Advancing Vineyard Health: Insights and Innovations for Combating Grapevine Red Blotch and Leafroll Diseases (2025)
Chapter: Appendix C: Conclusions and Recommendations
Appendix C
Conclusions and Recommendations
This table includes all of the committee’s conclusions and recommendations, with research and actions identified as high priority designated as HP and those identified as medium priority designated as MP.
| GLD KNOWLEDGE GAPS TO ADDRESS TO HELP WITH DEVELOPING PROMISING SHORT- AND LONG-TERM SOLUTIONS |
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| GLD Biology, Virus-Host Interactions, and Host Defense Mechanisms |
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Conclusion 4-1: Despite decades of research, knowledge on the genetic and phenotypic complexity of GLD-associated viruses remains limited.
Conclusion 4-2: Fundamental studies using synthetic biology approaches can be applied to systematically investigate how different GLRaV genotypes influence disease outcomes. |
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Recommendation 4-1: Support research to generate more information about GLRaV-3 genetic variants on GLD development that could help guide GLD management.
Recommendation 4-2 (HP): Support foundational research to understand the intrinsic and extrinsic factors contributing to the efficient spread of GLRaV-3, including interactions with other vitiviruses. Research questions that need to be addressed include:
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Conclusion 4-3: Host factors required for GLRaV-3 infection and resistance in Vitis hosts have not been discovered, yet knowledge of these factors could create opportunities for developing novel control strategies.
Conclusion 4-4: The grapevine and GLRaV-3 genomes contain regions for generating non-coding RNAs whose role in infection and symptom development has not been explored. Conclusion 4-5: Further investigations into the extent of GLRaV-3 host range within (and beyond) Vitis may generate valuable information that could be exploited for GLD management. |
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Recommendation 4-3 (MP): Support research to identify host factors required for GLRaV-3 infection and resistance in Vitis hosts and to investigate the role of non-coding regions of grapevine and GLRaV-3 genomes in infection and symptom development.
Recommendation 4-4: Support research to examine the common and unique responses of red or black- and white-fruited wine grape cultivars to GLRaV-3. |
| GRBD KNOWLEDGE GAPS |
| GRBD Biology, Virus-Host Interactions, and Host Defense Mechanisms |
| Conclusion 4-6: Knowledge of the biological differences between the major GRBV variants (clade 1 and clade 2 isolates) is incomplete. |
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Recommendation 4-5: Support studies to advance understanding of the epidemiological consequences of GRBV genetic diversity and interactions with other viruses.
Research questions that need to be addressed include:
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Conclusion 4-7: Despite some progress in determining GRBV gene function, there are still major gaps in understanding the function of the GRBV genome with regard to specific roles of GRBV proteins in plant cells.
Conclusion 4-8: To date, virions have not been observed in GRBV-infected plants using microscopy; the lack of a tractable herbaceous model host that becomes systemically infected with GRBV limits the study of virus gene functions and virus-host interactions. |
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Recommendation 4-6 (MP): Support research to determine optimal model hosts (e.g., Pixie grapevine and/or herbaceous hosts) to facilitate the study of molecular GRBV-plant interactions and direct research efforts to transfer this knowledge to wine grape cultivars.
Research questions that need to be addressed include the following:
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| Conclusion 4-9: Current knowledge about latency and incubation periods after GRBV inoculation is insufficient. Questions about latency and incubation, which may vary among grapevine cultivars and under different environmental conditions, need to be refined because the answers could directly impact GRBD management recommendations to growers. |
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Recommendation 4-7 (HP): Support research to elucidate latency periods in different cultivars and rootstock-scion combinations, including the time from virus inoculation until vector acquisition, time until symptom expression, and time until the virus is detectable in plant and/or vector tissues.
Research questions that need to be addressed include the following:
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| KNOWLEDGE GAPS REGARDING EFFECTS OF MIXED INFECTIONS, ENVIRONMENTAL FACTORS, AND ROOTSTOCK-SCION INTERACTIONS |
| Complex Effects of Mixed Infections and Effects of Environmental Factors |
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Conclusion 4-10: Infection of grapevines with multiple viruses has been reported, but how mixed infections affect disease severity and evolution of GLRaVs and GRBV (or GLD and GRBD) has not been thoroughly investigated.
