Pacific Flatheaded Borer: An old pest is new again in Oregon’s rapidly expanding hazelnut industry

Progress report for GW19-195

Project Type: Graduate Student
Funds awarded in 2019: $24,825.00
Projected End Date: 09/30/2021
Host Institution Award ID: G145-20-W7503
Grant Recipient: Oregon State University
Region: Western
State: Oregon
Graduate Student:
Major Professor:
Dr. Nik Wiman
Oregon State University
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Project Information


Eastern filbert blight (EFB), endemic to the eastern US, is a disease devastating to the European hazelnut, Corylus avellana. Accidentally introduced to the Pacific Northwest in 1973, it once threatened to eliminate Oregon’s hazelnut industry (Davidson 1973), which produces 99% of US hazelnuts. Anticipating decline, the industry invested heavily in the Oregon State University hazelnut breeding program, facilitating the release of varieties with single gene resistance to EFB. This triggered major expansion of hazelnut acreage, with 39,716 acres planted with resistant varieties in the last five years (Pacific Ag Survey, personal communication 2018). The shifting of the industry from old, blighted orchards to new plantings provided opportunity for the Pacific Flatheaded Borer (PFB), Chrysobothris mali Horn (Coleoptera: Buprestidae), to cause problems for hazelnut growers. Literature suggests that PFB are attracted to stress signals emitted by establishing trees (Burke 1929). Female borers find vulnerabilities in the bark to lay their eggs. Larvae hatch and feed on the cambium layer, leading to girdling, loss of transpiration, and ultimately death of the tree. Trees that survive initial attacks can be severely weakened, risking trunk failure due to wind or nut load. Inadequate knowledge of PFB has resulted in devastating losses for some growers, risking the exponential growth of the industry. Understanding the phenology and effective management practices for PFB are critical to local hazelnut farmers success and the sustainability of the industry.


Research Questions:

  1. What is the phenology of PFB in new hazelnut plantings?
  2. Can traps help monitor PFB populations?
  3. How can we protect young hazelnut trees from PFB?


Our research will address the insufficiencies regarding monitoring and management options for PFB. We will discuss our findings at nut grower meetings and workshops that typically attract hundreds of growers. Education in emergence timing, population counts, and effective plant protections will undoubtedly help our industry manage PFB.

Project Objectives:

Our goal is to provide farmers, new and established, with resources for managing the PFB, which has contributed to devastating crop and financial losses in Oregon’s hazelnut industry. By assisting farmers, we additionally help strengthen and grow the industry and reduce negative impacts on the environment. We will accomplish this by conducting research on borer biology and phenology, monitoring, and plant protection. The research will form the basis for Extension resources provided to the industry.

Research objectives:

  1. Develop phenology data for PFB. There is no information on when PFB emerge and attack trees. These data act as the foundation for pest management; identifying when PFB life stages vulnerable to management are active.
  2. Develop PFB monitoring traps. There are no effective monitoring tools to identify PFB populations. The development of monitoring traps will improve application timing and limit unnecessary pesticide applications when population counts are below economical thresholds.
  3. Evaluate plant protection strategies against PFB. We will evaluate simple physical trunk barriers, deterrents, systemic insecticides, organic, and reduced-risk insecticides as treatments. Grower implementation of efficient protection strategies will lower farmer cost and limit environmental contamination.

I’ve uploaded this Gantt Chart timeline:

Gantt Chart

The chart details specific tasks and dates relating to my three objectives: develop phenology data for PFB, develop PFB monitoring traps, and evaluate plant protection strategies against PFB.

I’ve also included educational outreach events and dates of the following: Orchard Pest and Disease Management Conference, Nut Growers Society Meetings, Annual Hazelnut IPM Field Day, and the Entomological Society of America Meeting.


