Effective Management of Thousand Cankers Disease of Walnut through Disruption of Insect Vector Behavior

Progress report for SW20-913

Project Type: Research and Education
Funds awarded in 2020: $349,770.00
Projected End Date: 09/30/2022
Host Institution Award ID: G334-20-W7899
Grant Recipients: University of California; University of California, Division of Agricultural and Natural Resources; USDA - Forest Service, Pacific Southwest Research Station; USDA - Agricultural Research Service (ARS)
Region: Western
State: California
Principal Investigator:
Dr. Richard Bostock
University of California
Co-Investigators:
Dr. Daniel Kluepfel
USDA - ARS, Crops Pathology and Genetics Research Unit
Dr. Steven Seybold
USDA Forest Service
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Project Information

Summary:

Thousand cankers disease (TCD) is a threat to English walnut (Juglans regia) and Paradox rootstock in California orchards, to California native walnut species, and to eastern black walnut in forests, plantations, and landscapes throughout the USA.  TCD is caused by a fungal infection following attack by the walnut twig beetle (WTB, Pityophthorus juglandis), which aggregates and transmits the pathogen, Geosmithia morbida.  Multiple infections girdle and kill branches and stems, with TCD often becoming lethal to the tree.  Current management options (only partially effective) are limited to general cultural practices (i.e., maintain tree vigor) and sanitation of infested materials.  Successful TCD management in orchards must include a more targeted strategy that includes the capacity to determine which host trees are likely to become infected and the ability to detect and deter the vector. Chemical ecology studies of the interaction between the WTB, pathogen, and plant host have identified an aggregation pheromone-based lure for WTB detection and repellent compounds to disrupt WTB host location, feeding behavior, and aggregation.  This project extends our studies on characterization of candidate attractive compounds to enhance the lure and incorporates field trials to further evaluate an optimized lure and a repellent mixture, initially in commercial orchards.  Common bacterial root, crown and stem diseases of walnut are often associated with TCD-affected trees, and orchard surveys will define the strength of this association. We will determine how these stresses may influence susceptibility of trees to beetle attack and pathogen colonization.  This information will inform our development of a risk rating system that draws in part from a clearer understanding of the association between predisposing stresses and TCD to guide grower deployment of WTB lures and repellents. Education and outreach to walnut producers, PCAs, and other stakeholders through face-to-face meetings, publications, and various online resources will be important activities and central to project success.  The Western SARE survey and evaluation tool will be used to assess grower awareness of TCD and its risk factors, as well as interest in adopting the WTB lure and repellent in orchard management programs.  This program will also engage our statewide network of UCCE orchard systems advisors who work with walnut growers by providing the latest research findings.  The principal outcome of this project will be enhanced competitiveness through increasing sustainability and resilience of walnut orchards as indicated by development and demonstration of an improved lure to monitor WTB populations and repellents to disrupt aggregation behavior. These fit well within an integrated pest management program, with potential for large-scale development and adoption by growers throughout California and elsewhere.

Project Objectives:

Note: The COVID pandemic forced closure of our laboratories during the first three months of the grant and has continued to constrain staffing, travel, and education and outreach efforts. Record-breaking wildfires in the region during 2020 prevented fieldwork and trapping studies during periods when WTB are normally most active (smoke inhibits them), delaying experiments until 2021. Supply chain issues in repellent availability and other materials also caused unanticipated delays. The death of Dr. Seybold and consequent loss of his expertise, research facilities, collegiality and inspiration created a huge void. COVID-related challenges also impacted personnel, resulting in staffing changes and revisions to the project scope. Changes in the following sections are incorporated, with further explanation in the Results and discussion section.

Four objectives underscore the overall goal of developing effective management tools for TCD and include ongoing plans. Objective 1: We will continue to field test a repellent mixture for disrupting WTB aggregations and protecting trees from attack in an experimental orchard and a commercial orchard. Our current lure, MBO, for monitoring WTB populations works well. Objective 2: Determine if tumor-emergent WTB can carry and mediate transmission of crown gall bacteria. Objective 3: Develop a tree risk-rating system based on association between TCD incidence and occurrence of crown gall diseases. Objective 4: Conduct education and outreach with input from our producer cooperators and UCCE Orchard Systems farm advisors to the extent possible within restrictions imposed by pandemic, health department and university policy.  The research has largely been conducted in the Bostock lab (UCD), with support from members of the Kluepfel lab (USDA ARS). Dr. Fichtner serves as Extension/Outreach Representative. Although not formally listed as a cooperator, Dr. Kari Arnold, UCCE Area Orchard and Vineyard Systems Farm Advisor, Stanislaus County, is contributing to outreach and education efforts.  Researchers supported by the grant currently or previously include Megan Siefker (Lab Assistant, June 2020-present), Jason Simmons (graduate student; April 2020- March 2021), and Dr. Corwin Parker (post-doctoral associate; January-December, 2021).

