Insecticides should be applied every two weeks beginning about two weeks after petal fall. Continue applications until the first of August. I recommend spinosad. It’s the active ingredient in several organic pesticides and is effective on a wide range of insects, including codling moth.
My favorite way to prevent worms is to place codling moth traps in the trees. A pheromone sex attractant lures male moths into the trap from which they cannot escape. If the males are all trapped, the females lay infertile eggs. Although not 100 percent effective, this works quite well if you don’t have a lot of unprotected apple or crabapple trees nearby without traps. Hang one trap in small trees and three traps in larger trees. Traps are available at many full service nurseries and garden stores and online.