Source: UNIVERSITY OF CALIFORNIA, DAVIS submitted to
ECOBIOLOGY, IMPACT, AND MANAGEMENT OF GRAPEVINE RED BLOTCH VIRUS AND ITS VECTOR(S) IN CALIFORNIA AND OREGON VINEYARDS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
ACTIVE
Funding Source
OTHER GRANTS
Reporting Frequency
Annual
Accession No.
1020210
Grant No.
2019-51181-30020
Cumulative Award Amt.
$3,172,836.00
Proposal No.
2019-03159
Multistate No.
(N/A)
Project Start Date
Sep 1, 2019
Project End Date
Aug 31, 2025
Grant Year
2019
Program Code
[SCRI]- Specialty Crop Research Initiative
Project Director
Oberholster, A.
Recipient Organization
UNIVERSITY OF CALIFORNIA, DAVIS
410 MRAK HALL
DAVIS,CA 95616-8671
Performing Department
Viticulture & Enology
Non Technical Summary
Grapevine red blotch disease, caused by the virus Grapevine red blotch virus (GRBV) is an urgent problem for the $162 billion US grape industry. GRBV is a prominent disease found in the majority of grape growing regions in California and Oregon. The grape industry currently lacks best practices for detecting and preventing spread of GRBV within and among vineyards. The discovery of S. festinus as a vector of GRBV significantly increased the possibility of better understanding the epidemiology of GRBD and ultimately its management. However, GRBD spread also occurs in vineyards where S. festinus has not been found. Therefore, information on potential additional vector species in these regions is paramount. Replanted vineyards in California and Oregon have experienced reinfections and a better understanding on the prevalence of GRBV and assessment of risk factors are needed. Proposed research will address knowledge gaps involving the epidemiology of the virus as driven by studies on its vectors and determining how the disease affects grapevine performance and grape quality. The economic impact of GRBV infection on producers and nurseries will also be determined. Sustainable GRBV management strategies developed from the project will be implemented to enhance economic and social impacts and to reduce the impact on environment. This project brings together researchers, extension specialists and stakeholders from CA and OR to help solve a significant new problem facing this valuable specialty crops industry. Outreach activities will be extended to the other states and can thus impact the grape industry in the country.
Animal Health Component
45%
Research Effort Categories
Basic
37%
Applied
45%
Developmental
18%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2041131200020%
2121131110110%
2151131113020%
2161131106020%
6011131209020%
4021131202010%
Knowledge Area
212 - Pathogens and Nematodes Affecting Plants; 601 - Economics of Agricultural Production and Farm Management; 204 - Plant Product Quality and Utility (Preharvest); 215 - Biological Control of Pests Affecting Plants; 216 - Integrated Pest Management Systems; 402 - Engineering Systems and Equipment;

Subject Of Investigation
1131 - Wine grapes;

Field Of Science
2090 - Statistics, econometrics, and biometrics; 2020 - Engineering; 1101 - Virology; 1130 - Entomology and acarology; 1060 - Biology (whole systems); 2000 - Chemistry;
Goals / Objectives
Grapevine red blotch disease, caused by the virus Grapevine red blotch virus (GRBV) is an urgent problem for the $162 billion US grape industry. This proposal aims to bridge knowledge gaps while generating strategies to manage GRBV. We intend to determine virus presence and spread in states across the US, and baseline knowledge on the risk of GRBV to wine grape production in states where acreage is increasing. Research includes studies on the role of its vector(s) in GRBV spread; economic assessment of GRBV impact on grape production, wine quality, and nurseries; as well as identification of sustainable management options. The latter will have the dual goals of reducing its spread across the US and determine its economic impact on all facets of the wine grape industry, including growers, nurseries, wineries, and state and federal regulatory agencies.Objective 1. Assess the prevalence and rate of spread of GRBV and the impact of red blotch disease on production and fruit quality in US grape production areas.Sub-objective 1.1 Determine prevalence and spread of GRBV in US grape production areas.Subobjective 1.2 Identify alternative hosts and reservoirs of GRBV.Subobjective 1.3 Establish the effect of GRBV infection on grape, juice and wine quality.Subobjective 1.4 Assess economic impact of red blotch disease on wine and grape production and nurseries.Objective 2. Identify and develop sustainable strategies to manage GRBV and its vector(s).Subobjective 2.1 Determine presence and biology of potential treehopper vectors in symptomatic vineyards and associated crop and non-crop landscapes.Subobjective 2.2 Improve knowledge of GRBV acquisition and transmission by its vector(s).Subobjective 2.3 Identify sustainable IPM strategies for the management of GRBV vector(s).Subobjective 2.4 Identify effective and economically viable strategies to eliminate GRBV sources (infected vines, vineyards, nurseries and landscape plants).Subobjective 2.5 Evaluate viticultural practices to mitigate the impact of GRBV on infected grapevines in relation to fruit production and quality.Subobjective 2.6 Develop cost-effective GRBV diagnostic tools - a prototype device to detect sub-visible changes in grape leaves at early stages of GRBV infection.Subobjective 2.7 Development of a field level detection method based on isothermal amplification.Objective 3. Implement and evaluate grapevine red blotch disease management programs.Subobjective 3.1 Evaluate grape industry knowledge of red blotch disease and management.Subobjective 3.2 2 Provide stakeholders with results, management guidelines and other outcomes of the Grapevine red blotch disease SCRI project activities.
Project Methods
Methodology, effort and evaluation per (sub)objective:Objective 1:(1.1) Determine GRBV prevalence in at least 5 major CA and OR grape-growing regions or AVAs through surveys and document GRBV spread in states or AVA's; determine genome characteristics of GRBV isolates from these locations.(1.2) Determine GRBV infection status in weeds and perennials proximal to grapevines infected with the virus in CA and OR vineyards in 1.1 by survey. Determine if horizontal spread of GRBV is occurring between grapevines and weeds and perennial hosts.(1.3) Collect samples for transcriptomic and metabolomics analysis and harvest of grapes with resulting wines made. and collect data transcriptomics, metabolomics and sensory analysis.(1.4) Collection of data regarding grape quality, yield and production costs from field trials and data regarding price and price discounts for grapes from GRBV-infected vineyards and analysis of the economic impacts at the vineyard and regional levels.Overall better understanding of GRBD epidemiology will be achieved and the risk of hosts capable of serving as replicative hosts of GRBV in virus management by rogueing will be determined. The impact of GRBV infection on grape, juice and wine composition through multivariate analysis will be determined. Better understanding of the determinants of economic impacts and their relative importance at the vineyard and regional levels will be achieved.Objective 2:(2.1) The seasonal ecology, distribution and biology will be determined of all possible vector insects in relation to virus distribution and spread in key study vineyard. Virus epidemiology will be determined in the vineyard through vector insects occurrence, together with improved virus monitoring and transmission biology experiments.(2.2) Vector transmission studies using either laboratory or field derived infected plants and known (TCAH) or potential vectors. Vectors will be tested for acquisition and plants will be helped for 2 years to develop symptoms. All plants used in inoculations studies will be tested at various times post inoculation, for up to 2 years. Results will be compiled and tests refined for any insects that can transfer the pathogen from infected to clean plant material(2.3) Field studies to determine efficacy of practices such as girdle removal, vineyard floor management, use of antifeedants, and vibration in reducing GRBV spread will be conducted. Experimental practices that reduce GRBV spread by vectors will be integrated with as appropriate in large-scale vineyard evaluations; costs and benefits of practices will be determined(2.4) Collection of data regarding the costs of practices examined in field studies. Analysis of the cost-effectiveness of the experimental practices implemented in the large-scale vineyard evaluations will be conducted.(2.5) Identify vineyards with known history of infection and spread of GRBD to establish viticulture management experiments. Conduct replicated and randomized field experiments to provide sufficient volume for enological analysis, further establish the translocation impediment of phloem transport to mitigate this effect. (2.6, 2.7) Establish the correlation between multispectral features of grape leaves and isothermal amplification data with red blotch diseases. Establish specificity and sensitivity of the multispectral imaging and isothermal amplification approach to detect GRBV.Epidemiology trends from ecology, distribution and biology will inform growers to more effectively mitigate the spread of the virus. Information will be compiled on known and potential vectors in terms of transmission efficiency or the lack thereof. Recommended sustainable IPM strategies for the management of GRBV and its vector(s) will be identified. Better understanding of the determinants of the cost-effectiveness of recommended sustainable IPM strategies and the potential for strategies that can manage GRBV at the regional level to be cost-effective will be achieved. Recommendations of management practices that may be used by grape growers to mitigate the effects of GRBD while providing acceptable berry composition to be used in winemaking will be provided. A portable low-cost device that can be used in a field setting for detection of early stages of GRBV infection will be developed.Objective 3:(3.1) Stakeholder Advisory Panel meets and establishes preferred methods and frequency of updates and communication with Project Directors and investigators; stakeholder surveys developed and implemented; baseline knowledge for GRBD established. Stakeholder Advisory Panel regularly interacts with Red Blotch Project Team and provides recommendations for mid-course corrections; surveys successfully distributed and results compiled, guiding improved stakeholder outreach and extension.(3.2) Holding extension meetings; holding hands-on workshops. Documentation of increased stakeholder knowledge of GRBV and vector identification and management.Stakeholder Advisory Panel and Red Blotch Project Team develop Sustainable IPM strategies and develop needs and plan for future research. Surveys will indicate increased knowledge of GRBV, its vector(s), and management. Sustainable IPM strategies for the management of GRBV and its vector(s) will be made broadly available to stakeholders in CA, OR and across the US by online publications.