Note Modified Project Timeline: Field testing of the WTB repellent is a central activity of this project (Objective 1). Ms. Siefker and Dr. Parker have overseen this work which was delayed until year 2. Following Dr. Parker’s departure in January, 2022, Ms. Siefker, with assistance of Dr. Bostock, is continuing this work in spring, 2022. Completion of trials and associated data analysis will be a major milestone and completed by the project end date. Objective 2, the impact of bacterial crown and stem diseases on incidence and severity of TCD is directed by Drs. Bostock and Kluepfel. We are determining if tumor-emergent WTB carry crown gall bacteria, an important milestone and scientific discovery, and initial data indicate that this is so. Objective 3 concerns developing an orchard risk-rating system informed by several orchard surveys. Objective 4 is the education/outreach component of the project, and is cooperative effort of Drs. Bostock and Parker and UCCE Farm Advisors. The original Gantt Chart timeline, with additional detail and interim and end-of-project milestone indicators, and logic model are attached. However, we have significantly departed from that timeline and reduced the scope of the project for the reasons indicated above.

Timeline:

Field testing of the lure and repellent in our producer cooperator orchards is central to the goals of the project (Objective 1). Drs. Seybold and Audley, with assistance of Dr. Bostock, will oversee this work conducted over years 1 and 2 during the indicated periods. Completion of trials and associated data analysis will be a major milestone. Within this objective, we will complete ongoing analyses of VOCs and extractives from walnut bark and fungal tissue during Apr-Nov of year 1, under the direction of Drs. Bostock, Seybold and Simmons. Although not critical for successfully testing the field repellent, the results will be informative for Objective 2, and may identify compounds to enhance the MBO lure, which would be an important milestone. Objective 2, the impact of bacterial crown and stem diseases on bark chemistry that influence WTB behavior, will be directed by Drs. Bostock, Kluepfel and Simmons, with input from Dr. Seybold (years 1&2). Identifying a chemical “signature” of trees predisposed to attack by WTB would be an important milestone. We will also determine if tumor-emergent WTB carry crown gall bacteria, an important milestone and scientific discovery if such is the case (directed by Kluepfel, Bostock and Simmons). Objective 3 (led by Dr. Seybold) concerns developing an orchard risk-rating system informed by orchard surveys during summer and winter in both project years. Validating association between other stress factors and TCD will be an important milestone. Objective 4 is the Education/Outreach component of the project, under principal direction by Dr. Fichtner, with support by Drs. Bostock, Seybold and Kluepfel. This program will be ongoing throughout the two-year project, and is described elsewhere in the proposal. A Gantt Chart timeline, with additional detail and interim and end-of-project milestone indicators, and logic model are attached.

Gantt Chart - Bostock

LogicModel-Bostock WSARE

Cooperators

Click linked name(s) to expand/collapse or show everyone's info
  • Al Albertson - Producer
  • Megan Siefker (Researcher)
  • Dr. Corwin Parker
  • Brent Barton - Producer
  • Hal Crain - Producer (Educator)
  • Dr. Elizabeth Fichtner
  • Stan Lester - Producer
  • Jerry Moore - Producer (Researcher)
  • Jason Simmons

Research

Hypothesis:

The central hypothesis of this research is that cost-effective deployment of the walnut twig beetle (WTB) repellent for mitigating thousand cankers disease (TCD) in commercial walnut orchards in California will require knowledge of the repellent's range of efficacy from a point source, understanding seasonal patterns in WTB flight behavior, and identification of trees that are most at risk of attack by WTB.

