- Author: Ben Faber
Critical Leaf Nutrient Thresholds to Diagnose Deficiencies in HLB Trees
By Arnold Schumann, Laura Waldo, Tripti Vashisth, Alan Wright and Kelly Morgan
Huanglongbing (HLB) disease severely impacts the nutrient status of citrus trees, particularly by stunting the feeder roots and causing measurable deficiencies of nutrients in the roots and canopies. Visible symptoms of nutrient deficiencies on citrus foliage are characteristic but not diagnostic of HLB disease.
Recent HLB research efforts have focused on manipulating nutrient deficiencies with fertilizer applications to mitigate HLB symptoms and help keep affected trees alive and productive. Efficient diagnosis of nutrient imbalances in HLB-affected trees (both deficiencies and excesses) is necessary to make fertilizer remedies cost-effective and productive. Published thresholds defining deficient, low, optimal, high and excess ranges of nutrient concentrations in citrus leaves were derived long before HLB spread in Florida. Therefore, we conducted a series of survey studies to verify and improve those existing thresholds in HLB-endemic Florida citrus groves.
Traditionally, nutrient thresholds were obtained empirically from long-term replicated fertilization trials conducted decades ago, most notably where “missing nutrient” experiments would, over many years, cause those nutrients to become deficient in trees not receiving certain fertilizers. By comparing treatment plots to fully fertilized control plots, the fruit yield reduction and other symptoms caused by the nutrient deficiency could be quantified.
Critical threshold concentrations (CTCs) derived for each nutrient from those studies were then published and used as thresholds to diagnose leaf tissue samples collected from commercial groves. In the current study, we used a sample survey method and the Diagnosis and Recommendation Integrated System (DRIS) instead of “missing nutrient” experiments in order to save considerable time.
STUDY SETUP
Leaf tissue samples were collected quarterly from 2016 to 2018 in three citrus-growing regions of Florida (11 locations from the Central Ridge, five from the east coast Indian River and six from the southwest Flatwoods). Soil samples were collected annually, and tree canopy measurements, leaf size, starch content, quantitative polymerase chain reaction (qPCR) assay and other measurements were conducted periodically for the same sites. In this article, we will focus only on the leaf tissue nutrients of sweet orange trees and assume that most of the sampled trees were HLB-positive, based on the qPCR analyses.
ABOUT DRIS
In an April 2009 Citrus Industry article, DRIS was introduced as a promising method for interpreting nutrient levels in plant tissues. See “Potential use of DRIS for leaf nutrient diagnosis in Florida citrus” (www.crec.ifas.ufl.edu/extension/trade_journals/trade_journals2009.shtml).
The DRIS method produces an index for each plant nutrient calculated from a series of leaf concentration ratios of that nutrient with all other measured nutrients, relative to a set of nutrient norms (standards) that were previously calculated from a high-yielding grove. We obtained the DRIS norms from leaf samples collected in the summer of 2003, from a 22-year-old block of Hamlin orange trees on Cleopatra mandarin rootstock near Fort Meade, Florida, spaced 20 by 25 feet and with an average fruit yield over four years of 770 boxes per acre. The leaf sampling for DRIS norm development coincided with a peak yield of 970 boxes per acre in the 2003–04 season, prior to Hurricane Charlie and the appearance of HLB in Florida.
DETERMINING DEFICIENCIES
The application of DRIS to diagnose nutrient deficiencies in leaf tissue from HLB-affected trees is best done in conjunction with the CTCs. The CTCs are the thresholds for each nutrient that determine whether a given tree or grove would be responsive to fertilizer supplying that nutrient. Traditionally the CTCs occupy a spot on the plant response curve for each nutrient concentration of about 90 percent maximum yield or growth.
When multiple deficiencies occur, as is often the case with HLB-affected trees, the DRIS indices provide information about the relative severity and ranking of the deficiencies, which the CTCs do not accomplish. Dealing with multiple nutrient deficiencies efficiently is important because of the biological stoichiometry that determines the ideal proportions of nutrients in a plant, just as, for example, a water molecule consists of exactly two atoms of hydrogen and one of oxygen.
