Several customers have asked:
Why have my apple tree's leaves turned yellow and are prematurely dropping?
A number of questions today concerning yellowing leaves and premature leaf drop on apple trees. Apart from drought (root stress) the most likely reason is Apple Scab disease. If your fruits are showing the distinctive marks as per the photo, then this too is scab. Some varieties are more prone to it than others.
A fungicides containing myclobutanil -
For the most effective control, you need to cover the whole tree. Unfortunately, most gardeners will not have sprayers capable of treating large, old trees.
Apple scab -