Last sumer I was spraying mine with a copper based fungicide as a remedy for peach leaf curl and some other fungal infection going on ....aw it did was to make the leaves sort of yellow and more then half of them fell ...there were green leaves falling by the slightest of breeze ...
I think cooper should be done when the tree is not active, this year I sprayed it 2 times in fall after the leaf fall, and again 2 times in spring before flowering , and no more then and now have dark green leaves and the tree is l loded with fruit set