Materials and methods:

As originally conceived, objective 1 was to focus on i) characterizing semiochemicals that attract or disrupt WTB aggregations, and ii) field-testing lure and repellent mixtures in commercial orchards using methods established in our laboratories (Audley et al.  2020b; Homicz et al. 2021).  However, as explained in our previous report, we had to narrow our focus to only study the repellent. Flight responses are measured by trap catches to the standard MBO lure. We have field-tested known WTB repellents in various combinations (Audley et al. 2020a; Audley et al. 2020c), which were evaluated for their potential to reduce flight response to MBO-baited traps (positive control) and then later as a potential behavioral disruptant to reduce colonization and damage to baited trees. Based on trapping results, commercial availability, and cost of the semiochemicals tested, we concluded that a two-compound repellent consisting of R-(+)-limonene and trans-conophthorin at defined release rates may constitute an effective tool for protecting trees from colonization by WTB (Audley et al. 2020a; Blood et al. 2018). We evaluated this repellent mix at the USDA’s Juglans National Clonal Germplasm Repository in Winters, CA, and the Plant Pathology Armstrong Research Farm at UC Davis, using the current MBO lure as attractant.

Note: The procedure as originally proposed was simplified to accommodate limited staffing and a restricted experimental window. Our final report will provide more detail about the current procedure. To test the repellent under orchard conditions, trees assigned to the positive control treatment group receive a single 15 ml plastic bottle of the MBO lure (Chen and Seybold 2014). Trees assigned to the repellent treatment group receive the MBO lure plus the repellent.

Objective 2 seeks to determine if infection by the crown gall pathogen, Agrobacterium tumefaciens, influences host apparency and susceptibility to WTB attack. Our field observations indicate attack by WTB and severity of TCD is often higher in orchards with a history of crown gall (Seybold et al. 2016). Crown galls appear to have a capacity to provide a substrate for enhanced development of new WTB adults. The potential association of WTB with A. tumefaciens is continuing to be examined by processing tumor-emergent WTBs for the presence of A. tumefaciens with both an A. tumefaciens selective isolation medium and species-specific PCR (Yakabe et al. 2012). These data will facilitate development of informed management decisions to sustain long-term orchard health, and contribute to the basis for a tree risk-rating  system with respect to the deployment of the repellent.

Objective 3 is related to objective 2 in further exploring the association of crown gall and TCD in English walnut orchards. Previous surveys of 'Chandler' walnut trees revealed a strong interaction between the number of WTB entrance/emergence holes (= holes) through the outer bark on Paradox rootstock and main stems and incidence and severity of crown gall disease of the rootstock (Seybold et al. 2016). These holes are a sign of attempted and completed reproduction by WTB. Thus, there is risk-rating potential for this disease to serve as an indicator for predisposition of trees to attack by WTB and a subsequent long-term decline of tree health.

Due to travel restrictions and staffing limitations, as well as a reassessment of useful parameters to include in a risk rating scheme, we revised our orchard survey plan. In spring and summer 2021 we intensively surveyed a local commercial English walnut orchard (grower J.H Meek & Sons, Inc., Woodland, CA) with a history of crown gall and TCD. We assessed incidence/severity of crown gall disease (measured as stem gall circumference), TCD symptoms as expressed as staining of branches, scion trunk, and rootstock, and number of WTB entry/exit holes. Results of these assessments were presented in our previous progress report.

 

Research results and discussion:

The following describes progress during the first year of the project, including efforts into the first quarter of year two, referencing where appropriate the changes in the original project plan due to the challenges mentioned in the revised objectives section.

  • Publication of studies relevant to project. Four papers were published in peer-reviewed journals, appearing during the first year (2020) of the project. The studies reported in these papers, supported mostly from prior funding, are central to the continuing studies on the repellent and the main theme for this project. A fifth paper, a new isothermal PCR assay we developed for in situ detection of Geosmithia morbida in TCD-afflicted walnut trees, was submitted to Plant Disease in late 2020. The paper is being revised to add additional experimental results and will be resubmitted soon. The following papers were published:

Audley JP, Bostock RM, Seybold SJ. 2020. Trap assays of the walnut twig beetle, Pityophthorus juglandis Blackman (Coleoptera: Curculionidae: Scolytinae), reveal an effective semiochemical repellent combination. J. Chem. Ecol. 46:1047-1058.

Audley JP, Homicz CS, Bostock RM, Seybold SJ. 2020. A study of landing behaviour by the walnut twig beetle, Pityophthorus juglandis, among host and nonhost hardwood trees in a northern California riparian forest. Agric. For. Entomol. 22:338-348.

Audley JP, Dallara PL, Nelson LJ, Hamud SM, Bostock RM, Seybold SJ. 2020. Trapping failure leads to discovery of potent semiochemical repellent for the walnut twig beetle. J. Econ. Entomol. 113:2772-2784.