Liebig's law of the minimum applied to plant growth, and often visualized as a leaking barrel, (Figure 1) demonstrates that it is the most limiting nutrient that limits growth and yield, regardless of the amounts or types of other nutrients available. Another analogy is that a gasoline engine will not run faster if only the gasoline flow is increased without proportionately increasing the air (oxygen) supply, such as if the choke control is active. The engine may flood and stall if too much gasoline is supplied without increasing the most limiting ingredient for combustion at that time (oxygen).
For example, consider the results in Table 1 of leaf tissue analysis from an HLB-affected tree.
DRIS indices have a theoretical optimum at zero, with more negative values indicating possible nutrient deficiency, and increasing positive values indicating possible nutrient excess. In the Table 1 example, Mg<Mn
Figure 1. Scatter plot of leaf manganese Diagnosis and Recommendation Integrated System (DRIS) indices versus manganese concentrations in HLB-affected citrus. The breakpoint between red and green regression lines indicates the location of the critical threshold concentration (CTC = 22.1 mg/kg).
CALCULATING CTCs
To examine the validity of currently available CTCs for nutrient diagnosis in HLB-endemic Florida citrus, we used scatter diagrams of the DRIS indices for each nutrient plotted against the nutrient concentrations. This technique has been used before in other crops to determine CTCs from nutrient survey data, including loblolly pine, cotton and signalgrass. Figure 2 shows that the scatter plot for manganese in our survey of HLB-affected groves follows two data trends of different slopes, with the breakpoint indicating the CTC for that nutrient on the x-axis. We used segmented linear regression to determine the correct breakpoint.
The process was repeated for each nutrient in order to determine the preliminary CTCs listed in Table 2. The optimal nutrient ranges in Table 2 were estimated from the intercept of the regression line with zero on the y-axis (DRIS). By comparing our new CTCs with published CTCs, it appears that deficiency diagnoses for copper, boron, potassium, manganese and zinc could be underestimated by currently available CTCs when used for HLB-affected trees.
The optimal nutrient concentrations calculated from this study are mostly in agreement with ranges previously published by the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS), except that boron and potassium optimal levels were estimated slightly higher in the survey than those previously published. These results are preliminary, and in this study, CTCs could only be calculated for those nutrients where deficiencies occurred in the survey data. We plan to augment this survey with more leaf nutrition data to better define and expand CTC estimates to be used for diagnosing HLB-affected citrus for all nutrients.
Please contact us if you have leaf nutrient data from your groves that you are willing to share in this study, or if you would like to use the DRIS program which will be published online to a UF/IFAS web page.
SUMMARY
In this article we provided updates on research efforts to improve the nutrition of HLB-affected Florida citrus by revising the diagnostic CTC of nutrients in leaf tissue. We also revisited the DRIS method for improving diagnosis of multiple nutrient deficiencies that are common in HLB-affected groves, including potassium, magnesium, manganese, zinc, iron, boron and copper. Additional leaf nutrient data will be obtained for an expanded survey, to be analyzed and corroborated with results of recently completed micronutrient fertilization experiments.
Acknowledgements: We thank the grower cooperators who offered their groves for our nutrient surveys, including Gapway Groves, Ben Hill Griffin Groves, OrangeCo, Brent Shirard, Michael Monroe and English Brothers. We are grateful to the Citrus Research and Development Foundation for financial support of this project.
Arnold Schumann (schumaw@ufl.edu) and Laura Waldo are soil scientists, and Tripti Vashisth is a horticulturist, all at the UF/IFAS Citrus Research and Education Center in Lake Alfred. Alan Wright is a soil scientist at the UF/IFAS Indian River Research and Education Center in Fort Pierce. Kelly Morgan is a soil scientist and center director at the UF/IFAS Southwest Florida Research and Education Center in Immokalee.
