How to Keep Codling Moths Away from Apple Trees

Marla Koss -- Apples damaged by codling moth larvae.
Marla Koss -- Apples damaged by codling moth larvae.

How to Keep Codling Moths Away from Apple Trees

The codling moth is a sneaky critter. To start with, it is a camouflage expert. Unlike other moths that are easy to see against green foliage, the codling moth looks like tree bark, it holds its wings tented over its back to look even more like tree bark. It’s only a half inch long or so and does most of its flying around just before and after sunset, when it is even harder to see.

The codling moth (Latin name Cydia (Laspeyresia) pomonella) sneaks around because it wants to lay eggs on newly formed apples. The larvae hatch, burrow into baby apples and munch away. A “worm” in an apple is usually a codling moth larva.

Keeping codling moths away from apples can be difficult. The larva burrows inside the apple, where it can’t be picked off or sprayed with pesticide. Codling moths reproduce like crazy. In the San Francisco Bay Area, they can have two generations in one year. If one gardener manages to get rid of the codling moths in their yard, and a neighbor two doors down has an infected apple tree, the moths can come right back. Despite the difficulties, we must fight on, in defense of our apple trees. Are we not gardeners? How can we bow down to a tiny insect?

Tools for this fight fall into four categories, and it is urgent to plan ahead before the next growing season.

Keeping the area around apple trees raked, thinning apple clusters to one or two fruits per cluster and removing any damaged fruit as soon as possible is key to all types of codling moth management. Codling moth larvae often spin cocoons in dropped leaves. For some reason, moths like to lay eggs where two apples touch. Infested fruit often drops prematurely: keeping the area around the tree raked keeps the moths from completing their life cycle. Thinnings and raked leaves go in the city green bin: it is not likely that a home compost bin will get hot enough to kill eggs and larvae.

Codling Moth Traps
Traps can be bought at Pagano’s Hardware, Encinal Hardware and our local plant nurseries. They serve two purposes: to determine when moths are starting to show up, in the event it is necessary to start spraying, and to catch moths that are starting to check out your trees. Plastic milk or soda bottles can be repurposed as D.I.Y. adult moth traps, using apple cider vinegar and molasses. Instructions are here:

Traps will not suppress codling moths if there are a lot of these pests around the tree. Hang several as high as possible around each tree.

Bags that go around each apple and kaolin (clay) spray can thwart the moth. The University of California extension service suggests buying paper lunch bags in bulk (the kind that measure 7 ¼ x 4 inches), cutting a slit in the bottom, poking the apples through when they are less than one inch in diameter, then stapling the bags shut. This method is time consuming, but non-toxic. The extension service says that this method is highly effective. Some say that paper bags attract earwigs. Nylon mesh does not work, the caterpillars eat right through the bags.

A traditional method is putting a sticky barrier collar around the tree. This only has some effect on smooth barked apple varieties, and since codling moth caterpillars don’t necessarily crawl up tree trunks, the moths can still get the apples.

Kaolin clay spray is a newer, and more effective method. The clay, marketed under the brand name “Surround,” forms a white barrier that not only repels pests, but causes irritation, confusion, and is an obstacle for feeding and egg-laying. However, the spray must be applied per package directions early enough in the year to interfere with egg-laying. Start spraying when the flower petals begin falling in spring. Timing is crucial to prevent damage.

Due to the damage they cause to beneficial insects and to the environment in general, insecticides should be a last resort. A new product, CYD-X, is a virus that specifically targets codling moths and causes minimum harm to everything else. It must be applied once a week during egg hatching time, so it is critical to precisely calculate when eggs will hatch. The UC Extension service’s calculator will help:

A lot of gardening is management: you want some plants to grow, not others, you want butterflies and bees and ladybugs in your yard, but not ants and slugs and codling moths. Managing codling moths is difficult but worth it. Keep your mind firmly on apple pie as you battle that bug.

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