That worm in your apple is a codling moth!
The codling moth is tricky to get rid of. Here's why. The adult lays its egg very near a developing apple. When the egg hatches, the larva makes a bee-line right into the apple. It doesn't want to eat the apple, but will chomp through the apple to get to the seeds. Once the larva gets inside the apple, there is not much one can do to get rid of it, short of throwing away the apple. Therefore, better strategies to eradicate the codling moth should concentrate on other stages of development.
The first thing an adult moth wants to do is mate. In a small orchard, or single tree, you can use a monitoring trap. The male is attracted to the trap because it smells like a female. It sticks in the trap and then can't mate with a real female. This is not enough to do the job, especially if there is a large population. It is useful to monitor when the moths are flying. There are mating disruption hormones available, but they would not be useful in a small orchard. There are also now available a lure that attracts both males and females, and these might be more effective for the home orchard. Hopefully you have some birds or bats that eat moths. They won't completely deplete the population, but maybe they can do their part to help. It wouldn't hurt to have birdhouses and bat houses around.
Once the codling moth has laid its eggs, there are several things you can do to prevent the egg from making a larva. Parasitic wasps will invade the eggs with their own eggs, and then the egg hatches a wasp instead of a codling moth. Oil sprayed on the tree at frequent intervals can smother the egg. Lacewing larvae will eat codling moth eggs as well as aphids.
As mentioned above, the larval stage quickly gets inside the apple and then cannot be reached. Even so, there are some things you can try. Bacillus thuringiensis (Bt) is a type of bacteria that makes the larva sick if it eats it. The Bt doesn't last very long and is especially sensitive to UV light, so to make it more effective, you can mix fish oil in with your spray, which protects the Bt a little longer from the UV. You can also mix in some molasses to make it yummier for the larva. Then make sure you spray often, like once a week during the time that the larvae are hatching. Another thing you can spray on the tree, which is probably more effective than the Bt, is Granulosis virus. The reason it is more effective is that it needs fewer virus particles to infect the larva, and it is in a particle that protects it from UV. The downside is that the product is pretty expensive for a small orchard, although it can be stored for up to 2 years.
Another way you can protect the apple is to bag the apple when it is small, before the egg has hatched. You can use either sandwich bags, paper bags, or footies coated with surround (a special kind of kaolin clay). It is very time-consuming. You can learn more about this from the Home orchard society.
After the larvae have entered the apple, they will pupate and produce another generation if it is summer time. Therefore, getting the infected apples off the tree and away from the orchard is important. Immature infected fruit should be put in the trash can. Remove any fallen apples immediately. If the apple is mature and infected, then by all means cut out the wormy part and throw that part away. The rest of the apple is perfectly good to eat. You can also put cardboard bands around the trunk and large limbs of the tree, especially if the tree has smooth bark. The channels of the cardboard should run parallel to the trunk. The larvae enter the cardboard looking for a good hiding place to pupate. they pupate in the cardboard and you can remove the cardboard and burn it or throw it away with the pupae.
At the end of the season in the fall, the larvae will find a hiding place in the bark, or cardboard bands to spend the entire winter. This is a good time to make a last attempt at killing, or at least reducing the population. Make sure you take your bands off the tree and burn them. I also pick off loose bark and squish the larva if I find one. At this point if the weather is still warmish, you can spray beneficial nematodes on the bark of the tree. This will work best if you spray the tree afterward with a fine mist of water to keep the tree moist for a period of time - or do the spray in a misty rain. This will keep the nematodes alive until they have a chance to find and infect the larvae.
Most likely no one thing will completely eradicate your codling moths. You will need to combine several methods, if not all, to reduce the numbers. You can also assume that if your population is high you will need to chink away at it over a few years. After you have a smaller population to worry about, fewer applications will be needed.
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