Has there been a spray applied within the last month?   Are there similar spots on other plants in the vicinity?  I suspect this is a burn due to droplets of some chemical.  Sometimes you can get a clue by looking at the distribution of the spotting within the tree.  If the spotting is more intense close to the ground, perhaps it is herbicide.  If it is more conspicuous on one side of the tree, the drift may have come from that direction.  Certain chemicals can cause leaf spots under hot conditions--oils, captan, neem oil. 

The only spray applied was yesterday, some seven for Apple aphids, however these spots started appearing last week. No other spray has been applied in the area in the last month.

I think you need to do more sleuthing work for some sort of chemical spray that occurred.   Maybe drift from an adjacent property...field crops.  Look at other plants in the area for similar types of damage.  Drift can go more than 1/4 mile under the right conditions.