I never spray my fruit trees. Because I don't have to. Have not had
fireblight for a long time. I see the older trees' branches and
trunks have a lot of different colored lichens on them. Doesn't seem
to bother the trees but I'm not sure. Trees in the woods here also
have a lot of lichens growing on them. Do lichens hurt trees?
Lichens do secrete acids to dissolve rocks.