By Johanne Ryker, UC Master Gardeners of Placer County
Q: We recently moved into a new home that has a small orchard with various fruit trees. I was very disappointed when I went to pick my apples and pears and discovered they all had worm holes and what looked liked worm-infested fruit. What would cause this and can this affect other trees in our orchard?
A: A common problem that occurs in both apple and pear trees, as well as English walnut trees, is an insect that is referred to as a codling moth. To reduce future damage caused by this serious pest is going to take some time and patience on your part.
First, I would recommend that you remove all fruit that has dropped to the ground. This practice is referred to as sanitation. Sanitation should be the first step in controlling or reducing codling moth. Removing infested fruit from the tree and promptly picking up dropped fruit from the ground is most critical in May and June, but should continue throughout the season.
The worms you found in your apples will eventually become larvae and overwinter as full-grown larvae within thick, silken cocoons under loose scales of bark and in soil or debris (which includes fruit left on the ground) around the base of the tree. Then, in early spring, from mid-March to early April, they emerge as adult moths. The moths are only active a few hours before and after sunset, and they mate when the sunset temperatures exceed 62°F. This is also the best time to hang traps in your tree(s) that are designed to attract the male moth and discourage mating of both male and female moths.Otherwise, a female moth that has mated can deposit 30 to 70 tiny disc-shaped eggs on fruit, nuts, leaves, or spurs.
Also at this time, you will need to check you blossoms, leaves, and emerging fruit for signs of damage from eggs that may have been deposited and remove promptly. This will help reduce infestation as well as encourage larger fruit when the existing damaged blossoms and fruit are removed. It is also a good idea to band the base or trunk of the tree with cardboard to discourage the mature worms or larvae that you may have missed from climbing back up into the tree under loose scales of bark to overwinter.
Codling moth traps are available from many commercial sources, such as hardware stores, garden centers, or online. These traps usually have a sticky cardboard bottom and are baited with a pheromone (sex attractant) lure. The lure mimics the scent of a female moth, attracting males to the trap. Capturing the males reduces mating and therefore the number of eggs that are laid.
Using traps can help to reduce codling moth populations but won't completely eliminate damage. However, depending on the population of the coddling moth and your willingness to set traps, remove infested fruit, and stay on top of this problem, you should have quite a few apples that are free of major worm infestation next year.
Visit UCANR Pest Note, Codling Moth, for more information.