I live on Lake Mindemoya on Manitoulin Island. Since the lake is only a few meters from the house, mornings are always quite damp. This growth has been appearing on my trees the last couple years and has been getting worse. I am not sure if it is hurting the trees or not besides the fact it looks horrible. I just noticed last week that it is starting to appear on my 8 year old Harlequin Maple and on my lilac bushes. Can you please tell me if it will harm the trees and if there is a way that I could remove some of it.
Thank you for contacting Toronto Master Gardeners.
From your photo it looks like your trees are growing Lichens. This is common and you will often see it when you walk in the forest. It can grow on healthy trees as well as trees that are struggling. Lichens thrive in damper locations and this spring has certainly been damp. They do not hurt the tree and should be left alone. Trying to scrub or wash them off could damage your trees bark.
I have attached a link to our library which answers your question in more detail. I have also included a link for further reading.