I manage home orchards in the Northeast and advice on fungicides is a very regional question and also affected by what stonefruit you are trying to protect, from varieties to species. I believe that pest pressure is significantly higher with commercial fruit production than in smaller home orchards for two reasons. 1: Higher tree populations close together encourage more pests and much quicker resistance development. 2: The need for absolutely pristine fruit.
I can only speak for areas within 100 miles of my own orchard, which is the region I’m experienced with. I’m about 40 miles north of NYC.
When I read Olpea suggesting weekly sprays to protect fruit it is like he is speaking from a different planet than the one where I protect peaches, plums and nectarines in about 100 home orchards. I use Indar and Pristine mixed with Captan at highest legal rates. Pristine and Indar are both registered for apples and I need materials I can use on both to simplify spraying these orchards, some of which only have a few trees and some more than a hundred of mixed varieties.
I haven’t had to apply fungicides more than once for several years during summer to protect stonefruit from rot for anything but nectarines and even they may just need a shorter interval spray before harvest- 2 weeks instead of a month. Here are my spray guidelines for home orchards in my region.
Incidentally, vigorous plum and peach trees benefit from summer pruning as a cultural control to brown rot. Sun needs to reach the fruit and dry off dew and rain quickly. Moderate growth is the aim of orchard keepers once trees reach adequate productivity, but in the humid regions a lot depends on the soil in achieving the Goldilocks balance. Vigorous growing trees may have an advantage of being harder to kill, but their fruit tends to be harder to protect from diseases and nutrient deficiency disorders like corking and fruit rots in some types of apples. They may also be more susceptible to brown rot for stonefruit species. .