With all of the rain we have had this year it may be too much water. Mature trees should be doing fine with the amount of rain we have been receiving weekly. I would hold off on the irrigation. 

If you continue to see brown and curling leaves, it may be Apple Scab. Below  is the information I have been sending to people as it is very common this year. 

You may have Apple Scab. We are getting a lot of questions about it this year. It will not kill your tree unless it suffers for many years in a row.

Be sure to clean up all fallen leaves and debris this summer and do a thorough clean up in the fall because the fungi will over-winter in the debris.

Dispose of the leaves in your municipal compost. Do not compost these at home as your home compost will not get hot enough to kill the pathogens.

https://extension.umn.edu/plant-diseases/apple-scab

https://hort.extension.wisc.edu/articles/applescab/