No need for fungicide, as these are lichen, a harmless organism (and not entirely fungal either, as mentioned on the linked page). The areas of flaked-off bark are not typical of cherry, though it is unrelated to the presence of the lichen. If the tree appears to be in decline, another issue is responsible, and could be tied to soil conditions or root health. Our web page Ornamental Cherry Trees: Identify and Manage Problems can help to narrow-down what might be going on in that situation.

Miri