Flatheaded Borer Management in Specialty Tree Crops

By Drs. Bill Klingeman¹ , Karla Addesso² , Jason Oliver² ,Fulya Baysal-Gurel² , Amy Fulcher¹ , Kim Jensen 4 , Kevin Moulton³ ,Bode Olukolu³ , Alicia Rihn⁴ and Anthony Witcher²

¹ Plant Sciences Department, The University of Tennessee, Knoxville, TN

² Tennessee State University, Otis L. Floyd Nursery Research Center, McMinnville, TN

³ Entomology and Plant Pathology Department, The University of Tennessee, Knoxville, TN

⁴ Agricultural and Resource Economics Department, The University of Tennessee, Knoxville, TN

New Momentum in the Effort to Manage Flatheaded Borers: a Long-time Production Problem

In 2015, nursery industry representatives met with research and Extension faculty to assist in updating a Nursery Pest Management Strategic Plan (Braman et al. 2015). During that process, commercial grower and landscape management professionals identified key pest arthropods that most negatively affect their operations and client landscapes, are poorly understood, or that have the fewest options for effective management. Flatheaded borer beetles were among the top 5 pests identified which met the three grower impact criteria. In 2019, a follow-up two-day workshop was sponsored as part of a USDA-NIFA Specialty Crop Research Initiative planning grant and hosted at the TSU Otis L. Floyd Nursery Research Center in McMinnville, TN (Fig. 1). At that workshop, Extension, research and industry members gathered stakeholder input and prioritized research and extension needs related to flatheaded borers. Outputs and outcomes from that meeting can be found at https://southernipm.org/partners/working-groups/wood-borers/ flatheaded-borer.

Fig. 1. Many of the SCRI grant cooperators participated remotely or in-person to provide input on research needs and priorities during the two-day planning workshop in McMinnville (photo by David Held, Auburn University).

Results from that effort enabled flatheaded borers in the genus Chrysobothris to become the focus of a much larger research and outreach initiative, which has now been funded through a four-year USDA Specialty Crop Research Initiative grant. The grant is co-led by Drs. Karla Addesso and Jason Oliver, who will be assisted by four additional team leaders, faculty co-investigators from several states, and cooperators from multiple universities, organizations and projects, and the USDA [sidebar]. Authors here represent the team of TSU and UT research and Extension faculty who will work alongside colleagues in several states to undertake a series of experimental projects (Fig. 2) during a 4-year multistate and multi-disciplinary effort.

Fig. 2. A word tree captures the diversity and frequency of topics that will be addressed by the flatheaded borer (FHB) grant team during this four-year project (image from Bill Klingeman, University of Tennessee).

Flatheaded Borers are Increasingly a Management Challenge and Economic Threat to Specialty Crops

Chrysobothris flatheaded borer species of concern are native to North America and found across the United States. Within the genus, larvae of flatheaded borers (Fig. 3) cause aesthetic injury and economic crop losses to many nursery, nut, and orchard tree species. For example, flatheaded borers routinely cause in excess of 40% losses of some nursery tree species that are produced in the southeastern U.S. (Fig. 4 & 5) (Oliver et al. 2010). The Oregon Hazelnut Commission, which represents more than 80,000 hazelnut orchard production acres, recently ranked Pacific flatheaded borer (C. mali) as the number one priority pest in young hazelnut orchards. About half of the acreage in Oregon consists of trees less than 11 years old. In August 2018, C. mali were also found attacking smaller limbs and branches of walnut trees in California. By 2019, 90–100% of the newly planted walnut trees in two walnut orchards covering 300 acres had visible flatheaded borer damage (Rijal, pers. obs.). Walnut and pecan trees are attacked by C. sexignata and other flatheaded borer species in the eastern U.S., with attacks occurring on the main trunk and larger branches of mature trees. In 2018, Hurricane Michael severely damaged about 17% of Georgia’s pecan acreage: impacting more than 700,000 trees. In August 2019, many new replacement pecan transplants have begun to show flatheaded borer damage (Acebes-Doria, pers. comm.). Other species of flatheaded borers are important pest of arborvitae and juniper in western nurseries. Chrysobothris species have also emerged as a threat to Florida blueberry production, where damage to blueberry stems results in production of fewer marketable fruits.

Fig. 3. A FHB larva extracted from an infested pin oak tree (photo by Frank Hale, University of Tennessee).

Fig. 4. Damage caused by maturing FHB larvae can be very apparent on the main trunk of smooth and thin-barked trees like red maple (photo by Jason Oliver, Tennessee State University).

Fig. 5. Smaller stems can also be attacked, like on the exposed branches of weeping ‘Traveler’ redbud trees (photo by Bill Klingeman, University of Tennessee).

How the Research Team will be Addressing Knowledge Gaps and Examining Options for Flatheaded Borer Management in Specialty Crop Systems

The overall objective of this team’s work is to better identify and understand the species in the genus Chrysobothris, to improve field monitoring efforts through improvements to traps and trapping capabilities, to examine chemical and non-chemical options for flatheaded borer management, and to document the economic costs, benefits, and consequences of adoption or lack of adoption for management strategies that may be developed.

