Yes as @benthegirl points out it’s hard to grow peaches organically in hot and humid weather. I tried and thought things were going great for four years and then brown rot showed up and decimated things. I tried for another six years and then gave up. It’s not like I wasn’t getting any fruit, I would get about a third to half the harvest. But I had to use them immediately or they would rot a few days after picking.
My spray schedule is here:
There are organic options in there as well as synthetic disease control options. I don’t use wide spectrum bug killers, those I think you can generally avoid.
Oh and I also don’t think rootstocks matter much on peaches. Some people don’t like citation but it’s been OK for me. About half of my stocks I grew from pits (well, they grew themselves, they just showed up one spring). I pick the more vigorous ones.