Table 1. Leaf tissue analysis of HLB-affected orange trees
Figure 1. Manganese concentration of leaf tissue
Table 2. Critical nutrient concentration thresholds
- Author: Ben Faber
News from the Ventura County ACP-HLB Task Force
Winter 2019 area-wide treatment cycle has begun
This is a reminder that the Winter 2019 area-wide management (AWM) treatment window opened Jan.7. You are encouraged to file pesticide use reports (PURs) electronically through CalAgPermits, Agrian, or another system that allows treatments reports to be rapidly filed and recognized. Treatment reminders will be emailed (mailed for those without an email record) about 2-3 weeks prior to the treatment window. In some instances, our contact list may only have contact information for your farm manager, pest control advisor, or pest control operators. If you are not receiving emails, please contact one of your grower liaisons (see contact information below) to receive information about ACP, HLB and your citrus.
Website redesigned
The Citrus Pest & Disease Program (CPDPP) launched a redesign of its website to provide members of California's citrus industry easier access to the key maps, regulatory updates and events they need to stay informed on the fight against HLB in California. The website is at www.citrusinsider.org.
HLB confirmations continue to increase
At least 1,024 residential trees had been confirmed as infected with HLB as of January 2019. No HLB-positive trees have been found in commercial groves. The HLB quarantine boundaries and the latest tally of HLB confirmations, updated weekly, is available online at https://citrusinsider.org/maps-and-quarantines/.
Report neglected and abandoned citrus
Help prevent neglected and abandoned citrus from serving as a breeding ground for ACP and the spread of HLB by reporting its location County Agricultural Commissioner's office at (805) 388-4222. If your citrus is not worth the resources required to protect it from ACP and HLB, it may be a good time to consider removing the trees. Tree-removal assistance is offered to small growers through the California Citrus Mutual and Bayer's ACT NOW program. For more information contact Joel Reyes at jreyes@cacitrusmutual.com or (559) 592-3790.
Calendar
UCR Citrus Day (Jan. 29)
This year's UC Riverside Citrus Day will be on Tuesday, Jan. 29. Agenda and registration information can be found by clicking here.
International Research Conference on HLB/Citrus Virologist Conference (March 10-15)
The joint International HLB and Citrus Virologist conference will be at the Riverside Convention Center in Riverside, CA. Registration and more information can be found here.
Citrus Pest and Disease Prevention Committee meeting (March 12)
The CPDPC is charged with advising the state on management of the Citrus Pest and Disease Prevention Program. The CPDPC and subcommittee meetings are open to the public, and options for participation include in person or by webinar and conference call. Click here to view and register for upcoming committee and subcommittee meetings. Attendance is free.
esources
University of California ACP area-wide materials list and ACP monitoring protocols
Movement of bulk citrus materials list
Ventura County AWM maps and schedule
Citrus Pest and Disease Prevention Program
Ventura County ACP-HLB Task Force mailing list signup
Contact your grower liaisons if you have additional questions:
Sandra Zwaal
(949) 636-7089
Cressida Silvers
(805) 284-3310
- Author: Ben Faber
Interested Parties should email a resume to jobs@citrusresearch.org
DEADLINE: WEDNESDAY, JANUARY 2, 2019
CALIFORNIA CITRUS RESEARCH BOARD JOB DESCRIPTION
JOB TITLE: CRB Canine Project Manager
REPORTS TO: CRB President
CLASSIFICATION: Regular – 12 month, exempt, at-will or Independent Contractor
LOCATION: Riverside, CA or Remote
WORK HOURS: Typically Monday through Friday; frequent extended hours and weekends, travel subject to operational demands
SUMMARY: The Citrus Research Board Canine Project Manager provides important support to the CRB for follow-through and implementation of a strategic plan developed by citrus HLB diagnostic stakeholders to transition canines for use and commercialization in California. Problem-solving, communications, writing, priority setting, time management and business development skills are necessary.
The Citrus Research Program(a.k.a. Citrus Research Board) is a grower-funded and grower-directed program established in 1968 under the California Marketing Act as a mechanism for enabling the California citrus growers to sponsor and support needed scientific and technical research to further the goals of the California citrus industry. The program is administered by the Citrus Research Board, which is commonly referred to as the CRB.
ESSENTIAL JOB DUTIES:
- Serve as the lead support staff for the implementation of the strategic plan described in the summary above.
