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The codling moth, Cydia pomonella (Linnaeus) was introduced to North America from Eurasia and is an important pest of apples worldwide. Other North American hosts include pear, quince (Cydonia oblonga Mill), hawthorn (Crataegus spp.), crab apple (Malus spp.) and walnut (Juglans spp.). Codling moth adults fly into orchards from nearby abandoned orchards, or from hosts in surrounding woodlots (apple, quince, hawthorn and crab apple). In some areas adults overwinter in orchards.
Codling moth eggs are 1-2 mm in diameter, flattened, elliptical and almost transparent. Their small size means they are rarely seen on fruit. Newly emerged larvae are about 2-3 mm in length and pale creamy white with a black head capsule. Mature larvae are approximately 12-20 mm in length and are cream or pink with a brown or black head (Figure 4-90). There are five larval instars. Larvae are distinguished from other worms (oriental fruit moth and lesser apple worm larvae) that also feed in the fruit by the absence of an anal comb. Pupae are brown and vary in size from 10-12 mm in length. The adult is approximately 9-12 mm in length with a wingspan of 19 mm. It is grey brown in colour with alternating bands of grey and white. Tips of the forewings are bronzed (Figure 4-91). Adults are mainly active at dusk. In Ontario there are two generations of codling moth per year, except in the coolest areas (Georgian Bay) where there is only one generation.
Figure 4-90. Codling moth larvae (Alex Molnar, Agriculture and Agri-Food Canada, London)
Figure 4-91. Codling moth adult
Codling moth overwinters as mature larvae in silken cocoons under loose bark on the tree trunk and limbs. Cocoons are also found in leaf litter under the tree, piles of wood, brush, posts and occasionally mulch. Recent research shows larvae can overwinter in storage bins and on the walls of packing sheds and other buildings adjacent to the orchard. In mid to late April, larvae pupate inside the cocoon. The first adult usually emerges around bloom, while peak emergence occurs within four to five days after the first moth has emerged. Adult emergence is highly dependent on weather conditions. Cool temperatures delay emergence by 10-12 days. High temperatures cause early emergence in the spring and result in the deposition of more eggs. Late emerging first generation adults may not appear in orchards until six or seven weeks after petal fall. Some regions (California and Washington) report seeing late peak flight (a double peak) for first generation codling moth. There is some uncertainty as to why this may occur, but it could be related to selection of codling moth over time to escape insecticide applications.
After mating, female moths can lay up to 100 eggs. Eggs are laid individually on the fruit or leaves. Eggs hatch in 6-14 days depending on temperatures. Larvae then search out the fruit where they anchor themselves and begin to dig into the fruit. After entering fruit they feed inside the apple for approximately three weeks, then leave fruit to seek a site to pupate (tree trunk or larger branch of the tree). Pupation generally lasts 14-21 days. Some larvae do not pupate at this time, but remain as larvae until the next year. Second generation adults begin to appear in orchards as early as July. Moths lay eggs over two months and mature larvae of the second generation start leaving the apples in mid August and continue until apples are removed from the orchard or temperatures drop. In some areas (Michigan) unusually high daily temperatures during the summer result in a partial third generation of codling moth. This third generation results in worms in the fruit at harvest if control measures are not taken. It is often called a suicide generation because larvae are unable to complete their development due to the onset of winter.
Larvae damage the fruit by:
- feeding minimally on the outside of fruit creating small "stings"
on the fruit surface (Figure 4-92)
- tunnelling into fruit, and feeding on the pulp and seeds causing extensive interior breakdown of tissue (Figure 4-93)
Figure 4-92. Sting (Dr. Ian Scott, Agriculture and Agri-Food Canada, London)
Figure 4-93. Seed feeding
Fruit with extensive tunnelling often aborts prior to harvest, while fruit with surface feeding may remain on the tree until harvest. This injury causes internal breakdown of the fruit often leading to premature drop. The exit hole - where mature larva emerged - is often plugged with frass. Exit holes can occur on the side or bottom of fruit (Figure 4-94 and Figure 4-95). Fruit damage from oriental fruit moth and codling moth is similar, but codling moth larvae usually feed on the fruit seeds, while oriental fruit moth larvae only feed on the fruit flesh. If uncontrolled, codling moth can damage 50% to 90% of the crop. First generation damage appears in orchards in late June to August, and second generation damage appears in orchards from late August through to October. Second generation larvae are considered to cause the greatest amount of damage.
