year and are currently begining to bud.
Wright County Minnesota
Expert Response
My guess would be sooty mold, a common fungus that grows after an infestation of a honeydew-secreting insect, such as aphids or scale:
https://extension.usu.edu/planthealth/ipm/ornamental-pest-guide/diseases/sooty-mold
Sooty mold is mostly harmless. However, there is a disease of maples called sooty bark disease that is more common in the Pacific Northwest. I can't identify your tree from that photo, so I can't be for certain it is not a maple. This is from Washington State University:
https://treehealth.wsu.edu/sbd/
In either case, you should have a certified arborist look at the trees:
https://www.treesaregood.org/Find-an-Arborist
https://extension.usu.edu/planthealth/ipm/ornamental-pest-guide/diseases/sooty-mold
Sooty mold is mostly harmless. However, there is a disease of maples called sooty bark disease that is more common in the Pacific Northwest. I can't identify your tree from that photo, so I can't be for certain it is not a maple. This is from Washington State University:
https://treehealth.wsu.edu/sbd/
In either case, you should have a certified arborist look at the trees:
https://www.treesaregood.org/Find-an-Arborist