- Work as a liaison with the detector canine owners (USDA-APHIS), trainers (F1 K9), researchers and California citrus HLB diagnostic stakeholders (CRB, Citrus Pest & Disease Prevention Program/Committee, California Citrus Mutual and others) to communicate progress in implementation of the plan.
- Serve as a member of the CRB staff, unless established and designated as an independent contractor.
- Under the direction of the President and/or the Chief Research Scientist, write “white papers”, reports, concept documents and other canine detector-related documents.
- Provide staff and organizational assistance to the HLB Detector Canine Transition Team. This involves working with representatives of the various stakeholder groups, researchers, government officials and others.
- Draft transition team meeting notices and agendas. Prepare and submit minutes in a timely, correct and professional manner.
- Provide vision, ownership, accountability and leadership for project management. Details include involvement in strategic planning, follow-through on the subsequent strategic plan, reporting to the CRB and other stakeholder groups, negotiating contract terms with vendors and commercialization of the canine detector teams.
- Perform other duties as assigned by the Chief Research Scientist and/or the President.
DESIRABLE QUALIFICATIONS:
- Clear, effective written and oral communication.
- Self-starter and can-do spirit with pride in the outcome of the final project.
- Leadership, thoroughness, accuracy, objectivity and integrity.
- Knowledge, experience and ability to relate the science of HLB detector canines to the citrus industry and the public in order to establish their credibility and gain confidence in them as an early detection technology.
- Ethical conduct and the ability to exercise confidentiality.
- Ability to create, organize and publish data.
- Ability to meet deadlines and organizational goals.
EXPERIENCE AND EDUCATION:
B.A. or B.S. in a relevant science field is required. PhD preferred. Industry experience in science communication, entrepreneurial commercialization, and/or research project management may be substituted. Solid experience and knowledge of Microsoft Outlook, Word, DropBox, Office 365, PowerPoint and Excel is strongly advised. Must have legal authorization to work in the U. S.
SPECIAL REQUIREMENTS:
- Possession of a valid California Driver's License and clean driving record.
- Frequent out-of-town, multi-day business trips will be necessary.
- Preparing and delivering oral presentations and written progress reports.
- Ability to work both independently and in group settings for problem-solving, coordination and collaboration.
- Competent use of standard office equipment such as computers, scanners, database management software, telephones and photocopiers.
- Lifting of boxes and other field materials weighing up to 35 pounds.
- Ability to spend significant time in citrus orchards and training facilities, including the observation of canine detector teams during extended periods of heat and cold.
EOE STATEMENT:
The Citrus Research Board is an equal employment opportunity employer without regard to race, color, national origin, gender, age, marital status, religion, disability, sexual orientation, pregnancy, or veteran status or other characteristics protected by the law.
- Author: Ben Faber
The best way to delay arrival of HLB in our area and minimize its impact is to keep ACP suppressed down to the lowest level possible. By treating in coordination with neighbors in an areawide approach, grower ACP treatments can have a greater impact on ACP populations than treating independently and out of sync with neighbors. Best Management Practices, such as making sure all equipment arriving and leaving your grove is free of citrus stems and leaves, can also greatly reduce the risk of HLB-positive psyllids entering your grove.
CITRUS REMOVAL PROGRAM: Citrus trees that are neglected or abandoned may harbor ACP and HLB, increasing risk to other citrus in the area. Abandoned and neglected trees may be reported to Cressida Silvers at 805-284-3310, or the county Ag Commissioner's office. The Citrus Matters ACT NOW program may be able to assist in citrus removal. For more information contact Joel Reyes at jreyes@cacitrusmutual.com or (559) 592-3790.
Asian Citrus Psyllid / ACP
There have been no ACP detections in San Luis Obispo County since our last update.
Huanglongbing / HLB
The most recent map and totals for HLB detections are posted at the website https://citrusinsider.org/maps/. As of November 16, the total number of trees that have tested positive for the HLB bacterium is 948, still all in LA, Orange, and Riverside Counties. All HLB detections have been on residential properties and the infected trees have been or are being removed. No HLB has been found in commercial groves to date.
