Source: UNIVERSITY OF FLORIDA submitted to NRP
SP: IPM APPROACH THAT DELIVERS ECONOMIC VIABILITY TO CITRUS PRODUCTION WITH HLB
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
ACTIVE
Funding Source
OTHER GRANTS
Reporting Frequency
Annual
Accession No.
1031576
Grant No.
2023-70029-41267
Cumulative Award Amt.
$1,128,391.81
Proposal No.
2023-06866
Multistate No.
(N/A)
Project Start Date
Sep 15, 2023
Project End Date
Sep 14, 2026
Grant Year
2023
Program Code
[ECDRE]- Emergency Citrus Disease Research and Extension Program
Recipient Organization
UNIVERSITY OF FLORIDA
G022 MCCARTY HALL
GAINESVILLE,FL 32611
Performing Department
(N/A)
Non Technical Summary
The long-term goal of this project is to render huanglongbing (HLB) functionally irrelevant by developing an IPM system that yields economic return from cultivating citrus despite widespread occurrence of HLB disease. The research simultaneously addresses three aspects of the HLB pathosystem and will: (i.) Develop economic thresholds for Asian citrus psyllid (ACP) based on vector density or tree phenology to reduce unnecessary insecticide sprays facilitating investment in other therapeutic strategies while not compromising vector suppression. (ii.) Evaluate viability of trunk-injected oxytetracycline (OTA) as a therapeutic to reduce bacterial populations, and (iii.) Integrate use of gibberelic acid for disease symptom mitigation. Costs and benefits of implementing improved threshold-based ACP management with use of antibiotics and phytohormones will be evaluated and compared across treatments established in FL and TX. These IPM-based thresholds integrated with pathogen and disease management protocols will be provided to growers via direct contact through annual meetings, online resources, and printed materials for implementation across FL, TX, and CA. The goal is building economically sustainable citrus production despite HLB infection. The program we are developing is inherently adjustable to the conditions of the location where it will be implemented and therefore generalizable rather than region specific. This proposal directly addresses the critical needs described under Part I, B of the 2023 ECDRE RFA: 1) Management of Asian citrus psyllid (ACP) on commercial citrus groves (Priority area # 2), and 2) Development of therapeutics, including antimicrobials and nutritional materials that improve citrus production (Priority area # 4).
Animal Health Component
100%
Research Effort Categories
Basic
0%
Applied
100%
Developmental
0%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
21609991130100%
Knowledge Area
216 - Integrated Pest Management Systems;

Subject Of Investigation
0999 - Citrus, general/other;

Field Of Science
1130 - Entomology and acarology;
Goals / Objectives
The long-term goal of this project is to render huanglongbing (HLB) functionally irrelevant by developing an IPM system that yields economic return from cultivating citrus despite widespread occurrence of HLB disease. The research simultaneously addresses three aspects of the HLB pathosystem: 1) minimizing vector populations, 2) reducing pathogen load and likelihood of transmission, and 3) ameliorating disease symptoms.The central hypotheses are: 1) threshold-driven sprays for Asian citrus psyllid (ACP) will effectively maintain low vector populations while creating cost savings that allow diversion of funds toward antibiotic and phytohormone therapies; 2) combining trunk-injected oxytetracycline (OTC) with phytohormone therapy will allow cultivation of citrus despite HLB infection and bring diseased trees back into production, and 3) IPM-based HLB management that combines spray thresholds, antibiotics, and phytohormones is economically feasible.
