by Jay Brunner, originally published 1993
Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae)
Codling moth belongs to the family Tortricidae. This is one of the largest families of moths, with about 950 North American species. It includes a number of important tree fruit pests, e.g., codling moth, oriental fruit moth and leafrollers. The moths are small, usually gray or brown, and their wings have bands or mottled areas. The front wings are usually square tipped. While at rest, the moths hold their wings roof-like over the body. Codling moth originated in Asia Minor but has been a principal pest of apple and pear in North America for more than 200 years. With the exception of Japan and part of mainland Asia, it is found wherever apples are grown throughout the temperate regions of the world. Its larvae bore deep into the fruit, making it unmarketable. If uncontrolled, codling moth can destroy most of the crop. By the first half of the 20th century, it was a major pest in all apple growing districts of North America. It was not until synthetic organic insecticides became available in the late 1940s that it could be maintained at very low levels in commercial orchards. It can produce from 1 to 5 generations per year, depending on the climate.
Codling moth prefers apple but also attacks pear, large-fruited hawthorn and quince. In California, races of codling moth attack prune and walnut. Pears are resistant to attack when small because of their hardness but may become heavily infested in late summer as they mature. Infestations in stone fruits such as apricot and cherry are extremely rare and usually occur only where heavy infestations of apple or pear are nearby.
The codling moth egg is oval, flat and, when first laid, almost transparent. It is about 1/12 inch (2 mm) long. Eggs are laid individually on leaves or fruit and are almost impossible to find, especially in a commercial orchard.
The newly hatched larva is only about 1/10 inch (2 to 3 mm) long. Its head is black and the body is creamy white. The full grown larva is 1/2 to 3/4 inch (12 to 20 mm) long, has a brown or black head capsule and thoracic shield. The body is usually creamy white but turns slightly pink when mature. Unlike other caterpillar larvae that feed inside the fruit, such as oriental fruit moth and lesser apple worm, the codling moth larva feeds in the center on flesh and seeds. The others feed on flesh away from the center.
The codling moth pupa is brown and about 1/2 inch (12 mm) long. It lies inside a cocoon spun by the mature larva beneath bark scales on the tree or in a sheltered place at the base of the tree.
The adult codling moth is about 1/2 inch (12 mm) long. At first glance, it seems a nondescript dull gray, but closer inspection shows the wings are crossed with fine alternating gray and white bands. The wings are tipped by a patch of bronze-colored scales that reflect in sunlight (Figure 24). The moth holds its wings tent-like over its body when at rest.
The codling moth spends the winter as a mature larva in a cocoon. Larvae are found under loose bark scales on the tree, in litter at the base of the tree, in wood piles, on picking bins in the orchard or on farm buildings near packing sheds where culled apples might have been dumped. Overwintering larvae begin changing into pupae when the first apple blossoms show pink color. The first adult moths begin to emerge about full bloom of Red Delicious. Peak emergence is usually 17 to 21 days later, though this depends on temperature. Adults continue to emerge for 6 or 7 weeks and are most active on warm evenings when temperatures are above 60 °F. Moths mate and begin laying eggs within a day of emerging. First generation eggs are laid primarily on leaves, although some are found on fruit. They take 8 to 14 days to incubate.
Newly hatched larvae find fruit and enter either at the calyx end or through the side. They bore through the skin and feed on the fruit flesh for a few days, then move towards the core where they feed on seeds and flesh. As they feed, they push excrement out of the apple through the entry hole, which is gradually enlarged and often serves as an exit hole. When the larvae are fully grown in three to four weeks they leave the fruit in search of sheltered places to spin cocoons. The larvae may pupate and emerge as second-generation adults or remain as larvae until the following spring.
Each year, some first generation larvae enter diapause, a state of delayed development and inactivity. The rest stay in the cocoon for 2 to 3 weeks, then emerge as adults. Second generation adults begin emerging in early July. Adult activity peaks in mid-July to early August and continues into early September. Second generation larvae are in the fruit from mid-July until late September. Mature larvae of the second generation leave apples as early as mid-August in search of overwintering sites.
In exceptionally warm years a partial third generation may be produced. Moths representing a third flight emerge in late August or early September and deposit eggs. While larvae will enter fruit, causing severe damage in some cases, they usually do not complete development before winter conditions arrive or the fruit is harvested.
Damage is caused by feeding of the larvae in fruit. There are two types of damage: deep entries and stings. Deep entries occur when larvae bore to the center of the fruit and feed on seeds. Brown frass, or excrement, extrudes from the entry hole or a new hole destined to be an exit. In pear, this type of injury is first noticed in the calyx. On more mature fruit, a new entry is often surrounded by a red ring.