Our multi-state research team will be investigating these questions in projects that involve many different experimental approaches. Some of these projects are briefly described in our six main project objectives.

1. Chrysobothris species, including members of the C. femorata species group, are very difficult for non-experts to differentiate (Fig. 6), so more reliable methods of identifying species and larvae attacking host plants are needed. Using NextGen genome sequencing, advanced molecular diagnostic resources will be developed by: a) sequencing the genomes of up to 30 economically and ecologically important Chrysobothris species, b) identifying genetic sequences that are informative for species identification and characterizing chemicals on borers (e.g., cuticular hydrocarbons) that can potentially be used for more rapid species determination, and c) preparing voucher specimens and GenBank accession data for project participants and their diagnostic laboratories.

Fig. 6. Chrysobothris femorata complex and other buprestids similar in appearance: A) C. femorata. (Photo by Jason Hansen, formerly UT, now USDA APHIS PPQ).

Fig. 6. B) C. adelpha. (Photo by Jason Hansen, formerly UT, now USDA APHIS PPQ).

Fig. 6. C) C. rugosiceps. (Photo by Jason Hansen, formerly UT, now USDA APHIS PPQ).

Fig. 6. D) C. viridiceps. (Photo by Jason Hansen, formerly UT, now USDA APHIS PPQ).

Fig. 6. E) C. quadriimpressa. (Photo by Jason Hansen, formerly UT, now USDA APHIS PPQ).

Fig. 6. F) C. shawnee. (Photo by Jason Hansen, formerly UT, now USDA APHIS PPQ).

Fig. 6. G) C. cribaria. (Photo by Jason Hansen, formerly UT, now USDA APHIS PPQ).

Fig. 6. H) C. sexsignata. (Photo by Jason Hansen, formerly UT, now USDA APHIS PPQ).

Fig. 6. I) C. wintu (western U.S. species, not found in Tennessee). (Photo by Jason Hansen, formerly UT, now USDA APHIS PPQ).

2. There is need to better document the life history traits, including ecology, seasonality and host plant preferences of key Chrysobothris species. In turn, beetle life history knowledge is expected to lead to improved grower management. Team members plan to: a) develop degree-day models to predict borer emergence (Fig. 7) and oviposition for better timing of spray treatments, b) identify the origin of infestations in tree crops and better understand female egg-laying behavior and methods to prevent attacks, and c) evaluate factors like plant cultivar, ambient temperature, and presence of natural enemies or plant pathogens, that influence larval survival within trees.

Fig. 7. An adult FHB emerges from a maple trunk in the lab (photo by Axel Gonzalez, Tennessee State University).

3. Better traps and more reliable methods of trapping adult (flying) Chrysobothris beetles are needed to assist with monitoring seasonal activity, assessing population growth and change, and to determine effectiveness of management methods. To meet these needs, our teams will: a) evaluate live trap designs, b) optimize trap color and type for use in production systems (Fig. 8); c) (in association with Obj 4a) identify field conditions or tree characteristics that increase tree susceptibility to borers, d) investigate auditory and visual signals that may improve trap effectiveness for important pest species, and e) test new adult lures with effective trap designs and deployment strategies to potentially intercept adults before they enter tree crops or for mass-trapping strategies.

Fig. 8. Purple panel traps can be coated with sticky adhesive and attract adult FHB during active flight times in a growing season (photo by Nadeer Youssef, Tennessee State University).

4. Identify production practices that reduce Chrysobothris attacks. To address this objective, we will: a) identify plant stress factors that increase borer attacks, b) evaluate cultural management methods (i.e., cover crops or trunk barriers) that can reduce borer attacks, and c) identify tree cultivars that have low susceptibility to borer attack (Fig. 9) and evaluate trait differences among cultivars with high and low borer susceptibility that could be useful for future plant breeding programs to develop borer resistance in tree crops.

Fig. 9. (LEFT) An olfactometer is set up in a greenhouse pilot study to test FHB preference for volatile chemicals emitted by different host plants (photo by Axel Gonzalez, Tennessee State University). • Fig. 10. (RIGHT) Intelligent spray technology applied to maple trees at Walker Nursery in Morrison, TN (photo by Amy Fulcher, University of Tennessee).

5. Develop effective chemical and biological management strategies for Chrysobothris borers. Teams working on this objective will work toward improving treatment efficacy by: a) evaluating new active ingredients, including insecticides with reduced pollinator impacts, b) determining tolerance levels for bearing crops, c) identifying entomopathogenic nematode species with greatest impact on flatheaded borers and develop methods to improve nematode persistence and efficacy, d) optimizing timing of trunk spray treatments, e) identifying natural enemies of borers and develop strategies to conserve natural enemies (in association with Obj. 2b), and f) determining if flatheaded borer control can be enhanced and detrimental effects minimized with the utilization of targeted intelligent precision sprayer technology (Fig. 10).

