- Author: Ben Faber
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- Author: Greg Douhan and Georgios Vidalakis
The California Department of Food and Agriculture (CDFA) regularly performs surveys across the San Joaquin Valley (SJV) to monitor for potential insect and pathogen issues for California agricultural producers. In October of 2021, CDFA inspectors began performing a multi pest survey for citrus in addition to the routine inspections for the Asian citrus psyllid and Huanglongbing in residential properties. In March of 2022, a surveyor came across some unique leaf symptoms on a residential lemon tree in the city of Tulare, CA. Samples from the initial find in Tulare County were sent to CDFA's Plant Pest Diagnostic Center in Sacramento, California (https://www.cdfa.ca.gov/plant/PPD/) and tested positive for the citrus yellow vein clearing virus (CYVCV), a putative new member of the genus Mandarivirus associated with the yellow vein clearing disease of citrus. This result was subsequently confirmed by the United States Department of Agriculture, Plant Pathogen Confirmatory Diagnostics Laboratory (https://www.aphis.usda.gov/aphis/ourfocus/planthealth/ppq-program-overview/science-technology/plant-pathogen-confirmatory-diagnostics-laboratory).
After consulting with the United States Department of Agriculture regarding sampling strategies, delimitation surveys are continuing to determine the extent and distribution of CYVCV in California. Once a positive tree has been identified, CDFA returns to the property and surveys all citrus trees within a 1-mile delimitation radius around the detection, additionally CDFA conducts delimitation surveys in arcs around the delimitation core. Around the initial detection core in the city of Tulare, CDFA has already conducted 7-mile and 6-mile arcs and around the new core CDFA is conducting a 4-mile arc delimitation survey. All samples are sent to CDFA's Plant Pest Diagnostic Center for molecular testing. A total of 578 trees have tested positive so far for CYVCV in the city of Tulare and recently two trees tested positive in the city of Visalia, but no findings in commercial citrus groves in the SJV have been reported thus far.
Symptoms of CYVCV disease include vein clearing when viewed from the top of the leaves and water soaking when viewed from the bottom of the leaves. Symptomatic leaves may also be curly or have some crinkling. Researchers from other parts of the world have reported that the virus is vectored by the citrus white fly (Dialeurodes citris) and several aphid species (Aphis spiraecola, A. craccivora, and A. gossypii.), all of which occur in California. Currently scientists are performing experiments to determine vector transmission under California conditions. There have also been single reports of virus detection on some weed species and CYVCV can also spread by grafting techniques as well as by pruning tools.
The disease was first identified in Pakistan in 1988 on lemon and sour orange trees. The virus disease was then found in India on ‘Etrog' citron, ‘Rangpur' lime, sour orange, and lemon trees in India in 2003. The disease was subsequently found in Turkey, Iran, and China. Lemons and sour orange seem to be the most susceptible types to this disease, but most citrus species, varieties, and hybrids tested thus far developed the disease with varying symptomatology. Finally, there has also been one report of CYVCV infecting wild grapes in Turkey in 2020. In the study from Turkey, the infected wild grapevine was climbing on an infected citrus tree. There was no evidence of serious impacts on the wild grapevine.
It is also important to note here that the citrus yellow vein clearing virus (CYVCV) is not related to and should not be confused with the citrus yellow-vein associated virus-like RNA (CYVaV). CYVaV was recently identified to be associated with the citrus yellow-vein disease reported once in California in the 1950s in a few limequat trees, but since then, it has not been reported again in California.
The report of CYVCV from the city of Tulare, California was the first account of this virus in North America, and the impacts of this disease on the citrus economy are not clearly known at this time. Researchers in China have reported up to 80% loss in production in some lemon groves but the losses are usually less in most instances. CDFA continues with delimitation surveys around the positive finds to define the extend of the infestation and if any commercial citrus operations, groves or nurseries, are infected or are at risk. For updates on this and other citrus pests in California visit ‘Citrus Insider' at https://citrusinsider.org/.
- Author: Ben Faber
Seven entities recently received $21.7 million to conduct research into combating and preventing HLB at the farm level. The funding is from the U.S. Department of Agriculture's National Institute of Food and Agriculture (USDA NIFA) Emergency Citrus Disease Research and Extension program.
The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) received the majority of the funding, more than $16 million.
PROJECTS LED BY UF/IFAS
The largest grant, at approximately $8.6 million, is for development, evaluation and delivery of citrus HLB management approaches by targeting its nature as a pathogen-triggered immune disease. The principal investigator is Nian Wang. The goal is to develop HLB management approaches for existing groves and non-transgenic HLB-resistant and HLB-tolerant citrus varieties.
Other UF/IFAS projects are:
- A coordinated network for the improvement of HLB research and Extension outputs, funded at $2 million. Megan Dewdney is the principal investigator. The project tackles the task of gathering and organizing the research findings available to growers.
