Apple tree sprays

I live in the Pacific northwest in Washington state. I'm moved my parents home. I have two Apple trees. One is a gravelstein tree and don't know the other one. The past few years the trees got invaded by caterpillars and or deceased.
I did put fertilizer spike around the trees but the trees look sick the leafs are all curls and the bark is peeling off.
I was hoping that someone can help me by suggesting things I could do.

Thank you,  ken

Ken, I would look into Diatomaceous Earth.  You can buy food safe version of this product, and consume it for your own health.  This is simply diatoms that have been dried out.  Their body structure creates very sharp micro cuts on insects, and dries the insects out.  It's very good against many types of pests, and is safe for your own pets.