Progress 09/01/23 to 08/31/24

Outputs
Target Audience:Our target audiences were UC Cooperative Extension (UC ANR) Farm Advisors that work with wine grapes and/or pest management, wine grape growers, vineyard managers, pest control advisers (PCAs), grape nursery managers as well as wine producers. Presentations highlighting research results were also given during national and international conferences attended by researchers and stakeholders in viticulture and enology. The results were presented to the industry advisory board and to the stakeholders at a Grapevine Red Blotch Symposium held at the American Society of Viticulture and Enology national conference in June 2024, Portland, OR. Changes/Problems:We have successfully completed project goals related to the field aspects of the project but have continued to have difficulties with sometimes erratic qPCR results due to equipment issues and availability of primers. Our work to refine knowledge of transmission by Spississtilus festinus has been delayed due to the loss of the alfalfa planting next to our UC Davis vineyard which served as our insectary for this species. The alfalfa stand was re-established in late spring 2024 and we have been seeing increased populations once again. Some data to confirm for a second year that grapes are an overwintering host for Tortistilus albidosparsus eggs was lost due to the accidental pruning of infested grape canes by a pruning crew even though the experimental rows were clearly labeled. What opportunities for training and professional development has the project provided?A postdoctoral researcher at UC Davis continues to be trained in grape vine viruses and diseases and is learning new assay methodology. The project also supported the training of two graduate students and two undergraduate students during the reporting period. They were trained in grape and wine chemical analysis as well as sensory evaluation. Additionally, undergraduate students and research assistants were trained in how to conduct field work, analyze data, and prepare research posters. Dr. KC's lab at Southern Oregon Research and Extension Center provided a two-hour long hands-on training on GRBV detection using LAMP assay. The workshop was organized during Grape Field Day on August 13, 2024. The trainees included growers, vineyard managers, and extension professionals. How have the results been disseminated to communities of interest?Project results were disseminated in person during field visits and SCRI project advisory committee meetings, at professional and stakeholder meetings, and by responding to email and phone calls from stakeholders. Presentations were also given at stakeholder meetings. A day long grapevine red blotch symposium was organized and held in collaboration with the 75th annual American Society of Viticulture and Enology conference in Portland, OR. Communities of interest targeted by these activities include winegrape growers and vineyard managers, grapevine nurseries, and pest control advisers (PCAs) as well as wine producers. Other communities of interest included UC Cooperative Extension, Farm and IPM Advisors working on grapes and researchers working on this disease and its vectors. What do you plan to do during the next reporting period to accomplish the goals?We will complete PCR analysis of the samples from our Tortistilus albidosparsus transmission studies, publish results in a peer-reviewed journal, and continue to disseminate our research outcomes at professional and stakeholder meetings. Collection of GRBV spread data for 2023 in two vineyards will be completed and a manuscript will be completed. The tHDA based detection with LAMP and qPCR-based detection methods for sensitivity will be compared and a manuscript written. Furthermore, field work in the potassium fertilizer trials will be completed and a manuscript submitted for publication. Ongoing machine learning efforts are focused on developing an unsupervised prediction model using NIR and GRBV data collected from the field, with the goal of creating a prototype detection device for practical field application. Simultaneously, work is underway to optimize a thermostable helicase-dependent isothermal amplification method, which is expected to further improve virus detection accuracy. This multi-faceted approach combines advanced spectroscopic techniques and machine learning to enhance early and late-stage detection of GRBV, with significant potential for field implementation. Findings are currently being compiled into a manuscript. Additionally, the chemical analysis of all wines will be completed, and a manuscript will be prepared for publication. Economic analysis of the impact of GRBV infection will also be finalized. Based on results, a IPM guidelines document will be developed.

Impacts
What was accomplished under these goals? Obj.1: Assess prevalence, rate of spread, and impact of Grapevine Red Blotch Virus (GRBV) on production and fruit quality in US wine grape production areas. Subobj. 1.1: Determine prevalence and spread of GRBV. The OR studies were concluded in 2022, and one manuscript was published. In CA, red blotch disease spread was assessed in vineyards planted with GRBV-free grapevines in Napa and Sonoma counties. Our Cabernet Sauvignon block at the Oakville Experiment Station has been kept free from floor vegetation since planting by disking in spring, and only one new infection has occurred. In our Sonoma County Pinot noir vineyard, the grower had rogued and replanted infected vines until spring 2022 but did not rogue in 2023. There were 302 grapevines with new GRBV symptoms found in 2023 increasing incidence by 15.7%. Overall infection is now 62%. Our Barbera block in Amador County was not surveyed in 2023 as GRBV incidence had reached >80% in 2022 and the grower removed the block. Subobj. 1.2: Identify alternative hosts and reservoirs of GRBV. Work under this objective was concluded in the prior year report. Subobj.1.3: Establish the effect of GRBV infection on grape, juice and wine quality. The final sampling and winemaking from two Merlot and two Cabernet Sauvignon sites in Napa and San Luis Obispo counties occurred in 2022. Grape chemical analysis was completed as well as wine sensory evaluations through descriptive analysis. Data indicate that wines made from GRBV+ grapes can be distinguished from wines made with healthy grapes even with a new infection. Wines made from GRBV+ fruit were seen as greener with attributes such as "cooked vegetables", "green stems" and "herbal". GRBV+ wines also had less body and astringency. These attributes significantly impact the quality of the wine. Both Cabernet Sauvignon and Merlot wines are made to be full-bodied wines with ripe fruit characters, a style preferred by the US market and targeting the luxury to super luxury pricing tier. Subobj.1.4: Assess economic impact of red blotch disease on wine and grape production and nurseries. Data to be obtained from project scientists and data requiring grape grower and/or vintner input/collaboration were identified as well as potential industry collaborators. Obj.2: Identify and develop sustainable strategies to manage GRBV and its vector(s). Subobj. 2.1: Determine presence and biology of potential treehopper vectors in symptomatic vineyards and associated crop and non-crop landscapes. Species collected for potential vectors for transmission tests in southern OR included three treehoppers (Spissistilus festinus, Stictocephala bisonia and Tortistilus sp.), and one cixiid (Melanoliarus aridus). Transmission tests using an artificial feeding substrate were continued in 2023. Results indicate that insects that tested positive for GRBV also transmitted the virus into the solution via feeding. The UC Davis group continued to collect treehoppers from vineyards in Amador, Napa, and Sonoma counties in 2023 and 2024, to expand knowledge of their biology. Monitoring seasonal development and movement of T. albidosparsus over a 6-month period resulted in the first comprehensive biological data on this species. This species was also found to oviposit on grapevines in the field which has implications for its vector potential and management. Subobj. 2.2: Improve knowledge of GRBV acquisition and transmission by its vector(s). Studies conducted in 2023 and 2024 using nymphs emerging from eggs laid in overwintering hosts outside of vineyards and reared to adults more precisely defined acquisition time and successful transmission. Use of the artificial transmission substrate for evaluating transmission was validated for two treehopper species. Subobj 2.3: Identify sustainable IPM strategies for the management of GRBV vector(s). The third and final year of comparing the effect of clean cultivation versus groundcover on potential vector activity was 2022. A trial at the SOREC research vineyard compared clean cultivated plots and plots planted with a mix of grass and trefoil. Insects captured with yellow sticky traps was generally very low as were number of girdles per vine. However, a significant effect was observed with fewer girdles being found in the clean cultivated plots. Subobj.2.4: Identify effective and economically viable strategies to eliminate GRBV sources (infected vines, vineyards, nurseries, and landscape plants). The UC Davis group continued monitoring a vineyard where intensive rogueing and replanting is used as a strategy for reducing within-vineyard spread. Observations indicate that rogueing may not be very effective in limiting GRBV spread in vineyards if they are surrounded by other GRBV-infected vineyards. Subobj.2.5: Evaluate viticultural practices to mitigate the impact of GRBV on infected grapevines in relation to fruit production and quality. Potassium fertilization work in GRBV+ vines has been extended to encompass different application methods/rates, formulations, and cultivars. A new phosphorus fertilizer trial was initiated in an adjacent block also infected with GRBV. Subobj.2.6&2.7: Develop cost-effective GRBV diagnostic tools. Supervised and unsupervised machine learning models were developed to detect GRBV presence with results compared to RT-PCR analysis. FTIR spectroscopy proved effective in identifying early-stage grapevine infections. Chemometric analysis revealed significant differences in the carbohydrate contents of GRBV-infected vs non-infected grapevines. Spectral features in the range of 1250-600 cm?¹ were identified as key indicators for developing the models used for early-stage prediction of GRBV infections. GRBV and NIR spectroscopy were successful in detecting late-stage infections in the field with chemometric analysis of NIR spectral bands in the 400-800 nm range revealing significant differences between infected and healthy plants. Obj.3: Implement and evaluate grapevine red blotch disease management programs. Subobj.3.1&3.2: Evaluate grape industry knowledge and extend results of GRBV research. Surveys of California and Oregon wine industry knowledge on GRBV have been conducted during planned workshops. GRBV related knowledge and research findings related to this grant were shared at both industry focused events and national and international conferences. One article was published in a grape and wine magazine during the evaluation period with several manuscripts in progress.

