Codling Moth: Avoiding Fruit Worms In Your Trees
The codling moth does lots of damage in commercial orchards every year. We discuss how to handle codling moth infestations!
Apples have become one of the most iconic fruits in our diets, but it’s come a long from the mountains of Eurasia to kitchen tables around the world. Apples are a member of the rose family (Rosaceae) which also includes pears, peaches and quinces. For over a thousand years, growers along the silk road cultivated and traded fruits. The increase in the popularity of apples also unintentionally spread a small but destructive tag-a-long: the apple codling moth (Cydia pomonella).
The codling moth begins its life as a worm and almost everyone can relate to finding a worm in their fruit. As children, we often see imagery of the friendly green worm inside a big red apple. In France, there is a common idiom, “le vers et dans le fruit” or “the worm is in the fruit” meaning that the damage is already done. Today, the codling moth is a major pest in most places where apples are grown and can cause extensive fruit damage. They are also a serious threat to walnut growers who reportedly use 10% of their farming budget on controlling this pest.
Fruit production can often be considered advanced gardening because it requires a lot of investment in time and space. Many apple and pear trees don’t start producing fruits until a few years after planting. It can be discouraging to battle pests after waiting patiently to taste the literal fruits of your labor. In this blog, we’ll go over various methods to help you control codling moths and ultimately enjoy an abundant harvest.
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Codling Moth Overview
It is not uncommon for codling moths to have more than two generations per year depending on local temperature and climate. Under favorable conditions, codling moths can even go up to four generations between spring and fall. Mature male and female moths are 1/2 to 3/4 inch long and gray or brown in color. Male codling moths also have some bronze banding and spotting on their wings.
Life Cycle of Codling Moths
Starting in early spring when the first fruit blossoms form, adult female moths will emerge from their winter pupation sites to lay oval-shaped eggs that hatch in six to 14 days. A single female moth can lay up to 100 eggs that are near-transparent and very hard to spot! The first generation of eggs is mostly found on leaves. Throughout the growing season, female moths will continue to emerge and lay eggs on different parts of the tree including on the bark and fruits.
As with many insects, this moth is the most destructive in its lifecycle as a voracious larva. A newly hatched codling moth larva starts from around 1/10th of an inch long with a black head and a cream-colored body. The codling moth larva will turn a slight pink color as it ages and it can grow up to 1/2 to 3/4 inch. In walnuts, codling moth larvae feed directly on the kernel. In pome fruits like apples and pears, the larvae will burrow through the flesh of the fruit to feed on the seeds.
After 3-5 weeks, full-grown codling moth larvae will leave the fruit to pupate, leaving behind a pile of excrement called brown frass. Nobody wants to bite into a worm so look out for this telltale sign that the fruit might be contaminated!
Once mature larvae exit the fruits, they will look for protected pupation sites to spin cocoons. Leaf litter around the tree and its bark are some of the most common places. In two to three weeks, most mature larvae will pupate and emerge as second-generation adult moths to start the destructive process again. A few first-generation larvae will go dormant instead and reemerge the following spring.
The peak season for moths in North America is in July. Second and third-generation moths are particularly disruptive when their eggs are laid directly on growing fruits and their larvae can access their food source easily.
The last generation of larvae overwinters in cocoons directly under bark or in the surrounding leaf litter of the host tree. Many of these larvae are eaten by birds, but enough will persist through the winter and even under freezing temperatures to wreak havoc the following spring.
Common Habitats for Codling Moth
Codling moths can be found in temperate regions where apples are grown. Some countries like Japan have very strict import and quarantine treatment for agricultural products and are able to limit codling moth populations. Codling moth adults are not active during the day and prefer to hide under loose bark, leaf litter, or some other sheltered area. They become more active around dusk and are most active during warm summer nights.
What do Codling Moths Eat?
The codling moth got its name from an English cooking apple called the codling apple because it was such a common problem amongst apple growers. As its name indicates, this moth is particularly adapted to feed on apples. However, other fruits such as peaches, plums, and quinces are also susceptible.
Walnuts are another one of their favorite food sources. The fruits can be damaged by surface feeding wounds or by tunnel as the codling moth larvae move through the fruit to feed on the seeds. Left untreated, codling moth larvae can damage 80-90% of the fruit. Walnuts infected with codling moths are completely inedible.
How to Get Rid of Codling Moth
There has been a lot of research and literature on the control of codling moths because of their economic impact on commercial orchards. Traditionally, commercial growers depended on chemical pesticides which had adverse environmental and health effects. Codling moths populations also started to develop resilience to these chemical controls. Since then, there has been more funding for integrated pest management research and we can adapt some of these techniques to use in the home orchard.
In recent years, home gardeners can purchase a new biological insecticide, CYD-X or the codling moth granulosis virus, as a target codling moth control method. A codling moth larva must ingest CYD-X for the virus to attack its digestive tract. The virus will kill the larva three to seven days later. Time your insecticide applications carefully. Thoroughly spray fruits after you see signs that the first generation of eggs have hatched. Continue to spray weekly throughout the growing season until the harvest. CYD-X is currently approved for organic production in commercial and home orchards.