Conclusion 4-11: The effects of changing climatic conditions and other factors (biotic and abiotic) that modulate disease cycles, including temperature, humidity, carbon dioxide, ozone, drought, and vineyard management practices, on virus-vector-host interactions have not been determined. |
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Recommendation 4-8: Support research on the effects of mixed infections on GLRaV and GRBV evolution and the diseases they cause, as well as research on the effects of environmental factors, grapevine management practices, and changing climatic conditions on GLD and GRBD virus-vector-host interactions and epidemiology. Industry trends and stakeholder input could be used as a guide for prioritizing scion-rootstock combinations to use in experiments.
Research questions that need to be addressed include:
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| Identification of Rootstock-Scion Interactions Relevant to Virus Transmission |
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Conclusion 4-12: A variety of factors, including the scion cultivar, genetic background of rootstock, rootstock-scion interactions, virus profile in individual grafted vines, synergistic interactions between co-infecting viruses, and environmental conditions, could contribute to the presence and severity of symptoms from GLD and GRBD.
Conclusion 4-13: Resistant rootstocks along with other control strategies could help to mitigate negative effects of viral diseases in vineyards. |
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Recommendation 4-9 (MP): Support research on the presence and diversity of viral resistance in grapevine rootstocks with different genetic backgrounds in order to inform the incorporation of resistant rootstocks into virus control strategies.
Recommendation 4-10: Support research to determine the contribution of planting with infected, non-certified vines on virus spread. |
| KNOWLEDGE GAPS IN GLRaV-3 AND GRBV DIAGNOSTICS AND DETECTION |
| Cost-Effective Field-Deployable or Laboratory-Based Tools for Large-Scale Detection of GLRaV-3 and GRBV |
| Conclusion 4-14: There is a need for additional affordable diagnostic tools that can detect GLRaV-3 and GRBV infections early and are suitable for extensive use in commercial vineyards. |
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Recommendation 4-11 (HP): Support research to develop new, simple, and affordable high-throughput tests for GLRaV-3 and GRBV.
Research may include the following:
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Conclusion 4-15: Canine olfactory capacity could be used for GLRaV-3 and GRBV field detection, but the most effective, practicable, and cost-effective way to employ dogs for monitoring and early detection has yet to be determined. Canine detection may be best suited for nurseries rather than commercial vineyards.
Conclusion 4-16: Research to profile plant responses to GLRaV-3 and GRBV (and their vectors) may reveal unique VOC profiles that could establish a basis for the development of handheld EN or DMS devices for pathogen detection in the field. |
| Recommendation 4-12: Support research to identify VOCs unique to GLRaV-3 and GRBV infection or relevant vector infestations and determine the detection efficiency of VOC-based methods compared with other diagnostic tools. |
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Conclusion 4-17: Remote sensing technology has the potential for remote or in-field diagnosis of GLD and GRBD in individual vines; however, testing the efficacy of this approach will require scalable deployment of remote sensing devices for detection of infected vines in a large-scale area.
Conclusion 4-18: Remote sensing technology can be a part of a multi-layered system to guide sampling efforts by taking advantage of different spectra and resolutions to address specific goals. Conclusion 4-19: In addition to leaves, remote sensing devices can also potentially be used on other visible parts of the vines to detect grapevine viruses. |
| Recommendation 4-13 (HP): Support studies on the use of remote sensing technology to facilitate large-scale and early detection of GLD and GRBD in various tissues of commercial cultivars (including white-fruited cultivars) to increase the reliability, specificity, and sensitivity of detection with this technology. |
| Improved Methods for Detection of New GLRaV-3 and GRBV Variants |
| Conclusion 4-20: As GLRaV-3 and GRBV continue to evolve in vineyards and non-crop habitats, nucleic acid-based assays used for virus detection will need to be upgraded to enable reliable detection of newly emerged virus variants. |
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Recommendation 4-14: Support research to determine the feasibility of using RCA or other single-stranded circular DNA detection techniques to help detect GRBV at very low concentrations and for universal GRBV detection.
Recommendation 4-15 (HP): Support research aimed at improving GLRaV-3 and GRBV detection with nucleic acid-based methods that can be used in the field at large scales. |
| Optimal Sampling Strategies and Sample Size for Accurate Estimation of GLRaV-3 and GRBV Prevalence |
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Conclusion 4-21: Consensus is lacking on the most effective sampling technique and minimum sample size for accurately estimating GLRaV-3 and GRBV prevalence across different vineyard settings, regions, and nursery increase blocks.
