JoAnne Skelly: Worm control in apples begins now

If you had apples with worms last year, it is likely you will have wormy apples this year too, unless you take precautions.

Worms in apples are the larvae of codling moths. These relatives of butterflies also attack pears, plums and walnuts. Each female moth lays 30-70 tiny disc-shaped eggs singly on the fruit, spurs or nearby leaves. After hatching, the white to light pink “worms” with dark heads bore into the fruit. Later, the caterpillars leave the fruit and look for sites for pupate overwinter before becoming adults in the spring. Moths are active only a few hours before and after sunset, and they mate when sunset temperatures exceed 62 degrees. There can be two to three generations per year.

Control of codling moth starts with good sanitation. Cocoons (pupae) overwinter in protected areas under the bark on trunks, in debris under the trees or in soil. To reduce new populations, gently remove the loose bark on the trunk and destroy any cocoons you find. Get rid of any fallen apples or leaf litter from last year. Do not compost any of these materials. From late spring through harvest, pick up fallen apples daily to reduce reproduction sites.

Another method to manage these annoying pests is to select varieties less susceptible to damage, such as early maturing apples and pears. A labor-intensive way to keep the worms out of fruit is to bag as many individual fruits as you want to eat. Do this when the fruit are 1/2- to 1-inch in size. Thin the fruit to one per cluster. Then cover with a standard brown lunch bag or generic Ziploc-type bag and seal it. The apple will grow inside. Red apples will be a light color when they develop in the brown bag, but those in plastic bags will be true red. You may have to poke a tiny hole in the plastic bags if water or condensation accumulates.

Timing the application of insecticides for codling moth control is difficult. Products must be applied just as the eggs are hatching, but before the caterpillars go into the fruit. According to Michael Janik at Michael’s Apples, first spray at 100 percent petal drop. Determine mating time using pheromone traps. Spray twice per hatch 7-10 days apart.

For excellent detailed information on the timing of insecticides, sign up at for the most recent newsletter. Or read the article from University of California at Davis:

JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at


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