Publications

  • Type: Other Status: Published Year Published: 2024 Citation: Olaya, C., Reddy, K., Patel, S., Zalom, F.G., and Sudarshana, M.R. Detection of grapevine red blotch virus in gridles caused by feeding injury from treehoppers peaks in the summer months in a California vineyard. Submitted to Plant Disease. Submitted on Sept 30, 2024.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: A. Levin. 2024. Can we mitigate GRBD symptoms with viticultural practices. ASEV National Conference Red Blotch Symposium, Portland, OR, June 18, 2024
  • Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: F. Zalom. 2023. Presence and biology of potential GRBV vectors in symptomatic vineyards and associated crop and non-crop landscapes. GRBV SCRI Annual Stakeholder Meeting, Davis, CA, November 17, 2023
  • Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: F. Zalom. 2023. GRBV acquisition and transmission by its vector(s). GRBV SCRI Annual Stakeholder Meeting, Davis, CA, November 17, 2023
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: F. Zalom and M. Sudarshana. 2024. An update on the spread of Grapevine red blotch virus. North Coast IPM Meeting, Santa Rosa, CA. January 17, 2024
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: F. Zalom. 2024. Recent studies on treehoppers and GRBV spread in vineyards. Bayer Crop Science Meeting, Rutherford, CA, February 26, 2024
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: F. Zalom. 2024. Grapevine red blotch virus and vectors. National Academy of Sciences Grapevine Viruses Committee Meeting, Davis, CA, March 4, 2024
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: F. Zalom. 2024. Role of Treehoppers in Grapevine Red Blotch Disease Epidemiology. Recent Advances in Grapevine Virus (GRBV) Vectors and Management Symposium, American Society of Enology and Viticulture Symposium, Portland, OR June 18, 2024
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: M. Sudarshana. 2024. Prevalence and spread of GRBV in California: impact of host, reservoirs and vectors. Recent Advances in Grapevine Virus (GRBV) Vectors and Management Symposium, American Society of Enology and Viticulture Symposium, Portland, OR June 18, 2024
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: V. Walton. 2024. Integrative studies of vector-related virus epidemiology. Recent Advances in Grapevine Virus (GRBV) Vectors and Management Symposium, American Society of Enology and Viticulture Symposium, Portland, OR June 18, 2024
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: R. Rai, N. Nitin. 2024. Spectral and imaging features of leaves to predict early-stage GRBV infection. Recent Advances in Grapevine Virus (GRBV) Vectors and Management Symposium, American Society of Enology and Viticulture Symposium, Portland, OR June 18, 2024
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: A. Oberholster. 2024. Impact of grapevine red blotch disease on grape and wine composition and wine style. Recent Advances in Grapevine Virus (GRBV) Vectors and Management Symposium, American Society of Enology and Viticulture Symposium, Portland, OR June 18, 2024
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: DeShields and KC 2024. Characterization of grapevine red blotch virus transmission by treehoppers using an artificial feeding system. APS-Pacific Division Annual Meeting, Corvallis OR, March 27, 2024.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: KC and DeShields 2024. Grapevine Red Blotch Virus: Lessons Learned in Seven Years. Recent Advances in Grapevine Virus (GRBV) Vectors and Management Symposium, American Society for Enology and Viticulture, Portland, OR June 18, 2024.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: DeShields and KC 2024. Current Strategies for the Detection of Grapevine Red Blotch Virus. 2024 Sustainable Ag Expo
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: A. Levin. 2024. Grapevine Red Blotch Disease: Virology, Vectors, and Viticulture. Emerging & Future Challenges in Viticulture, Zoom, April 17, 2024
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: Sudarshana, M.R., Olaya, C., Kishorekumar, R., Scully, H., Vo, J., Kurtural, K., Zalom, F.G. 2024. Spread of grapevine red blotch virus in replanted vineyards which implemented least to maximum virus management practices. Annual Meeting of the American Phytopathological Society, Plant Health 2024. July 2024
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: N. Nitin, Rai, R., Spectroscopy and Data Analytics for The Early Detection of Red Blotch Viral Infection in Grapevines, National Academies of Sciences, Engineering, and Medicine (NASEM) workshop on Grapevine Diseases.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: Boghozian, A.M. Medina-Plaza, C., Kishorekumar, R., Sudarshana, M.R., Oberholster, A. 2024. Impact of grapevine red blotch virus (GRBV) infection on grape skin cell wall composition over two growing seasons. 2024. Presented at the Annual meeting of the American Society for Enology and Viticulture. June 2024
  • Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: Singh, P., Sculley, H., Reddy, K. Boghozian, A.M., Medina-Plaza, C., Anita Oberholster, A. and Sudarshana, M.R. 2024. Temporal Dynamics of Grapevine Red Blotch Virus Titer in Infected Grapevines is Influenced by Fruit Maturity Stages. Poster presented at the Annual Meeting of the American Society of Plant Biologists. June 2024.


Progress 09/01/22 to 08/31/23

Outputs
Target Audience:Our target audiences were UC Cooperative Extension (UC ANR) Farm Advisors that work with wine grapes and/or pest management, wine grape growers, vineyard managers, pest control advisers (PCAs), grape nursery managers as well as wine producers. Presentations highlighting research results were also given during national and international conferences attended by researchers and stakeholders in viticulture and enology. The results were presented to the industry advisory board and to the stakeholders at the annual outreach symposium at UC Davis. Changes/Problems:Project goals related to the field aspects of the project were successfully completed, but results associated with PCR results for presence of GRBV in transmission samples have been slowed by a postdoc leaving the project as well as the departure of the graduate student who had been conducting the analyses in 2022. New staff has been appointed and the backlog of samples that are awaiting PCR analysis will soon be addressed. The backlog in sensory and wine analysis due to COVID-19 safety delays are also being addressed. What opportunities for training and professional development has the project provided?The project supported the training of two project scientists, two post-doctoral fellows, three graduate students and two undergraduates in skills needed to conduct the research discussed. How have the results been disseminated to communities of interest?Project results were disseminated in person during field visits and SCRI project advisory committee meetings, at professional and stakeholder meetings, and by responding to email and phone calls from stakeholders. Communities of interest targeted by these activities include winegrape growers and vineyard managers, grapevine nurseries, and pest control advisers (PCAs) as well as wine producers. Other communities of interest included UC Cooperative Extension, Farm and IPM Advisors working on grapes and researchers working on this disease and its vectors. What do you plan to do during the next reporting period to accomplish the goals?PCR analysis of samples from 2023 Tortistilus albidosparsus transmission studies will be completed. A second full season of data on T. albidosparsus biology and movement will also be collected as it relates to GRBV transmission. We also plan to more precisely determine the acquisition period of GRBV by Spississtilus festinus. Analysis of rogueing and replanting infected grapevines as a management approach will also be completed. Collection of GRBV spread data for 2023 in two vineyards will be completed and a manuscript will be completed. The tHDA based detection with LAMP and qPCR-based detection methods for sensitivity will be compared and a manuscript written. Results from the potassium fertilizer and carbon transmission trials will be submitted for publication and an outreach event to industry will be organized. The development of machine learning models for NIR and RGB images will be completed. Additionally, the chemical and sensory analysis of the 2022 wines made from GRBV positive and negative wines will be completed as well as the economic analysis of the impact of GRBV infection. Based on results, a IPM guidelines document will be developed. Findings will be shared at a GRBV symposium held in conjunction with the 75th American Society of Viticulture and Enology Conference in Portland, OR.

Impacts
What was accomplished under these goals? Obj.1: Assess prevalence, rate of spread, and impact of Grapevine Red Blotch Virus (GRBV) on production and fruit quality in US wine grape production areas. Subobj. 1.1: Determine prevalence and spread of GRBV The study in OR was concluded in 2022 and one manuscript was published. In CA red blotch disease spread in vineyards planted with GRBV-free grapevines in Amador, Napa and Sonoma counties continued and will be completed in fall 2023. Subobj. 1.2: Identify alternative hosts and reservoirs of GRBV. Work under this objective was concluded in the prior year report. Subobj.1.3: Establish the effect of GRBV infection on grape, juice and wine quality. Two Merlot and two Cabernet Sauvignon sites in Napa and San Luis Obispo counties were utilized. In 2022 the last samples were taken from these sites with subsequent winemaking. At one site, berry samples were collected at pre-veraison, veraison, post-veraison and harvest for transcriptomic and metabolomic analysis to relate disease expression to years of infection, symptoms, and environmental factors. Berry chemistry at harvest and yield data per vine were recorded for all sites. Due to COVID-19 safety regulations, the sensory evaluation of wines from the 1st year was only completed in spring of 2022. Thus, all wines will need to undergo 18 months of bottle aging prior to sensory analysis. In spring of 2023, the wines made from the 2021 harvest were sensorially evaluated. Results indicate significant differences between wines made from healthy vs GRBV-infected fruit. Subobj.1.4: Waiting for completed wine compositional and sensory analysis for economic determinations. Obj.2: Identify and develop sustainable strategies to manage GRBV and its vector(s). Subobj. 2.1&2.2: Determine presence and biology of potential GRBV vectors and improve knowledge of GRBV acquisition and transmission by its vector(s). Sampling vineyards in southern OR for potential vectors was focused on collecting insects for use in the transmission tests. The insect species collected consisted of three treehoppers (Spissistilus festinus, Tortistilus sp., and Stictocephala bisonia), and one cixiid (Melanoliarus aridus). Transmission tests using an artificial feeding substrate were continued in 2023 as the results of the work done in 2022 was generally positive. These in vitro assays followed the technique described in Kahl et al. (2021). In 2022, the in vitro technique was used on over 200 treehoppers that were collected from both infected and uninfected vineyards, along with S. festinus collected from an unsprayed alfalfa field. The results indicated that in most cases the solution being fed upon by insects that tested positive for GRBV, also tested positive for GRBV, indicating that the virus was transmitted by the insect into the solution via feeding. These in vitro transmission assays were continued in 2023. Rick Hilton retired at the end of June 2023 but further research on vector transmission of GRBV using the in vitro method was conducted at OSU-SOREC by Drs. Achala KC and Govinda Shrestha and their respective labs during the 2023 field season. In fall 2022, collection of treehoppers (Membracidae) as vectors were continued from vineyards in Napa, Sonoma, and Amador counties to determine presence of GRBV in the collected specimens. Transmission studies were initiated using an artificial transmission system (ATS), factitious legume hosts and uninfected grapevines with two membracid species. Salivary glands from individual insects were dissected and results compared for detection of GRBV using the ATS and factitious hosts. In 2023, nymphs were collected from outside of vineyards, reared to adults and allowed to feed on GRBV-infected vines or uninfected vines for varying lengths of time to validate results from the previous year. Results from 2022 indicate that the proportion of treehoppers capable of transmission increased with longer acquisition periods of up to 20 days. PCR analysis of 2023 studies are underway for the 2023 insect collections. Treehoppers collected are sequenced to confirm species identification and distribution. Seasonal development and movement of Tortistilus albidosparsus was monitored over a 5-month period resulting in the first comprehensive biological data on this species. Subobj 2.3: Identify sustainable IPM strategies for the management of GRBV vector(s). The third and final year of comparing the effect of clean cultivation versus groundcover on potential vector activity was 2022. A trial established at the SOREC research vineyard compared clean cultivated plots and plots planted with a mix of grass and trefoil. Recovery of insects, primarily with yellow sticky traps, was generally very low. However, information on treehopper feeding activity was again collected and while the number of girdles per vine was generally low, a significant effect was observed with fewer girdles being found in the clean cultivated plots. Subobj.2.4: Identify effective and economically viable strategies to eliminate GRBV sources (infected vines, vineyards, nurseries, and landscape plants). We continued monitoring a vineyard that has been using intensive rogueing and replanting as a strategy for reducing within-vineyard spread. The vineyard, which is surrounded by neighboring GRBV-infected vineyards, has continued to increase in infections to date. Subobj.2.5: Evaluate viticultural practices to mitigate the impact of GRBV on infected grapevines in relation to fruit production and quality. Potassium fertilization work in GRBV+ vines has been extended to encompass different application methods/rates, formulations, and cultivars. A potted vine trial was initiated to investigate carbon translocation and partitioning in GRBV+ grapevines to follow up on previous work. Subobj.2.6&2.7: Develop cost-effective GRBV diagnostic tools. Machine learning based on supervised and un-supervised models to detect the presence of GRBV was developed and results compared with RT-PCR analysis. RGB and NIR spectroscopy were effective in detecting the disease during the late stages. Data analysis is being conducted to determine the effective wavelengths and imaging bands for implementation in the field. Optimization of a thermostable helicase-dependent isothermal amplification method is also currently in progress. Obj.3: Implement and evaluate grapevine red blotch disease management programs. Subobj.3.1&3.2: Evaluate grape industry knowledge and extend results of GRBV research. Surveys of California and Oregon wine industry knowledge on GRBV have been and will be conducted during planned workshops and symposia. GRBV related knowledge and research related to this grant were shared at both industry focused events and national and international conferences. One peer-reviewed manuscript was published during the evaluation period.

