Almost everyone has bitten into a "wormy" apple or pear, an unpleasant experience. A "worm" in homegrown fruit is not really a worm, but most likely a codling moth caterpillar. Called "one of the most damaging insects of apples and pears,"1 it can be a problem in commercial orchards as well as for backyard fruit trees.
Alternative techniques for dealing with codling moth have been widely accepted by farmers, and have reduced orchard pesticide use by 80 percent according to U.S. Department of Agriculture estimates.2 Successful nonchemical techniques are also available for home gardeners. These include some based on care of trees and fruit, some trapping techniques, a bagging technique, as well as a tiny wasp and a virus that kill these moths. For best results, use a combination of techniques.
Identifying Codling Moths
The codling moth is a gray moth about 3/4 inch across. Usually its wings are marked with copper lines and a gold or bronze spot. Mature caterpillars are white with a brown head and about 3/4 inch long.1
In order to successfully manage codling moths, you'll need to understand the life cycle of this insect. It spends the winter as a caterpillar in a cocoon, usually under loose bark on a tree trunk or in some other protected spot. Adults emerge from the cocoon in April or May. The females lay eggs on leaves and small fruit for about a month. When the eggs hatch, the young caterpillars feed on the surface of the fruit for a few days, then burrow into the center. They feed about three weeks, then tunnel out of the fruit and find a place to spin a cocoon. In the Northwest, there can be between one and three generations per year.1
Resistant Varieties Can Help
If you're planting new trees, choose varieties that will minimize future codling moth problems. Early maturing apples, like Jonagolds, Gravensteins, Galas, Macintoshes, and Red Delicious, are less susceptible to codling moth than late-maturing varieties.3Planting trees with semidwarf rootstocks is helpful. The smaller trees will make it easier for you to manage codling moths.3
Thinning Your Apple Crop
Thinning apples so that your tree has only one apple per fruit cluster is generally recommended in order to keep your tree vigorous. (It also allows your tree to produce a good crop every year.) Thin apples when fruit are small (the size of a marble or walnut). When you thin your crop, be sure to remove any fruit that have small holes made by codling moth caterpillars. Bury these apples, or put them in a black plastic bag in the sun for a month. Composting doesn't destroy all the caterpillars.3
Picking up Dropped Apples
Collect any dropped fruit weekly because caterpillars leave dropped fruit quickly. Dispose of them the same way as thinned apples.3
There are three ways to trap codling moths: pheromone traps, black light traps, and homemade traps. Pheromones are attractants produced by female moths to attract males. Pheromone traps release this attractant chemical and also have a sticky surface for trapping moths. They catch only males. Such traps have "shown mixed results" according to the University of California Division of Agriculture and Natural Resources. They are most effective when your trees are at least a mile from other trees being used by codling moths (apples, pears, and walnuts). To use pheromone traps, start in early spring. Hang the traps in trees twenty to fifty feet away from your fruit trees. Hang one to four traps per tree (depending on the size of the tree) about six feet off the ground.4
The U.S. Department of Agriculture's national sustainable agricultural information center recommends black light traps. These can be purchased, and attract both male and female moths.5 You can also use homemade traps that catch both male and female moths. Fill a plastic gallon milk jug with 1 cup vinegar, 1/2 cup molasses, 1/8 teaspoon ammonia, and 5 cups of water. Cut a 2 inch hole in the jug, just below its shoulder. Hang up to 3 traps per tree, depending on the size of the tree.4
You can make simple traps for caterpillars from ordinary corrugated cardboard. Use a four-inch-wide strip and wrap it snugly around the tree trunk. The corrugation should be vertical (up and down the trunk). You can use staples to attach the cardboard to the trunk; it should be at least a foot and a half above the ground. Caterpillars will crawl under the cardboard and use the "tunnels" as protected spots to spin their cocoons. Once they have spun their cocoons, remove the cardboard and destroy it.4 The trick to using this method is timing it properly. You can catch the overwintering generation of caterpillars by putting up bands in August and destroying them between November and January.4 For other generations, watch the traps and destroy and replace them when you see cocoons.6
In the early 90s, two California extension agents tested a novel pesticide- free technique for protecting apples from codling moth. The technique uses paper lunch bags to protect developing apples. Use the bags by cutting a two inch slit in the bottom of the bags. Put this opening over fruit when the fruit is between one and two inches in diameter and staple the open end of the bag closed around the fruit. Then leave the bags on the tree until harvest. The bags also protect the fruit from sunburn. Although the technique is time consuming, "for individuals with few trees, bagging can result in quality fruit without significant loss due to codling moth."7
The Home Orchard Society has written hands-on advice about bagging apples with paper bags and even nylon footies. See resource list at the end of this article for links to this information.
