Garden Detective

Codling moth ruins her first apple crop

Codling moth larvae, which look like little pink worms, infest an apple. On the outside is brown frass, often the only telltale sign of the pests inside. Eradicating this problem takes diligence.
Codling moth larvae, which look like little pink worms, infest an apple. On the outside is brown frass, often the only telltale sign of the pests inside. Eradicating this problem takes diligence.

I have a Red Delicious apple tree that I planted three years ago, and this is the first year I have apples on it. Each winter, I faithfully apply dormant spray and fertilize with organic-only fertilizer each spring. Unfortunately, my first crop of apples is an utter loss. The attached photo reflects a brown mass growing from the blossom end of each baby apple. Each time I find an infected apple, I remove it from the tree, but the problem continues to appear on more and more apples. Clearly, I’m doing something wrong. I would appreciate it if you could tell me what I’m dealing with and how I can avoid it in the future.

Sharon Andrews, Elk Grove

According to UC master gardener June Bleile, the brown mass at the blossom end of your apples is the frass produced by codling moths that are feeding on the interior of the apples.

The codling moth is one of the most difficult pests to manage in the home orchard. The pest overwinters as a full-grown larvae under loose bark, under debris such as fallen leaves, or in the soil until the weather warms up around mid-March to April and then emerges as a moth. The moth is most active in early evening, depositing single eggs on the young fruit. Within hours after the eggs hatch, the larvae bore into the fruit to complete their development within the fruit. When mature, they leave the fruit and drop to the ground where the cycle begins again.

Codling moth is difficult to manage because it spends most of its life within the fruit, out of the reach of insecticides and natural enemies. You can reduce the codling moth population through a combination of non-chemical approaches such as sanitation, bagging, thinning and trunk banding.

A few tips are listed below, but a complete description of this pest’s identification, life cycle, damage and management can be found in “Pest Notes” online at It is ideal to make codling moth management a neighborhood project, because your trees can be infested by moths from your neighbor’s trees, despite your own best efforts at keeping populations of this pest down.

Several methods are available for reducing codling moth that don’t require using insecticides, including selecting varieties that are less susceptible to damage. Thinning out and removing infested fruit on the tree is especially important. Sanitation is vital in any codling moth control program. Every week or two, beginning about six to eight weeks after bloom, check fruit on trees for signs of damage. Remove and destroy any infested fruit showing the frass-filled holes. Removing infested fruit before the larvae are old enough to crawl out and begin the next generation can be a very effective method for reducing the population. Clean up dropped fruit as soon as possible after they fall, because dropped fruit can have larvae in them.

Where populations are moderate to high and many infested trees are nearby, insecticide applications might be necessary to bring populations down to low levels. To be effective, the timing of insecticide spray applications is critical, and several applications are necessary, especially with newer, less toxic pesticides.

The most effective way to time insecticide sprays is with a pheromone trap and a degree-day calculation. Additional information on timing degree-day calculations is available at

In most backyard situations, the best course of action might be to combine a variety of the non-chemical and/or low toxicity chemical methods and accept the presence of some wormy fruit. If eating wormy fruit, cut out damaged portions, because they might contain toxins (aflatoxin) generated by mold.


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