Figure 4-94. Fruit damage on side of fruit
Figure 4-95. Fruit damage on calyx
Monitoring and threshold
Place pheromone traps (4 traps in each 4 ha block) baited with a diamond trap and a pheromone lure in each orchard prior to bloom to establish biofix. Proper trap placement is essential to monitor codling moth populations. Place traps in mid canopy for orchards not using pheromone disruption, and in the top third of the canopy for orchards receiving mating disruption. Place traps on the north side of the tree, 30-50 m apart, in the portion of the orchard most likely to be entered by wild hosts such as areas near woodlots or near abandoned/poorly sprayed orchards. Remove leaves and branches from a 30 cm area around each trap. Change lures and traps for each generation and remove in September.
Monitor pheromone traps twice weekly and record male moth trap catches. Pheromone trap counts are not necessarily an indication of the potential damage from the insect. Use traps to determine first sustained moth catch, this information is used in conjunction with a degree day model, to predict when the eggs are hatching and when to apply insecticides targeting larvae. Although regional consultant reports provide useful information on when this pest is present in an area, growers are encouraged to place traps in each orchard, since pest emergence and pressure varies from orchard to orchard.
There are few effective cultural or biological controls to help manage codling moth. Predators, such as ground beetles (Carabidae), ants and crickets, and parasitic wasps, attack larvae as they leave fruit and crawl towards tree trunks, but do not provide economically acceptable levels of control.
Some areas of the United States recently began using mating disruption in conjunction with insecticides to manage codling moth. Growers in the northeastern United States and Canada are not advised to use mating disruption alone to manage codling moth because it is less effective in controlling codling moth than other pests (oriental fruit moth). Mating disruption also works best in larger, uniform orchards that are relatively square. It is not recommended in orchards less than 4 ha in size. The larger the contiguous block of mating disruption, the more effective it will be. A whole farm approach of combining mating disruption with insecticides or granulosis virus is proving very efficacious in Michigan. Effectiveness of mating disruption also declines if there are high levels of mated females flying from neighboring orchards or abandoned trees.
Proper monitoring and timing of insecticides is essential for managing codling moth. If insecticides are applied too late, larvae will have tunneled into the fruit where they can no longer be controlled by insecticides. The developmental model to predict timing of codling moth sprays is:
DDC = (maximum °C + minimum °C ÷2)- 10°C
The accumulation of these degree days is initiated by the biofix - first sustained moth catch. For insecticides targeting larvae, OMAFRA recommends spraying at 125 DDC (base 10°C) after biofix. Apply ovicides at 50 DDC (base 10°C) after biofix. For second generation codling moth, apply larvicides at 600 to 625 DDC (base 10°C) after biofix from the first generation flight. To determine the best timing of a particular insecticide to control codling moth, see OMAFRA Publication 360, Fruit Production Recommendations.
Until recently, organophosphates (OP) were the main products used for codling moth control. In the last few years, several alternative materials (e.g. insect growth regulators (IGR) and neonicotinoids) have been registered in Canada. Be aware that some new materials do not provide subsequent control of apple maggot - often present in orchards at the same time as second generation codling moth. See OMAFRA Publication 360, Fruit Production Recommendations for more information on the options available for managing these pests.
Research shows codling moth populations in Washington, Oregon, Michigan and elsewhere have developed resistance to OP insecticides (Guthion, Imidan, Zolone). Preliminary research conducted by Agriculture and Agri-Food Canada suggests OP resistance is present in some apple orchards in Ontario. To deter the development of pesticide resistance, always rotate chemistries between generations wherever possible. Use one chemistry for first generation codling moth (e.g. insect growth regulators) and a different chemistry (e.g. neonicotinoids) for second generation. Do not rotate chemistries within a generation.
Ontario research has shown the use of a border spray program to be a very effective way to manage codling moth. In a border spray program, apply an initial cover spray of OP insecticides to eradicate any codling moths residing in the orchards. Subsequent border sprays of OP are used in a four-tree wide (20 m) zone around the perimeter of the orchard to control codling moths migrating into the orchard after the initial cover spray. The efficacy of using border sprays with new chemistries (e.g. neonicotinoids, insect growth regulators) is currently not known - using border sprays with these chemistries is not recommended. If damage is detected during routine monitoring of the orchard, replace a border spray program with a cover spray program. Only use border sprays in orchards: greater than 4 ha in size, square or rectangular in shape, with no history of codling moth of apple maggot infestations, not near any abandoned orchards, without OP resistant codling moth populations. Border sprays reduce the amount of insecticide used considerably, resulting in environmental and economic benefits. Border spray programs are also considered less harmful to beneficial insects and may increase natural biological control.
Conduct a careful assessment of pest damage to fruit in the orchard
at or just prior to harvest. If a significant increase in injury
is observed in a given year, return to cover sprays during the summer
months the following season. Reassess at that time to determine
whether the problem was rectified and a return to border sprays
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