Trichogramma wasps are minute wasps that lay their eggs in moth eggs, including the eggs of the codling moth. When the wasp eggs hatch, the juvenile wasp eats the moth egg. Trichogramma wasps are available commercially. If you want to try using these wasps, release two or three batches one week apart when the moths start to lay eggs3(approximately mid-April in the Northwest1). The wasps are usually sold as pupae on little cards which you put in small cups hung in the tree. The wasps feed on nectar and pollen so will do best if there are flowers nearby.3
Woodpeckers have been observed eating significant numbers of codling moth caterpillars. These birds feed on the caterpillars after they leave the fruit at the end of the summer and during the fall when the larvae are in cocoons on the trunk of the tree. Other important codling moth predators are nuthatches and creepers.8
Codling Moth Virus
The codling moth granulovirus offers "potential for effective and selective control"9 of codling moth and "has been considered the most effective biological control agent ever tested against the codling moth."8 The virus is available commercially and should be applied weekly for best results.8 According to their manufacturers, "inert" ingredients in commercial codling moth granulovirus products include glycerin, water, and insect parts associated with growing the virus.10,11
A wide range of nonchemical solutions for codling moth problems are available. By using a combination of the techniques summarized in this article, you can have worm-free and pesticide-free apples and pears in your backyard.
Home Orchard Society: Bagging resources
- Growing worm-free, spray-free apples by Quinten Fadness. (Pome News, Spring 2000) http://www.homeorchardsociety.org/article/6/
- Bagging apples by William Collins. (Pome News, Summer 2003)http://www.homeorchardsociety.org/article/8/
- Nylon Footies: Excellent Insect Barrier by Ted Swensen. (Pome News, Winter 2007) http://www.homeorchardsociety.org/article/47
Berry, R.E. 1998. Insects and mites of economic importance in the Pacific Northwest. 2nd edition. Corvallis OR: OSU Bookstore, Inc. p. 56.http://pnwpest.org/pdf/reb56.pdf.
Stelljes, K.B. 2001. Areawide pest management: An effective strategy for many pests. No coddling for this moth. Agricul. Res. (Nov).http://www.ars.usda.gov/is/AR/archive/nov01/.
Brown. M. Undated. Codling moth control in home orchards and backyard gardens. University of California, Santa Cruz. The Center for Agroecology and Sustainable Food Systems. http://zzyx.ucsc.edu/casfs/gardenideas/moths.html(link no longer active).
Univ. of California. Div. of Agriculture and Natural Resources. 1999. Codling moth. Pest Notes Publ. 7412.http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7412.html.
Appropriate Technology Transfer for Rural Areas. 1999. Organic and low-spray apple production. Horticulture production guide. http://www.attra.org/attra-pub/apple.html.
Ohio State University Extension. Undated. Codling moth on fruit trees.http://ohioline.osu.edu/hyg-fact/2000/2203.html.
Bentley, W.J. and M. Viveros. 1992. Brown-bagging Granny Smith apples on trees stops codling moth damage. Calif. Agriculture. 464:30-32.
Oregon State University Integrated Plant Protection Center. Undated. Codling moth information support system: Natural enemies of codling moth and leafrollers of pome and stone fruits.http://www.ipmnet.org/CodlingMoth/biocontrol/natural/.
Lacey, L.A. et al. 2004. Field evaluation of commercial formulations of the codling moth granulovirus. Western Oregon Pest and Disease Management Conference. Portland OR.http://entomology.tfrec.wsu.edu/wopdmc/proceedings2004.html.
Certis USA. Undated. Cyd-X biological insecticide. Product and formulation.http://www.certisusa.com/pest_management_products/insecticidal_viruses/cyd-x_biological_insecticide.htm.
Biotepp Inc. 2004. VirosoftCP4 material safety data sheet.http://www.biotepp.com/en/index.html.
Orignially published as:
Cox, C. 2005. No "worms," no pesticides: Managing codling moths in backyard trees.Journal of Pesticide Reform 25(2): 7-8.
Revised 2009. Links updated 2010.
Photos courtesy of Clemson University.