Matthew,
I can sympathize with you regarding your thought about wanting to give up growing fruit trees. A lot of us in high pest and disease pressure areas have that thought once in a while.
This thought is more pronounced when we grow “high maintenance” fruit trees like stone fruit, peaches, nectarines, cherries, plums, etc.
There are more than plum curculio but since you need help with this # 1 pest, we will only focus on it.
I think you may have seen Scott’s Low Impact spray program.
Low-Impact Spray Schedule (2019 Edition).
It is not just Surround. Scott has used several approaches to make his low impact spray works for him. I mixed Spinosad and/or BT with Surround to fight against OFM, another serious peach enemy. Surround alone can help esp if you start early and reapply when needed. @mroot said, it could be that your area is very high PC pressure you need to move up your first spray to petal fall.
Like someone said, the chemical I see people here use that appears work with very well is Imidan (from very clean fruit they show). Imidan is not supposed to be sprayed in residential areas so that disqualify a lot of us living in urban areas. Also, as of this year, with new definition, shipping Imidan is a lot harder. Places like Keystone Solution does not ship it anymore
https://www.keystonepestsolutions.com/imidan-insecticide-70-w-5-pounds-399
The others chemical that gain more popularity among backyard growers is the new Sevin with zeta-cypermetrin as the main ingredient. The old stand by is Triazicide (Gamma-cyhalothrin). You are right that the old Sevin (with cabaryl as the main ingredient) has fruit thinning effect.
Other chemicals with brand names like Avaunt, Actara, Delegate. I was told are effective against PC. Those are a commercial grade and may come with some restrictions when using any of them.
Besides what to use, when to use it is as important. Some people can use these chemicals effective and need only 2-4 spray to get the pests and diseases under control.
@alan wrote about his synthetic spray schedule.
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