Publications

  • Type: Journal Articles Status: Published Year Published: 2023 Citation: DeShields, J., and KC, A. N. 2023. Comparative analysis of grapevine red blotch disease progress over time using LAMP and PCR based detection methods. American Journal of Enology and Viticulture: 74 (1) 0740015. DOI: 10.5344/ajev.2023.22047
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: F. Zalom and M. Sudarshana. 2022. Update on treehoppers and grapevine red blotch virus research. Current Issues in Vineyard Health, UC Davis Extension Conference. Davis, CA, December 3, 2022.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: M. Sudarshana. C. Olaya, R. Kishorekumar, H. Scully, J. Vo, K. Kurtural and F. Zalom. 2023. Evaluation of management of grapevine red blotch virus spread in vineyards by rogueing infected vines. 20th conference of the International Council for the Study of Virus and Virus-Like Diseases of the Grapevine, Thessaloniki, Greece September 26, 2023.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: KC, A. N., 2023. Grapevine red blotch disease: an update on diagnosis and management. OSU Grape Day, Corvallis, OR 2023.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: Vaughn Walton, Daniel Dalton, Rick Hilton, Kent Daane, Frank Zalom and Mysore Sudarshana, Integrative studies of vector-related virus epidemiology, The Southern Oregon Grape day in Central Point, April 5, 2023.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: KC, A. N., and DeShields, J. 2023. Grapevine red blotch disease diagnosis: opportunities and challenges. International Congress of Plant Pathology, Lyon, France.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: DeShields, J. B., Levin, A. D., and KC, A. N. 2023. Grapevine red blotch virus latency and its effect on grapevine fruit quality. American Society for Enology and Viticulture.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: M. Rosenberg, C. Medina Plaza, L. X. Lim, C. Olaya, H. Scully, M. Sudarshana, A. Oberholster, 2023. Impact of Grapevine Red Blotch Disease on Grape and Wine Composition and Wine Sensory Attributes. 74th American Society of Viticulture and Enology Conference, Napa, CA


Progress 09/01/21 to 08/31/22

Outputs
Target Audience:The project has completed its first three years of funding and outreach and extension events have been undertaken to share data. Our target audiences are UC Cooperative Extension (UC ANR) Farm Advisors that work with wine grapes and pest management, wine grape growers and vineyard managers, grape nursery personnel as well as winemakers and winery owners. In person meetings have increased since COVID-19 safety restrictions have relaxed in the last year and were used in addition to emails, phone and videoconferences and field visits with project cooperators. A hybrid Grapevine Red Blotch Disease Symposium was held at UC Davis in March 2022 where all major collaborators/PIs presented their work. The symposium was attended by 147 people from mainly the grape and wine industry, although fellow researchers, students and media were also in attendance. In addition, several PIs and collaborators attended and presented at grape days, technical and research conferences. The target audiences are mostly grape and wine industry professionals. However, interactions with fellow scientists for peer-reviewed feedback also occur by attending meetings and conferences. The PIs and collaborators on this project also met with the advisory board that represents fellow scientists, nurseries, vine testing facilities and grape and wine industry representatives in late 2019, 2020, and 2021 and will meet again in December of 2022. Changes/Problems:Although we initiated several new studies and successfully collected biological samples related to those studies, a major problem arose when Bio-Rad, the company that produces Ssofast EvaGreen Supermix, a key component of our real-time PCR analysis methodology that facilitates fast, highly specific DNA amplification became backordered in May 2022. The product is still not available at the time of this report preparation. As a result, we have had to obtain products with somewhat similar spectral properties which required modification of our usual methodology. Further, validation of results obtained for comparison to previous results was necessary to ensure data quality. We have only recently began catching up with PCR analysis of our sample backlog following this delay. Furthermore, due to Covid-19 constraints, we were limited in the earlier period to collect field data and performing lab analysis, including sensory studies. For this reason, we will be requesting a no cost extension for the project. What opportunities for training and professional development has the project provided?Four graduate and four undergraduate students are being trained in the scientific methodology needed to achieve project goals. This ranges from insect to plant sampling, insect detections, insect biology studies, ecological studies, viral analysis, plant physiological measurements, biochemistry, chemistry, and winemaking. A graduate student in the UC Davis Entomology Graduate Group working on this project completed his M.S. thesis in September 2021 and continued to work as a grad student researcher for part of the current year. During this time, he continued to develop valuable laboratory and field research techniques that directly led to his employment in a permanent position with an agricultural diagnostic laboratory in New York state where he is currently employed. Furthermore, 6 post-doctoral fellows and two project scientists have been developing new skills and knowledge. New technology is also being investigated for disease detections and more. How have the results been disseminated to communities of interest?The results were disseminated to communities of interest through presentations at the industry symposium held on 03/16/2022 at UC Davis and to the industry advisory board. Presentations were also given at national and international scientific conferences and at local grape meetings. Project results were additionally disseminated in person during field visits, and by email, phone calls and videoconferences. Presentations are mentioned above under 'Other Products'. Communities of interest targeted by these activities include winegrape industry members including growers, grapevine nurseries, and pest control advisers (PCAs). Other communities of interest included UC Cooperative Extension Farm and IPM Advisors working on grapes and researchers working on this disease and its vectors. What do you plan to do during the next reporting period to accomplish the goals?We plan to confirm the status of Tortistilus albidosparsus and possibly other treehopper species as a vector of GRBV. Furthermore, the utility of non-grapevine transmission assays in GRBV studies will be validated. The acquisition period of GRBV by Spississtilus festinus will be determined more precisely and the rate of spread of GRBV in infected vineyards will be related to number of infected treehopper girdles. Several manuscripts will be completed in the coming year and an outreach event is being planned in March and April 2023 in OR to relate new knowledge to the industry. Furthermore, the development of machine learning models for NIR and RGB images will be completed and the sensitivity of the IR spectroscopy approach to discriminate GRBV from other viral infections such as leaf roll viruses will be compared. This will result in a recommended portable set up to detect red blotch virus in the field. Wine compositional and sensory analysis of wines made from healthy versus red blotch diseased fruit will continue and the obtained data will be used to access its economic impact. Economically viable strategies will be identified for the improvement of IPM management strategies.

