My red oak has kermes scale. I've had it root treated for a year and it's still active. One arborist told me you can't get rid of it. True? Is it possible my mountain ash can have it?
Denver County Colorado trees and shrubs
Here is a fact sheet on kermes scale from the Kansas Extension servie: http://hnr.k-state.edu/extension/info-center/common-pest-problems/common-pest-problem-new/oak-kermes.... It only affects oaks. I would consult another tree company to get an opinion on the treatability of your tree.