Homicz CS, Audley JP, Chen Y, Bostock RM, Tauber CA, Seybold SJ. 2021. Walnut twig beetle landing rates differ between host and nonhost hardwood trees under the influence of aggregation pheromone in a northern California riparian forest. Agric. For. Entomol. 23:111-120.

Accepted with revision: 

Simmons JD, Yaghmour MA, Seybold SJ, Bostock RM.  Development of a recombinase polymerase amplification assay with qualitative end-point detection for Geosmithia morbida, the causal agent of thousand cankers disease in walnut. Plant Dis. (in revision)

In addition, Jason Simmons completed the M.S. degree in Plant Pathology on 31 March 2021 with thesis of the same title as the above manuscript.

  • Trapping of WTB. We processed a backlog of trap catches from walnut twig beetle (WTB) flight monitoring projects that took place in walnut orchards at Wolfskill Experimental Orchards in Winters, CA and the Armstrong Plant Pathology Research Field in Davis, CA between 2013 and 2019. These samples were collected from 4-unit Lindgren funnel traps baited with the male aggregation pheromone of the WTB. Four traps from each site were emptied weekly and saved in labeled ziplock bags. Trap catches were sorted under a dissecting scope and counts of male and female WTB as well as other associated insects were recorded. While many of these samples were processed immediately after collection, a large number of them were placed in cold storage and recovered in early 2020 after the passing of Dr. Seybold. Processing these samples was important because data from these long-running experiments identify peak flight trends, enabling us to maximize WTB trapping numbers at experimental sites for repellent trials. Figure 1 captures annual trends at the two sites for the 2015 to 2019 trapping seasons, the most complete trapping datasets.

It is apparent from the graphs that there is variation between years, between sites, and among traps within sites, but there are general trends. There is a peak flight period beginning late May/early June that often extends into July. There can also be another period of flight activity later in the summer, beginning in August and extending through late October. In some years, there was another upsurge in WTB activity in early spring (March-April) at the Wolfskill site. We are examining archived weather data at these two sites to determine if there is a relationship between WTB flight activity and temperature and possibly other factors. 

Figure 1. Left panel, WTB trapping numbers at the Armstrong Research Farm. Right panel, WTB trapping numbers at the Wolfskill Experimental Orchards. Years are indicated.

 

  • Objective 1. Walnut bark chemistry and repellent field tests. COVID restrictions and regional wildfires in 2020 (WTB flights are inhibited by smoke) prevented field assessments of repellent efficacy until 2021. Two sites, one at the Wolfskill Experimental Orchards in Winters, CA, and another at the Armstrong Plant Pathology Research Farm, were sampled weekly for 7 weeks, from 9/1/2021 until 10/19/2021. Although a more detailed analysis of the results will be presented in our final report in 2022, at this time we can say that the repellent cocktail of R-(+)-limonene and trans-conophthorin has an effective distance of about 2 meters from the point source, but not beyond that. This is consistent with our view that in order to be cost-effective, any deployment of the repellent in orchards will likely involve targeting single-trees identified as high risk (see Objective 3) during periods of peak WTB flights. We are repeating these trials in spring 2022 (April-June) at the Juglans NCGR and in a commercial orchard owned by one of our producer cooperators. 

Although several hundred bark samples, including samples from both G. morbida-inoculated and non-inoculated trees, were obtained from Juglans major, Juglans californica, and ‘Paradox’ hybrid rootstock (Juglans regia X Juglans hindsii), and extracted according to the protocols described in the materials and methods, only a small number of these were analyzed and partially interpreted. The loss from the project of the graduate student researcher responsible for this objective due to health issues in March 2021, as well as closure of co-PI Seybold’s analytical lab facility following his death, has precluded further progress on this aspect. Thus, we were unable to continue the portion of objective 1 concerning walnut bark chemistry and the search for tree host and fungal semiochemicals that influence WTB behavior.

  • Objective 2: Assess influence of walnut bacterial diseases – crown gall and shallow bark canker – on bark chemistry and WTB attraction, and determine if tumor-emergent WTB can mediate transmission of crown gall bacteria (years 1-2).  We are unable to pursue the bark chemistry/WTB attraction studies for the reasons indicated above. However, we are actively investigating tumor-emergent WTB for the presence of crown gall bacteria with support from the Kluepfel laboratory.  Initial results are promising, with evidence that WTB can carry Agrobacterium. Work is underway to verify isolated bacteria are tumorigenic Agrobacterium tumefaciens.  This work is continuing during April-June 2022.

