Once inside the apple, the worms are shielded from the toxic effect of most pesticides. So pesticides must be applied during adult moth activity so that the pesticide residue covers the fruit surface before egg hatch. Pesticide sprays should start 17-21 days after full bloom (about 10 days after most of the flower petals drop from the tree) to target the newly hatched worms before they bore in to the fruit. The simplest approach is to reapply the every 10-14 days until fruit harvest. Be sure to read the product label and note the preharvest interval (time between last pesticide application and fruit harvest allowing the pesticide residue to dissipate before harvest). For a list of effective pesticides on codling moth, homeowners can contact their local WSU Extension office or access the WSU Hortsense website at http://pep.wsu.edu/hortsense/scripts/query/displayProblem.asp?tableName=plant&problemID=22&categoryID=3
A more environmentally safe approach would be to time two pesticide applications for each generation of adult moth activity as monitored by monitoring traps. The monitoring traps come in various designs and contain a pheromone lure that attracts male moths that get entangled in a sticky surface. When the trap starts catching fresh male moths in May, July, and late August, it is time to apply the first pesticide application. Then, apply the second pesticide 10 to 14 days later for each codling moth generation.