Impacts
What was accomplished under these goals? Obj.1: Assess prevalence, rate of spread, and impact of Grapevine Red Blotch Virus (GRBV) on production and fruit quality in US wine grape production areas. Subobj. 1.1: Determine prevalence and spread of GRBV We have been monitoring and mapping vineyards where red blotch disease is present and patterns of GRBV is consistent with being spread by a vector in California's Napa Co., Sonoma Co. and Amador Co. In vineyards where disease scouting followed by removing and replanting infected vines was practiced in addition to floor management, infected vines remained relatively stable (<1%), while spread in a vineyard that did not follow these practices was 81.2% over 3 years. However, another vineyard implementing roguing and replanting still saw 45% cumulative infection. Surveys in Oregon indicated GRBV incidence ranging from 2.81 to 59.7% in older vineyards while in younger blocks it was 0.29 to 1.11%. This work has been published recently (Achala et al., 2022, Am. J. Enol. Vitic. 73:116-124). Subobj. 1.2: Identify alternative hosts and reservoirs of GRBV. Surveys and testing of native plants and weeds in vineyard landscapes have indicated that only Vitis species are the natural hosts of GRBV (Wilson et al., 2022 Phytofrontiers 2(1):66-73). Subobj.1.3: Establish the effect of GRBV infection on grape, juice and wine quality. Two Merlot and two Cabernet Sauvignon sites in Napa and San Luis Obispo counties were utilized. At one site, berry samples were collected at pre-veraison, veraison, post-veraison and harvest for transcriptomic and metabolomic analysis to relate disease expression to years of infection, symptoms, and environmental factors. Berry chemistry at harvest and yield data per vine were recorded for all sites and small-scale winemaking was conducted to determine impact on wine composition and sensory characteristics. Due to COVID-19 safety regulations, the sensory evaluation of wines from the 1st year was only completed in spring of 2022. Thus, all wines will need to undergo 18 months of bottle aging prior to sensory analysis. Results indicate significant differences between wines made from healthy vs GRBV-infected fruit. Subobj.1.4: Waiting for completed wine compositional and sensory analysis for economic determinations. Obj.2: Identify and develop sustainable strategies to manage GRBV and its vector(s). Subobj. 2.1&2.2: Determine presence and biology of potential GRBV vectors and improve knowledge of GRBV acquisition and transmission by its vector(s). Vineyards in CA and OR were sampled to evaluate the activity of possible GRBV insect vectors. Yellow sticky cards, sweep net and visual observations were utilized. Because GRBV transmission to grapevines takes such a long time, we validated other approaches to transmission including an artificial transmission system developed by Canadian researchers in 2021 and transmission to cowpea and snapbean as proposed by New York researchers. As part of the validation, we compared results to detection of GRBV in the salivary glands of individual insects. We detected transmission by both Spississtilus fesinus and Tortistilus albidosparsus using ATS and will validate these results next year. We continue to sequence CO1 in membracids used in transmission studies to confirm species identification. In collaboration with the Foundation Plant Services (FPS) at UC Davis, two vineyard blocks were sampled where every vine has been tested for GRBV over the past five years. Data are being analyzed to determine hemipteran seasonal abundance, regional differences in the known vector (three-cornered alfalfa hopper), and relationship between infected vines and vector presence at FPS. Subobj 2.3: Identify sustainable IPM strategies for the management of GRBV vector(s). A waterproof electronic insect trap that plays back vibrational signals is being refined for use. Recorded signals (e.g. stridulation and wingbeats) from potential vector species could be used for insect biology studies, trapping and pest control. Software allows for signals to be increased in frequency as soon as unique communication from insects are recorded from the environment. Subobj.2.4: Identify effective and economically viable strategies to eliminate GRBV sources (infected vines, vineyards, nurseries, and landscape plants). We are monitoring a vineyard that has been using rogueing and replanting as a strategy for reducing within-vineyard spread. The vineyard, which is surrounded by GRBV-infected vineyards, continues to see increased infections. Subobj.2.5: Evaluate viticultural practices to mitigate the impact of GRBV on infected grapevines in relation to fruit production and quality. Results from two years of field trials examining the effects of foliar potassium fertilization on healthy and infected vines have been shared at meetings and a manuscript is being prepared. Furthermore, results from manipulation of source:sink ratios in healthy versus GRBV infected vines have been published (Tanner et al., 2022). In 2022, investigations into the impact of different irrigation regimes were continued and data are currently being processed. Subobj.2.6&2.7: Develop cost-effective GRBV diagnostic tools. Leaf samples from May to Oct were collected and analyzed from both irrigated and non-irrigated fields in Napa using FTIR, near IR spectroscopy and RGB imaging. NIR and RGB images were done in the field using a portable set up. Machine learning based supervised and un-supervised models were developed to detect the presence of GRBV and compare to results with RT-PCR analysis. Machine learning models using the carbohydrate region of IR spectral, achieved 95% prediction accuracy to detect GRBV at early stages of the disease. RGB and NIR spectroscopy were effective in detecting the disease during the late stages. Obj.3: Implement and evaluate grapevine red blotch disease management programs. Subobj.3.1&3.2: Evaluate grape industry knowledge and extend results of GRBV research. Surveys of California and Oregon wine industry knowledge on GRBV have been and will be conducted during planned workshops and symposia. GRBV related knowledge and research related to this grant were shared at both industry focused events and national and international conferences. A day long Grapevine Red Blotch Disease Hybrid Symposium was organized at UC Davis in March of 2022 and was attended by 147 people. Furthermore, five peer-reviewed manuscripts were published.

Publications

  • Type: Journal Articles Status: Published Year Published: 2022 Citation: Tanner, J.D., M. Dimitrios, Y. Runze, N. Torres, L.E. Marigliano, M. Zumkeller, A. Oberholster, S.K. Kurtural (2022) Cabernet Sauvignon Grapevine (Vitis Vinifera L.) Non-Structural Carbohydrates and Flavonoids are Not Redistributed with Source-Sink Manipulation in Plants with Grapevine Red Blotch Virus. Available at SSRN: https://ssrn.com/abstract=4112960 or http://dx.doi.org/10.2139/ssrn.4112960
  • Type: Journal Articles Status: Published Year Published: 2022 Citation: Wilson, H., Hogg, B. N., Blaisdell, K. G. Anderson, J. C., Yazdani, A. S., Billings, A. C., Ooi, K. M., Almeida, R. P. P., Cooper, M. L., and Daane, K. M. 2022. Survey of vineyard insects and plants to identify potential insect vectors and non-crop reservoirs of Grapevine Red Blotch Virus. Phytofrontiers 2(1): 66-73 doi: 10.1094/PHYTOFR-04-21-0028-R
  • Type: Journal Articles Status: Published Year Published: 2021 Citation: Billings, A.C., K. Flores, K. McCalla, K.M. Daane, and H. Wilson. (2021). Manipulation of Ground Covers to Reduce Three-Corned Alfalfa Hopper, Spissistilus festinus (Hemiptera: Membracidae), and other Suspected vectors of Grapevine Red Blotch Virus. Journal of Economic Entomology 114(4): 1462-1469. https://doi.org/10.1093/jee/toab115
  • Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Zalom, F. and M. Sudarshana. 2021. Biology and role of treehoppers in grapevine red blotch disease. Pierces Disease Research Symposium, Virtual Presentation, December 16, 2021.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Zalom, F. and M. Sudarshana. 2022. Role of Treehoppers in Red Blotch Epidemiology. UC Davis Grapevine Red Blotch Disease Symposium, March 16, 2022
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Olaya, C., F. Zalom, and M. Sudarshana. 2022. Recognition and spread of grapevine red blotch disease, what have we learned in the last 10 years. UC Davis Grapevine Red Blotch Disease Symposium, March 16, 2022.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Zalom, F. and M. Sudarshana. 2022. Association of Treehoppers and Grapevine Red Blotch Virus in Northern California Vineyards. Pacific Branch Entomological Society of America Meeting, Santa Rosa CA. April 12, 2022.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Olaya, C., F. Zalom, and M.Sudarshana. 2022. Analysis of girdles caused by feeding damage from membracids indicate Grapevine red blotch virus is vectored in the vineyards in the summer months. Plant Health 2022, American Phytopathological Association annual meeting, Pittsburgh PA, August 8, 2022.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Oberholster et al. (2022) Impact of Red Blotch Disease on Grape and Wine Composition and Quality. Napa Valley Vintners, CIA Copia, Napa, CA, May 11, 2022.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Oberholster A., et al. (2022) Impact of Red Blotch Disease on Grape and Wine Composition and Potential Mitigation Strategies. Grapevine Red Blotch Disease Symposium, Hybrid Event, UCD Conference Center, Davis, CA, 16 March 2022.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Oberholster et al. (2022) Latest Update on Grapevine Red Blotch Virus. Sonoma County Grape Day, Santa Rosa, CA, February 8, 2022.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Oberholster A. (2021) Working Towards Sustainability in the Wine Industry. UCD Conference Center, V&E Alumni Celebration, Davis, CA, December 3, 2021.
  • Type: Journal Articles Status: Published Year Published: 2022 Citation: Achala, N. KC., J.B. DeShields, A.D. Levin, R. Hilton, and J. Rijal. 2022. Epidemiology of Grapevine Red Blotch Disease Progression in Southern Oregon Vineyards. American Journal of Enology and Viticulture 73:116-124. doi: 10.5344/ajev.2022.21031.


