When you find a “worm” in a homegrown apple, it might be the larvae of the codling moth. This pest is as destructive to fruit trees as it is widespread—it is found anywhere in the world where apples are grown, with the exception of East Asia and Africa.
Codling moth is not a new pest; it was introduced to the United States with European settlers more than 200 years ago. Its primary host are apples, but it can also attack other fruit, including pears. The fruit not only becomes unpalatable, but the damaged parts of apples can contain aflatoxins, which are carcinogens produced by molds.
Before synthetic insecticides became available after World War II, there was no treatment available for orchards to keep the codling moth at a low level. Most of these organochlorine insecticides are no longer used due to their environmental impact. The approach to control the pest, however, has remained the same: take preventative measures to eradicate the moths and newly hatched larvae before they can attack the fruit. Once the larvae are inside the fruit, it is too late to control the pest, be it with insecticides or any other method.
If you live in an area with commercial orchards, your apple trees might be targets for codling moth.
What Does Codling Moth Look Like?
Although it’s the larvae of the codling moth that do the damage, it is important to be familiar with its entire life cycle, and how it looks in its other stages so you know what to look out for, and when.
Life Cycle of the Codling Moth
The codling moth goes through a complete metamorphosis: egg, larva, pupa, and adult. The number of generations per year increases depending on how warm the climate and weather are. Two, three, and even four generations per year are not unusual.
The mature larvae overwinter in a thick cocoon under the scales of bark and in plant debris or soil around the base of host trees. In the early spring, the larvae pupate and the adult moths emerge around the time when the apples start to bloom.
The adult moths are only active when temperatures climb above 60 degrees F, and during the hours before and after sunset. To mate, the moths need temperatures at sunset of at least 62 degrees F. At night, a female lays individual eggs, 70 to 100 eggs total, on leaves, stems, or developing fruit. The eggs hatch within six to 20 days.
The emerging larvae deeply bore into the core of the developing fruit to feed on the seeds for a duration of about three to five weeks, then exit the fruit. They drop off the tree and crawl to a sheltered location such as plant debris on the ground around the tree or bark crevices, and spin a cocoon for their pupa.
The next generation of adult moths emerges in mid-summer and the life cycle restarts. The larvae that you find in apples harvested in the fall are usually from the second or third generation.
Larvae and Adult Moth Identification
The newly hatched larva is only about 1/10 of an inch long and then grows to ½ to ¾ inch in length when mature. The color of the body ranges from creamy white to pinkish in older larvae. The head is dark brown to black.
The pupa is about ½ inch long, brown and covered in a thick cocoon.
The adult moths are ½ inch long. Their grey-brown color blends in well with the tree bark, so they are not easy to detect. Two characteristics distinguish them from other moths: the bottom third of the mottled wings is bronze-or copper-colored, and when resting, they hold their wings over their body like a tent.
The scale-like, oval eggs are very difficult to find not only because they are so small and laid individually, but also because they are almost transparent when laid.
Two Ways to Get Rid of Codling Moth
The focus of codling moth control should be to keep population numbers low by preventative methods (see below). In case of a high level of infestation, however, the application of an insecticide might be necessary.
Regardless of the insecticide you use, the proper timing and frequency of the application is crucial. You need to kill moths and newly hatched larvae before they enter the fruit. In a moderate infestation, it might be enough to spray the first generation in the spring and keep the population numbers low during the rest of the season with other methods. If you are dealing with a heavy infestation, or you want blemish-free fruit, repeated applications might be needed.
Trapping As the First Step
While trapping codling moth is usually not sufficient to manage an infestation, it is an important step for insecticide application—it tells you when the moths are out and when to spray. There are special traps for codling moths that can also be used to monitor other pests such as oriental fruit moths. Only the males are attracted by the trap. For monitoring purposes, one trap per backyard is usually sufficient, and it lasts for about eight weeks. Place the trap at least two weeks before bud break and check it every few days. Clean out the trap after each inspection.
If you trap codling moths, spray your apple trees promptly. And if you don’t find any, there should be no need to apply an insecticide.
