I am opposed to the use of Neem Oil as a pesticide. Its main use in commercial agriculture is as a surfactant. It has zero viability as a chemical toxin - even towards aphids. It will kill weaker insect and arachnid individuals by sticky entanglement, but studies have shown that stronger individuals survive thus breeding stronger populations.
That said, the chemical compound Azadirachtin is present in Neem seed and when distilled or biosynthesized to sufficient concentration will harm a number of insect pests. Products containing a viable concentration are all manufactured by biosynthesis because it is difficult and costly to obtain a high enough concentration by distillation.
Where are you located (region)? This can be a factor in controlling some pests.
Here’s a list of active ingredients I found in pesticides labeled for Peach Borer at CDMS that I would consider using:
Azadirachtin (see above)
Chlorantraniliprole (ingestion or contact)
Diflubenzuron (ingestion or contact) (classified as non-carcinogenic)
Novaluron (e.g. Pedestal, Rimon® 0.83EC) ** check this out
When pure neem is used you have 250x the concentration compared to the usual 1 tbsp per gallon of a neem oil in water spray. So the amounts of Azadirachtin are also magnified by that amount and is about the same as adding one tbsp of pure Azadirachtin to a gallon of water. Also raw neem oil contains many other bioactive compounds besides Azadirachtin so you are getting more than just that compound.
Every spray has survivors. If not commercial orchards would not be spraying the same poison for the same pests over and over. The main difference is now my peach trees are not dying, and the borer is overall only a minor annoyance.
I don’t think neem oil is very useful at the 1 tbsp per gallon kind of thing, in fact the reason why I tried it full strength on borers is I bought a bunch but it was not working on anything in my sprayer so I was going to throw it out…coating the peach tree trunks was just an experiment with something I was going to toss otherwise.
I would also think it is because new ones migrate to my trees from elsewhere each year. Meaning even if I had a spray that killed every single last borer (or any pest for that matter) in my orchard, I would still have more within days or weeks or the following year because bugs that weren’t on my property when I sprayed it will move in sometime after I sprayed. I would think that is another reason I have to repeatedly spray for the same pest. Even if I wipe them out with one spray, others will move in from off-site locations. Right?
I paint the bottom 4” or so… making sure to get much of it right at the soil line. I don’t know if it helps much if the borers are deep into the wood already. When I find a tunnel I get to the bottom of it right away with my poker so never tried putting neem in…