Progress 09/01/20 to 08/31/21

Outputs
Target Audience:The project has completed its first two years of funding and some outreach and extension have been undertaken to share preliminary data. Our target audiences were UC Cooperative Extension (UC ANR) Farm Advisors that work with wine grapes and pest management, wine grape growers and vineyard managers, and grape nursery personnel. In person meetings were limited to email, phone and videoconferences and field visits with project cooperators due to COVID-19 safety restrictions. Some in-person seminars did take place before and after meeting restrictions. The target audiences are mostly grape and wine industry professionals. However, interactions with fellow scientists for peer-reviewed feedback were also undertaken by attending meetings and conferences. The PI's on this project also met with the advisory board that represents fellow scientists, nurseries, vine testing facilities and grape and wine industry representatives in late 2019, 2020, and 2021. Changes/Problems:Covid-19 safety restrictions remained a hinderance to lab studies during fall 2020 and winter and early spring 2021 as the number of individuals who could access our laboratories concurrently was limited, and both field work and in-person outreach to stakeholders due to travel restrictions were limited. The restrictions became less intensive during the summer and fall. Delays in processing samples in the laboratory have been largely overcome, and although field work commenced later than hoped our goals have largely been met. Additionally, sensory studies had to be delayed until winter 2021 due to safety concerns. What opportunities for training and professional development has the project provided?A graduate student in the UC Davis Entomology Graduate Group completed his M.S. thesis September 20, 2021 and learned important laboratory and field research techniques. Three graduate students will graduate in 2021 and were trained in the scientific methodology needed to achieve project goals. This ranges from insect to plant sampling, insect detections, insect biology studies, ecological studies, viral analysis, plant physiological measurements, biochemistry, chemistry, and winemaking. Furthermore, 6 post-doctoral fellows have been developing new skills and knowledge. New technology is also being investigated for disease detections and more. How have the results been disseminated to communities of interest?Research findings were presented using mostly online platforms in the past year due to COVID safety regulations. GRBV related knowledge and research outcomes related to this grant were extended twenty-four times in the past year through twenty grape industry focused webinars attracting more than 1,500 attendees as well as at international conferences for feedback from fellow researchers. Industry audiences (our stakeholders) comprised mostly of grapegrowers, winemakers and consultants, but also included vineyard and winery workers as well as owners. Extension materials were also distributed to stakeholders. Shared information are further disseminated through industry representatives taking knowledge back to their own organizations, and media representatives summarizing research outcomes from extension events. One advantage of the online platform is that a wider audience can be reached and attendance is not limited by traveling requirements. Additionally, six peer-reviewed papers were published focused on related grapevine red blotch virus research in the last year. What do you plan to do during the next reporting period to accomplish the goals?Vineyard sites in which insect vectored spread of GRBV is believed to be occurring will continue to be investigated to identify potential vectors and host plants for the candidate vectors and GRBV, and to study transmission by these insects as well as their biology. Understanding the life cycle and biology of potential vector species are key to the development of successful management strategies to limit GRBV spread. In the third year, cost-effective diagnostic tools for GRBV detection will be explored and economic analysis of GRBV impact on grape and wine quality (value) will commence.

Impacts
What was accomplished under these goals? Obj.1: Assess prevalence, rate of spread, and impact of Grapevine red blotch virus (GRBV) on production and fruit quality in US wine grape production areas. Subobj. 1.1: We have been monitoring and mapping vineyards where red blotch disease is present and patterns of GRBV is consistent with being spread by a vector in California's Napa Co., Sonoma Co. and Sierra Foothills regions as well as in Oregon's Willamette Valley and southern Oregon. In vineyards where disease scouting followed by removing and replanting infected vines was practiced, infected vines remained relatively stable, while incidence in vineyards that did not follow these practices increased by almost 30-fold after 3 years. Subobj. 1.2: Plant sampling encompassed 36 non-crop plant genera or species across 21 families including 15 annuals and 21 perennials. From this broad range of plants, only Vitis spp. was found to be positive for GRBV, and this includes samples from both cultivated (Vitis vinifera) and wild grape (Vitis californica). Subobj.1.3: Four vineyard sites were sampled in Napa and San Luis Obispo counties, two Merlot and two Cabernet Sauvignon. At one site berry samples were collected at pre-veraison, veraison, post-veraison and harvest for transcriptomic and metabolomic analysis to relate disease expression to years of infection, symptoms, and environmental factors. Berry chemistry at harvest and yield data per vine were recorded for all sites and small-scale winemaking was conducted to determine impact on wine composition and sensory characteristics. Subobj.1.4: Start in 2021. Obj.2: Identify and develop sustainable strategies to manage GRBV and its vector(s). Subobj. 2.1: Vineyards in Napa and Sonoma counties as well as southern OR were sampled to evaluate the activity of possible GRBV insect vectors. In total, 4,004 Hemipterans across 13 families were tested. Insects that tested negative or positive were not consistently associated with any specific host plant that also frequently tested positive. The insect species tested to date have consisted of three treehoppers (Spissistilus festinus, Tortistilus albidosparsus, and Stictocephala bisonia), one cixiid (species still to be determined), and two leafhoppers (Colladonus reductus and Osbornellus borealis). Subobj. 2.2: Improve knowledge of GRBV acquisition and transmission by its vector(s). Transmission of GRBV by suspected and confirmed insect vectors using field vines for virus acquisition and inoculation was evaluated. Transmission studies have explored the ability of Spissistilus festinus and Scaphytopius graneticus to acquire the virus from infected vines and subsequently inoculate non-infected vines. S. festinus has been confirmed by another study as a vector and we found that discing the groundcovers in the early growing season reduced S. festinus activity abundance in the canopy and is a possible way to control this insect vector. Transmission assays conducted in 2020 in OR using potted vines yielded no results as the test vines suffered very high overwintering mortality. Transmission tests using an artificial substrate were conducted in September of 2021. Over one hundred S. festinus collected from an organic alfalfa field and exposed to red blotch infected grapevines were tested in this manner as well as a few Stictocephala bisonia. Subobj 2.3: Identify sustainable IPM strategies for the management of GRBV vector(s). A biweekly survey of north coast CA vineyards was made in spring 2021 to field validate the S. festinus model. Salivary glands are being tested for presence of GRBV. A replicated vineyard block was planted in southern OR to examine the effect of clean cultivation versus mowing row middles on potential vector activity. In CA, a study was conducted in 2019-2020 to determine the impact of mowing vs. discing between vine rows on S. festinus populations. Results indicate that discing the groundcover in early spring reduced the abundance of S. festinus in the canopy for the rest of the growing season. Infection status of asymptomatic vines next to symptomatic vines was evaluated in southern OR. Of 420 asymptomatic vines surrounding 42 symptomatic vines, only 2 tested positive for GRBV suggesting that neighboring asymptomatic vines do not need to be removed when removing symptomatic vines. A waterproof electronic insect trap that plays back vibrational signals is being refined for use. Recorded signals (e.g. stridulation and wingbeats) from potential vector species could be used for insect biology studies, trapping and pest control. Software allows for signals to be increased in frequency as soon as unique communication from insects are recorded from the environment. Subobj.2.4: Identify effective and economically viable strategies to eliminate GRBV sources (infected vines, vineyards, nurseries and landscape plants). Will start in 2021. Subobj.2.5: Evaluate viticultural practices to mitigate the impact of GRBV on infected grapevines in relation to fruit production and quality. Field trials were conducted in 2020 and 2021 in CA and OR vineyards. The effects of foliar potassium (K) fertilization on healthy and infected vines were evaluated in both seasons. Foliar K did not improve sugar translocation to fruit, but rather dehydrated berries, thus explaining the increased Brix at harvest. Field trials were also repeated for applied water amounts, source:sink alteration as well as ABA homologue applications. Neither of the trials were successful in altering sugar translocation, or the feedback inhibition brought on by GRBD. Subobj.2.6: Develop cost-effective GRBV diagnostic tools - a prototype device to detect sub-visible changes in grape leaves at early stages of GRBV infection. Leaves were collected from vineyards at Plymouth and Oroville, CA at different times (May - Oct) and tested for GRBV infection using qPCR assays. Significant changes in water soluble components were observed even at early stages of infection. Furthermore, the changes in pigment and water content were evaluated based on hyperspectral images and near infrared spectra of both infected and non-infected leaves collected at different times. At early stages (May-June), pigment and water content of infected and non-infected leaves were not changed significantly. For late season (Sep - Oct), the pigment and water content of infected and noninfected leaves were changed significantly. Using these data sets, we are developing artificial neural network models to predict infection at the early and late stages. Subobj. 2.7: In 2020, we started testing Loop Mediated Isothermal Amplification developed by Romero et al. (2019). At dormant stages, all methods including LAMP resulted 100% positive results when samples were collected from basal and middle samples. When the ability of these methods to detect negative vines was analyzed, we observed higher percentage of false positive by LAMP assays and we are currently working on troubleshooting this assay. Obj.3: Implement and evaluate grapevine red blotch disease management programs. Subobj.3.1: Surveys of California and Oregon wine industry knowledge on GRBV will commence in year 3. Subobj.3.2: Results were presented using mostly online platforms in the past year due to COVID safety regulations.GRBV related knowledge and research related to this grant were extended twenty-four times in the past year and extension materials were distributed to stakeholders. Research results were shared at both industry focused events and national and international conferences. For example, progress in all GRBV research areas was delivered to the grape industry through 20 webinars attracting >1,500 attendees.

