Maple tree and ornamental crab have a greenish-grey fungus looking stuff on bark. bark is flaking off trees?

Question:under the flaking bark are holes bored into the trunk. a few limbs on the maple are dead but not yet on the crab. the maple trees in the park strip have a few small patches of this stuff appearing on the bark. i don't want this stuff spreading about the neighborhood. what is it? can i treat it? how can i prevent it from spreading to other trees?

Answers:
Does it look similar to the picture in the link I posted below? If it is...that is lichen. Lichen itself is not a problem, it occurs in areas of plentiful moisture. It can present itself on dead or dying branches because they are starting to rot and hold more water. The holes bored into the tree underneath would indicate an insect problem. Without seeing the bug I would not be able to assist, but you would need to treat the treat for infestation if there are holes in the tree. You often see lichen in dead or dying branches where insects are present first as it makes the branches even more hospitable to the lichen.