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WSU Decision Aid System Update May 2023

Written by Liesl Oeller, Washington State University, May 3, 2023

Spring is here, and tree fruit pest management has begun. Below are updates on the codling moth, pear psylla, fire blight, and apple bloom models. For updates specific to your location, subscribe to DAS.

Codling Moth

Many areas in Washington and Oregon have reached 100 degree days, which means it’s time to set up codling moth mating disruption.

Codling moth mating disruption should be considered the foundation of any apple pest management program. When mating disruption products are applied before the first moths emerge, mating is reduced thereby limiting the number of codling moth eggs laid in the orchard. Fewer eggs laid means smaller populations that will need to be controlled with insecticides. Read more about how codling moth mating disruption works.

We’ve had a slow start to the codling moth model in 2023 compared to previous years (Fig 1). With the cool Spring we’ve had thus far, the codling moth model is just getting started in many areas (Fig 2).

May 3rd graph of codling moth degree days comparing 2021, 2022, and 2023
Figure 1. Graph comparing codling moth degree days on May 3 in 2021, 2022, and 2023. This year the codling moth phenology model is behind previous years due to a cool Spring.
map of Washington with blue spots for
Figure 2. Map of codling moth degree days on May 3, 2023 in Washington State.

Pear Psylla

Last month we held the 2023 pear psylla workshop, and thank you to all who attended! Dr. Robert Orpet from Washington State University gave a great talk on pear psylla phenology and management strategies. The DAS director Dr. Dave Crowder discussed the DAS pear psylla model and upcoming features to the platform.

For more updates on current pear psylla conditions, sign up for Pear Entomology Weekly. newsletters! Brought to you by WSU Tree Fruit researchers Robert Orpet and Molly Sayles, this newsletter has updates with weekly scouting data, degree days, and management guidelines. To subscribe, email

Apple Bloom

We’ve had a slow start to the codling moth model in 2023 compared to previous years (Fig 1). Another important model in early May are the apple bloom models. Apple bloom has been pushed back due to cool temperatures, and the Gala model is behind compared to previous years (Fig 3). In some locations, bloom is below 30% when in previous years apple bloom was complete.

May 3rd graph of Apple Bloom comparing 2021, 2022, and 2023
Figure 3. Graph comparing percent of open flowers of apple variety Gala on May 3 in 2021, 2022, and 2023. This year the apple bloom model is significantly behind previous years due to a cool Spring.

Fire Blight

Sudden warm weather after weeks of cool temperatures has caused the risk of fire blight to spike. Any wetness event in the near future puts orchards at risk of fire blight infection. The total risk value (TRV) in many areas of Washington is well above the 350 TRV threshold for extreme infection risk in areas where fire blight occurred last year (Fig 4). If you are a DAS subscriber, you can check your station for specific risk values in your location. Note that weather conditions and TRV can change suddenly during tree fruit bloom, so check DAS regularly for updates. For more information on fire blight, visit the WSU Fire Blight Page and subscribe to the WSU Tree Fruit Extension newsletter. For any further questions on fire blight, contact Tianna DuPont, WSU Extension.
(509) 713-5346

map of Washington with green spots
Figure 4. Map of total risk value (TRV) for fire blight on May 3, 2023 across Washington State.


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Liesl Oeller

Liesl Oeller
Washington State University
(509) 335-5815


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