Project Methods
In Year 1, we will establish field trials comparing insect-based versus flush phenology-based treatment thresholds for timing spray decisions versus a monthly calendar spray schedule applying 10-12 insecticides per year (Obj 1). We will also quantify the effect of gibberellic acid on annual tree growth phenology and associated psyllid population density fluctuations (Obj. 2).Experimental design. A two year-long experiment will be initiated in the spring of 2024 in sweet orange (Citrus sinensis L. Osbeck) var 'Valencia' and 'Hamlin' groves under standard agricultural practices for citrus. Trees will be planted approximately 3 m apart with 6 m between rows and were 6-8 years old at the time of the study, with an estimated initial HLB infection level of 100 % in FL and 40-60% in TX. The treatments will be arranged in a randomized complete block design with six replicate plots per treatment. Replicates will be 4 ha blocks at minimum. The experiment will be conducted in concert with grower collaborators in Florida and Texas. Treatments will directly compare the 0.2/tap insect threshold versus a flush phenology decision making protocol for timing of insecticide applications. Threshold treatments will also be compared with and without application of GA to quantify how the phytohormone treatment affects annual tree growth and associated vector populations.The insecticide treatment will consist of a program that will intend to represent what growers have done to maximally control ACP populations--8-10 annual sprays of formulations labelled for ACP. Gibberellic acid (GA) with a surfactant will be applied by airblast spray similarly to insecticides at 34 mg/L every thirty days. All data parameters will be collected every 30 days.Economic threshold determinations. The economic threshold value will be calculated as the mean number of adults per tap from twenty randomly selected trees per plot (Monzó and Stansly, 2015). If the mean reached or exceeded the target economic threshold (0.2 psyllids / tap sample), all replicate plots assigned to that treatment threshold were sprayed. The calendar insecticide program was designed to maintain ACP numbers as close to zero as possible with rotation implemented to mitigate resistance development. Using our threshold value, the number of total insecticide applications will vary depending on psyllid population density. For the flush phenology threshold, applications will be made when >50% of tree branches are expressing flushing simultaneously per block based on a random sample of 10 trees/replicate using the sampling method of Hall and Albrigo (2007).Pest and natural enemy assessment. We will sample pests and natural enemies weekly. To collect ACP, a 22 × 28 cm white plastic sheet will be held horizontally about 30 cm underneath a randomly chosen branch, which will be then struck sharply three times with a 40 cm length of PVC pipe. Adult ACP falling on the sheet will be quickly counted (Monzo et al., 2015). Additionally, all other arthropods that drop on the card will be counted.Harvest and yield evaluation. Marketable fruit will be harvested each year in December in experimental plots. We will harvest all the fruit from each tree and count the total number per tree. We will then record fruit weight from a sub-sample of 40 fruit per tree selected at random. To estimate how the different treatments affected profits, we will combine the management costs per hectare with the estimated yield losses per hectare due to HLB. As the economic threshold decreases, spray frequency and management costs increase. All prices will be based on the product used or the closest comparable products. Average fruit prices ($2.7 USD per kg of solids) will be estimated using data obtained from the National Agriculture Statistical Service (NASS, 2020). Yield losses, expressed as USD per hectare, caused by ACP and associated with each simulation will be obtained using the equation proposed by Monzo and Stansly (2017) for groves under high HLB incidence.Experimental design. A second 2-year experiment will be established in the first year of this investigation to examine combined use of an insect-based treatment threshold with trunk injection of OTC and/or GA application. Field trials with will be conducted in concert with grower collaborators and will consist of large 4 ha replicates as described above. Treatments will be applied to CLas-infected mature (>6 yr old) 'Valencia' and 'Hamlin' trees with 'natural' CLas titer and considerable appearance of decline due to HLB. The insecticide treatment will be the same as described for Obj. 1-2. Oxytetracycline (ReMedium) will be injected into mature trees at 100 mL/tree (11,00 ppm solution), according to the product label, in March and October of each year using ChemJet tree injectors. Insecticides and GA will be applied by airblast application as described above.Leaf and insect sampling. Leaves will be sampled directly prior to the initiation of the experiment to establish the infection rates in all plots at the onset and then monthly thereafter. Prior to treatment, four leaves will be removed from each tree, two from each side of the apex of the tree and two from each side of the base of the canopy, for initial titer (T0) using quantitative real-time polymerase chain reaction (qPCR) assays. To monitor the effect of treatments on the CLas titer of each tree, leaf samples will be removed from the same branches as the TI samples after 2, 7, 30, 60 and 90 days.Detection of CLas in plants and psyllids. Dual-labeled probes will be used to detect CLas in ACP and citrus plants using an ABI 7500 qPCR system (Applied Biosystems, Foster City, CA) in a multiplex TaqMan qPCR assay described in (Li et al. 2006).Tree health. Tree growth will be assessed annually in experiments 1 and 2 to determine the effect of OTC injection and or GA application. Tree size measurements (height, canopy, width, and trunk diameter at tree base) will be recorded at time zero, then every 3 months during the experiments from five trees in the second row of each replicate. New leaf growth (flush) will be assessed monthly during the growing season by quantifying the number of flushes in an open 0.3m3 cube placed into three random positions per five trees of each replicate (Hall and Albrigo 2007). Fruit quality (Brix and acid concentration), fruit size, and fruit yield (number of fruit and fruit weight per tree) will be assessed annually in experiment 1 to quantify the effect of treatments on tree health.In Year 2, we will evaluate the results from Year 1 and refine IPM-based management based on effective spray thresholds. We will also investigate the effect of therapeutic antibiotic applications and hormone treatments on ACP phenology. We will conduct a yield assessment in IPM blocks versus conventional groves and make new ACP management recommendations based on the use of effective spray thresholds that optimize spray input to maximize profit. We will also conduct a cost-benefit analysis to compare the profitability of the proposed IPM protocol (See Objective 4 below) with standard practices by considering yield data in Year 2 as well as the costs (and savings) of materials, labor, and applications.In Year 3, we will implement new ACP management recommendations based on effective spray thresholds and conduct a cost-benefit analysis (Objective 4) to determine the overall profitability of the proposed IPM protocol compared to standard practices. The most effective and economical combination of vector, pathogen and disease symptom management treatments will be implemented on a farm-scale level with grower cooperators in FL and TX. We will collaborate with other research teams and organizations to share knowledge and resources and present our findings at industry conferences and workshops.

