Hello,

There are several agents which may cause the white patches on your beech trees, including beech bark disease, beech blight aphids and even lichen which will not harm the tree. Read more here: https://www.canr.msu.edu/news/is_it_beech_bark_disease

And here: https://ag.umass.edu/landscape/fact-sheets/beech-bark-disease

Lichen are actually composed of two organisms, algae and fungi in a symbiotic relationship. They are harmless to the host on which they are attached. I’m attaching a bulletin about them from MSU Extension. Read more here:

https://www.canr.msu.edu/news/what_are_lichens_and_what_are_they_doing_on_my_tree

However, it is difficult to diagnose it from a picture. You can submit a sample and picture to the MSU Extension Plant and Pest Diagnostic Lab for a more thorough evaluation. To learn how to submit a sample go to: https://www.canr.msu.edu/pestid/

A certified arborist would be able to assess your trees. To find an arborist in your area, go to www.treesaregood.org, the website of the International Society of Arboriculture.

Thank you for contacting Ask Extension.