Conclusion 4-22: Virus detection in vectors and other phloem-feeding insects may be an alternative to testing grapevines for viruses. |
| Recommendation 4-16 (HP): Support research evaluating optimal sampling methods and minimum sample size for accurate estimation of GLVaV-3 and GRBV prevalence in vineyards to inform the development of best practices for adopting new technologies and for integrating multiple detection methods to improve accuracy and scale (i.e., using both molecular methods and remote sensing technology). |
| Standards for Diagnostic Testing in Nurseries, Commercial Vineyards, and Certification Programs |
| Conclusion 4-23: Laboratory protocols for diagnostic testing of GLRaVs and GRBV have not been standardized. |
| Recommendation 4-17 (HP): Support efforts to develop standardized GLRaV-3 and GRBV diagnostic testing protocols that, once verified and certified, could be adopted by all laboratories that provide testing services for nurseries and commercial vineyards. |
| Conclusion 4-24: HTS offers robust virus detection and discovery of new GLRaV-3 and GRBV variants, but HTS protocols need to be standardized, affordable for large-scale testing, and validated for use in diagnostic virus testing. |
| Recommendation 4-18: Support efforts to develop universally accepted guidelines for using HTS in GLRaV-3 and GRBV diagnostics. |
| KNOWLEDGE GAPS REGARDING GLRaV-3 AND GRBV VECTORS |
| Vector Transmission |
| Conclusion 4-25: While there are reports about potential additional insect vectors of GRBV, there has not been definitive evidence that other insects in addition to TCAH can transmit GRBV to grapevines. |
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Recommendation 4-19 (MP): Support research to identify additional vectors of GRBV using rigorous experimental approaches.
Research to identify additional vectors should employ the following best practices:
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| Conclusion 4-26: There are gaps in the understanding of GLRaV-3 transmission, particularly with regard to the role of different vector species and their distribution in California; the mechanisms of GLRaV-3 acquisition and transmission; the transmission efficiency of diverse GLRaV-3 isolates; the acquisition, retention, and inoculation periods of all vector species; and how environmental factors influence GLRaV-3 transmission dynamics. |
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Recommendation 4-20 (HP): Support research on the mechanisms and timing of acquisition, retention, and transmission of all GLRaV vector species, as well as the influence of environmental conditions and host genotype on GLRaV transmission dynamics.
Research to identify additional vectors should employ the following best practices:
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| Virus-Vector Interactions |
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Conclusion 4-27: Knowledge of virus localization in the vectors and the precise role of viral retention sites in vector transmission would improve knowledge about the mode of transmission for GLRaV-3 and GRBV.
Conclusion 4-28: The roles of vector endosymbionts, genes, proteins, and metabolites mediating transmission have not been studied for GLRaVs or GRBV. This information is needed to understand transmission dynamics and to develop novel tools for disrupting transmission for the management of GLD and GRBD. |
| Recommendation 4-21: Support studies to identify interactions between GLRaVs and GRBV and their vectors that are required for transmission, as well as studies to identify genes, proteins, and metabolites involved in virus transmission to develop control strategies based on interference of virus-vector interactions. |
| Vector Plant Preference and Behavior Manipulation by GLRaVs and GRBV |
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Conclusion 4-29: GLRaV-3 and GRBV have only been reported to occur on Vitis and non-cultivated grapevines, but the relative contributions of different host species or varieties in GLRaV-3 or GRBV spread are not known.
Conclusion 4-30: Comprehensive studies to understand host plant utilization and preferences of vectors have not been completed. Conclusion 4-31: Vector behavior might change in response to plant infection by GLRaV-3 and GRBV (i.e., changes in insect behavior mediated through the host plant), which may affect the settling, feeding, fitness, and dispersal behavior of the vectors. |
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Recommendation 4-22 (MP): Support research on virus-vector-host interactions to determine how the different species or varieties of Vitis and non-cultivated grapevines contribute to virus spread, as well as how GLRaV-3 or GRBV infection of the host can alter vector behavior.
Recommendation 4-23 (MP): Support research to broaden the understanding of complex interactions among the virus, vector, and host to enable the development of models of disease spread and strategies to prevent disease transmission. Possible research approaches include the following:
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Conclusion 4-32: There are major knowledge gaps regarding TCAH overwintering behavior, seasonal GRBV spread to grapevines, and differences among distinct grapevine-growing regions in California.