Stings are shallow entries where the larvae died or gave up and tried another place. Both types of damage make the fruit unmarketable, but deep entries are a problem in stored fruit because bacteria and fungi in them lead to fruit rot.
Pheromone traps can be used to monitor adult activity. Place traps in the orchard by the pink stage of apple flower-bud development. Examine traps each day until first moths are captured, usually about full bloom. Trap placement and maintenance are critical for reliable information. Place traps at mid-canopy height and within the canopy of the tree, making sure the entrance is not blocked.
The wing-type trap, such as Pherocon(r) 1CP, is recommended as a monitoring standard. This trap must be well maintained to work properly. Make sure the trap maintains its proper shape, change pheromone caps every 4 weeks (or as recommended by the manufacturer) and change trap bottoms after catching 30 moths, or every time a cap is changed. Stirring the adhesive surface of the trap will increase its effectiveness in areas where dust is prevalent. Moth capture in pheromone traps is used to initiate the codling moth degree-day model but can also be used to determine the need to apply sprays.
To assess fruit damage, examine fruit at the end of the first generation, in early July, and again just before harvest. Examine 25 fruit per tree from at least 40 trees per block of 5 acres. In large trees, most damage occurs in the upper half, so sample in this area. It is critical to assess fruit damage when sprays are not applied because of low trap catch or if soft insecticides or mating disruption are used for control.
Some organic growers have banded trees with cardboard strips as a monitoring or control technique. Mature larvae migrating down the tree in search of shelters to spin cocoons will enter these bands. Bands can be removed and examined after the first generation or after harvest. If the intent is to estimate the population, 40 bands per block are recommended. This technique is much more efficient on young trees with smooth bark. In older trees the bark should be scraped and the bands attached in the scraped area.
Several parasitoids attack codling moth. However, it is impractical to rely upon them alone to suppress codling moth populations to levels that would result in acceptable crop loss. Most conventional insecticides are toxic to these natural enemies. Where mating disruption or soft insecticides are implemented, parasitoids can be an important component of the control program.
Trichogramma minutum is a parasitoid of codling moth eggs. It can parasitize a high percentage of eggs in favorable conditions. Another parasitoid, Ascogaster quadridentata, was introduced to the United States from France as a possible control for codling moth. It attacks the codling moth egg but does not kill the host until the larva is nearly full grown. This parasitoid is easily reared in the laboratory.
Insecticides have been the primary control tactic used against codling moth for over 50 years. Since the early 1980s a degree-day model has been used to help time insecticide applications to make better use of chemical controls. The lower and upper thresholds for codling moth are 50°F and 88°F. A horizontal cutoff is used when calculating degree-days using maximum and minimum temperatures. A degree-day look-up table for codling moth is available.
Please note: in 2009 WSU implemented a new codling moth model that did not depend on a biofix (details are available in the WSU Crop Protection Guide for Tree Fruit; EB0419).
Pheromone traps are used to establish the biofix (biological fix point) for the model. Place traps in the orchard at about 160 degree-days from March 1 or at the pink stage of Red Delicious flower bud development. First codling moth usually fly at full bloom. The codling moth model is started with the first consistent catch of moths in traps. Traps within a region should be placed in locations where codling moth populations are known to be fairly high. The first consistent moth catch is when several moths are caught in a single trap in one night or when a majority of traps within a similar growing region catch one or more moths on the same night.
In some years, a few moths may be captured on one night and it appears to be a good biofix. Then, a cold period follows when no more moths are captured. If this period is prolonged, 7 to 10 days, ignore the first moth catch and start the model based on the next consistent moth capture. In many apple and pear orchards, codling moth populations are very low and moths may not be caught until several days after biofix for the region. If you do not trap moths, use the date of full bloom to begin the degree-day accumulation for the codling moth model.
Set the degree-day total to zero at biofix. Apply the first control spray after 250 degree-days are accumulated, which coincides with first observed entry where codling moth pressure is high. Timing of the second spray will depend on the product used. Some insecticides provide 21 days of residual control, while others may only provide 10 to 14 days. The target of most conventional insecticides is the young larva hatching from the egg. The goal is to kill the larva before it can bore into the fruit. The egg hatch period lasts 30 to 45 days, so usually only two control sprays are required against each generation.
