Spray and thin apple trees now
If you want apples without worm holes, regular biweekly spraying with a fruit tree spray is necessary. If you do not have a lot of untreated apple trees nearby, you can probably protect most apples from worms by hanging codling moth traps in the trees. It takes about 3 traps for a medium sized apple tree. Codling moth traps contain a sex attractant which traps the male moths. Without fertilization, the female moth’s eggs are sterile.
Early June is also a good time to begin thinning apples to increase fruit size and quality. By looking carefully as you thin, you can often eliminate apples which have already been entered by a worm. The holes are very apparent while fruit is small.
Apples have clusters of five flowers in a group. If all five flowers are well pollinated, they may all develop to maturity. More typically, three or four will continue to develop while one or two will remain small and fall off. The tree can only produce enough food to develop one large apple per cluster. If two are allowed to develop, most fruit will be medium in size. When three or more mature, they are generally all small, unless there are no other nearby fruit clusters within 6 inches.
In thinning, I generally only leave one fruit per cluster and remove the others. If there is more than six inches to the next cluster I leave two fruits. Leave the largest apple in the cluster, which is usually the center one. Of course those which have worm holes or other damage should be removed even if they are the largest so a better quality fruit can develop