Conclusion 4-33: Population models may help predict TCAH generation development associated with TCAH movement into vineyards; models may need to include information other than temperature to accurately predict population development and movement behavior. |
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Recommendation 4-24 (MP): Support research on the seasonal virus spread of GRBV by TCAH, focusing on year-long TCAH abundance and overwintering behavior throughout California.
Studying seasonal spread of GRBV by TCAH could involve the following:
Recommendation 4-25: Support research to investigate TCAH host preference and movement behavior, which could help in the development of a trap crop strategy for intercepting TCAH at vineyard borders. Studying TCAH host preference could involve the following:
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| RESEARCH AND ACTIONS THAT MAY YIELD THE MOST PROMISING MANAGEMENT SOLUTIONS |
| Clean Plants |
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Conclusion 5-1: Using clean planting material is the first line of defense in establishing healthy vineyards because viruses can spread via clonal propagation of grapevines.
Conclusion 5-2: There are concerns regarding the reliability of results from testing laboratories; these stem from questions about whether testing for GLRaVs and GRBV is being done using the most up-to-date protocols to detect all variants and from the fact that commercial testing laboratories are largely unregulated in their technical standards, potentially resulting in inconsistencies in diagnostic results across laboratories. |
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Recommendation 5-1 (HP): Encourage the adoption and implementation of higher sanitary standards in registered mother blocks using robust, evidence-based sampling strategies; state-of-the-art, sensitive, and reliable diagnostic methods and roguing of infected vines to maintain disease-free stock and provide clean planting materials for growers.
This could include engaging FPS in exploring the potential of developing a ring-test process or similar validation scheme to better assure the validity and reliability of diagnostics from laboratories working with the industry. |
| Roguing Infected Vines |
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Conclusion 5-3: Roguing has been shown to be effective in GLD management and in mitigating GRBD spread, but it can be difficult for growers to justify removing infected but still productive vines and replacing them with new vines that will not immediately bear fruits. Both roguing and roguing followed by replanting also complicate viticultural practices in vineyards.
Conclusion 5-4: There is insufficient information available for developing effective roguing schemes for GLD and GRBD. Specifically, more data are needed on the determination of threshold decision points, the cost-effectiveness of roguing under various conditions, and the influence of movement patterns and flight behavior of TCAH and other potential GRBV vectors on the spread of GRBD. Conclusion 5-5: Roguing schemes need to be optimized for California production regions in light of differences in market economics and in the environmental conditions that affect vector and virus dynamics. Additional epidemiological research may reveal the optimum roguing and replanting schemes for both GLD and GRBD in different production regions and for vineyards with differing business models. |
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Recommendation 5-2 (HP): Support research to develop optimal roguing and replanting schemes and techniques to manage GLD and GRBD and to facilitate their implementation by growers.
This could include studies to determine:
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| Vector Management |
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Conclusion 5-6: Contact insecticides are not effective in controlling mealybugs due to the cryptic nature of mealybug behavior. Systemic insecticides will not likely disrupt feeding quickly enough to stop transmission of GLRaVs, but they could be effective in reducing mealybug populations. In addition to their crypsis, the sessile nature of mealybugs suggests that systemic insecticides, even if slow acting, could reduce secondary spread of GLRaV-3. Primary spread from mealybugs entering vineyards would require a more rapid kill time.
Conclusion 5-7: Knowledge of factors that affect the efficacy of insecticides (e.g., physiology of the plant, environmental conditions, soil type, insect behavior, insecticide application method) is important in developing improved guidelines for their application. Conclusion 5-8: Reliance on a small set of insecticides for mealybug control increases the likelihood that mealybugs will develop resistance to them. Conclusion 5-9: A better understanding of GRBV acquisition and transmission dynamics is needed to improve the effectiveness of insecticide application as a control tactic against TCAH, and appropriate economic or action thresholds are needed to guide insecticide application programs. |
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Recommendation 5-3 (HP): Support research to determine the optimal conditions for the application of systemic insecticides to achieve better mealybug control.
Recommendation 5-4 (HP): Develop and implement insecticide resistance management programs and support research to develop new active ingredients for mealybug management, including by evaluating the efficacy of natural products, such as plant essential oils, that could provide additional options for both organic and conventional vineyards. Recommendation 5-5 (HP): Support research to determine the optimum conditions for the application of insecticides to achieve better TCAH control and to establish economic or action thresholds to guide insecticide application programs. |
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Conclusion 5-10: Mating disruption tends to be most effective in reducing mealybug populations when used over longer timescales and on larger spatial scales. More information is needed to determine the optimum number and type of pheromone dispensers to use to ensure coverage in time and space while reducing the cost of employing this technique.
