Most info coming out of NCSU is for commercial orchards in the mountains, however much of it also applies to home apple trees. https://apples.ces.ncsu.edu/apple-arthropod-management/ Is a good place to start. It speaks of IPM, watching your trees for insect population buildups, and using appropriate controls. Insecticidal oils are recommended for some problems. https://apples.ces.ncsu.edu/apple-pest-management/ will help you identify harmful and beneficial insects you might find on your trees. 
Finally, NCSU also has a guide for home production of apples and other fruits, and discusses diseases as well. 
Good luck, and happy eating.  

The link for home apple production: https://content.ces.ncsu.edu/disease-and-insect-management-in-the-home-orchard