- Targeted production of non-transgenic HLB-tolerant trees through complementary approaches, funded at approximately $1.5 million. Zhonglin Mou is the principal investigator. The first goal of this project is to produce non-genetically modified HLB-tolerant citrus trees by editing or silencing the promising target genes.
- HLB-resistant rootstock candidates for the citrus industry: Validating and understanding disease resistance, funded at approximately $1.2 million. The principal investigator is John Chater. This project will advance knowledge about why some rootstocks appear to be more tolerant to HLB than others.
- Providing individual protective covers and brassinosteroids to prolong health and improve fruit yield and quality in newly planted trees, funded at $800,000. Fernando Alferez is the principal investigator.
- Toward a reliable insect cell culture-based technique for culturing CLas bacteria (the causative agent of HLB), funded at approximately $793,000. Kirsten Pelz-Stelinski is the principal investigator. The project aims to have a culture system that serves as an essential research tool for increased understanding of CLas biology and for effective, rapid screening of antimicrobial agents against CLas.
- Accelerating the delivery of conventionally developed HLB-tolerant citrus scions and rootstocks as pathogen-free budlines for replicate multi-site testing, funded at approximately $536,000. The principal investigator is Jude Grosser. Successful adoption of this technology will reduce the current clean-up time by 1.5 to 2 years, and significantly increase the number of selections that can be processed.
PROJECTS LED BY OTHER INSTITUTIONS
- Virus-induced gene silencing using insect specific viruses to manipulate psyllids as a strategy to control HLB is a University of California-Davis project led by Yen-Wen Kuo.
- A method for generating an optimally attractive scent for Asian citrus psyllid biocontrol is a University of Connecticut project led by Alexander Aksenov. UF/IFAS' Lukasz Stelinski is a co-investigator.
- Endophytes as sources of antimicrobials to control HLB is being led by Kateel Shetty of Florida International University.
- Scalable low-cost organic nanocarriers for efficient foliar uptake of registered anti-HLB agents is a Purdue University project led by Kurt Ristroph.
- Citrus yellow vein-associated virus induced gene silencing vector for vaccinating seedlings and controlling HLB in infected fruit-bearing trees is a University of Maryland project led by Anne Simon.
- Molecular strategies to block psyllid transmission of the HLB pathogen is a USDA Agricultural Research Service project led by Michelle Heck.
Sources: USDA NIFA and UF/IFAS
Deformed HLB-infected fruit
- Author: Ben Faber
SANTA BARBARA COUNTY CITRUS UPDATES
Save the Date! Santa Barbara County Citrus Meeting
Thursday, June 15, 9 am - 12 pm, at the County Employee University Building, 267 Camino del Remedio, Santa Barbara
Intended for citrus growers, PAC/QAC/QAL/PCA holders, and farm labor contractors in Santa Barbara County. Topics include updates on ACP/ HLB treatments & research, regulatory updates on HLB and other citrus pests, and an update from the new County Ag Commissioner, Jose Chang. DPR CEUs have been requested. RSVP to cressidasb@gmail.com, or call 805 681-5600 for more information.
Asian Citrus Psyllid Update
The next ACP Area Wide Management treatment window for growers will be September 3 - 23. In the meantime, please continue to regularly monitor new flush for signs of the psyllid, and consult with your pest management professional if ACP is present. Tender new citrus flush is ideal habitat for ACP to feed, lay eggs and build new populations, and an increase in ACP numbers and feeding can increase the risk of HLB. If your citrus is no longer being cared for or is not worth the resources required to protect it from ACP and HLB, consider removing it.
HLB Quarantine Update
As of May 26, a total of 5.115 trees and 709 ACP have been confirmed positive for the bacterium that causes HLB. Trees confirmed positive are treated for ACP and removed, and the HLB quarantine may be expanded. Additional ACP treatments and HLB detection surveys are conducted on a recurring basis to remaining citrus within 250 meters of each detection.
Counties where HLB has been detected via PCR testing are Los Angeles, Orange, San Diego, Riverside, San Bernardino and San Diego, with the majority of detections in Orange County. To see a map of the current HLB quarantine areas, and other details of locations and numbers of HLB detections, please visit maps.cdfa.ca.gov/WeeklyACPMaps/HLBWeb/HLB_Treatments.pdf.
HLB Detection Response Guide for Growers
To ensure California citrus growers are well prepared in the event of a potential commercial grove detection of Huanglongbing (HLB), the Citrus Pest and Disease Prevention Program (CPDPP) has developed the Response Guide for a Confirmed HLB Positive Detection in a Commercial Grove, which details the steps taken by CDFA and actions required of the property or grove owner, as outlined in CDFA's Action Plan and Information for Citrus Growers/Grove Managers.
