This may help...

Leaf curl is a fungal disease but can be treated by spraying at the appropriate times with any fixed copper fungicide or sulfur. Both of these are approved organic treatments.

Nature, that is a helpful, common sense link with good IPM techniques. I'm a big fan of Surround® WP, by the way.

What is the soil these trees are growing in like?

Is the soil pH in the 6.3 to 6.8 range?

Are cover/ green manure crops part of the management of the soil?

Perhaps this from a commercial organic peach grower will be of some help.

https://woodleaffarm.com/growing-peaches/

kimmq is kimmsr

I control PLC (peach leaf curl) on my peaches and nectarines with proper pruning. By opening up the canopy to allow more air flow and sun light penetration, PLC can be almost eliminated (I have done it). Your climate may be different. Note that a few leaves with PLC is nothing to fret about.

Borers attack stressed trees, so you have to eliminate the cause of the stress (wrong trees, wrong location, sunburn, water stress). I get a few infested branches here and there due to drought stress in our intense Summer heat. I've managed these outbreaks by removing infested branches and removing them from the property. Without knowing your location or the severity of your infestation it's hard to say for sure what the best approach might be,