 

  • Objective 3: Develop an orchard risk-rating system based on association between TCD incidence and occurrence of root, crown and stem diseases and other site-related stresses (years 1-2). We are focusing on the association between crown gall and TCD because anecdotal observations over the years in various orchards suggest that trees severely affected by crown gall are often affected by TCD. Data from three commercial orchards are being analyzed, but the data from one of these orchards (Meek’s orchard) are most robust and compelling. This is an older commercial orchard with a very high incidence of crown gall and significant incidence of TCD. However, the orchard continues to be commercially viable and the grower has kept it in production. Data were collected from over 200 trees selected at random during spring and summer of 2021. For each tree, we determined diameter at breast high (DBH), and estimated crown gall severity based on the percent of the circumference of the tree base galled, bark staining as a TCD symptom, and WTB strikes. The TCD/WTB severity assessments were parsed for rootstock, scion (main trunk), and visible branch symptoms. ANOVAs on crown gall vs. TCD/WTB severity were performed and the crown gall percent vs. TCD/WTB severity data are summarized in Figures 2 A-E.

There are highly significant associations between crown gall severity and scion and branch stains (TCD symptoms) as well as between crown gall severity and WTB strikes in scions and rootstocks. The only comparison that did not have a high significance was rootstock TCD stains, which was generally very low across the board. Factorial ANOVAs using crown gall percent*tree DBH indicated that DBH was not a factor.

Figure 2. Box plots of crown gall severity (percent of base) vs. TCD symptoms (stains) or WTB strikes in a commercial orchard. A) crown gall vs. rootstock stains; B) crown gall vs. scion stains; C) crown gall vs. rootstock WTB strikes; D) crown gall vs. scion WTB strikes; E) crown gall vs. branch stains. See text for further explanation.

 

Key research findings summary

  • There is a peak flight period beginning late May/early June that often extends into July. There can also be another period of flight activity later in the summer, beginning in August and extending through late October.
  • The repellent mixture has an effective distance of about 2 m from a point source, making single-tree deployment the most likely format if it is to be used successfully in a commercial orchard.
  • Initial results indicate that trees with crown gall disease are at high risk of WTB attack and TCD.
  • The WTB can emerge from crown galls and may carry crown gall bacteria. It is unknown whether crown gall-contaminated WTB can transmit the bacteria to cause crown gall.

References

Anonymous. 2019. R Core Team,  R: A language and environment for statistical computing. https://R-project.org/. Vienna, Austria.

Audley, J. P., Bostock, R. M., and Seybold, S. J. 2020a. Trap assays of the walnut twig beetle, Pityophthorus juglandis Blackman (Coleoptera: Curculionidae: Scolytinae), reveal an effective semiochemical repellent combination. J. Chem. Ecol. 46:1047-1058.

Audley, J. P., Homicz, C. S., Bostock, R. M., and Seybold, S. J. 2020b. A study of landing behaviour by the walnut twig beetle, Pityophthorus juglandis, among host and nonhost hardwood trees in a northern California riparian forest. Agric. For. Entomol. 22:338-348.

Audley, J. P., Dallara, P. L., Nelson, L. J., Hamud, S. M., Bostock, R. M., and Seybold, S. J. 2020c. Trapping failure leads to discovery of potent semiochemical repellent for the walnut twig beetle. J. Econ. Entomol. 113:2772-2784.

Blood, B. L., Klingeman, W. E., Paschen, M. A., Hadziabdic, E., Couture, J. J., and Ginzel, M. D. 2018. Behavioral responses of Pityophthorus juglandis (Coleoptera: Curculionidae: Scolytinae) to volatiles of black walnut and Geosmithia morbida (Ascomycota: Hypocreales: Bionectriaceae), the causal agent of thousand cankers disease. Environ. Entomol. 47:412-421.

Chen, Y. G., and Seybold, S. J. 2014. Crepuscular flight activity of an invasive insect governed by interacting abiotic factors. PLoS One 9:15.

Homicz, C. S., Audley, J. P., Chen, Y., Bostock, R. M., Tauber, C. A., and Seybold, S. J. 2021. Walnut twig beetle landing rates differ between host and nonhost hardwood trees under the influence of aggregation pheromone in a northern California riparian forest. Agric. For. Entomol. 23:111-120.

