Spraying Apple tree: Spring or Fall

When is the best time to spray an Apple tree ? Spring or Fall ?

Spring was when we always did ours when I was a kid. Think said when the leaves were the size of a squirrels ear.

Depends on what you are spraying for. Overwintering insects a horticultural oil or bordeaux mix in fall after leaf drop maybe again before green up. Fungal or bacterial like fireblight after green up and there is a set schedule as the bloom progresses. If to protect the fruit like for coddling moth you may need post bloom sprays.
Main thing identify the problem treat accordingly.