Apple Pests: How to Win the Battle

Question: My apples were infested with codling moth last year. What can I do to have worm-free fruit this year?

J.G., Yorba Linda

Answer: Methods for reducing population numbers that do not require the use of insecticides include sanitation, bagging the fruit, mass trapping and trunk banding. Pruning trees to a height where the canopy is easy to reach will also simplify management of this pest.

Sanitation

If your trees are not isolated from other codling moth host trees and your neighbors do not also follow these sanitation practices, this method alone will only control a small percentage of the population.

A portion of the codling moth population will overwinter as pupae in protected areas on tree trunks and in rubbish around the base of a tree. Remove rubbish and loose bark in winter.

Every week or two beginning about six to eight weeks after bloom, check fruit on trees for signs of damage and remove and destroy any infested ones. Also, clean up dropped fruit as soon as possible. This will help reduce populations of the next generation, because dropped fruit and nuts may still have larvae in them. Cleaning up is especially important in May and June.

Bagging Fruit

You can control pests by enclosing fruit on the tree in bags, making them inaccessible to codling moth larvae. Bagging can be done on fruit over the entire tree or on as many fruit as desired.

To bag the fruit, thin fruit to one per cluster. The best time to do this is when the fruit is from one-half to 1 inch in diameter. Use No. 2 paper bags (standard lunch bag size) that measure 7 1/4x4 inches. Cut a 2-inch slit in the bottom of the bag and slip this opening over the fruit to form a seal around the stem. Staple the open end shut.

While this technique does not affect the maturity or quality of the fruit, it may have an impact on the color development of red varieties. On the plus side, bagging fruit protects it from both codling moth and sunburn. In addition, thinning the fruit to one per cluster results in larger fruit at harvest.

Pheromone Traps

Pheromone traps are baited with a synthetic sex attractant (pheromone) that mimics the chemical female moths use to lure males for mating.

There are two ways home gardeners can use pheromone traps:

* To mass-trap male moths in an effort to reduce the size of the mating population, or

* to help determine the need for an insecticide treatment.

Mass trapping with pheromones may help reduce populations, but the effectiveness of this method in backyards has shown mixed results.

Another mass-trapping technique that some backyard growers have reported success with is a homemade moth trap consisting of a 1-gallon plastic milk jug containing the following:

* 1 cup cider vinegar

* 1/3 cup dark molasses

* 1/8 teaspoon ammonia

* enough water to make 1 1/2 quarts of liquid.

Cut a 2-inch diameter hole just below the shoulder of the jug. Hang the jug in the tree using a wide strip of cloth to protect the tree branch. Use up to three traps per tree for large trees.

Trunk Banding

A traditional nonchemical method for controlling codling moth is to trap mature larvae in a trunk band of Tanglefoot, burlap bags or corrugated cardboard as they climb up the trunk to pupate under loose bark.

Trapped caterpillars or pupae must be killed before they can emerge as adult moths that can lay a second generation of eggs. For effective control this method must be used in conjunction with other control methods.

Corrugated cardboard is preferred for trunk banding. Use a 4-inch wide strip of large-core corrugated cardboard (size Flute A 18-inch rolls) and wrap it around the trunk of the tree so that the corrugation tubes are vertical and the band is snug against the trunk.

Staple bands to trees about 18 inches or more from the ground and reinforce the staple with duct tape; pick the smoothest part of the trunk.

Place these bands on trunks after bloom, just before the caterpillars drop from the trees to seek pupation sites. Generally this occurs by the end of May along the coast.

The codling moth caterpillars will crawl up the tree and into the corrugated cardboard to pupate. Remove the cardboard bands before moths begin to appear (approximately the end of May or June) and destroy caterpillars and pupae.

To help control the overwintering generation, put new trunk bands up in August and remove and destroy them between November and January.

Chemical Control

Proper timing of insecticide applications is critical if they are to be effective against codling moth.

Chemicals must be applied just as eggs are hatching. Once the caterpillar has gone into the fruit or nut, it’s protected from pesticides. To know when to spray, check fruit at least twice a week for entry holes or stings that indicate larvae have begun boring into fruit.

Spray as soon as you see the first sting. Unless insecticide applications are properly timed, the nonchemical methods will probably provide more reliable control.

Only a few insecticides are available to home gardeners for managing codling moth. For a recommendation on the best insecticide to use in your area, consult your local California Certified Nursery Professional, the Agricultural Commissioner’s office or the University of California Master Gardener hotline.

Other materials such as Bacillus thuringiensis, cryolite, and pyrethrin/rotenone combinations have not been found to be effective at controlling codling moth.

This information has been summarized from the UC Pest Management Guidelines. The full text and photos can be found at: https://www.ipm.ucdavis.edu/.

Have a problem in your yard? University of California Cooperative Extension Master Gardeners are here to help. You can reach the hotline at (714) 708-1646 or ucmastergardeners@yahoo.com. Calls and e-mail are picked up daily and are generally returned within two to three days.