Publications

  • Type: Journal Articles Status: Published Year Published: 2021 Citation: Rumbaugh, A.C., R.C. Girardello, M.L. Cooper, C. Plank, S.K. Kurtural, A. Oberholster. Impact of Rootstock and Season on Red Blotch Disease Expression in Cabernet Sauvignon (V. vinifera). Plants 10 (8), 1683.
  • Type: Journal Articles Status: Published Year Published: 2021 Citation: Copp, C.R., KC, A.N., Levin, A.D. Cluster thinning does not improve fruit composition in grapevine red blotch virus-infected Vitis vinifera L. American Journal of Enology and Viticulture 73(1).
  • Type: Journal Articles Status: Published Year Published: 2021 Citation: Copp, C.R., Levin, A.D. Irrigation improves vine physiology and fruit composition in grapevine red blotch virus-infected Vitis vinifera L. American Journal of Enology and Viticulture 72(4):307-317.
  • Type: Other Status: Published Year Published: 2021 Citation: Billings, A.C. Current research in GRBV: confirmed vector S. festinus and possible vector S. graneticus. Napa County, CA in-person all-day field day. 2021
  • Type: Other Status: Published Year Published: 2021 Citation: Oberholster, A. The Impact of Red Blotch Disease on Grape and Wine Composition. Virtual On the Road in Alameda and Contra Costa, Mar. 2021
  • Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Olaya, C., M.R. Sudarshana and F.G. Zalom. 2021. La mancha roja de la uva: una amenaza para la produccion de uva de vino en California y Estados Unidos, invited presentation at a Colombian Association of Phytopathology webinar, September 11, 2021, (https://youtu.be/ophiFsGRYDg)
  • Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Billings, A.C., K. Flores, K. McCalla, H. Wilson and K.M. Daane. 2020. Testing three possible insect vectors of grapevine red blotch virus using field transmission studies. ESA conference 2020.
  • Type: Other Status: Published Year Published: 2020 Citation: Daane, K. M., Billings, A.C., K. Flores, K. McCalla, and H. Wilson. Current knowledge of grape red blotch associated virus vectors. NCPN-Grapes Tier II Committee Meeting. Davis, CA. Feb. 2020.
  • Type: Other Status: Published Year Published: 2020 Citation: Daane, K. M., Billings, A.C., K. Flores, K. McCalla, and H. Wilson. Trying to understand the spread and control of ⿿Red Leaf⿝ in vineyards. Central Coast Wine Grape Seminar. Salinas, CA Mar. 2020.
  • Type: Other Status: Published Year Published: 2020 Citation: Billings, A.C., K. Flores, K. McCalla, H. Wilson and K.M. Daane. 2020. Grapevine red blotch virus: what we know and what we are trying to find out. IPM North Coast seminar. Santa Rosa, CA
  • Type: Other Status: Published Year Published: 2020 Citation: Daane, K. M. Meet the experts. Sustainable Ag Expo & International Sustainable Winegrape Summit. The Vineyard Team. Nov. 2020 (live webinar, CV19).
  • Type: Other Status: Published Year Published: 2020 Citation: Daane, K. M. BIFS project for areawide control of red leaf vineyard pathogens. Lodi Breakfast Workshop. Dec. 2020 (live meeting via ⿿go to meeting⿿, CV19).
  • Type: Other Status: Published Year Published: 2020 Citation: Daane, K. M., Billings, A.C., K. Flores, K. McCalla, and H. Wilson. Ecobiology, impact and management of grapevine red blotch virus and its vector ⿿ Objective 2.1. SCRI Stakeholder Meeting, UC Davis Host. Dec. 2020 (live webinar, CV19)
  • Type: Other Status: Published Year Published: 2021 Citation: Daane, K. M., Billings, A.C., K. Flores, K. McCalla, and H. Wilson. Developing an areawide program for mealybugs and the leafroll virus. JAVA Areawide Grower Consortium. Jan. 2021 (live webinar, CV19).
  • Type: Other Status: Published Year Published: 2021 Citation: Daane, K. M., Billings, A.C., K. Flores, K. McCalla, and H. Wilson. Update on Red Blotch Vector Research. NCPN-Grapes Tier II Meeting. Feb. 2021 (live webinar, CV19).
  • Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Billings, A.C., K. Flores, K. McCalla, H. Wilson and K.M. Daane. 2021. Understanding and controlling grapevine red blotch virus vectors. Pacific Branch ESA conference 2021.
  • Type: Other Status: Published Year Published: 2021 Citation: Daane, K. M., Billings, A.C., K. Flores, K. McCalla, and H. Wilson. Update on red blotch associated virus and its potential vectors. E&J Gallo Winery Technical Seminar Series. (live webinar, CV19). Apr. 2021.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Daane, K. M., S. Bolton, K. Beal, C. Starr, C. Storm, E. Amaral, L., Whitted, K. McCalla, A. Billings, N. Mercer, T. Martin, K. Flores, M. Cooper, H. Wilson, B. Hogg, and R. Almeida. BIFS - Refinement and Implementation of an Areawide Program for Vineyard Pathogens and their Insect Vectors. CDFA Office of Pesticide Consultation and Analysis ⿿ Annual Conference (live webinar, CV19). Jun. 2021.
  • Type: Other Status: Published Year Published: 2020 Citation: Kurtural, S. K., Cultural Practices to Mitigate Grapevine Red Blotch Disease. North Coast IPM Seminar. December 2020
  • Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Copp, C.R., DeShields, J., Clark, R., Stowasser, M., Levin, A.D., ASHS National Conference, ⿿Grapevine Red Blotch Virus alters leaf carbon metabolism and export but not chlorophyll fluorescence in Vitis vinifera L.,⿝ Denver, CO. (August 2021).
  • Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Levin, A.D., DeShields, J., and KC., A.N., 72nd ASEV National Conference, ⿿Foliar potassium application has limited effect on berry composition in Grapevine Red Blotch Virus-infected grapevines.,⿝ Virtual. (June 2021).
  • Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: KC, A.N., DeShields, J., and Levin, A.D., 72nd ASEV National Conference, ⿿Comparative diagnostic methods Grapevine Red Blotch Virus (GRBV),⿝ Virtual. (June 2021).
  • Type: Other Status: Published Year Published: 2021 Citation: Levin, A. Grapevine Red Blotch Virus: Research Updates Leading to Improved Management. Knight⿿s Grapevine Nursery Open House. Phoenix, OR. August 12, 2021.
  • Type: Other Status: Published Year Published: 2020 Citation: Levin, A.D. Grapevine Red Blotch Disease: What we learned and where do we go next? 2020 Oregon Wine Research Institute Red Blotch Webinar Series. Zoom. December 15, 2020.
  • Type: Other Status: Published Year Published: 2020 Citation: Levin, A.D. Grapevine Red Blotch Disease: Grape and wine composition. 2020 Oregon Wine Research Institute Red Blotch Webinar Series. Zoom. December 8, 2020.
  • Type: Other Status: Published Year Published: 2020 Citation: Levin, A. D. Efficacy of vineyard management practices for mitigating the effects of Grapevine Red Blotch Disease. 2020 Oregon Wine Research Institute Red Blotch Webinar Series. Zoom. October 27, 2020.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Levin, A. D. Where Are We Now? A Deeper Understanding of Grapevine Red Blotch Virus Effects on Grapevine Physiology. 2020 Oregon Wine Research Institute Red Blotch Webinar Series. Zoom. October 20, 2020.
  • Type: Theses/Dissertations Status: Accepted Year Published: 2021 Citation: Bollinger, M.R. 2021. Monitoring of Treehopper (Hemiptera: Membracicade) Populations in Northern California Vineyards. M.S. Thesis submitted to Entomology Graduate Group, UC Davis.
  • Type: Journal Articles Status: Under Review Year Published: 2022 Citation: Bollinger, M.R., C.R. Kron, B.W. Bahder, M.R. Sudarshana, and F.G. Zalom. Seasonal and Within-Plant Distribution of Feeding Damage to Vitis vinifera caused by Spissistilus festinus (Hemiptera: Membracidae). Amer. J. Enol. Vitic.
  • Type: Journal Articles Status: Accepted Year Published: 2022 Citation: Wilson, H., B.N. Hogg, K.G. Blaisdell, J.C. Anderson, A.S. Yazdani, A.C. Billings, K.M. Ooi, R. Almeida, M. Cooper and K.M. Daane. Survey of vineyard insects and plants to identify novel vectors and non-crop reservoirs of grapevine red blotch virus. PhytoFrontiers.
  • Type: Journal Articles Status: Published Year Published: 2021 Citation: Billings, A.C., K. Flores, K. McCalla, K.M. Daane, and H. Wilson. Manipulation of Ground Covers to Reduce Three-Corned Alfalfa Hopper, Spissistilus festinus (Hemiptera: Membracidae), and other Suspected vectors of Grapevine Red Blotch Virus. Journal of Economic Entomology 114(4): 1462-1469. https://doi.org/10.1093/jee/toab115


Progress 09/01/19 to 08/31/20

Outputs
Target Audience:The project has completed its first year of funding and limited outreach and extension have been undertaken due to preliminary data generated as well as restrictions under current COVID-19 safety regulations. It severely impacted travel, sampling, appointment of both graduate and post-doctorate workers. Some in-person seminars and webinars did take place before and after meeting restrictions. The target audiences are mostly grape and wine industry professionals. Although interactions with fellow scientists for peer-reviewed feedback are also undertaken. The PI's on this project also met with the advisory board that represents fellow scientists, nurseries, vine testing facilities and grape and wine industry representatives in Oct and Nov of 2019. The next meeting will be scheduled after Thanksgiving 2020. Due to slower progress than expected because of several mitigating circumstances (COVID-19, natural disasters and more), the meeting has been delayed from its intended time of mid-November 2020 and will take place virtually. The PI, co-PI and collaborators met virtually in May 2020 to discuss progress, collaborations, and stumbling blocks. Changes/Problems:COVID-19 shelter-in-place and later travel and research safety measures at the different academic institutions have and had a significant impact on current milestones. The most important impact has been on new hires as it was extremely difficult to appoint new personnel especially with visa processing centers closed. Furthermore, access to field trials and laboratories for research were severely limited. Some objectives were majorly impacted and others marginally depending on the research activities needed and the individual personnel needs. However, progress have been made in most objectives on which we will build during the second year of funding. What opportunities for training and professional development has the project provided?In the first year of this project three undergraduate and five graduate students as well as six post-doctorates have been trained in the scientific methodology needed to achieve the goals of this project. This ranges from insect to plant sampling, viral analysis, plant physiological measurements, biochemistry, chemistry, and winemaking. New technology is also being investigated for disease detections and more. How have the results been disseminated to communities of interest?In-person seminars and workshops prior to March 2020 as well as scheduled zoom meetings to reach stakeholders during the pandemic. Anita Oberholster, Kaan Kurtural, Frank Zalom, and Mysore Sudarshana presented a UC Davis Dept. of Enology and Viticulture 'Office Hours' webinar on 'Grapevine Red Blotch Virus' on May 5, 2020. Anita Oberholster also presented at the Current Wine and Winegrape Symposium on February 11, 2020. Co-PI Kent Daane did two presentations as listed below: Current knowledge of grape red blotch associated virus vectors. NCPN-Grapes Tier II Committee Meeting. Davis, CA. Feb. 2020. Trying to understand the spread and control of "Red Leaf" in vineyards. Central Coast Wine Grape Seminar. Salinas, CA. Mar. 2020. In Oregon, an in-person all-day GRBV workshop was held in Salem, OR in Nov. 2019 that was attended by more than 60 industry members representing all phases of wine grape production. Seminars covered all aspects of GRBD including effects on grapevine physiology and potential cultural management strategies, entomology and potential pest management strategies, virology and diagnostics, and wine production and sensory. In fall 2020, OSU researchers organized a virtual GRBV webinar series (due to COVID-19 restrictions on in-person meetings), covering similar topic areas as in 2019. As of this reporting, three webinars have been held with an average of ~120 viewers each, and seven more are planned into Dec. 2020. What do you plan to do during the next reporting period to accomplish the goals?Vineyard sites identified and used during the 2019-2020 funding cycle will be investigated further to identify potential vectors, host plants and study insect biology. Furthermore, the synergistic impact of environment (climate) and GRBV impacts will be studied. Viticultural practices that showed promise in GRBV mitigation will be expanded upon. Furthermore, transmission studies with potential vectors will continue. Understanding the life cycle and biology of potential vectors are key to the development of successful management strategies. In the second year, cost-effective diagnostic tools for GRBV detection will be explored and economic analysis of GRBV impact on grape and wine quality (value) will commence.

