Life history and habits

The codling moth overwinters as a full-grown caterpillar within a cocoon, pupating in winter or early spring. Adults typically emerge in spring within days of apple bloom, although individuals overwintering near buildings or other warm areas may emerge sooner. Peak emergence usually comes a week after eclosion of the first moth and continues over six or seven weeks. Mating occurs within a few days of adult emergence, and egg laying tends to increase as nighttime temperatures exceed 16.6°C (62°F). Each female lays 30 to 70 eggs, deposited singly on leaves and fruit. The eggs will hatch in six to 14 days, depending on temperature, and larvae bore into fruit within 24 hours of hatching. After entering the fruit, larvae tunnel to the core and feed on developing seeds. Larvae develop through five instars before reaching maturity. Once mature, larvae exit the fruit and seek a protected site to spin a cocoon, usually beneath bark or underneath debris around the base of the tree. Larvae that emerge in mid-late summer pupate the following spring after overwintering. In addition to apples and pears, other hosts include crabapple (Malus spp.), cherry (Prunus avium), peach (Prunus persica), English walnut (Juglans regia), hawthorn (Crataegus spp.), and quince (Cydonia oblonga). Infestations of codling moth in wild crabapple can be significant sources of moths that migrate to nearby orchards. This species produces two to three generations each year in Colorado.

Injury

Caterpillars tunnel through the flesh of apples, often attacking areas that provide some cover, such as the end, calyx, stem end, or where two fruit touch. The entry point of young larvae is called a sting and is characterized by a light red circular pattern. In pears, this pest primarily enters fruit at the calyx end and infestations tend to occur later in the growing season. This pest can also infect pears and is rarely found in cherries, peaches, and large-fruit crab apples. Although caterpillars tunnel through the fruit flesh, most of the feeding occurs on developing seeds in the core. When the caterpillars are fully grown, they tunnel out of the fruit, creating larger wounds and leaving behind piles of brown excrement. In some areas, codling moth can infest up to 90% of fruit.

Monitoring

Fruit should be inspected regularly for the presence of entry or exit holes and frass. In commercial orchards, it is recommended that insecticides be applied when 0.5% of fruits are infested with codling moth larvae.

Several traps can be used for managing codling moth. Some traps are helpful in detecting when moths are active, which allows for more effective insecticide applications. The spring emergence of moths can be easily monitored using the use of pheromone traps, which can attract males or females depending on the pheromone emitted by the lure. Lures for monitoring traps last 30-60 days depending on the type of lure and should be stored in the freezer until needed. When the earliest blooming fruit variety is at the first pink stage, traps should be deployed about 6-7 feet high at the exterior of the canopy and parallel to the prevailing wind direction.

Biological control

There are many natural controls of codling moth: some parasitic wasps and a host of generalist predators (e.g., assassin bugs, minute pirate bugs, green lacewing larvae). These predators provide important supplemental control on unsprayed trees or trees where insecticides are selective in their effects. Trichogramma wasps have a great biological control potential. Due to the serious nature of codling moth injury, where a single larva can destroy a fruit, natural enemies often will not provide effective control. However, releasing Trichogramma wasps can be used as a supplemental approach with mating disruption.

Cultural control

Infested fruits should be removed, and thinning fruit clusters can improve spray coverage. Piles of culled fruit should be removed and destroyed, as well as fruits that drop due to infestation with first generation larvae. Debris should be removed from the vicinity and tree base, and bark flaps can be removed from older trees to reduce the availability of pupation and overwintering sites. Fruit bins, woodpiles, and brushes should also be removed. Individual fruit can be enclosed in a small paper bag to exclude codling moth. Abandoned orchards and wild hosts should be removed within a quarter mile of active orchards to reduce immigrating moths.

Deploying cardboard or burlap bands on tree trunks can provide pupation sites for codling moth, which can then be collected and destroyed before first-generation moths emerge. Bands can be deployed again in the early fall to reduce the density of overwintering individuals. Banding is most effective in smaller orchards of trees that have smooth bark and are located away from nearby sources of moths. While there are no apple or pear varieties that are completely resistant to codling moth, varieties that produce firmer fruits are generally less susceptible to infestation.

There is promising preliminary research indicating that netting the trees can be effective in suppressing codling moth as well. Nets prevent the moths from accessing oviposition sites and reduce moth numbers. This approach can be labor intensive, and more research is needed to validate it.

Mating disruption is one approach that can be effective against codling moth. This approach involves saturating an orchard with a sex pheromone emitted by female moths, which delays or prevents mating by disrupting the ability of male moths to locate females and is only recommended in orchards with at least 10 continuous acres. Regular monitoring is necessary to determine the efficacy of this approach and evaluate whether supplemental insecticide applications are required. This is an organic-certified approach that can reduce reliance on insecticides. Mating disruption has a high up-front cost, but after two or three seasons, it can be less costly than conventional management with insecticides. It is worth noting that mating disruption is more effective in square-shaped orchards than narrow rectangular orchards, and the adoption of mating disruption to neighboring orchards of the minimum size will improve effectiveness. This approach is not recommended in newly planted orchards since the pheromone dissipates more quickly given the lack of foliage. For more information on mating disruption, including monitoring practices, common causes of failure, and descriptions of different products, visit the Utah State University webpage.

Chemical control

There are limited numbers of insecticides on the home/garden consumer market available for managing codling moth. All require repeated application, timed for periods when eggs are being laid and hatching, and thorough coverage of fruit. Horticultural oils are safe for humans and non-target organisms and can be effective against codling moth. They should be applied multiple times when first-generation eggs are being laid and once during egg-laying of subsequent generations. However, it is recommended that horticultural oils be applied on cloudy days to minimize damage to plants.

When moths are only captured in border traps deployed in large orchards (>10 acres), insecticides can be applied to four or five border rows to reduce the number of applications required throughout the growing season. In orchards using the mating disruption technique, insecticide treatments are usually necessary to suppress the first generation of codling moth. It is recommended that insecticides with differing modes of action be rotated to prevent resistance from developing in the pest population.

References

MSU. (n.d.). Managing Codling Moth in Commercial Orchards. Montana State University. Available https://agresearch.montana.edu/warc/guides/apples/apple_pest_codling_moth.html

Murray, M. 2020. Codling Moth Mating Disruption. Utah State University – Extension. Available https://extension.usu.edu/pests/research/codling-moth-mating-disruption

UCIPM. 2015. Codling Moth. University of California – Agriculture and Natural Resources. Available https://ipm.ucanr.edu/agriculture/apple/codling-moth/#:~:text=Important%20Links-,Description%20of%20the%20Pest,fruit%20later%20in%20the%20season.

USU. (n.d.). Codling Moth. Utah State University – Extension. Available https://extension.usu.edu/pests/ipm/notes_ag/fruit-codling-moth