Codling Moths: How to Safely Control This Fruit Tree Pest

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Dr. Louis A. Falcon, professor of entomology at Berkeley and chief developer of the codling moth virus spray, stands beside a ready-for-action sprayer at Molly Breen's orchard.
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Believe it or not, this healthy-looking tree used to lose about 60% of its apples to codling moth damage. But now, thanks to the codling moth granulosis virus, its apples are virtually worm-free!
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Pheromone traps were one of the important tools used at Pike Mountain Orchard to monitor the codling moth population.

Three years ago Pike Mountain Apple Orchard, nestled in the foothills of the Sierra Nevada mountain range in northern California, faced a ruinous infestation of codling moths. In fact, the 12-acre spread (containing 988 trees laden with Golden and Red Delicious and Rome Beauty apples), under the management of organic farmer Molly Breen, lost a whopping 60% of its 1981 crop to the voracious insects. However, today–thanks to entomologist Dr. Louis A. Falcon, of the University of California at Berkeley, and the codling moth virus he championed–Molly’s orchard has been saved! Current moth damage is down to a mere 2%, and (according to the local agricultural commissioner) Pike Mountain apples are now among the finest grown in all of northern California.

The story behind this miraculous turn of events should prove valuable to anyone whose crops are prey to codling moths and who’s looking for an environmentally safe means of getting rid of these despoilers of fruit and nut trees.

Codling Moth Virus

Molly Breen, a fervent proponent of organic farming techniques, came to Pike Mountain Orchard in 1974. Since the 30-year-old orchard had sat abandoned for half a decade prior to her arrival, she had her work cut out for her. Over the next few years Molly saw to it that–among other chores–tons of manure, rock phosphate, and fertilizer were added to the soil, and that clover was established as a ground cover. Finally, thanks to her conscientious use of primarily biodynamic farming practices, the orchard was restored to peak production. But as the trees became healthier and more productive, they also became increasingly infested with hungry codling moths.

Meanwhile (unbeknownst to Molly), Dr. Louis Falcon was hard at work trying to develop a new microbiological insecticide that would control the codling moth in its destructive larval stage. (As you may know, it’s the larvae–not the moths–that bore into the fruit. Adult codlers lay their eggs on the fruit, and as the apples develop, the newly emerged larvae eat their way into the fruit to feed on the seed.)

Dr. Falcon began researching a treatment for codling moths in 1963, when a microorganism called Codling Moth Granulosis Virus (CMGV) was first discovered in Mexico. The disease, which was reported to be nearly 100% fatal to codling moths, caused the larvae to become puffy and lethargic . . . then to liquefy . . . and finally to literally drip off the host plant.

In the years following his introduction to the virus, Dr. Falcon began rearing codling moths in his lab and testing the effects of the disease on them in an effort to determine whether CMGV might provide an effective natural control for these orchard menaces. In the early stages of his research, he infected live larvae with the virus and then crushed them into a paste that could be mixed with water to form a sprayable solution.

Soon, however, his project outgrew the confines of the small university laboratory, so the entomologist persuaded an interested company, the Sandoz Corporation, to mass-produce the virus on a trial basis, in order to allow him to expand the scope of his experimentation. From 1980 to 1982, the company manufactured what it called SAN406 (a CMGV preparation) and supplied it to Falcon and his assistants. With plenty of the preparation available, the scientists were soon ready to “road test” their product in an actual moth-ridden orchard.

Testing Codling Moth Spray

Dr. Falcon got wind of the situation at Pike Mountain Orchard and contacted Molly Breen to ask if she might be willing to allow him to use her larvae-infested land as a SAN406 test plot. Molly’s orchard was selected because it provided a good outdoor laboratory for conducting replicated experiments. It was well isolated from other orchards, no chemical pesticides had been used for many years, and the trees were in good condition. Delighted by a chance to save her apples, Molly agreed to help by monitoring equipment, spraying when requested, and managing the trees and fruit so as to provide the data needed to assess the impact of CMGV upon fruit production and upon the orchard ecosystem.