Seybold, S. J., Dallara, P. L., Hishinuma, S. M., and Flint, M. L. 2013. Detecting and identifying the walnut twig beetle: Monitoring guidelines for the invasive vector of thousand cankers disease of walnut. in: University of California Agriculture and Natural Resources, Statewide Integrated Pest Management Program, Oakland, California.

Seybold, S. J., Dallara, P. L., Nelson, L. J., Graves, A. D., Hishinuma, S. M., and Gries, R. 2015. Methods of monitoring and controlling the walnut twig beetle, Pityophthorus juglandis. United States Patent Publication Number 2013/0014428A1. United States Patent and Trademark Office. United States.

Seybold, S. J., Fichtner, E. J., Lampinen, B. D., Leslie, C. A., Hasey, J. K., Y., C., and Bostock, R. M. 2016. Impact of walnut twig beetle on English walnut health, productivity, and management: A synthesis of biotic and abiotic methods of assessment.

Yakabe, L. E., Maccree, M. M., Sudarshana, P., McClean, A. E., Parker, S. R., Wechter, W. P., Presting, G., Marutani-Hert, M., and Kluepfel, D. A. 2012. Novel PCR primers for detection of genetically diverse virulent Agrobacterium tumefaciens biovar 1 strains. Journal of General Plant Pathology 78:121-126.

Participation Summary
4 Producers participating in research

Research Outcomes

1 New working collaborations

Education and Outreach

5 Consultations
1 Curricula, factsheets or educational tools
4 Journal articles
1 Online trainings
1 Published press articles, newsletters
1 Other educational activities: Lead instructor (Bostock), Remote teaching of PLP120 Introductory Plant Pathology in spring quarter, 2020 to 33 UC Davis students (TCD and other tree diseases are discussed)

Participation Summary:

90 Farmers participated
100 Ag professionals participated
Education and outreach methods and analyses:
  • Discussion of TCD and recent research findings at Statewide Virtual Walnut Series, 22 February 2022, presented by Dr. Kari Arnold within her talk entitled “Identifying Diseases of Walnut and Management Strategies” (information provided and talk attended by Dr. Bostock; Virtual Day 1 program is attached VIrtual Day 1). Although the SARE evaluation form could not be used for this outreach event, attached is the “Impacts and Demographics…”Impacts and Demographics Statewide Virtual Walnut Series 2022  summary for the program (courtesy of Dr. Arnold). There were ~194 attendees that included pest control advisors (PCAs), certified crop advisors (CCAs), private applicators, crop consultants, orchard managers, orchard owners, orchard employees, and others.
  • Dr. Bostock and Ms. Siefker were interviewed by Vicky Boyd, a contributing writer for the online trade magazine “West Coast Nut”, for a feature article entitled “Death By A Thousand Cankers” that appeared in the March 2022 issue. Our funding support by Western SARE was acknowledged in the article. This magazine has a wide readership in the industry in the western USA.  West Coast Nut article
  • Scientific journal articles: The research papers published during year one of the project have the following citation scores in Google Scholar (as of 14 April 2022).    
    1. Audley JP, Bostock RM, Seybold SJ. 2020. Trap assays of the walnut twig beetle, Pityophthorus juglandis Blackman (Coleoptera: Curculionidae: Scolytinae), reveal an effective semiochemical repellent combination. J. Chem. Ecol. 46:1047-1058.  4 citations
    2. Audley JP, Homicz CS, Bostock RM, Seybold SJ. 2020. A study of landing behaviour by the walnut twig beetle, Pityophthorus juglandis, among host and nonhost hardwood trees in a northern California riparian forest. Agric. For. Entomol. 22:338-348.  6 citations
    3. Audley JP, Dallara PL, Nelson LJ, Hamud SM, Bostock RM, Seybold SJ. 2020. Trapping failure leads to discovery of potent semiochemical repellent for the walnut twig beetle. J. Econ. Entomol. 113:2772-2784. 5 citations
    4. Homicz CS, Audley JP, Chen Y, Bostock RM, Tauber CA, Seybold SJ. 2021. Walnut twig beetle landing rates differ between host and nonhost hardwood trees under the influence of aggregation pheromone in a northern California riparian forest. Agric. For. Entomol. 23:111-120.  0 citations
  • A set of PowerPoint modules with voice over containing updated information on thousand cankers disease tailored for English walnut growers is in preparation and will be completed by the end of the project.

Education and Outreach Outcomes

Key areas taught:
  • TCD biology and etiology; recent research findings; impact in California walnut orchards.

Information Products

    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.