We have 3 Red Haven peach trees 4 years old. They are covered with 1-1/2 inch peaches. There are many yellow leaves on the ground. There is good new growth. Early spring they each got a “bean can” of 12-12-12
The two main causes I can see is low water and low iron. We had 2 inches of rain 4-5 days ago and the lawn is lush green, so I don’t think it’s water issues. This happened last year as well.