Spinosad is another biological control substance and it’s made from Saccharopolyspora spinosa, a naturally occurring soil bacterium. Spinosad is more toxic than CYD-X to beneficial insects and should be sprayed a maximum of six times per season. Do not use seven days preharvest. Spinosad and CYD-X can be mixed with 1% horticultural oil to increase their overall effectiveness against codling moths. Similar to CYD-X, spinosad also disrupts the life cycle of the eggs and prevents new generations of moths from reaching maturity.
Sanitation is an extremely important pest control practice. Because most apples require multiple trees to cross-pollinate in order to fruit, if one tree has a heavy infestation of codling moths, it will inevitably spread to surrounding trees. As your fruits form, it’s important to inspect the fruits weekly to check for signs of codling moth and remove affected fruits immediately. Pick up any fallen fruit and tidy the area around the base of the tree to limit potential codling moth habitat. Pay especially close attention from May through June leading up to peak moth season.
Thin large clusters of fruits to just one or two. Thinning not only helps with overall sanitation, but it also encourages the remaining fruits to grow larger. After the fruit has reached 1/2 to one inch in diameter, you can bag the fruits with paper bags (No. 2 brown lunch bags work) or cotton bags to create a physical barrier against the moths. Make sure the bag is tightly sealed around the fruit to prevent adult moths from reaching them. Be aware that heavy winds could be an issue for the bags! If you live in a windy area, you can use kaolin clay as a physical control against these moths.
A traditional way to control codling moth populations is to wrap the trunk of a tree with a 1 1/2 to 2-inch band of corrugated cardboard or burlap to encourage adult females to lay eggs on them instead of on the host plant. This method works well on trees that have a smooth bark where there are few natural crevices. However, you must be vigilant in removing these bands or this method can backfire. Many commercial growers use trunk banding or pheromone traps to monitor the population of codling moths and better time their insecticide use.
Codling moths themselves can become a part of the food chain for other insects. Research to find the right parasitoid, parasitic insects that kill its host before the hosts can reach maturity, have been ongoing since the early 1900s. Commercial growers have seen some success with releasing parasitic wasps in combination with other control techniques. Trichogramma platneri is a parasitic wasp native to the western part of the United States that lays eggs within the eggs of the codling moth eggs and inhibits the moths from completing their life cycle. This parasitoid has been shown to be most effective west of the Rockies where it is naturally adapted. These wasps can be purchased online and released at home, but you must time the release correctly to make sure that there are enough moth eggs for them to parasitize.
Preventing Codling Moths
Preventing codling moths, like with many other crops, can start with carefully selecting what you plant. Early maturing apples like Galas and Red Delicious and late leafing walnuts are less susceptible to codling moth damage because their fruit production time is off sync with peak moth activity. Apple trees naturally grow very tall which makes it hard for the home gardener to inspect for and manage pests in the tree canopy. However, you can purchase apples that are grafted onto a dwarf rootstock which limits the height of the mature tree.
You can use different types of traps to monitor the number of moths and get ahead of controlling codling moths. Moths are drawn to sugary liquids and you can easily create a liquid trap using a diluted mixture of water mixed with molasses, juice, or beer and placed near or in the tree.
Alternatively, you can use codling moth pheromone traps that imitate female sex pheromones to lure male moths onto a sticky surface. You may need to place two to four pheromone traps per tree and replace them monthly. Be careful when you remove male moths from pheromone traps as not to transfer the sex attractant onto other surfaces. Set sugar or pheromone traps out as soon as the days start to warm. When you have captured a few initial moths, you can expect eggs to be laid a few days later. Many commercial apple growers use pheromone traps to determine degree days for spraying apple trees for worms.
Mating disruption is another form of pheromone control. According to researchers at Colorado State University, this method is not recommended for home gardeners or commercial growers with less than 10 acres of trees. The mating disruption technique uses a large amount of female sex attractant pheromones to confuse male moths and prevent mating. However, it does not affect females moths that have already mated or moths who can fly outside of the mating disruption area to mate.
As always, it’s a good practice to encourage beneficial insects, birds, and bats in your garden or orchard. They can help limit the emergence of the first generation of moths by feeding on the pupae before spring and can manage future generations at various stages of the moth’s life history from eggs to adults.
Frequently Asked Questions
Q: Can you eat apples with codling moth?
A: Yes, you can still eat apples with some codling moth damage by cutting away any contaminated pulp and brown frass.
Q: Where do codling moths come from?
A: Codling moths originated from Central Asia, likely near modern-day Kazakhstan, along with their primary food sources like apples and walnuts.
Q: How do you make a codling moth trap?
A: Homemade lures can be used to trap codling moth adults. Like many other garden pests, these insects are attracted to the scent of fermenting sugars. Mix one part molasses, juice, or beer to seven parts water with a few drops of soap and place the mixture in an open container. Hang the trap within the tree canopy.