Progress 09/15/23 to 09/14/24

Outputs
Target Audience:Pest management in Florida citrus has been significantly transformed since 2005 due to the introduction of citrus greening disease (huanglongbing). The insect vector of greening, the Asian citrus psyllid (ACP, Diaphorina citri), was first detected in Florida in 1998, and rapidly established throughout the state. There is no current cure for citrus greening and the impact of the disease on Florida citrus production has been substantial. The disease limits citrus production by reducing yield, decreasing fruit quality, and can eventually kill trees. Since 2012, there has been a $418 million annual loss of revenue to growers due to this disease alone, and orange production in 2018 was at an 80% decrease since pre-infection yields. The threat of this diseasehas required much more intense chemical pest management in Florida citrus than in previous industry history. This project focuseson development,scientific evaluation, and delivery of current and new technologies for management of ACP,as well as development and dissemination of new integrated pest management tactics that are compatible with the current unique needs of the Florida citrus industry. As these technologies are proven effective or successfully developed, wedisseminate pest management recommendations to the Florida, Texas, and Californiacitrus industriesbased on the outcomes of ourresearch. The intended target audience are citrus growers in Florida, Texas, and California.The intended impact is to add new technologies and products to Florida, Texas, and California citrus pest management professionals that render citriculture more sustainable, productive, and economical. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project has led to the recruitment of two graduate students and has allowed for the initiation of training of a post-doctoral scholar on a part-time basis initially. The graduate students and post-doctoral scientists will be trained in entomology, integrated pest management, and sustainable agricultural practices. How have the results been disseminated to communities of interest?The extension portion of this project focuses on development and integration of antobiotics, gibberelic acid, and threshold-based sprays forAsian citrus psyllid to sustainably management huanglongbing (HLB) in citrus. In 2023, one presentation was deliveredat the Citrus Expo in Tampa and one presentation at a meeting organized at the SWREC in Immokalee, FL (presented virtually). A thirdpresentationfocusing on psyllidbiology and management was delivered at the 'Citrus insect, mite, and nematode workshop' held at the Citrus Research and Education Center In Lake Alfred, FL. In 2023, development of the web site, "Science for Citrus Health" continued. We held monthly meetings to organize information and update the website. Currently, there are 32 Research Snapshots on the site, broken into five categories (some articles are posted in more than one category); Early Detection Techniques, Disease Management, Psyllid Management Tools, and General Topics. The BT technology snapshot proposed within this project is found in the Psyllid Management section. The general topics section provides information on future scientific approaches, such as antibiotics and genetic engineering as well as a discussion on the evolution of citrus. By the numbers, in 2023, there were 4 extension talks presented to groups of growers, production managers, or industry personnel in Florida and elsewhere. Also, one article in Citrus Industry Magazine was published. I also engaged in several phone call consultations as part of my extension responsibility. What do you plan to do during the next reporting period to accomplish the goals?We plan to initiate experiments on frequency of Gibberilic acid application. Theseplots will be laid out in the field with grower collaborators and treatments will be applied. In addition, preparation of enterprise budgets will begin that account for the costs of the new IPM practices developed here; and the cost of management, feasibility, and risk of adopting IPM-based management practices in citrus.

