These growths are called lichens. They are a fungus and algae combination that are found all over the world. They need a natural surface, clean air and time in order to grow.

Lichens are not considered harmful to trees. That being said, lichens will grow on slow-growing or declining trees. Crabapples and serviceberry are slower growing but if the trees are declining, lichens are not the cause of the decline. 

If you are concerned about the trees' health, you might have a certified arborist look at the trees in order to give you an assessment of their condition. A certified arborist may also give general advice on caring for the trees.

There are some practices that you might employ in order to make sure the tree have a good growing environment.  You should make sure that they have a properly mulched tree ring.  A yearly addition of compost to the tree ring would provide important nutrients to the trees.

In times of low rain, the serviceberries need an addition of an inch of water each week. If established, crabapples need .3" to .4" of added water during droughts.

Dead, dying or crossing branches should be trimmed.  Water sprouts, shoots growing at the base of the trees, should be cut down. It's best to trim when the trees are dormant before flower buds are visible, or right after blooming.

I have listed several links below for additional information.  If you have any further questions about any of this information, please do not hesitate to write back. 

Thanks for asking Ask Extension.

Betsy B. - MGV

https://ohioline.osu.edu/factsheet/plpath-gen-12

https://www.canr.msu.edu/news/what-s-that-growing-on-my-tree

https://extension.psu.edu/serviceberry-in-the-garden-and-in-the-kitchen

https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2987&context=extension_curall#:~:text=Crabapples%20are%20an%20excellent%20addition,in%20many%20shapes%

https://extension.umd.edu/resource/pruning-trees-home-landscape/