Conclusion 5-11: Mating disruption has been shown to decrease vine mealybug populations and damage, but no studies have been done to determine the impact of mating disruption on GLRaV-3 spread. Conclusion 5-12: Knowledge about the mating disruption mechanism in mealybugs (i.e., competitive or noncompetitive) and about mealybug biology, behavior, and generation development could help identify optimal times for dispersing pheromones to disrupt mating. In-field or predictive population models of mealybug generation may also help guide timing of mating disruption activities. Conclusion 5-13: Studies are needed to determine how long mating disruption can suppress mealybug populations and guide the use, frequency, and timing of insecticide applications to keep mealybug populations low. Conclusion 5-14: Studies are needed to determine and compare the short- and long-term efficacy and economics of various techniques for applying pheromones in mating disruption programs. Conclusion 5-15: Studies are needed to inform integrated pest management (IPM) decision making by elucidating the potential impacts of biological control tactics such as leveraging natural enemies alongside mating disruption programs. Conclusion 5-16: Mating disruption is not likely to be a practical management tactic for TCAH, as leafhoppers do not appear to use long-range sex pheromones to locate mates but instead use substrate-borne vibrational signals that occur off of grapevines. |
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Recommendation 5-6 (HP): Support research to generate information needed for improving the efficacy of mating disruption for mealybug control and to determine the benefits (economic and otherwise) of employing this technique as part of an integrated approach to manage insect vectors in grapevines.
This could include studies to determine:
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| Conclusion 5-17: Emerging research suggests that the use of UV-C light could help to suppress pest populations without negatively impacting crop yield. However, further refinement of this method is needed to make it an effective tool for vine mealybug management in vineyards. |
| Recommendation 5-7: Support research to further refine UV-C treatment of grapevines to complement other IPM strategies to suppress field populations of mealybug vectors in vineyards. |
| Cultural Control |
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Conclusion 5-18: Removal of vegetation (such as legumes, which serve as reproductive hosts) between rows of grapevines in the spring may reduce populations of TCAH within vineyards, but information about the costs and benefits of this practice is lacking.
Conclusion 5-19: Trap crops have been shown to reduce the spread of non-persistently transmitted viruses, but the feasibility of using trap crops to control GRBV, which is persistently transmitted by TCAH, has not been determined. |
| Recommendation 5-8 (MP): Support research to determine the costs and benefits of removing vegetation that harbors TCAH in and around vineyards and the use of trap crops to inform grower decision making regarding the employment of these methods for managing TCAH in vineyards. |
| Biological Control |
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Conclusion 5-20: Parasitoids, predators, and EPFs have been identified that could be further studied for development as biocontrol agents for use in IPM programs targeting mealybugs.
Conclusion 5-21: EPF strains currently available for use on grapevines require repeated applications to be effective and may lose virulence when exposed to high temperatures and UV light; identification and mitigation of factors that degrade EPFs could help improve their utility in IPM programs or in situations where the use of chemical insecticides is not an option. Conclusion 5-22: Because ants support mealybug survival in vineyards, more emphasis on ant management is needed to help suppress mealybug populations and increase the impact of other biocontrol strategies. Conclusion 5-23: There is a dearth of research on biocontrol of TCAH; if research is pursued, it will be important to address the impacts of ants, which tend TCAH nymphs, on potential biocontrol agents. |
| Recommendation 5-9: Support research to find, evaluate, and develop more efficacious biocontrol agents and guide their integration with other management tactics within IPM programs or in situations, such as organic production systems, where chemical insecticides are not an option for vector management in grapevines. |
| Sanitation |
| Conclusion 5-24: Cleaning harvesting and pruning equipment, tools, and workers’ protective equipment has been shown to limit the dispersal of mealybugs; however, there is a general lack of publicly available information about best practices for sanitation in vineyard settings, and the degree to which sanitation measures are employed is unknown. |
| Recommendation 5-10 (HP): Support research to determine the most effective and practical farm and worker equipment sanitation measures and harvesting and pruning strategies that can help minimize the spread of insect vectors. |
| Physical Barriers |
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Conclusion 5-25: Information about TCAH flight behavior and movement could be used to devise and evaluate possible barriers such as screening fences and kaolin clay to impede TCAH movement from riparian areas to vineyards.
