I don’t know if they are harmful, but I have wondered the same thing

i would contact your local COUNTY extension office.. and find out if this is an epidemic in your area.. and what they recommend..

and then report back to us ...

a systemic tree drench would take care of it.. imo.. its not a spraying thing.. unless done professionally.. especially since with scale. there is a very short finite window to spray them... whereas.. as suckers.. a systemic will do the job ...

ken

Here is what the local arborist said. They are extremely knowledgable.

good.. good... but i would be very surprised of they had a 2 month crawler phase.. its usually less than a week..

and if you dont hit them BEFORE they grow that thick shell.. then ALL spray is useless...

and. personally.. spraying a 30 foot tree is NOT DIY.. unless you have a hazmat suit.. respirator.. and life insurance for the wife and kids... or hubby as the case may be ...

ken