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News / Life / Clark County Life

Gardening with Allen: Thinning will help apple crop

By Allen Wilson
Published: May 20, 2023, 6:01am

My apple trees had more blossoms this spring than I have ever seen. I understand that when apple trees have a heavy crop one year, they tend to be very light the next year. Is there anything I can do to reduce this year’s crop? What is the best way to keep worms out of the apples?

The biannual bearing of apples is quite common. Trees store food for next year’s crop. When they have a year with a very heavy crop, there are limited food reserves for the next year, resulting in a smaller crop.

Apple trees produce flowers and fruit in clusters of five. If all five are pollinated and set, fruit will be very small. Orchardists try to reduce fruit to one per cluster. In fact, they often spray to prevent pollination of the rest of the flowers after one has set.

You can thin heavily to reduce your apple crop. You first need to wait a couple of weeks because the tree will naturally drop some fruits. Blossoms that were not pollinated will not develop into fruit. With a very heavy set, you will need to leave only one fruit per cluster of five. In fact, where clusters are less than 3 or 4 inches apart, you may want to remove some clusters entirely. Always leave the largest apple in the cluster. If you leave two apples in a cluster you will get medium-size apples, three or more and the apples will be small.

Prevent worms

Now is also the time to prevent wormy apples. The small, dirty-white codling moth lays eggs on apples that hatch into larvae (worms) and eat into the apple. Moths are most likely to be seen at dusk.

Insecticides should be applied every two weeks beginning about two weeks after petal fall. Continue applications until the first of August. I recommend spinosad. It’s the active ingredient in several organic pesticides and is effective on a wide range of insects, including codling moth.

My favorite way to prevent worms is to place codling moth traps in the trees. A pheromone sex attractant lures male moths into the trap from which they cannot escape. If the males are all trapped, the females lay infertile eggs. Although not 100 percent effective, this works quite well if you don’t have a lot of unprotected apple or crabapple trees nearby without traps. Hang one trap in small trees and three traps in larger trees. Traps are available at many full service nurseries and garden stores and online.