New Tricks for an Old Pest

Photos by Keith Granger, Wendy Jones & Mike Doerr

by Nadine Lehrer and Keith Granger, WSU Tree Fruit Research & Extension Center

North Central Washington’s tree fruit growers have known for years that working together yields results. The codling moth areawide project of the mid 1990s is a good example. Apple growers were having trouble with the codling moth insect, which bores into fruit and devastates crops if left uncontrolled. Some of the pesticides used to control it were losing effectiveness; others disrupted predator-prey systems or environmental goals.

A new technology, however, presented an opportunity for improving codling moth control in an ecologically minded way: Mating disruption is a technique in which orchardists hang small pheromone-emitting dispensers throughout their orchards. The pheromone, or insect hormone, is a chemical normally produced by a female codling moth to attract males. In an orchard in which pheromone dispensers are hung, male codling moths are thrown off track by the overabundance of female pheromone and have difficulty finding a mate, minimizing the number of eggs laid to produce the next generation of codling moths.

Mating disruption works best in large contiguous blocks of orchard, so growers involved in the areawide project coordinated their pheromone mating disruption strategies with one another. And when they got together, they also discussed other things that were happening in the orchard – insect monitoring, pest pressure, new pesticides and application timing, and successes and failures of those willing to try new technologies. Within three years, codling moth was no longer a problem in many of these regions, and supplemental spraying had dropped significantly. This was more than the result of successful pheromone use; it was the strength of neighbors working together and sharing information, resulting in better pest management decisions and more effective pest control.

Now, 10-15 years later, many orchards in Washington State use mating disruption to manage codling moth populations. This means that growers can spray fewer strong chemicals and still produce a clean, crisp, bug-free apple. But, once again, there are changes taking place in orchard pest management. In 2006, one of the most widely used pesticides for codling moth control, Guthion, was scheduled for permanent phase-out. With several alternative chemical and non-chemical ways to control codling moth, however, growers have options for managing without it. These alternative methods are more complicated and require more intensive orchard management such as insect monitoring that enables the grower to target sprays to precise points in the insect life cycle. All together this change in management requires (and fosters) a greater understanding of both the insect life cycle and the overall orchard ecosystem.

Now, once again, growers have found a need to collaborate. Washington State University’s Pest Management Transition Project (PMTP) was established in 2007 to help growers adjust to pest management without Guthion. PMTP revived the areawide model, convening regional groups of growers to discuss new pest management technologies on a monthly or bi-monthly basis. Fourteen groups, involving 180 growers and pest management consultants, began meeting in 2008. These groups built on pre-existing relationships and established new ones as they improved their understandings of evolving pest management tools. Beginning with codling moth mating disruption as a base, PMTP helped growers add a suite of new and more sustainable pest control technologies and strategies to their toolboxes.

As growers have known for years, working together can bring greater sustainability to Washington’s tree fruit industry. For more information on PMTP, please see the project website at http://pmtp.wsu.edu.