Conclusion 5-26: Installing protective screens over citrus trees is effective for keeping them disease-free; however, this tactic is costly and may be most applicable for smaller acreages of crops with a high return on investment. Conclusion 5-27: Covering individual vines with mesh bags may be a less costly tactic for vector exclusion; this approach has been widely adopted by citrus growers in Florida as an IPM tool to control HLB. Conclusion 5-28: Reflective mulches have the potential to reduce leafhopper populations in grapes without any detrimental effects on vine physiology and berry quality; however, these mulches degrade over time. |
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Recommendation 5-11 (MP): Support research to evaluate the efficacy of physical barriers in deterring TCAH movement from natural or vineyard-adjacent habitats to vineyards.
Recommendation 5-12 (MP): Support research to evaluate the efficacy of reflective mulches in reducing the abundance of insect vectors in vineyards and research on improving the longevity and durability of reflective mulches. |
| Areawide Pest Management |
| Conclusion 5-29: Areawide pest management, which is well suited for pests that move beyond the boundaries of individual farms, can help in managing insect-vectored viruses in vineyards across larger areas. |
| Recommendation 5-13 (HP): Support efforts to develop areawide GLD and GRBD vector management programs for regions of California with different threat levels from these diseases, along with activities to encourage grower participation in these programs. |
| Coordinating Management of Multiple Vectors |
| Conclusion 5-30: Pierce’s disease, GLD, and GRBD are all spread by hemipterans, and insecticides used to control one vector species may also affect the other vectors; hence, it is important to coordinate vector management tactics for vectors of all three diseases. |
| Host Plant Resistance to Viruses and Vectors |
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Conclusion 5-31: Host plant resistance is an effective and sustainable tactic for controlling vector-borne virus diseases, especially when used as a component of an IPM strategy.
Conclusion 5-32: The choice of approach (traditional breeding or bioengineering strategies such as transgenic approaches or gene editing) for achieving host resistance has implications for the length of time required to create a resistant grapevine cultivar, the expediency of obtaining regulatory approval, and consumer acceptance. Conclusion 5-33: RNAi-based resistance to plant viruses has been shown to be highly effective and durable for annual and perennial crops; this approach could produce a resistant grape cultivar within a relatively short period of time. Conclusion 5-34: Genome editing for developing host resistance to GLRaVs, GRBV, and their vectors requires knowledge of virus-host and vector-host interactions and the collaborative efforts of researchers from multiple disciplines. Conclusion 5-35: Gene-edited crops are not subject to the same regulatory processes as genetically modified organisms in the United States and could therefore lead to faster commercialization of a resistant grapevine cultivar; however, information on virus-host and vector-host interactions necessary for determining appropriate edits is not yet available. |
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Recommendation 5-14 (HP): Support research using traditional and bioengineering approaches for developing GLD and GRBD resistance; when conducting resistance screening assays, the biological vector should be used as much as possible.
Recommendation 5-15: Support research on the use of transgenic RNAi for developing plants with virus and/or insect resistance; creating a trangene(s) combining resistance to GLRaV-3 and GRBV could provide effective resistance to both viruses and help reduce the burden of regulatory approval. Recommendation 5-16: Develop grapevine as a model system to advance fundamental understanding of the entire network of virus-host interactions across cultivars. Recommendation 5-17 (HP): Establish multidisciplinary and trans-institutional collaborations to enhance synergies in pursuing bioengineering approaches, such as RNAi-mediated resistance and CRISPR/Cas-based genome-editing technologies, as an alternative to traditional breeding for resistance against GLD and GRBD. |
| Cross-Protection Strategies |
| Conclusion 5-36: The identification of a mild and asymptomatic strain of GLRaV-2 (GLRaV-2-SG) and a mild strain of GLRaV-3 (ID45) point to the potential to apply cross protection in GLD management. |
| Recommendation 5-18: Support research to explore cross protection as a possible tactic for managing GLD. |
| Risk Assessment Models to Guide Decision Making |
| Conclusion 5-37: The Bayesian Belief Network model, which can be used to assess the probability of GLRaV-3 and GRBV outbreaks, could be helpful in informing GLD and GRBD management decision making. |
| Recommendation 5-19: Support research to evaluate the potential utility of the Bayesian Belief Network model in informing growers’ decisions related to GLRaV-3 and GRBV management. |
| CONSIDERATIONS FOR FUTURE RESEARCH ON GRAPEVINE VIRUSES AND DISEASES |
| Genetic Pest Management Strategies |
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Conclusion 6-1: Genetic pest management strategies, in which the insect vector is modified rather than the plant, offer opportunities to curb the spread of disease by reducing vector populations or their ability to transmit viruses. The biology of mealybug vectors makes them good targets for genetic pest management.
