Apples, worms, and synthetic mating hormones

Sunset, March, 1989

In most Western climates, homegrown apples are plagued by codling moth larvae-3/4- inch-long, pinkish white worms. On the outside of the apple the only sign of their presence is a small puncture wound with a mound of brown excrement around it. On the inside, they bore into the core and damage the pulp and seeds.

You can still eat infested apples-if you don't mind cutting out the worm first. But grocery stores have so accustomed us to fruit free of insect damage and blemishes that most gardeners expect the same from their own crop.

To produce pristine apples, commercial growers rely on an arsenal of chemical controls. If you'll settle for something less than perfection, you have a safe alternative-codling moth pheromone traps.

What's a pheromone?

Insects produce certain chemicals, called pheromones, that regulate their behavior and communication. There are aggregation, alarm, and mating pheromones.

Codling moth traps use synthetic mating pheromones to attract males, which enter the traps and get caught in a sticky coating. Many orchardists set out pheromone traps to monitor the insect population so they can time sprayings.

For home gardeners, traps can be used in place of sprays. As well as catching male moths, the traps disrupt mating (males in the vicinity get confused by the synthetic pheromones and can't find the females). Abandoned apple, English walnut, or pear trees nearby can hinder success.

It usually takes two years to obtain good results from mass trapping, especially if trees were heavily infested last year. Research has shown that you can expect at least 85 percent control. To ensure success, you may want to use traps in combination with a nontoxic pesticide like Bacillus thuringiensis (spray when traps catch two or more male moths for two weeks in a row).

Set them out in early spring

Place traps in trees two weeks before flower buds open (if you're unsure when this occurs in your climate, ask your county's cooperative extension service). Use two traps in each full-size tree, one trap in each dwarf tree. Assemble traps according to directions, keeping your fingers off the glue and the center of the pheromone patch.

Hang the traps within the canopy (preferably in the lower third), at least 5 to 6 feet high and about an arm's reach from the outer ends of the branches. Foliage should be cleared away for 12 to 18 inches around the trap.

The only maintenance required is to make sure that the coating stays sticky If the trap contains more than about 100 moths or seems to be collecting a lot of dust, grit, or other insects, you should clean it out and stir up the glue or recoat it with a petroleum-based (not vegetable-based) adhesive.

Where to send for traps and adhesive If you can't find traps at a nursery or farm-supply store, order by mail (as soon as possible) from a source below.

The newest kind uses a controlled-release pheromone that lasts through the growing season. If you buy an old type, you need to replace the pheromone every three to four weeks.

Harmony Farm Supply, Box 451, Graton, Calif. 95444; (707) 823-9125. Traps cost $8.10 each (Calif. residents add 6 percent sales tax). For orders $15 and under, add $2.95 for shipping; $15.01 to $25, add $3.95; $25.01 to $50, add $4.95. Petroleum adhesive is $4.25 for a spray can.

Natural Gardening Research Center, Box 149, Sunman, Ind. 47041; (812) 623-3800. Traps cost $8.75 (add $2.50 for shipping one trap, $3.85 for up to four, $4.95 for five).