Click linked name(s) to expand
  • Joy Henkle
  • Michael Severeid
  • Loren Birkemeier
  • Randy Flaming
  • Darek Czokajlo


Materials and methods:

Develop phenology data for PFB:

We collect trees infested with PFB from collaborating grower orchards during the fall and winter. Trees are considered infested if they show signs of sawdust frass or girdling of the trunk, typical characteristics of PFB damage. We remove canopies and roots because borer larvae are typically found close to the soil line or in the lower 24 inches of the trunk. Each end of the trunk is capped with paraffin wax to prevent desiccation and borer mortality. We store infested wood in five-gallon buckets, arranged by grower field, with small holes drilled in the bottom of buckets for rain drainage. Buckets are labeled with location and date collected and individually covered with mesh to prevent borer escape. They are stored outside in field cages at North Willamette Research and Extension Center in Aurora, OR. Data loggers recording temperature and humidity are stored with the wood. In the spring, we begin dissecting a subset of borer sticks to monitor transition from overwintering larvae to pupae and finally adults, then we begin checking for borer emergence twice a week and continue through August. We count and record each emerged borer. At the end of August, we calculate the percent of PFB emergence throughout the season.

Develop PFB monitoring traps:

We've tested the following traps: purple lindgren (12-unit) multifunnel, green lindgren (12-unit) multifunnel, black lindgren (12-unit) multifunnel, clear sticky card, green sticky card, purple sticky card, and black sticky card. In late May, we set up monitoring traps at two collaborating grower orchards. There were three reps at each orchard, with each rep consisting of one purple lindgren (12-unit) multifunnel, one green lindgren (12-unit) multifunnel, one black lindgren (12-unit) multifunnel, one transparent sticky card, one green sticky card, one purple sticky card, and one black sticky card. Each trap contained an ethanol and alpha pinene lure. Purple and green larger sized (12- and 16-unit) multifunnel traps were found more effective in capturing Emerald Ash Borer (EAB), Agrilus planipennis, one of the most infamous and destructive flatheaded borer forest pests, than their smaller counterparts (Francese et al. 2013). The 12-unit multifunnel traps are more desirable because they require less maneuvering and cost less.

We placed the traps along the borders of the orchard separated by 50 feet to limit influence of other traps. Each multifunnel trap was coated with fluon (a water and polytetrafluoroethylene (PTFE)-based liquid), to make the surface of the trap slippery and prevent insect escape. Multifunnel traps coated with fluon caught significantly more EAB than untreated traps (Francese et al. 2013). We hung each trap from a post right next to a tree. We wrapped sticky cards around the trunks of the trees. Traps were monitored weekly through August. Each PFB caught was recorded. 

Evaluate plant protection strategies against PFB:

The project team planted weak hazelnut tree whips, or slender and unbranched shoots, into two plots in May of 2018. Our preliminary research has shown that planting trees late after dormancy and bud break is an effective way to induce attack by PFB. We've established one plot at North Willamette Research and Extension Center and a second plot near a collaborating grower's orchard in Newberg, OR. Each plot consisted of four replications, 10 treatments and a control per replication, and five trees per treatment totaling 220 trees. We randomized the treatments in each replication. Treatments varied in ingredient, rate, timing and application. We painted the trunks of trees except the untreated control with white latex paint, a common practice for newly planted trees to prevent sunburn. We gave minimal water to trees to induce stress. Timing of chemical applications were based on the adult emergence we found in our field cages. Spray applications were applied using a spray gun fitted with a solid cone diffuser and D8 nozzle attached to a hose reel. An air compressor (Rigid 4.5 gal. air compressor) powered by a gas generator (Ryobi 2,300-watt) was used to achieve the adequate pressure of 40 psi. We assessed borer damage in the fall/winter of 2018 to 2019. The presence of galleries, tunneling caused by the borer, was recorded. 

Research results and discussion:

Pacific flatheaded borer emergence:

We've seen consistent results of PFB emergence over a three-year period. As the graph illustrates, emergence has been recorded from late May through early August. Consistent results allow growers and researches the knowledge of when PFB are active and thus they can plan their management actions accordingly. 

PFB Emergence Data

Monitoring traps:

We've recorded two PFB catches in our traps throughout the summer of 2019. However, none were recorded on the sticky card traps that were wrapped around the trunks of the trees. New attractant and trap combinations are needed to develop an efficient monitoring approach.

