I had lots of questions about how we care for our apple trees. To tell the truth, we are novices in this area.
Thus far all we have done is applied composted chicken manure under the canopy of each tree - that means extending it out to where the branches reach out.
Also, we followed the guidelines reading about pruning the trees and have done our best to do that each of the last two late autumns/early winters.
I think that living so far north, we are probably less likely to attract many of the insects that others may be prone.
Sorry I don't have much to share in this area as we are learning as we go along - some is probably luck and some is for sure trial and error.