Impacts
What was accomplished under these goals? Hypothesis.The central hypothesis is that the combined use of antibiotics and gibberellic acid in citrus trees will lead to a significant increase in yields, while also reducing the abundance of CLas. Field trials were initiated in three commercial citrus groves located in Florida. Treatments were applied to 7-10-year-old, CLas-infected 'Valencia' trees on March 15, 2024. The treatments under evaluation are: 1) non-injected trees (negative control) 2) trunk injection of oxytetracycline (OTC) [Rectify formulation], 3) OTC (Rectify) + Gibberellic Acid, and 4) OTC (Fireline formulation as our standard). Each treatment also receives insecticides consisting of a program that is intended to represent what growers are doing currently--4-6 annual sprays of formulations labeled for ACPthatrotate the following modes of action: (thiamethoxam, imidacloprid, spinosyn, fenpropathrin, cyantraniliprole, methoxyfenozide, clothianidin, and diflubenzuron). Oxytetracycline (Rectify) was injected into mature trees according to the product label using ChemJet tree injectors. FireLine was injected at 70,000 ppm, as per Roldan et al. (2024, in press). Each treatment was applied to four replicate groups of 0.022 ha plots that consist of 3 rows, with ten trees/row comprising 30 trees per plot. All sampling (leaves, ACP, fruit, juice), transmission (acquisition and inooculation) assays, and CLas detection were conducted according to the methods in Roldan et al. (2023; 2024 in press). Recent activities: Mature Trees.In this report, results regarding tree infection at the onset of the experiment are presented. The first replication of acquisition assays was performed 30 days after injections, as this is when OTC is highly available on the leaves. Additionally, ACP populations and flush patterns were collected from April to May 2024 and are currently being processed and analyzed. Psyllid Population Sampling. Asian citrus psyllid (ACP) adults were sampled in all plots at each location and sampling date using a 22 × 28 cm white plastic sheet placed horizontally and 30 cm underneath a randomly chosen branch. Each branch was struck three times with a 40 cm length of PVC pipe. Adult ACPs falling onto the sheet were quickly counted. All trees per replicate plot were sampled in this manner monthly. Acquisition assays. Psyllid nymphs, which develop on immature leaf tissue, acquire CLas more efficiently than adults; therefore, acquisition of CLas from OTC-treated infected citrus trees was compared with acquisition from untreated infected trees, using the above-mentioned treatments. ACP adults (five female and five male) from uninfected laboratory cultures were on young leaf growth (flush) of treated or control infected trees for oviposition. Each treatment was replicated three times on individual trees. Following oviposition, adults were collected and preserved for CLas detection. Egg clutches were left on trees enclosed in mesh sleeves. After nymphs reached adulthood, psyllids and leaves from test plants were collected. Acquisition assays were repeated on the same trees every four months following treatments to determine the influence of treatments on pathogen acquisition over time. The effect of OTC injection on the acquisition of CLas was assessed by comparing the CLas titer in ACP caged on citrus trees before and after treatments and across time. Inoculation assays. A subsample of 10 ACP per treatment collected from the above trees was transferred to uninfected citrus seedlings in an insect-proof greenhouse. ACP was enclosed on plants for inoculation feeding for 7d. After that, ACP adults were collected for CLas detection using qPCR. Furthermore, leaves will be collected every 30, 45, 60, 90, 120, 150, and 180 days for CLas detection. Tree health.Tree measurements such as circumference at the graft union, tree width, and height were taken in April 2024 before the injection of antibiotics and are currently being processed and analyzed. CLas abundance.At time zero, all trees in treatments were CLas positive and showed similar CLas abundance. Data regarding 30 days after injection was collected in May 2024 and is currently being processed and analyzed. We are also initiating experiments comparing flush-based versus insect-based thresholds to trigger insecticide applications for Asian citrus psyllid. The locations for the experiments have been identified and plots have been laid out. The population and tree phenology assessments have begun. Detailed costs of experimental production practices and inputs used for experiments are being compiledand market conditions arebeing collected from sales representatives, and manufacturers. Cross-state analysis of cost of production of different treatments on field production systems are being initiated.

Publications