Monitoring Trap Catches

Plant Protections:

Currently, many growers apply the systemic insecticide imidacloprid, or another neonicotinoid, against PFB. We've evaluated several imidacloprid application possibilities including pre-soak, root drench, full tree spray. We assessed other systemic materials including clothianadin and diamides (F-4260+oil), and organic options (azadirachtin and kaolin clay + paint).

2018 Plant Protection Treatments

(All rates are calculated based upon a rate of 100 gal spray applied per acre. Surfactant is used in all spray applications. UTC - Untreated Control)

2018 treatments / 2019 galleries

(The presence of galleries is evidence of tunneling caused by the borer. We analyzed the symptom data using logistic binomial general linear model (GLM) followed by Dunnett’s multiple comparison test, which compares each treatment to the untreated control. Significance levels: * = .01, ** - .05).

 We've found neonicotinoid applications to be effective in our trial. However, we're seeing diamide treatments (F-4260 + oil) as a potential alternative. (Note: assail is a neonicotinoid.)

Participation Summary
4 Farmers participating in research

Educational & Outreach Activities

2 Curricula, factsheets or educational tools
2 Webinars / talks / presentations
1 Workshop field days

Participation Summary:

750 Farmers
250 Ag professionals participated
Education/outreach description:

Curricula, factsheets or educational tools: these examples give an overview of the issues we're facing with Pacific flathead borer and the research we're conducting to mitigate its impact. 

  • Flyer
    • 2019 Summer Pacific Flatheaded Borer Workshop
    • 2019 Nut Growers Society Summer Hazelnut Tour
    • 2020 Nut Growers Society Winter Meeting
  • Poster
    • 2020 Nut Growers Society Winter Meeting

Webinars, talks and presentations:

  1. Presentation
    • 2020 Orchard Pest and Disease Management Conference
      • Anthony Mugica (graduate student) and Tatum Keyes (intern) gave presentations on the biology and management of pacific flatheaded borer.

Workshop / field days:

  1.  2019 Summer Pacific Flatheaded Borer Workshop
    • The workshop took place at the North Willamette Research and Extension Center.
    • Nik Wiman (Orchard Crop Specialist - Oregon State University) and Dr. Jhalendra Rijal (IPM Advisor - University of California Cooperative Extension) gave presentations and then we gave a tour of our emergence trial and plant protection research plots. 

Outreach in progress and upcoming:

  1. Oregon State University Hazelnut Extension Facebook page
    • Multiple posts pertaining to Pacific flatheaded borer
    • Final results will be posted upon completion of trials
  2. A standalone Extension document for the Oregon State University Extension Catalog illustrating the results from this project.
  3. Research findings will be incorporated into the Oregon State University Hazelnut Pest Management Guide and the PNW Insect Management Handbook.
  4. Virtual student competition presentation at the annual Entomological Society of America Meeting in November 2020

Project Outcomes

Did this project contribute to a larger project?:
Project outcomes:

Air blast spraying is a common practice for applying imidacloprid, or neonicotinoids, against PFB. The adverse effects caused from insecticide drift is an issue with this application method. These methods typically call for multiple applications throughout the active PFB season. We've analyzed two alternative imidacloprid application methods, pre-soaking trees and root drench, which essentially eliminates drift and is only applied once in a season. It's possible that neonicotinoids may not always be an option and we don't want to rely on just one chemistry. Our diamide and organic treatments may act as a safer replacement to neonicotinoids in the future. 

Our focus moving forward with this project is looking at single vs. multiple and reduced rate applications. Pesticide applications are a substantial expense for farmers. If single and or reduced rate applications are found to be just as effective as multiple applications then we can help lower grower costs while minimizing pesticides introduced to the environment. 

Knowledge Gained:

Current management practices against PFB contain the use of neonicotinoids, typically imidacloprid. The use of neonicotinoids has raised major concerns for their adverse effects towards beneficial insects and the environment. This led us to looking for replacements, including diamides and organic options. Throughout this project and moving forward, we continue to search for more sustainable opportunities.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.