Citrus Pest and Disease Prevention Committee Meetings -- Webinar and In Person
All meeting agendas and eventually the minutes are posted at www.cdfa.ca.gov/citrus committee/. The 2022-23 schedule for the Full Committee is here, and the schedule for Subcommittees is here.
Upcoming Meetings
- Science Subcommittee, Thur June 8 at 1 pm, agenda and webinar link
- Finance Subcommittee, Tue June 13 at 2 pm, agenda and webinar link
- Interim CPDPC Full Committee, Wed June 28, agenda pending
- Operations Subcommittee, Wed July 12 at 9 am, agenda pending
- Outreach Subcommittee, Wed July 12 at 1:30 pm, agenda pending
- CPDPP Full Committee, Wed August 9 at 9 am, agenda pending
All meetings are free and open to the public to listen to or make public comment. Meetings are currently in person and accessible via phone and/or webinar. Links to register for and join meetings are included in agendas when posted.
For a list of current committee members, click here.
Additional ACP/HLB Resources
- CDFA Citrus Division website: https://www.cdfa.ca.gov/Citrus/
- General ACP/HLB
oInformation on the state ACP/HLB program including maps, quarantine information, and a signup option for email alerts: citrusinsider.org/
oBiology of ACP and HLB, detection maps and recommendations for monitoring, eradication and management: ucanr.edu/sites/acp/
oUC IPM recommendations for ACP insecticides
oWeb-based map to find out how close you are to HLB: ucanr.edu/hlbgrowerapp
oVideo on Best Practices in the Field, available in English and Spanish
oSpanish-only ACP/HLB presentation video presentation and audio-only recording.
- Research
oLatest Science Advisory Panel Report
oUC Ag Experts Talk presentations on management of various citrus pests and diseases are available for viewing here and here on YouTube.
oSummaries of the latest research to combat HLB: ucanr.edu/sites/scienceforcitrushealth/
oScience-based analyses to guide policy decisions, logistics, and operations: www.datoc.us
- Regulatory/Quarantine
oSign up for program updates from the Citrus Pest and Disease Prevention Division at www.cdfa/signup-email-updates.
oRegulatory requirements for moving bulk citrus: Information for Citrus Growers
oSummary of regulatory requirements in the event of an HLB detection in commercial citrus: citrusinsider.org/Regulatory-Flyer
oSanta Barbara County Ag Commissioner's Office
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Cressida Silvers
CA Citrus Pest and Disease Prevention Program
ACP/HLB Grower Liaison
Ventura, Santa Barbara and San Luis Obispo Counties
805 284-3310 (phone or text)
- Author: Ben Faber
The Citrus Research Board (CRB) is excited to announce the return of the 2023 Citrus Growers Educational Webinar Series. CRB will be holding four one-hour webinars scheduled for June 6, 13, 20, 27. Each webinar will highlight valuable research and practical discussions for growers.
Tuesday, June 6, 2023, at 10:00 AM
Tree Density and Pruning Affect Fruit Numbers, Size, Quality and Maturity of Navel Oranges
The series will kick-off on Tuesday, June 6, 2023, with Craig Kallsen, citrus and pistachio farm advisor for Kern County. This presentation will go over how tree density and pruning affect, fruit numbers, size, quality, and maturity of navel oranges.
Continuing Education Units: This webinar is approved for one-hour Crop Management from Certified Crop Advisers (CCA).
Tuesday, June 13, 2023, at 10:00 AM
Update on Sweet Orange Scab and Integrated Pre- and Postharvest Strategies for Decay Management
On Tuesday, June 13, 2023, Dr. Jim Adaskaveg, Professor & Plant Pathologist at the University of California, Riverside, will give an update on sweet orange scab and integrated pre- and postharvest strategies for decay management.
Continuing Education Units: This webinar is pending approval for One-hour "Other" from Department of Pesticide Regulations (DPR) and is approved for one-hour IPM from Certified Crop Advisers (CCA).
Tuesday, June 20, 2023, at 10:00 AM
Lemon Variety and Rootstock Research for California
On Tuesday, June 20, 2023, Dr. Glenn C. Wright, Associate Professor and Extension Specialist for Tree Fruit Crops at the University of Arizona, will discuss CRB-funded lemon variety and rootstock research for California.
Continuing Education Units: This webinar is approved for one-hour Crop Management from Certified Crop Advisers (CCA).
Tuesday, June 27, 2023, at 10:00 AM
California Water Availability and Crop Water Efficiency Strategies
On Tuesday, June 27, 2023, Dr. Franklin Gaudi, VP of Design at Laurel Ag & Water, will discuss California water availability and crop water efficiency strategies.
Continuing Education Units: This webinar is approved for one-hour Soil and Water Management from Certified Crop Advisers (CCA).