Conclusion 6-2: Multidisciplinary research teams composed of molecular biologists, entomologists, modelers, and field biologists or extension researchers are needed to develop genetic pest management strategies and to predict their real-world implications. Conclusion 6-3: Sociological aspects and consumer acceptance are important considerations when developing genetic pest management strategies. |
| Recommendation 6-1: Support basic research to enable genetic pest management strategies for GLD and GRBD vectors and support modeling and sociological research to predict whether these strategies will be effective in the field and be accepted by the public. |
| INSIGHTS AND ADDITIONAL RESEARCH DIRECTIONS FROM OTHER PATHOSYSTEMS |
| Tactics for Controlling Insect Vectors |
| Conclusion 6-4: RNAi has the potential for use in managing viruses, their insect vectors, and potential other grapevine pests. Applied RNAi biopesticides should have narrow activity based on target-specific dsRNA that will trigger RNAi suppression only in the targeted organism and no activity in other beneficial insects. Genetically engineered plants expressing dsRNA may more effectively manage mealybugs and other insects that reside under bark where it is hard to contact them with insecticide sprays. |
| Recommendation 6-2 (MP): Consider supporting interdisciplinary research teams to advance RNAi research for the suppression of vectors in vineyards. |
| Conclusion 6-5: Nanobodies present a promising strategy for managing grapevine viruses like GLRaV-3 and GRBV, given their high specificity and efficacy in targeting viral proteins. However, successful application in vineyards depends on overcoming challenges related to scalable production, cost-effectiveness, and long-term stability under field conditions. |
| Recommendation 6-3: Consider supporting research to advance the development of nanobodies for the control of GLRaV-3 and GRBV through transgenic or exogenous approaches. This could include monitoring and funding multidisciplinary, collaborative efforts to refine nanobody production methods to improve scalability and affordability, as well as supporting field trials to rigorously assess the performance and durability of nanobodies in diverse vineyard environments to ensure they are a practical and sustainable solution for virus management. |
| Conclusion 6-6: Trunk injection has been used for delivering pesticides directly to the plant vasculature to control diseases in citrus, almond, apricot, and palm trees. This delivery method, which is more precise and has a lower risk of non-target effects, may be applicable in controlling phloem-limited pathogens as well as phloem-feeding insects in vineyards. |
| Recommendation 6-4 (MP): Consider supporting research to investigate the potential utility of trunk injection to control vectors and viruses with various pesticides (including new approaches such as RNAi and nanobodies) in grapevines. |
| Prediction Models and Risk Indexes as Management Tools |
| Conclusion 6-7: Models have been valuable tools for stakeholders to understand pest risk, apply practices that mitigate risk, and know critical windows of time for scouting and management activities. |
| Recommendation 6-5 (HP): Fund research that will lead to the development of publicly available, regionally relevant insect population models and disease risk models that can be used to guide local and areawide management activities for GLD and GRBD. |
| ENGAGING A WIDER RANGE OF RESEARCHERS IN ADDRESSING RESEARCH NEEDS |
| Conclusion 6-8: Researchers who are not familiar with the PD/GWSS Board research and outreach grant program may not be aware that this program also funds research on other grapevine viruses and pests, such as GLRaVs and GRBV and their vectors. Allocating funding specifically for early and mid-career scientists may help expand the pool of researchers working on grapevine virus diseases. |
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Recommendation 6-6 (HP): To draw in diverse researchers, consider changing the name of the PD/GWSS Board research and outreach grants to accurately reflect the scope of its RFPs, which include multiple grapevine virus diseases and their insect vectors.
Recommendation 6-7: To increase awareness of the work of the PD/GWSS Board and bring in new scientists to address grapevine vector-borne diseases of national and global significance, expand efforts to promote the funding portfolio and RFPs to more diverse research communities via social media, professional societies, and other mechanisms. Recommendation 6-8 (MP): Consider offering specific funding for early- and mid-career researchers to encourage engagement in grapevine virus diseases research and build a network of scientists to address long-term questions. |
| Conclusion 6-9: In addition to traditional RFP cycles, research may be funded through other mechanisms, such as inviting researchers to address specific topics. |
| Recommendation 6-9 (HP): Consider developing additional funding mechanisms to address particular needs for GLD or GRBD research, such as through inviting specific researchers to address particular knowledge gaps or accepting off-cycle proposals for projects that have potential to generate information for dramatically improving GLD and GRBD management. |
| ADDRESSING THE NEED FOR LONGER-TERM STUDIES AND REPLICABILITY |
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Conclusion 6-10: The study of complex systems such as vector-borne diseases in perennial crops may take longer than three years and require more funding to accurately describe disease biology and make recommendations for disease or vector management.
