Article written by Madeline Wimmer, UMN Extension Fruit Production Educator.
Images: A Gravenstein apple showing signs of damage classic to codling moth (Cydia pomonella). A: frass at the apple calyx end is characteristic of codling moth larvae. B: When the frass is removed, a hole is revealed. C: the apple damage was localized to the apple core. Photos taken during a trip to Sonoma County, California (Zone 9b).
Introduction
A number of different lepidopteran pests (these are insects that become moths) are pests of apples, like red and oblique banded leaf rollers, oriental fruit moth, and codling moth. Of these, codling moth is a major pest of apples in the Upper Midwest. Codling moth adults can be distinguished from other moths by a dark copper-brown band located at their wing tips.
Life cycle and damage
Codling moths overwinter as mature larvae in cocoons under bark scales and debris. Adults tend to emerge between 175–220 degree days (DD, base 50°F) from January 1st and mate within days after emergence (traps should be put out in the orchard before this time). Female adults will then lay eggs on leaves near apple fruitlets during the first generation, which take between 8–14 days to hatch depending on the temperature.
The larvae, which are light pink with a dark head, emerge from the eggs and can cause damage to fruits superficially or internally as they try to enter the fruit. When a larva fails to enter, this can lead to a “sting,” which leads to superficial damage.
If a larva successfully enters, it will begin to feed on the apple, leaving frass in its trail, which usually plugs up the entrance hole with frass. Damage is usually limited to the apple core and developing seeds at this stage. This behavior differentiates codling moths from other moths (lepidopterans) like the oriental fruit moth (Grapholita molesta), which tend to move in more random patterns.
After the larva is fully grown, it exits the fruit and pupates for 2–3 weeks. After that point, a second generation of moths emerge and can be monitored similarly to the first generation.
Monitoring
Images: Ben Fontana, orchard manager at Apple Jack Orchards taking a delta trap set up with a codling moth pheromone (left) and sticky sheet with a pheromone cap from the inside of the trap to show two codling moths captured (right).
Traps are used as a means to monitor codling moth adult populations. The most effective traps are delta traps or wing traps combined with codling moth pheromone caps. These traps can be set out at eye-level around bloom time, and checked once every three days. The recommended trapping density is one trap per 2.5 acres; however, orchards under two acres in size may still want to deploy two traps total to account for edge effects.
When 2–5 moths are caught per trap for at least two trap checks in a row, this marks the biofix date when degree day accumulations are counted for management. Around 200–250 DD after the biofix date is when initial egg hatch can occur, but management is recommended to begin closer to 250 DD for larvicide application.
Growers should keep in mind that codling moths typically have a second generation that begins in July in Minnesota, which should be considered when planning management this year. Depending on the weather during a given year, a third generation may also develop, although this is less common, especially in northern regions.
Management
Conventional chemical management options can be found in the Midwest Fruit Pest Management Guide, starting on page 34.
Mating disruption is one non-chemical method for codling moth management, which is done during the first adult flight around bloom. Support for codling moth mating disruption can be found on page 26 of the Midwest Fruit Pest Management Guide, where information about different dispersal methods is available. Note that mating disruption is usually most effective for orchards that are 5+ acres in size, and more traps are usually needed to track adult populations since trap captures tend to be lower in orchards using mating disruption.
Additional practices include removing dropped fruits from the orchard throughout the growing season, and encouraging parasitoid populations through careful insecticide selection and avoiding broad-spectrum insecticides. Codling moth granulosis virus (CpGV) is another management option allowable under USDA Organic guidelines, in conjunction with oil applications to target codling moth eggs (i.e., ovicide).
References:
Codling moth (California Integrated Pest Management)
Codling moth (Washington State University Extension)
Oriental fruit moth (Washington State University Extension)
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