Armed with SAN406 . . . professional spray equipment . . . pheromone traps (insect-enticers filled with synthetic attractants smelling like female codling moths) . . . maximum-minimum thermometers . . . and computerized information about the life cycle of the insect, Dr. Falcon and his assistants descended upon the northern California orchard ready for action!

The entomologist explained to Molly that by checking the pheromone traps, she could determine whether the insects were actually present. If they were, it was critically important to apply the spray at exactly the right moment in the insects’ development: after the eggs had hatched and before the larvae had begun to tunnel into the apples. If used too early or too late, SAN406 would have little or no effect. Since the pace of the moths’ life cycle is governed by temperature, the correct spraying times could be pinpointed by daily monitoring of the maximum-minimum thermometers. Those readings could be fed into a computer, which would assimilate the data and issue instructions as to when to spray for the desired results. (Falcon’s computer program is aptly titled BUGOFF2.)

During the summer of 1982, Molly Breen and her crew diligently checked pheromone traps, read thermometers, and reported data to Dr. Falcon, who consulted the computer. Spraying dates and times were calculated, and the orchard was periodically drenched with SAN406. As it turned out, the orchard was so heavily infested with codling moths that Molly and her co-workers had to spray the solution fifteen times before it was fully effective. But the effort was well worth it, because that year Pike Mountain’s salable crop tripled! Packout rose from less than 2,500 crates of apples in 1981 to more than 8,000 in 1982. (SAN406 was also tested at three moth-infested northern California pear orchards during the same summer . . . with equally impressive results.)

Molly Breen was back in business and understandably enthusiastic about Dr. Falcon’s miracle moth-destroyer. “Our codling moth problem has finally been licked,” she told him. “There’s no doubt in my mind that the virus spray really works. It’s a major breakthrough for organic fruit growers everywhere!

In Molly’s eyes, one of the most impressive aspects of SAN406 is that it is specific to codling moths, whereas most commercially available insecticides destroy a wide variety of insects, including those that are helpful. The virus solution is also relatively safe to use . . . producing no known side effects. Plus, it doesn’t hurt the appearance of mature fruit as other sprays often do. In fact, Molly claims SAN406 actually improved the looks of her apples.

If there is a drawback to the CMGV spray, it’d have to be the fact that, in order to use it, an orchard-keeper has to maintain an accurate watch over the conditions affecting the moth’s life cycle. “But considering the dramatic results,” swears Molly, “monitoring is a chore I’ll do anytime!”

Codling Moth Control

On top of everything else, CMGV seems to be so effective that it may eventually eliminate the need for its use! Although Pike Mountain Orchard required fifteen sprayings during the initial test season, this past summer only nine dousings were required to rid the apples of codlers.

Although this quality is a plus for apple growers, it could be a minus in the eyes of potential manufacturers of the spray. Not too many business-minded folks are interested in creating and selling a product that could eventually eliminate its own market! And, to date, no company has jumped at the opportunity to manufacture this revolutionary microbiological insecticide. For various other reasons, even Sandoz Corporation has pulled out of the running: They produced SAN406 for two years, purely on an experimental basis, and have now withdrawn all funding from the project.

“We’ve failed to stimulate the right sources to come up with the economic backing needed to commercialize CMGV,” says Dr. Falcon. “I’ve tried to interest venture-capital firms in the project, but to no avail. Perhaps the solution rests with the fruit farmers themselves.”

Of course, no one can guarantee that a ground swell of public interest would make this organic spray available to the public, but there certainly is that chance. If you’d like to have further information concerning the current status of CMGV, or to find out what you might be able to do to help speed its availability, contact Dr. Louis A. Falcon, Division of Entomology, University of California, Berkeley.

EDITOR’S NOTE: Our research suggests that prospective manufacturers may be deterred by factors other than the decreasing dosage required. First, there may be no possibility of obtaining patent protection, since the spray is composed of a naturally occurring virus. Second, the production process is an obstacle: In an age of high-tech manufacturing, companies may reject the time-consuming operation of raising larvae on a massive scale. Finally, there are marketing concerns. Manufacturers fear that consumers will not buy a product that requires extra effort to use (e.g., taking temperature readings). . . and the fact that the spray kills only codling moths and some closely related species–while very good for the ecology–does narrow the market for the product.