Yeah, just saying "borer" is not enough. You need to identify the pest to be able to treat for it. Different pests have different treatable fife cycles.
Take oak borer, it has a 3 year larval stage that can easily be treated in the first 3 years as it feeds in the cambium, the third year it boars into the xylem. the fourth year is when it emmerges. Lastly, they have a cycle of heavier emergance durring odd years because of this.