The Practical Gardener: Codling Moth And You

Apr 2, 2016

The "paper bag technique" is one way to combat the ever-present threat of coddling moth.
Credit Valerie Winemiller / University of California

Codling moth larvae are the cause of the infamous “worm” in the apple or pear and is the immature stage of a small moth. This pest spends the winter as a mature larva in a pupal case on trunks of trees or in debris around the home orchard. When spring temperatures rise in March, the pupae mature and adult moths begin emerging in late March to April. Moths mate and lay eggs on leaves. Eggs hatch several weeks to a month later, and the larvae almost immediately bore into small fruit that has just begun to develop.

To control codling moth with insecticide sprays, you have to apply the spray onto the larva just after it hatches and before it bores into fruit.  Once inside the fruit, it is protected from any insecticidal treatments. This requires very careful timing. Sprays applied before the larvae hatch or after larvae bore into fruit won't be effective.

Though not as accurate as timing using a more complicated day degree models and pheromone traps, you can time effective sprays by regularly monitoring the fruit for the first stings on fruit. Stings are the entry points of larvae and are marked by tiny mounds of reddish-brown frass — or insect poop. You should start looking for them three to four weeks after bloom, and spray as soon as you see the first sting.

Effective homeowner spray products for codling moth include spinosad, carbaryl, and codling moth granulosis virus  called Cyd-X. Cyd-X is the safest product for use around bees and other beneficial insects but isn't available in many stores — you may have to purchase online. Spinosad is an organically acceptable product that is very safe for people, pets, and the environment, although it is more toxic to beneficials than Cyd-X. Spinosad, however, can be made even more effective by adding 1% horticultural oil to the spray mixture. After the first spray, two additional sprays at 10-day intervals should be applied. Carbaryl is also effective and doesn't need to be sprayed as often, but it is quite harmful to natural enemies and to bees.  

For those of you who don’t want to use insecticides at all, I suggest covering selected fruit with paper lunch bags four to six weeks after bloom when fruit is .5" to 1" in diameter. Cut a small slit in the bottom of the paper bag and slip it over the fruit.  Staple the bottom of the bag closed and you will have almost 100% control. Take the bags off about a week before harvest.

A few other things you can do to reduce codling moths in your home orchard is to thin your apples to one apple per cluster.  The codling moth female likes to lay her eggs where the two apples meet.  You can also make sure to clean up any fallen fruit.  This will reduce the number of codling moths in the next generation.