I have a fully grown, 25 year old ash tree. A few years ago some crunchy,
crab-apple type growths appeared on some of the branches.

Sounds like dried eriophyid mite galls. These microscopic mites commonly cause
deformed galls on ash trees that are originally green but dry to a crumbly dark
brown. Although unsightly, they rarely affect the health of the tree. For more
information see:
http://www.colostate.edu/Depts/CoopE...sts/emite1.htm
and
http://www.colostate.edu/Depts/CoopE...ests/galls.htm
sed5555