Garden Detective

Garden Detective: Codling moths bedevil her apple crop

Garden Detective: What’s wrong with these baby apples? Reader Sharon Andrews was stumped by these brown masses growing on her fruit. That frass is a sure sign of codling moth, master gardener June Bleile says.
Garden Detective: What’s wrong with these baby apples? Reader Sharon Andrews was stumped by these brown masses growing on her fruit. That frass is a sure sign of codling moth, master gardener June Bleile says.

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 fruit.

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 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 complete description of this pest’s identification, life cycle, damage and management can be found in the University of California’s 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 damage that don’t require using insecticides, including selecting fruit varieties that are less susceptible to damage.

Thinning out and removing infested fruit on the tree – such as you did – 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 (such as aflatoxin) generated by mold.

Many local gardeners try to control these pests with a homemade trap and lure that uses vinegar, molasses, ammonia and water. It doesn’t wipe out codling moths completely, but it is effective in reducing the population significantly. You need one trap per tree.

Keep the traps in the trees from late April through late September because there are up to six generations of these insects every year here in the Sacramento region.

Here’s the recipe: First, get a 1-gallon plastic milk or water jug. Mix together 1 cup cider vinegar, 1/3 cup dark molasses and a dash of ammonia. Add enough water to this mixture to make 1 1/2 quarts. Pour the mixture into the jug and hang the open jug in the tree. Change or renew the mixture as needed.


Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties. Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h& Please put “Garden Detective” in the subject field and include your postal address. To contact UC Extension directly, call:

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