Codling moths: identification & treatment options

Often the bane of both commercial and home apple growers alike, the codling moth is a common and destructive garden pest. Find out all about the cause of maggoty apples and how to prevent your crop from being affected.

Codling moths (Cydia pomonella), or rather their caterpillars, can be a real problem for not only apples (Malus domestica), but pears (Pyrus communis), quinces (Cydonia oblonga), peaches (Prunus persica), apricots (Prunus armeniaca) and walnuts (Juglans regia) as well. Read on to find out what to look out for if you suspect codling moths are in your garden and which control measures are available for home gardeners.

Signs of codling moths: what damage to look out for

The presence of codling moths in apples and pears is quite distinctive. A codling moth infestation is instantly recognisable by the visible bore or feeding holes on the side or top of the apples. But the real damage is on the inside of the fruit, where the core is often a patchwork of tunnels and the caterpillars’ brown or black excrement, known as frass. Apples infested by these pests are commonly known as maggoty apples. Sadly, fruits can be affected early in the season. If your crop appears to ripen and fall early, codling moths may well be the culprit. These pests may also strike later in the year, in which case you may be able to salvage any of the codling moth-infected fruits. Just make sure to discard any infected areas.

Tip: Codling moths can sometimes be confused with other pests, including the apple ermine moth and the apple sawfly. An apple ermine moth (Yponomeuta malinellus) infestation can be distinguished from one by apple codling moths as the latter does not produce a web to house its young. While the caterpillars of the apple sawfly (Haplocampa testudinea) also feed on apples, they tend to do so in late spring, whereas the codling moth larvae munch on the fruits later on in the summer.

What do codling moths and their larvae look like?

Adult codling moths are small and grow to only 2cm in length. Most often seen at dusk, the adult moths have lightly striped brown-grey wings with copper-coloured patches at the tips. Hatching from small white eggs, the larvae are yellow-white when young. Over the following weeks, they mature into red-brown caterpillars which reach up to 2cm in length and have a darker head.

The life cycle of a codling moth

Here in the UK, adult codling moths tend to first appear from May to June. Laying their eggs on mainly apples and pears, the small larvae hatch and burrow deep into the fruits to feed. In late summer, they tunnel out and overwinter under leaves or loose bark, ready to pupate the following spring.

Codling moth control: treatment options

While there are several codling moth treatment options available to the home gardener, they are growth stage specific. With fluctuating temperatures over the summer, it can be tricky to know when to use them. A small number of codling moths often do little damage and can be tolerated without a huge loss of the crop. Having said that, if numbers increase and damage is widespread, there are various ways of dealing with this pest.

Codling moth sprays

Only use sprays to control codling moths if other less harmful methods have not been effective. Organic insecticides that contain natural pyrethrins are the least potentially harmful and can be successful. They must be approved for use on fruits. However, due to their short action period, you may need to reapply more than once for the control to be effective. If organic sprays are not efficacious, you can also try other contact fruit-approved insecticides, like deltamethrin or cypermethrin.

To make a difference, any insecticides used will need to be applied to the tree and both sides of the foliage at the correct time as per the manufacturer’s instructions. Generally, spraying around the third week of June and again three to four weeks later proves effective. However, the codling moth’s life cycle is temperature-dependent and difficult to pinpoint. Pheromone traps can help to observe their presence and growth and indicate when to spray.

Codling moth traps

Even though pheromone traps are relatively poor at controlling codling moths, they can be a good indicator of the moths’ activity and highlight the correct time to use other measures. Widely available from garden centres and online retailers, pheromone traps contain a synthetic scent that imitates that of the females and lures in the male moths.

Using nematodes against codling moths

Nematodes parasitise codling moth larvae and prevent them from reaching adulthood and laying eggs. To apply, spray the tree’s trunks from September to March. Please note that nematodes are sensitive to external conditions and can only prove effective when applied on a cloudy day in temperatures above 12°C.

Using parasitic wasps against codling moths

For a more natural approach, you can encourage the codling moth’s predators, such as hedgehogs, ground beetles, and some species of parasitic wasps, to the area. Certain species of parasitic wasps, such as Trichogramma dendrolimi, like to feed on the small codling moth caterpillars and can be helpful in controlling their numbers. Being tricky to obtain, it is best to encourage parasitic wasps to come into the garden by providing some of their favourite sources of food, like fennel (Foeniculum vulgare), dill (Anethum graveolens) and yarrow (Achillea).

Using neem oil against codling moths

Derived from the neem tree (Azadirachta indica), neem oil is sometimes used as a contact insecticide to help control codling moths. However, as neem oil has the potential to harm other beneficial insects, you should only apply it at dusk when they are not about. When applying neem oil, follow the manufacturer’s instructions closely, as using too much can damage the host trees.

Other tips to reduce codling moth damage

Codling moths can be hard to prevent completely and small numbers can be tolerated. Here are a few further possible preventative measures to try:

• Gently shake smaller and dwarf trees in winter to help dislodge the larvae and lay a tarpaulin under the tree to help collect them for disposal.
• Find and remove overwintering larvae by brushing the tree’s trunk and searching under loose bark.
• Encourage insect-eating birds, such as blue tits and nuthatches, into your garden so that they can forage under the bark.
• Remove infected fruit from the tree before it falls to limit the next generation.

Unfortunately, codling moths are not the only pest that can damage apples or pears. Check out our article on other apple pests and diseases to learn more.