My post in the thread I linked above lists the few peaches that are brown rot resistant. But I don’t think the resistance is high enough that you can avoid spraying. Most peaches are susceptible or highly susceptible unfortunately.
Captan does need acidic spray water. It would be nice if they mentioned that on the label since it’s critical but they don’t. You would want to adjust the pH and check it with pH paper. A pH of 5-7 is okay with 5-6 being best. You can lower the pH with Citric acid which is found with canning supplies at stores.
Two helpful links for the importance of pH with spray materials