Answer: Sounds like peach tree borers and they are difficult to control. You can poke into each hole with a wire or paperclip to kill the larvae. Insecticide sprays can help control the pests but won't fix the damage they've already caused. In Ohio, Lindane or multipurpose orchard pesticide may be used, and some brands of chlorpyrifos (Dursban), endosulfan, and carbaryl (Sevin) are labelled for this use in home plantings. Insecticide should be applied to the bark by a paint brush or a hand sprayer. Here's a publication from Ohio State University that might be helpful to you: http://ohioline.osu.edu/hyg-fact/2000/2032.html
Good luck with your peach tree.
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