Timing of sprays against the second generation is also based on degree-day totals. Apply the first spray against the second generation at 1250 degree-days after biofix. Timings of subsequent sprays should be based on the residual life of the products used.
The degree-day model for codling moth can be accurate in predicting the first fruit entry compared with a calendar approach. In 10 years, the degree-day model predicted larval entry the same day it was observed and was at worst only 2 days early or late. By comparison, the calendar approach, which recommends the first spray 21 days after full bloom, was almost always early, in some cases by as much as 18 days.
Mating disruption is a promising control tactic for codling moth. Dispensers are placed in the orchard before first moth flight. The number of dispensers, placement and treatment intervals may vary depending on the type of product used. While monitoring for pests is recommended in any pest management program, it is essential in a pheromone-based program.
Soft pesticide programs
Codling moth has not been controlled satisfactorily with soft pesticides in the hot, dry regions of the West. Biological insecticides used alone have not provided satisfactory control, even when applied weekly. Neither have viruses proven effective. Organic growers have used combinations of biological and botanical insecticides plus sanitation with reasonable success. The botanical insecticides have probably provided most of the control in these programs. Use of summer oil sprays has shown promise for controlling codling moth on pear and may have a place in soft pesticide programs on apple.
Another use for pheromone traps is to estimate population levels to help make control decisions. The number of traps used, location and maintenance of traps, and the quality of the pheromone trap are all critical to the successful use of a threshold-based decision making program.
Use one trap (Pherocon(r) 1CP wing type trap or similar) for every 2.5 acres. Place in the orchard before the first moth is active. Trap placement within the orchard and tree will influence moth captures. Traps should not be placed at the very edge of a block. Placing a trap in the center of the 2.5 acres to be monitored by the trap is the standard approach, but placement toward a border with known high pressure is an acceptable alternative. Attach the trap to a limb within the tree canopy at a height of 6 to 7 feet. A pheromone cap loaded with 1 milligram of codlemone, the major component of the codling moth pheromone, should be used as a lure. Replace pheromone caps every four weeks.
Check traps once a week after the first moths are caught. After 30 moths have been captured, or if the trap becomes dirty in the meantime, change the trap bottom. The trap adhesive should be evenly distributed over the bottom of the trap. Count moths in traps weekly and remove. Record the catch separately for each trap in the orchard.
The idea behind using trap catch as a treatment threshold is that sprays are not applied if catch is below a certain number. Two threshold methods can be used with moth capture data:
- With the first method, the trap catch threshold is 2 moths on two consecutive weeks. Thus, if a trap catches 2 moths one week and 3 the next, a spray should be applied to that area (2.5 acres). However, if a trap catches 2 moths, then 1 moth, then 2 moths, a spray is not recommended. This method has worked well for some growers in British Columbia and Washington.
- With the second method, the degree-day model is incorporated with moth capture in pheromone traps. The same density of traps is used as in the other method, one trap every 2.5 acres. Moth capture in a trap is accumulated from biofix to 250 degree-days, the recommended time for the first control spray. The treatment threshold is 5 moths, so if 6 or more moths have been captured, then the area associated with the trap is treated and moth catch accumulation begins at zero again. It may be possible, where codling moth populations are low, to delay the first spray if moth catch remains below the threshold at 250 degree-days. If fewer than 6 moths have been captured, extend the moth accumulation period to 350 degree-days. If by 350 degree-days the threshold is not exceeded, do not apply a control. If it is exceeded, apply a control at once.
The number of sprays required to control larvae hatching from eggs deposited between biofix and 250 degree-days depends on the residual life of the product used. Conventional insecticides have a residual life of 10 to 21 days; some organic products are effective for only 2 or 3 days. At this point, whether the threshold is reached and a spray applied or not, begin accumulating catch from zero again. Accumulate moth catch for the next 21 days and if the threshold is again exceeded apply additional controls. If it is not, no further sprays against the first generation are needed.
For the second generation, the threshold is 4 moths. Start accumulating moth catch at 1000 degree-days after biofix. If 5 or more moths are captured in the next 250 degree-days, apply a control spray. If not, do not apply a control and start accumulating moth catch from zero again. In either event, accumulate moth catch over the next 21 days and treat if the threshold is exceeded.
Caution: The thresholds recommended here are for a trap density of one per 2.5 acres and are for each individual trap, not an average over the entire orchard. Control treatments should be applied to the part of the orchard represented by the trap where moth catch exceeded the threshold. However, an area larger than that represented by the trap may have to be treated, depending how the orchard is designed. The use of trap catch thresholds for codling moth usually reduces use of insecticides.