Hi Jon, 

Thanks for reaching out! It may not be necessary to treat the trees with anything until you discover any problems. Here is a helpful UMN Extension link with pests and diseases you may need to look out for: https://extension.umn.edu/fruit/growing-apples

Keeping the area around the trees tidy will help immensely with pests and disease. The apple maggot is one pest that you may wish to prevent against -- bagging or sticky traps would be recommended. Pages 14-16 of this article has more information: https://conservancy.umn.edu/server/api/core/bitstreams/ec31340c-0611-4f09-abe3-fd2bb03c7484/content

If you do end up using any chemical treatments, remember to read the treatment labels prior to use and always follow the directions attached to the treatment you are using. The label is the law. 

Good luck!