Conclusion 6-11: Replicability of results is an important issue, especially with GRBV because of knowledge gaps in virus biology and vector transmission. Conclusion 6-12: Collaborative research proposals provide a mechanism to support multiple research teams addressing the same research questions. |
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Recommendation 6-10 (HP): Consider funding longer-term projects (lasting more than three years), such as studies that advance control recommendations, translational research, and projects that integrate economic and societal impacts.
Recommendation 6-11 (HP): Consider funding research to replicate experimental results in more than one location and with different research teams to obtain more robust and reliable insights. Recommendation 6-12: Consider new ways to leverage available funds using different proposal and award structures to encourage collaboration. |
| KNOWLEDGE SHARING AND COLLABORATIVE RESEARCH |
| Interdisciplinary Approach to Vector-Borne Disease Research |
| Conclusion 6-13: GLD and GRBD research would benefit from an interdisciplinary approach, wherein findings and perspectives of experts from various disciplines and growers are integrated to gain a holistic understanding of a complex problem. |
| Recommendation 6-13: Consider allocating funding specifically for research projects that employ an interdisciplinary approach. |
| Fostering Information Sharing, Interactions, and Collaboration |
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Conclusion 6-14: Sharing of information and collaboration among researchers is essential to interdisciplinary research and to facilitating a “systems thinking” approach for solving complex problems.
Conclusion 6-15: Groups such as WERA20 and EVCWG have effectively facilitated the dissemination of information and the exchange of ideas about virus diseases in crops among researchers, extension agents, growers, and other stakeholders. |
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Recommendation 6-14 (MP): As an alternative to the annual Pierce’s disease symposium, consider coordinating with other organizations to hold sessions on GLD and GRBD at events such as the annual conference of the American Society for Enology and Viticulture and the Unified Wine and Grape Symposium. These sessions could also serve as a platform to facilitate new collaborations involving scientists working on other grape diseases or working in other wine grape producing regions.
Recommendation 6-15: Consider enhancing PD/GWSS Board participation in WERA20 annual meetings through sponsorship of workshops to build synergies and facilitate cross-pollination of strategies and technologies across specialty crops. Recommendation 6-16 (HP): Explore the feasibility of creating a working group, supported by the wine grape industry and funded by another entity, that can facilitate information sharing and foster collaboration among GLD and GRBD researchers. |
| EDUCATION AND OUTREACH |
| Information Dissemination |
| Conclusion 6-16: Gaps in communication and knowledge dissemination contribute to the underutilization of GLD and GRBD management practices, underscoring the importance of having more effective educational and outreach strategies as knowledge of GLD and GRBD advances. |
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Recommendation 6-17: Consider allocating funds for projects to advance innovative educational and outreach strategies to help improve grower and extension educator knowledge of GLD and GRBD and strategies for their control.
Recommendation 6-18 (HP): Provide opportunities for funded researchers to share findings and recommendations regarding grapevine viruses via a dedicated website or a virtual town hall that facilitates interactive discussions about GLD and GRBD among researchers, extension agents, and growers. |
| Grower Adoption of Disease Control Strategies |
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Conclusion 6-17: Successful control of vector-borne diseases relies not only on understanding the pathosystem and devising strategies to control the pathogen or its vector, but also on what growers decide to do, known as “willingness to adopt” (e.g., to participate in areawide pest management programs or not).
Conclusion 6-18: Social science research has shown that social networks play an important role in social learning (learning by observing others) and subsequently, in the adoption of innovations (e.g., pest management practices). |
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Recommendation 6-19 (HP): Support research to better understand the sociological aspects of managing vector-borne diseases through collective action (i.e., areawide pest management) and find ways to increase grower participation in areawide pest management programs.
Recommendation 6-20 (HP): Support research on understanding and improving the flow of information across grower social networks and on outreach efforts to understand the drivers and barriers to successful adoption of GLD and GBRD management practices. |
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