6. Address, from both producer and consumer perspectives, the cost/benefit economics and social acceptability of management methods that can be employed against Chrysobothris beetles. The project’s economics and social sciences team will: a) create budgets for alternative methods of borer control (e.g., drench, spray, cover crops, no treatment, etc.) to aid growers in selecting the best control methods for their specific production system, and b) measure consumers’ willingness to pay for tree species/cultivars that are not susceptible to borers, or to pay a premium price for ‘bee friendly’ production methods using discrete choice experiments. Understanding how the consumer market will respond to these changes is vital for growers who require a 3–5 year lead time to produce the trees that consumers are willing to purchase. Throughout this project, our research and outreach team will be working actively with an advisory board that includes industry and organization representatives from AmericanHort, the IR-4 Project, Nursery & Landscape Associations from Tennessee, Alabama, and North Carolina, the South Carolina Green Industry Association, representatives from three private nursery firms, as well as the California and Georgia pecan industries, the California Walnut Board, the Oregon Hazelnut Marketing Board, and the Florida Blueberry Growers Association.

This project received notice of funding in late summer 2020 and the project objective teams have been meeting regularly online to strategize research activity for the upcoming field season and to enlist collaborative cooperation with tree crop stakeholders. We are eager to learn from growers and landscape professionals who have experienced past losses, or who are actively working to minimize the effects of ongoing flatheaded borer activity at their production operations, orchards, and client landscapes.

For more information, or to participate in the teams research efforts, please contact Dr. Karla Addesso (kaddesso@tnstate.edu; 931-815-5155) or Dr. Bill Klingeman (wklingem@utk.edu; 865-974-7964). Look for our project results, which we will shared with you in future issues of Tennessee GreenTimes. Additional information will also be presented at the Southern Integrated Pest Management Flatheaded Borer Working Group site: https://southernipm.org/partners/working-groups/ wood-borers/flatheaded-borer/.

Sidebar

The USDA-NIFA SCRI Project Team for Flatheaded Borer Management in Specialty Tree Crops

Co-Project Director and Team Leaders

Dr. Karla Addesso Entomologist/Chemical Ecologist (PD & Team Leader) Otis Floyd Nursery Research Center, Tennessee State University

Dr. Jason Oliver Entomologist (Co-PD & Team Leader) Otis Floyd Nursery Research Center, Tennessee State University

Dr. Anthony LeBude Nursery Crops Extension Specialist (Team Leader) Horticulture Department, NC State University

Dr. Bill Klingeman Entomologist/Urban Landscape and Nursery Research (Team Leader) Plant Sciences Department, The University of Tennessee

Dr. Nik Wiman Entomologist/Orchard Crops Extension Specialist (Team Leader) Northwestern Research and Education Center, Oregon State University

Dr. Kimberly Jensen Agricultural & Specialty Crops Economist (Team Leader) Department of Agricultural and Resource Economics, The University of Tennessee

Project Co-Investigators

Dr. Amy Fulcher Sustainable Ornamental Plant Production Plant Sciences Department, The University of Tennessee

Dr. Anthony Witcher Sustainable Nursery Production Otis Floyd Nursery Research Center, Tennessee State University

Dr. Fulya Baysal-Gurel Plant Pathology Otis Floyd Nursery Research Center, Tennessee State University

Dr. Kevin Moulton & Dr. Bode Olukolu Entomological Taxonomy, Molecular Systematics, & Bioinformatics, Entomology and Plant Pathology Department, The University of Tennessee

Dr. Alicia Rihn Agricultural & Specialty Crops Economist Department of Agricultural and Resource Economics, The University of Tennessee

Dr. Angelita Acebes-Doria Pecan Entomologist, Department of Entomology, The University of Georgia

Dr. Shimat Joseph Nursery Entomologist, Department of Entomology, The University of Georgia

Dr. Brett Blaauw Apple Entomologist, Department of Entomology, The University of Georgia

Dr. David Shapiro-Ilan Pecan Research Entomologist USDA-ARS, Georgia

Dr. Juang-Horng Chong Ornamental Nursery, Research and Extension Entomologist Department of Plant and Environmental Sciences, Clemson University

Dr. David Held Nursery & Urban Landscape Entomologist Department of Entomology & Plant Pathology, Auburn University

Dr. Lloyd Nackley Nursery Crops & Plant Physiological Ecologist, Oregon State University

Dr. Clark Seavert Applied Economics, Oregon State University

Dr. Oscar Liburd Small Fruit & Horticultural Entomologist Entomology and Nematology Department, University of Florida

Dr. Jhalendra Rijal Area IPM Advisor and Entomologist University of California

Mr. Erfan Vafaie Extension Program Specialist IPM, Texas A&M

Dr. Cristi Palmer IR-4 Project

Collaborating Project Participants

Dr. Jill Calabro AmericanHort and HRI (formerly), Valent

Dr. Frank Hale Nursery & Landscape Extension Entomologist (UT)

Dr. Christopher Ranger Nursery Systems Research Entomologist (USDA-ARS, Ohio)

Dr. Kevin Chase Bartlett Tree Research Lab, NC

Mr. Joe LaForest Southern IPM Center

Ms. Amy Dismukes Nursery Extension Specialist, Tennessee State University