Clarification on Field Cleaning Requirements for Movement of Bulk Citrus
To clarify the approved mitigation measures for bulk citrus fruit movement, the California Department of Food and Agriculture (CDFA) has updated the Asian Citrus Psyllid (ACP)-Free Declaration form. The current options that allow growers to meet the ACP-free standard when shipping fruit to a different ACP regional quarantine zone are the “spray and harvest,” “field cleaning with machine” and “wet wash” methods. Field cleaning must be done by machine, not by hand.
To read the full article, click here: https://citrusinsider.org/2018/11/clarification-on-field-cleaning-requirements-for-movement-of-bulk-citrus/
Upcoming CPDPC Meetings
- Joint Science and Technology Subcommittee and Regulatory Task Force meeting Thur., December 6 at 1:30 pm in Sacramento. Agenda attached, including link to join by webinar/phone.
- CPDPC Operations Subcommittee meets Wed., December 12 at 9 am in Visalia. Agenda attached with link to join by webinar/phone.
- The next meeting of the CPDPC Full Committee will be January 9 in Visalia. Agenda is pending.
- All meeting agendas and eventually the minutes are posted at https://www.cdfa.ca.gov/citruscommittee/ . All meetings are free and open to the public, and accessible via webinar.
Additional Resources
- General information on the ACP/HLB program, including quarantine information: https://citrusinsider.org/
- Biology of ACP and HLB, detection maps and recommendations for monitoring, eradication and management : http://ucanr.edu/sites/acp/
- Summaries of the latest research to combat HLB: http://ucanr.edu/sites/scienceforcitrushealth/
And Now it's in Marin County
SACRAMENTO — Marin County has been placed under quarantine for the Asian citrus psyllid (ACP) following the detection of one ACP in the City of Novato. The entire county is included in the quarantine zone.
The ACP is an invasive species of concern because it can carry the disease huanglongbing (HLB), also known as citrus greening. All citrus and closely related species, such as curry leaf trees, are susceptible hosts for both the insect and disease. There is no cure once the tree becomes infected. A diseased tree will decline in health and produce bitter, misshaped fruit until it dies. In California, HLB has been detected at residential properties in Los Angeles, Orange and Riverside counties. This plant disease does not affect human health.
Residents with backyard citrus trees in the quarantine area are asked not to transport or send citrus fruit or leaves, potted citrus trees, or curry leaves from the quarantine area. For commercial citrus, the quarantine prohibits the movement of citrus and curry leaf tree nursery stock, including all plant parts except fruit, out of the quarantine area. The quarantine also requires that all commercial citrus fruit be cleaned of leaves and stems prior to moving out of the quarantine area. An exception may be made for nursery stock and budwood grown in USDA-approved structures that are designed to keep ACP and other insects out.
ACP quarantines are in place in Alameda, Contra Costa, Fresno, Kern, Kings, Madera, Merced, Monterey, Placer, San Benito, San Joaquin, San Luis Obispo, San Mateo, Santa Clara, Solano, Stanislaus, Tulare, Yolo, Imperial, Los Angeles, Orange, Riverside, San Bernardino, San Diego, Santa Barbara, and Ventura counties, as well as Marin.
Residents in the area who think they may have seen ACP or symptoms of HLB on their trees are urged to call CDFA's Pest Hotline at 1-800-491-1899 or a local agricultural commissioner's office For more information on the ACP and HLB, please visit: www.cdfa.ca.gov/go/acp. Residents are also asked to follow these steps:
- Inspect trees for the Asian citrus psyllid and Huanglongbing monthly, and whenever watering, spraying, pruning or tending trees. Psyllids are most noticeable when new leaves are growing on the tips of the branches.
- As part of your tree care, visit your local nursery or garden center to get advice on products that can help protect your citrus tree.
- Do not move citrus plants, foliage or fruit into or out of your area, and especially across state or international borders. This could unknowingly contribute to spread of the pest and disease.
- When planting a new citrus tree, be sure to get your tree from a reputable, licensed nursery in your local area.