Impacts
What was accomplished under these goals? Obj.1: Assess prevalence, rate of spread, and impact of Grapevine red blotch virus (GRBV) on production and fruit quality in US wine grape production areas. Subobj. 1.1: We have identified vineyards in California's Napa County and Sierra Foothills, and in Oregon's Willamette Valley and southern Oregon where grapevine red blotch disease (GRBD) is prevalent and patterns of GRBV is consistent with being spread by a vector that will serve as study sites for this project. Depending on vineyard, the number of vines surveyed ranged from 1,000 to 12,000 vines. Disease incidence ranged from 0.6 to 58.8% based on GRBD foliar symptoms at harvest, however, 100 leaf tissue samples were collected from each vineyard to confirm symptom-based observations. We will expand the surveys to more vineyards in 2020-2021 and repeat the surveys and symptom mapping for each vineyard for two to three additional years to determine the spread of GRBV within the vineyards. Subobj. 1.2: Activities started in Oct. 2020. Subobj.1.3: Three vineyard sites were identified in Napa and San Luis Obispo counties. A subset of vines was tested by qPCR and GRBV pos and neg data vines identified. Berry chemistry at harvest and yield data per vine were recorded. Wines were made from these vineyards as well as from subobj. 2.5 vine trials at Oakville Exp. Station. Winemaking is ongoing and chemical analysis and sensory evaluations will start in 2021. Subobj.1.4: Start in 2021. Obj.2: Identify and develop sustainable strategies to manage GRBV and its vector(s). Subobj. 2.1: Detailed studies were conducted on treehopper species in California and Oregon and leafhopper species in California. We determined seasonal phenology, distribution, and alternative hosts of Spissistilus festinus, Tortililus wikhami and T. albidosparsus and the leafhopper species Schaphytopius spp. It is clear that the treehoppers were not able to complete their lifecycle on cover crop Brassica spp. (Wild Mustard), but were able to complete their lifecycle on a range of other hosts, including apple, pear, oak, sorghum, pea, several grass species, and vetch. Generally, treehoppers were found mostly on vineyard edges, compared to the Schapytopius spp., which was found in relatively large numbers within the vineyard canopy. Subobj. 2.2: Controlled greenhouse and laboratory trials were conducted to determine the ability of treehopper populations to transmit GRBV. Collections of live S. festinus (Say), Stictocephala basalis (Walker), and T. albidosparsus (Stål) (Hemiptera: Membracidae) were made in proximity to commercial vineyards. One male Sp. festinus successfully transmitted GRBV, as determined by quantitative PCR (qPCR) and droplet digital PCR, to a single vine. Testing of individual insects using qPCR revealed that GRBV can persist inside the bodies of all three treehopper species; however, results to date showed no evidence following successive years of testing that GRBV can be transmitted by source populations of St. basalis or T. albidosparsus. Vector acquisition and inoculation of the GRBV causal agent is also being evaluated using field vines for acquisition and potted vines for inoculation. We have successfully shown S. festinus or Scaphytopius spp. on virus-infested vines have been positive for GRBV (e.g., acquisition). However, we have not yet observed transmission to clean vines at UC Berkeley for S. festinus and we are currently holding and testing vines for Scaphytopius. Subobj 2.3: We validated and published a phenology model to assist prediction of timing to initiate mowing to eliminate vineyard floor plant hosts of S. festinus in late winter and spring using field data collected in winter and spring 2020 at 3 northern CA commercial vineyard locations. A replicated experimental vineyard block was planted in southern OR that will enable comparison of clean cultivation to mowing vegetated vine row middles. The mowed plots were planted with a mix of grass and trefoil, and the groundcover is in the process of becoming established. Unmanaged orchard floor vegetation may serve as an overwintering reservoir for GRBV vectors in western US vineyards. We also developed and field-tested a substrate vibrational trap during 2020. The first prototypes were trialed in OR during 2020. Part of this work was characterization of unique vibrational signals produced by treehoppers. We successfully trapped T. albidosparsus in Northern Willamette Valley vineyards using the first prototype of the trap. Of particular importance is the adaptability of the trap and vibrational signals can be adapted to produce recorded vibrational signals of both treehoppers and leafhoppers. These traps can be used both for trapping as well as pest management. Subobj.2.4: Will start in 2021. Subobj.2.5: Three replicated trials testing various cultural practices were initiated in May 2020 on both healthy (GRBV-) and infected (GRBV+) vines in a commercial Pinot noir vineyard in OR and a Cabernet Sauvignon vineyard in CA. Experiments included manipulating vine water status (control and water deficit), crop load (100% and 30%), and vine nutrition. Experimental vines were confirmed for virus status during dormancy (2019-20), and experiments were laid out in a RCB design with 4-8 single-vine replicates. Yield and yield components (i.e. cluster number, berry number) were determined to primary and secondary metabolite analyses which are ongoing. In addition to agronomic data collected at harvest, leaf gas exchange, leaf nonstructural carbohydrates, leaf symptom development, and berry development were monitored regularly in selected GRBV- and GRBV+ vines throughout the growing season. Preliminary data indicate that restricting irrigation does not alleviate GRBV impact. Crop removal experiments revealed that carbon starvation is mediated by transient decreases in leaf photosynthesis and is not enough to overcome the effects of GRBD in grapevines. Subobj.2.6: To establish descriptors for prediction of early-stage red blotch infection, physicochemical changes of early-stage red blotch infected grape vine leaves were evaluated using FTIR, RGB color microscope and multispectral imaging technique. In addition, data for changes in anthocyanin, pectin and total phenolics were acquired. Currently we are analyzing data using PCA, regression models and machine learning models such as light GBM as a predictive model. Subobj. 2.7: A vineyard in Southern OR with history of GRBD has been identified. Nearly 300 vines were tested for GRBV in 2019 using PCR assay. In 2020, Loop Mediated Isothermal Amplification developed by Romero et al. (2019) were tested to understand field level detection ability of LAMP assays at different phenological stages. The samples collected at these stages from three canopy layers (base, middle, and top of canopy) will be compared and validated with PCR, qPCR, droplet digital PCR (ddPCR), and symptoms data. Obj.3: Implement and evaluate grapevine red blotch disease management programs. Subobj.3.1: Surveys of California and Oregon wine industry knowledge on GRBV will be completed by end of year 2. Subobj.3.2: In OR an in-person all-day GRBV workshop was held in Salem, OR in Nov. 2019 that was attended by more than 60 industry members. In CA three in-person presentations were given at different symposia in Feb. and Mar. 2020. In fall 2020, OSU researchers organized a virtual GRBV webinar series (due to COVID-19 restrictions on in-person meetings). As of this reporting, three webinars have been held with an average of ~120 viewers each, and seven more are planned into Dec. 2020. Similarly, CA held a 'Grapevine Red Blotch Virus' webinar on May 5, 2020 reaching 68 people live with a similar amount of people viewing the posted webinar later.

Publications

  • Type: Journal Articles Status: Accepted Year Published: 2020 Citation: Bick, E.N., C.R. Preto, and F.G. Zalom. 2020. Timing the implementation of cultural practices for Spissistilus festinus (Hemiptera: Membracidae) in California vineyards using a stage-structured degree day model. J. Econ. Entomol. 113: 25582562.
  • Type: Journal Articles Status: Accepted Year Published: 2020 Citation: Levin A.D. and A. KC. 2020. Water Deficits Do Not Improve Fruit Quality in Grapevine Red Blotch Virus-Infected Grapevines (Vitis vinifera L.). Frontiers in Plant Science 11:1292. DOI: 10.3389/fpls.2020.01292.
  • Type: Journal Articles Status: Accepted Year Published: 2020 Citation: Wilson, H., Yazdani, A. S., and Daane, K. M. 2020. Influence of riparian habitat and ground covers on threecornered alfalfa hopper Spissistilus festinus (Hemiptera: Membracidae) populations in vineyards. Journal of Economic Entomology 113(5): 23542361. doi: 10.1093/jee/toaa151