Apple Pest Management in the West: Strategies to Deal with Inevitable Change

Jay F. Brunner

Codling moth (CM) is the key pest in apple production in the western U.S. Most insecticides applied to orchards in summer, an average of about three, are for control of CM. Leafrollers are the second most important pest in apple. Two species are responsible for most of the crop loss attributed to leafrollers. Other pests include the San Jose scale, the leafminers, leafhoppers, aphids, spider mites, and several species of "true bugs." In total, apple growers annually apply six to seven chemical controls to protect their crop.

Apple growers are some of the most innovative and progressive in the world. Since the 1960s growers have integrated chemical control of CM with biological control of spider mites. Most Washington State apple growers have not applied a specific miticide for 30+ years because the western predatory mite has been effective in suppressing spider mite densities. Growers also take advantage of a small parasitic wasp that effectively controls leafminers in 75% of Washington’s apple orchards each year. Both of these biological control agents have developed a resistance to certain insecticides so have been able to survive in orchards. Apple growers use predictive models, treatment thresholds and reduced rates of insecticides to conserve natural enemies.

Passage of the Food Quality Protection Act of 1996 will eventually restrict the use of or eliminate most "traditional" chemical controls now used by apple growers. Growers are looking to new insecticides and other technology to control pests while conserving biological control agents. The use of pheromones to manage pests, an approach commonly referred to as "mating disruption," has gained importance as reliable dispenser systems have been developed and as research has demonstrated the utility of the approach.

In the early 1990s research at the USDA-ARS and Washington State University demonstrated the potential of mating disruption as a tactic for controlling CM in commercial apple orchards. These early studies showed that mating disruption was an effective control used alone when low CM populations were present but needed to be supplemented with insecticides when populations were moderate to high. Crop damage on orchard borders was observed to be consistently higher than in the orchard interior. Leafrollers were identified as a problem that increased in orchards treated with CM mating disruption products. There was some evidence that the level of biological control of some pests increased in mating disruption orchards.

In 1994 a new approach to use of pheromones was proposed, the areawide control of CM using pheromones. The main benefits of this approach were to reduce impact of border damage by treating larger areas and to allow small growers to participate in the use of this new technology. A five-year project with the following goals and involving three states was funded by the USDA.

• Using mating disruption as the primary control for CM,
• Reducing broad-spectrum insecticide use by 80%,
• Enhancing biological control of pests, and
• Monitoring changes of secondary pests and natural enemies.

The Codling Moth Areawide Management Project, or CAMP, was funded for five years (1995-1999). Five sites were selected, three in Washington and one each in Oregon and California. Sites ranged in size from 400 to 1200 acres. In the first year, codling moth mating disruption (CMMD) was supplemented by insecticides or, at one site, with release of sterile CM adults. Results were very promising with reduced insecticide use and CM damage to the crop. After three years, damage from CM had declined to very low levels and the need to supplement control with insecticides had declined dramatically. By the end of 1999 most all of the CAMP objectives had been met. Adoption of CMMD has grown at an incredible rate since the initiation of CAMP. In 1994 CMMD was used on only 11,000 acres in Washington; by 1997 the area treated had increased to approximately 25,000 acres; and in 1999 over 60,000 acres, or over 30% of the state’s apple and pear production, was treated with CMMD. It is expected that the use of CMMD will continue to increase for the next several years in western fruit growing areas.

A new generation of insecticides that are low in human toxicity and environmental impact and generally low in toxicity to biological control agents is being investigated by research scientists throughout the western U.S. New insecticides are more selective than their old counterparts and generally require integration with other tactics to be effective.

Jay F. Brunner
Tree Fruit Research and Extension Center
Washington State University
1100 N. Western Avenue
Wenatchee, WA 98801
Tel: (509) 663-8181 ext. 238
jfb@wsu.edu

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