- When grafting citrus trees, only use registered budwood that comes with source documentation, such as the budwood offered through the Citrus Clonal Protection Program.
- Be sure to dry out citrus tree clippings or double bag them before removing the plant material from the property.
–California Department of Food and Agriculture
- Author: Reggie Ellis @Reggie_SGN
VISALIA – Last week's California Citrus Conference marked a major milestone for growers, and it wasn't just the 50th anniversary of the Visalia-based Citrus Research Board (CRB). It was a resounding revelation that new research may cure the greatest threat to the citrus industry in the next few years.
Michelle Heck, PhD, told the crowd of citrus growers at the Wyndham Hotel on Oct. 10 that her team might only need that much time to inbreed a generation of Asian citrus psyllids that are incapable of transmitting the deadly tree disease known as huanglongbing (HLB). The disease has already destroyed China's citrus industry, decimated Florida and Texas growing regions and is currently killing the citrus industry in Brazil.
One grower commented, “China's been dealing with this for 100 years and Brazil for 14 years. We've had this for four to five years in California and we are already knocking on the door of nailing it. That's impressive!”
Heck, a molecular biologist with the USDA Agricultural Research Service, was the first to lead a team of scientists to study the proteins involved in the interaction of the pest, plant and pathogen. One of those proteins creates a blue color in the blood of some psyllids. Her research revealed that psyllids containing the blue protein are far less efficient at transmitting HLB to the plant than others. She then bred those psyllids and took their progency and raised them on orange jasmine hedges, better known as Murraya, a plant the psyllids are attracted but is HLB resistant. The combination of the pest and plant reduced transmission of HLB to healthy citrus leaves from 32% to 2.9%.
Heck said the next steps are to continue breeding the pests that are poor transmitters of the disease to create a line of psyllids that do not transmit HLB at all. She said it would take another two years to breed an “optimized line” of the psyllid but once that was complete, that line could begin mass breeding for release.
“By sheer numbers, we can tip the scales [in the fight against HLB],” she said, “but it's unknown if these lines will out compete other psyllids [in the field].”
One grower asked if the non-transmitting line of the pest would be considered a genetically modified organism, or GMO, a distinction that could hurt fruit grown in groves with the new pest. Heck said all of the psyllids would be bred natuarally, so there is no genetic alteration of the insect itself.
“This is something the anti-GMO groups should feel good about,” Heck said.
Best Case Scenario
Victoria Hornbaker, Statewide Citrus Program Manager for the California Department of Food and Agriculture (CDFA), called the current HLB situation in California a best case scenario. She said the Citrus Pest and Disease Prevention Program's (CPDPP) No. 1 priority is to quickly detect and remove diseased trees. Shortly after the discovery of the first HLB tree in 2012, California's myriad of citrus agencies worked together to quickly implement measures to control movement of fruit and nursery stock, monitor and suppress the ACP population, and begin working on ways to detect the disease and possibly cure it.
“Instead of all commercial groves being covered by a quarantine, we said we're going to quarantine the whole state,” Hornbaker said.
By limiting the movement of citrus in and out of different quarantine zones, there is less likelihood of transporting trees from an infected area to an uninfected area. If any infected trees are discovered, they are removed, destroyed and replaced with a healthy tree. There are many early detection techniques (EDTs) being studied throughout the country, including looking for patterns in leaves, chemicals produced by trees in response to HLB, and studying molecules of the bacteria causing the disease. A recent analysis of these EDTs showed that most are about 95% effective in identifying an infected tree, and that losing 5% of healthy trees is an acceptable loss compared to devastation caused by the disease spreading unchecked.
While early detection methods of ACP are still being perfected, the fight to control the spread of the psyllid is not. After research identified the microscopic parasitic wasp radiate terminaxia as the natural enemy of the psyllid, they began working to mass produce and release them. To date, more than 11 million wasps have bee released in citrus growing regions since 2013, the closest being in Kern County.
Reproduced from Sun Gazette:
http://www.thesungazette.com/article/news/2018/10/17/pests-that-spread-citrus-disease-are-key-to-cure/