Codling moth can be treated with an all-purpose fruit tree insecticide, or with insecticides containing pyrethroids (permethrin, esfenvalerate), or carbaryl (Sevin).
Keep in mind that broad-spectrum insecticides such as carbaryl (Sevin) do not only kill the codling moth and larvae but also pollinating bees, therefore it should never be sprayed during bloom. In addition, it poses a risk to human health and aquatic life, which prompted California to restrict its consumer use in 2020.
There are different options for chemical control with natural substances.
Products with Spinosyn are based on the soil bacterium called Saccharopolyspora spinosa which is toxic to insects like codling moth but safe for most beneficial insects as well as for humans, pets, and the environment. It requires repeated applications for each codling moth generation and per product label, there is a limit on the number of applications per season.
Codling moth granulosis virus (CYD-X) is a virus that attacks only the larvae of the codling moth. It is a highly specialized insecticide that kills the larvae within three to seven days after they ingesting it so it is crucial to start the applications as soon as the first-generation larvae have hatched. Since that might be tricky to determine, another telltale sign that the larvae have started feeding are entry holes in the developing fruit. The virus is safe for other insects, humans, pets, and wildlife and it is OMRI-listed for organic production. Products with CYD-X require several applications and there is no limit to the number of applications per season.
Horticultural oil is another option, however, it works best when applied in combination with granulosis virus or Spinosad products, mixed together in a tank sprayer.
As with all pesticides, make sure to always follow the directions on the label.
Signs of Codling Moth Damage
In addition to their preferred host, apples, codling moths also attack pears, quince, bigfruit hawthorn, and walnuts.
The larvae bore a hole through the skin of the developing fruit at the calyx (the blossom end). It is small at first and looks like a sting. As the larvae eat the flesh on their way to their primary target, the core, seeds, or their excrement is pushed out of the entry hole as brown, crumbly frass. The entry becomes enlarged and the larvae eventually exits the fruit through that hole. On apples and pears, there is sometimes a reddish colored ring around the entry hole.
The larvae also bore into walnuts to feed on the immature kernels. Walnuts on which the larvae have fed early in the season either do not make it to harvest, as they just drop off the tree, or the kernels become inedible.
What Causes Codling Moth
The adult moths can fly up to a mile in their search for mating sites or host trees. They can come from virtually anywhere in your neighborhood—adjacent back yards with an untreated codling moth infestation, or from orchards that do not have integrated pest management in place.
How to Prevent Codling Moth
There are several methods to prevent codling moth damage.
Selection of Varieties
Early-maturing apple and pear varieties are somewhat less prone to codling moth damage than late-maturing varieties and late-leaving walnuts.
A time-consuming but effective mechanical method to protect your fruit from codling moth is to bag each individual fruit right on the tree. This works only for apples with longer stems, and only when you thin out the apples to one per cluster.
When the apples are no larger than ½ to 1 inch, or about four weeks after the bloom, have a paper bag (the standard lunch bag size) ready. Make a two-inch cut in the bottom fold of the bag and gently slide it over the fruit. It needs to be a tight fit, so there is no gap between the stem and the bag. Staple the open end of the bag shut.
The apples will mature despite the paper bags, yet red varieties won’t develop as much color as when they are uncovered.
Keeping things clean is essential to keep codling moth populations at bay.
About a month to six weeks after they bloom, inspect your trees weekly. If you find any fruit with the suspicious holes or frass, remove them promptly. Promptly discard them in the trash; never keep them around any of your stored “good” apples.
Also pick up and discard any fallen fruits. Continue the cleanup until after the harvest is over and don’t leave any apples on the ground around the tree or on the tree.
Sanitation is also important during apple storage. There might be larvae in the harvested apples that will exit the apples during storage and then overwinter in the shed, garage, or barn. Inspect wooden apple crates for larvae or cocoons and destroy them.
What spray kills codling moth?
There are insecticides that kill both the moth and the larvae, and others that only kill the larvae. What you use depends on when you spray it.
Can you eat apples with codling moth?
Preferably not, at the mold caused by the insect damage is toxic.
When should you spray codling moths?
Ideally you put up a trap so you know the time of the adult moth flight, then you can time the spraying accordingly.