Developing a resistance management plan for codling moth in organic pome fruit

Commodities

• Fruits: apples, pears

Practices

Codling moth is the key apple and pear pest. Washington State produces 90% of US organic apples, worth $543 million annually, or one quarter of the state’s apple value. In addition, 20% of the pear-growing acreage in Washington is organic. On nearly every organic orchard and many conventional orchards, codling moth is treated with Cydia pomonella granulovirus (CpGV), due to its lack of non-target impacts and its organic certification. Mating disruption is used on >90% of the apple and pear acreage in Washington, but insecticides are needed to reduce codling moth densities enough for mating disruption to be effective (Jones et al. 2016). CpGV is typically applied at least weekly when codling moth larvae are present in orchards, but preliminary evidence suggests this heavy reliance is leading to insecticide resistance (Fan et al. 2022). This grower-initiated project proposes to evaluate CpGV resistance across Washington State apple and pear growing regions. In year one we will widely test for resistance development in organic orchards where management failures and CpGV overuse have occurred. We will also test for cross-resistance to other virus strains and species, such as Cryptophlebia peltastica nucleopolyhedrovirus (Wennmann et al., 2019). In year two we will evaluate resistance in conventional orchards near resistant codling moth populations to measure spill over and also evaluate the impacts of conventional management on persistence of resistant moths. Finally, we will evaluate the ability of horticultural oil to reduce survivorship of immature codling moth eggs. Throughout the project we will collaborate with growers and the codling moth taskforce to develop a resistance management plan. We will educate growers on the resistance management plan through a combination of grower-led discussions groups, extension presentations, and written documentation on a project webpage, Fruit Matters Newsletter, and integration into the WSU Tree Fruit Crop Protection Guide.

Objective 1: Evaluate codling moth resistance to Cydia pomonella granulosis virus in Washington organic orchards.

Objective 2: Work with growers to develop an economically and environmentally sustainable resistance management plan for organic codling moth management.

Objective 3: Present and discuss resistance management plan with stakeholders.