Possible scale on trees


Not sure if you can see what’s on this tree (and others): the gray, and some orange. Is it scale? or something else? will it harm the trees and if so, what should be done?
Thank you.



Thank you for contacting the Toronto Master Gardeners. I think it is lichen on the trees in your picture, not scale. Lichens are not plants, and they do not harm trees. They are a unique life form that is made up of fungus and algae that coexist symbiotically. Different forms of fungi and algae combine to create different forms of lichen which come in various shapes and colours including what is in your picture. They do not take any nutrients from the surface on which they are growing (they also grow on rocks), and they grow only when the weather is mild and humid, otherwise they are dormant. Typically lichens grow on old, weak or dying trees, but they are not the cause of this decline. Their presence could indicate that the tree needs attention. You might want to consult an arborist about what could be causing the trees’ decline. Here is more information about lichens :



And here is a link to the Landscape Ontario website if needed, to find a list of arborists in your area :


You asked whether what is on the trees in your picture might be scale (Hemiptera). Scale is a tiny insect (1/8” or so) that sucks sap from plants. It is usually found on stems and leaves and causes symptoms that are not visible on the trees in your picture (yellow leaves that wilt and drop, the presence of honeydew which attracts insects and on which a black fungus called sooty mold often grows). Here is more information about scale :


Interesting fact about lichens : they prefer areas with clean unpolluted air !

April 11, 2021