The codling moth (CM) is a worldwide pest of apples introduced into the U.S. from Europe by early American settlers. The CM caterpillar is one of the "worms" found in “wormy apples.”
The CM has a complete life cycle (egg – larva – pupa – adult) and may go through 2 or 3 cycles per year. Moths appear at the time the apple trees are in bloom to lay eggs on the leaves or developing fruit. The eggs hatch within 6 to 20 days and tiny young larvae (white, often tinged with pink, and with a dark head) bore into the end of the small fruit and tunnel to the core where they feed on the seeds. Larvae feed for about 3 weeks until 5/8 inch long and then leave the fruit to form a cocoon under loose bark or on the ground.
Apples damaged early in the season drop prematurely. Caterpillars of the second and third generations later in the summer are the “worms” found in the apples at harvest time. Caterpillars spend the winter within silken cocoons in the orchard and start the cycles over the following spring.
The traditional approach to CM control used by commercial orchards relies on a preventive spray program that kills moths and newly hatched larvae before they enter the fruit. Caterpillars inside the fruit can not be controlled. Control of the first generation is essential to limit the amount of damage in late summer.
Controls. Insecticides are usually needed when there is a demand for a high yield of blemish-free fruit. While natural controls such as predators (primarily birds) and parasites are important they do not prevent enough damage for financial success in commercial orchards. Natural controls may be adequate in home production situations where sorting of damaged apples is possible.
Pick up and eliminate fallen fruits on a weekly basis. You may further limit the number of moths by attaching corrugated cardboard strips (two to four inches wide) tightly to the tree trunk and scaffold branches in June and August. Remove and destroy the strips after cocoons are formed.
Thorough, regularly-scheduled, repeated applications of insecticide every 10 to 14 days are usually needed from after bloom to near harvest to achieve a very high rate of worm-free fruit. Use an all-purpose fruit tree mixture or the insecticide permethrin, esfenvalerate or carbaryl (Sevin) according to label directions.