Worms In Your Apples?

Codling Moth Worms in Apples

It is such a satisfying experience to reach up into an apple tree and pluck a shiny apple from a branch. But if you take a big, juicy bite and see that the remaining apple in your hand has brown yuck and half a worm inside -- and you just swallowed -- it may be time to take out the artillery!

The Codling Moth lays its larvae on the developing fruit and leaves of apples and pears, and it can also attack walnuts. When the eggs hatch, the young caterpillars feed on the surface of the fruit for a few days, then burrow into the center. They feed about three weeks, then tunnel out of the fruit and find a place to spin a cocoon. 

Biological control has been so successful for codling moth that chemical pesticide use has been greatly reduced. Several effective, non-chemical techniques are available for home gardeners. These include care of trees and fruit, trapping techniques, and beneficial insects. For best results, use a combination of techniques.

Identifying Codling Moths

The codling moth is a gray moth 1/2 to 3/4 inch long with mottled gray wings that blend well with most tree bark. The tips of the wings are marked with copper lines and a gold or bronze spot. The larvae are white to light pink "worms" with a dark brown head. Though we all recognize "wormy" apples, the larvae are actually caterpillars. A mature caterpillar is about 3/4 inch long.

Codling moth photo by Scott Bauer, USDA Agricultural Research Service, Bugwood.org

You need to understand their Life Cycle to successfully manage codling moths. They spend the winter as a caterpillar in a cocoon, usually under loose bark on a tree trunk, debris under the tree or in some other protected spot. Adults emerge from the cocoon in April or May. The females lay eggs on leaves and small fruit for about a month. The moths are only active a few hours, before and after sunset, and they mate when the sunset temperatures exceed 62°F. After mating each female deposits 30 to 70 tiny, disc shaped eggs on fruit, nuts, leaves, or spurs. After the eggs hatch, young larvae seek out and bore into developing fruit or nuts. When they reach full maturity they leave the fruit and drop from the trees to search out pupation sites and continue the life cycle in the soil or debris. Some crawl back up the tree to pupate in bark crevices. The rate of development will vary with temperature, proceeding more rapidly in warmer weather and climates. Depending on the climate, codling moths can have two to four generations per year.

Codling Moth Damage

If the codling moth is left uncontrolled, they can cause substantial damage, often infesting 20 to 90% of the fruit, depending on the variety and location. The larvae penetrate into the fruit and tunnel to the core, leaving holes in the fruit that are filled with reddish-brown crumbly droppings called frass.

Management of moths and worms

Codling moths can be very difficult to manage, especially if the population has been allowed to build up over a season or two. It is much easier to keep moth numbers low from the start than to suppress a well-established population. Begin implementing control measures early in the season.

If a backyard tree or orchard has high moth populations, it may take several seasons diligently practicing these non-chemical control methods to reduce codling moth damage to about 10 to 20% of fruit infested. If you have nearby orchards or backyard trees that have no control this can be a continual source of codling moths.

• Select varieties that are less susceptible to damage, such as early maturing apples and pears.
• Prune trees to a height where the canopy is easy to reach to facilitate non-chemical management of this pest.
• Thinning when fruit is small (the size of a marble or walnut) so that there is only one apple or pear per fruit cluster is a good practice to encourage a larger fruit size and provide less optimal laying sites.
• Be sure to remove any fruit that has small holes made by codling moth caterpillars. Composting doesn't destroy all the caterpillars, so place in a plastic bag and put in your trash. Collect dropped apples weekly because caterpillars move out of the dropped fruit quickly.
• Check fruit on trees for signs of damage every week or two, beginning 6 to 8 weeks after bloom and remove any worm-damaged fruit.

Trapping Moths

Hanging pheromone traps in each susceptible fruit or nut tree can help to reduce codling moth populations but won't completely eliminate damage.  The pheromone lure mimics the scent of a female moth, attracting males to the sticky trap. To use pheromone traps, start in early spring, right at the beginning of bloom. Hang one to four traps per tree (depending on the size of the tree) as high as you can reach.

Check the traps every week or two to remove dead moths and stir the adhesive to maintain its sticky quality. Refresh pheromone lures and change the sticky bottoms every 4 weeks or sooner if they become too dirty to capture moths.

Trunk Banding

Try the Paper Tree Wrap with the Stiky Stuff Sticky Coating. Remove the bands and destroy at the end of codling mating season, end of June or mid-July. Be sure to crush and kill any pupae remaining on the trunk after you remove the band.

To help control the overwintering generation, put new trunk bands up in mid-August and remove and destroy them between November and January. 

Bagging and Maggot Barriers

Excellent control can be achieved by enclosing young fruit in Maggot Barrier bags right on the tree to protect them from the codling moth. This is the only non-chemical control method that is effective enough to be used alone and in higher population situations. However, it is quite time consuming, so this method is most manageable on smaller trees with fewer fruit. You may bag all the fruit on the tree or just as many fruit as you think you will need. Keep in mind that any un-bagged fruit is likely to serve as a host and increase the pest population so it would be prudent to employ sanitation and mass trapping to keep the population in check. Bagging won't affect the maturity or quality of the fruit, but it will prevent full color development on red varieties. Leave the bags on the tree until harvest. The bags also protect the fruit from sunburn.

To increase the success of this technique check out Surround, derived from kaolin clay. This product label says it forms a hostile barrier to insect pests without affecting fruit growth.

Codling Moth Virus

The codling moth granulovirus, CYD-X offers an effective and selective control of codling moth and is OMRI Listed. The virus is extremely specific to the codling moth and will not effect native pollinators. The virus is available from PVFS and should be applied weekly for best results.

References for Further Information

• Integrated Pest Management, UC Davis: Codling Moth
• Michigan State University Extension: Organic Management of Codling Moth