Guest Commentary: Codling Moths and Apple Maggots Cause Damage to Your Apple Crops

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At this time of summer, you are probably closely monitoring your apples, waiting for those beauties to ripen for picking and eating. However, if you haven’t been doing your IPM (integrated pest management) homework, you may be in for a disappointment at first bite. Who doesn’t know about the worm in the apple? This worm is actually the codling moth larvae or apple maggot! The codling moth can destroy over 80 percent of your crop if neglected. These two troublemakers, unfortunately, love the apple as much as we do.

In western Washington, we will see at least two generations of codling moths during the summer. If you select early-maturing apple varieties, you may be able to avoid the third generation. Start watching for codling moths in late May by putting out detection traps. The moths, 1/2-inch long with grey and brown bands, appear at dawn and dusk. Upon appearance, begin applying a pesticide if you choose to, such as an organically approved spinosad or kaolin clay. It will be necessary to spray the trees every two weeks from mid-June until the end of August. Covering the fruit after thinning with a paper bag or nylon sock can also be effective.

The female codling moth lays its eggs on the fruit and leaves. The eggs hatch and the larvae burrow through the apple to the core. By early July the apples will be infested. You will notice an accumulation of brown, granular excrement (frass) on the surface of the fruit around the entrance hole. Destroy all infested fruit by putting it in a plastic bag and leaving it in the sun for a week.  

At maturity, the caterpillars are about ¾-inch long and light pink. They drop to the ground to pupate in cocoons in any small crevice on or around the tree. It is advisable to put two-inch strips of corrugated cardboard around the lower part of the tree trunk for the cocoons. The life cycle can be interrupted by removing and destroying the cardboard strips before the adult moths emerge.

The apple maggot, native to eastern North America, was first detected in Portland, Oregon, in 1979, and has since spread to 17 counties in western Washington and four in central and eastern Washington. It is illegal to transport noncommercial tree fruit to Oregon or across the Cascade Mountains to the apple-maggot-free areas of eastern Washington.



Unlike the codling moth, only one generation of apple maggot flies is produced in a year. To monitor apple maggots, hang sticky traps from the tree at eye level in early summer and replace them every three to four weeks. The fly is ¼ inch long and has a black banding pattern on the wings. Spray trees or cover fruit as for codling moths until no more flies are trapped.

The female flies lay their eggs in apples from the beginning of July through early October. The white, “headless”, legless maggots hatch in three to seven days inside the apple and burrow little brown trails through the flesh. The dimpling on the surface of the fruit may go unnoticed, but the damage is apparent when the fruit is cut open. The mature maggots emerge and drop to the ground, overwintering as pupae and emerging as flies the next summer to repeat the cycle. They can spread over an area of ¼ to ½ mile.

The integrated pest management techniques listed will be much more successful if you plant trees grafted onto dwarfing rootstock. Don’t allow these fruit-eating pests to deprive you of the pleasure of biting into that crisp, sweet apple.