This project evaluates young tree protection from ACP/HLB using approaches such as ground cover, insecticides, and irrigation management at three locations 1) Southwest Florida Research and Education Center (SWFREC), Immokalee, FL, 2) Citrus Research and Education Center (CREC), Lake Alfred, FL, and 3) Florida Research Center for Agricultural Sustainability, Vero Beach, FL. In this quarter treatments of 1) soil-applied neonicotinoids interspersed with sprays of a different mode of action insecticides on a calendar basis, and 2) rotation of insecticide modes of action sprayed twice on each major flush were implemented to the trees on UV reflective and bare ground. The irrigation deficit treatments to manage flush were also functional at the Immokalee and Lake Alfred locations to trees on UV reflective mulch and bare ground to synchronize flush to target spray applications on major flushes. All the trees were drip-irrigated with two emitters. A separate irrigation treatment using a microsprinkler was also evaluated at the Lake Alfred location.Sampling was conducted to monitor psyllid populations and flush abundance at all three experimental sites. Significant effects of ground cover on psyllid populations were observed at all three locations. At Immokalee, a reduction of 61% in the adult ACP numbers in the plants on mulch compared to bare ground was observed with an average of 0.20 and 0.51 adults per tap sample, respectively. The same level of reduction (61%) was observed at Vero Beach, with an average of 0.07 and 0.18 adults per tap sample on mulch and bare ground, respectively. An overall reduction of 69% using all data on adults was observed at Lake Alfred. At Immokalee, flush infestation with psyllid immatures averaged 22% on mulch and 36% on bare ground, a reduction of 39% on mulch. An average of 5% shoots on mulch and 9% on bare ground were infested at Vero Beach, a reduction of 44% on mulch.Data from April 2021 showed higher soil moisture averages from mulch treatment at all layers (8, 15 and, 45 cm) compared with bare ground. However, these differences were masked by rains in summer 2021. Soil analysis from Immokalee location showed that except for Mg, K, and B, all the other nutrient concentrations were higher in the mulch plots suggesting better nutrient distribution within the root zone and minimal leaching threat. The flush count was impacted by the ground cover treatment (mulch vs. bare) and the date of sampling. On average, more flush was observed on mulched trees than on unmulched trees. The trees on irrigation deficit treatments produced less flush compared to those on the full or conventional irrigation treatment and that trend persisted on the mulch or bare ground.Trees on the UV reflective mulch showed a significant difference in growth. At Vero Beach, compared with last measurements in March, an increase in the growth of rootstock averaged 20.9 mm and 16.8 mm on mulch and bare ground, respectively, whereas scion growth averaged 13.5 and 11.6 mm, respectively. Similar effects on tree health were observed at other locations. Overall, tree canopy density appears to be greater on mulched than bare ground trees at all locations and went up by 40% at the Lake Alfred and 30% at Immokalee. A detailed article Implementing UV reflective mulch and flush timed sprays for managing Asian citrus psyllid was prepared and submitted for publication in Citrus Industry magazine. We are continuing measurements on multiple variables relating to psyllid, HLB and tree health from all locations and hope to better understand the impact of mulch and flush treatments on tree growth and yield in the coming years. The start of this project was delayed significantly due to the logistics involved in setting up the trials in three regions. Therefore, we will need one more year after the end date of December 2021 for the successful completion of this project.
Importance of the dormant spray with regard to establishing threshold-based annual spray program. Previous research has demonstrated the importance of reducing ACP populations during the dormant winter period as an effective method to initiate the citrus growing season with low psyllid populations. Our initial results indicated that it may be difficult to implement the use of treatment thresholds without effectively managing psyllids during the dormant period using appropriately timed insecticides that are effective against both psyllid adults and nymphs. Because of the differences in dormant season spray applications between commercial growers, we were able to investigate this question by monitoring psyllid populations and associated citrus flushing in groves that were managed differently, yet located in close proximity to one another. In doing so, we were able to compare psyllid populations in groves: 1) lacking an effective dormant season application (Grove 1 below) versus those 2) where an effective dormant season treatment had been applied (Grove 2 below). These applications were made because of various goals and constraints (harvest period, available budget) facing each particular grower involved. Six and five insecticide sprays were performed at Grove 1 and Grove 2 groves, respectively, during the course of monitoring. Two insecticide rotations were compared; the first rotation (HB) consisted of Movento, Timectin, Minecto Pro, Timectin, and Micromite. The second rotation consisted of Exirel, Movento, Agri-Flex, Minecto Pro, and Apta. Grove 1 did not receive an effective dormant season application, while Grove 2 did. In Grove 1, Movento was sprayed during the dormant season and this spray occurred more than 10 d after budbreak, because of the difficulty in timing the spray in between harvest and bloom. Grove 2 did receive an Exirel spray during the dormant period, which is highly effective against all stages of ACP. This proved to be a highly effective dormant spray even though it had not been timed perfectly and occurred a week after budbreak of the first flush. Grove 2 was then sprayed by keeping ACP near the 0.2 psyllids/tap threshold the remainder of the season. In Grove 1, it was not possible to maintain ACP near the 0.2 ACP/tap threshold despite application of several sprays. In Grove 1, there was no opportunity for an untreated area given that monitoring of treatment effects was conducted within commercial citrus and the main purpose was to compare Groves 1 and 2 with the main treatment difference being an effective dormant season application. Therefore, all of Grove 1 blocks were treated the same and had relatively similar ACP populations. The most intense periods of vegetative growth (feather flush structures) occurred from January to March during both years, 2020-2021. The presence of feather flush structures at the beginning of 2020 was associated to high counts of ACP adults. However; during the same period on 2021, this association between vegetative growth and the number of psyllids was disrupted, and a significant reduction in adults was observed. To analyze the interaction between ACP adults with vegetative growth, autocorrelation analyses were performed. We found that between 0 to 3 weeks after vegetative growth was detected on trees, there was an increase in ACP adults with a statistical association value of 0.5 between occurrence of flush and psyllids. This result means that at least 50% of the adult ACP population present on these Valencia trees emerged from the eggs oviposited during the previous vegetative growth. Also, the effectiveness of each pesticide used in Grove 1 rotation was analyzed, indicating that the Movento spray was the least effective insecticide in the rotation program. Following application of Movento, the number of ACP adults on trees did not change. However, after Timectin and Minecto Pro sprays, there was a significant reduction in ACP adults observed in citrus trees. Six blocks consisting of Valencia (2 blocks) and Hamlin (4 blocks) citrus trees were examined. Similar intense periods of vegetative growth (feather flush structures) were observed on Valencia and Hamlin trees from January to March during both years, 2020-2021. Similar to the results obtained on Valencia trees in Grove 1, high counts of ACP adults were observed at the beginning of 2020 associated with high intensity of feather flush structures. However, during the same period in 2021, this association was disrupted. Autocorrelation analyses showed that 1 to 2 weeks after vegetative growth, a high number of ACP adults were detected on flushing Valencia and Hamlin citrus trees. The data revealed a higher association value of 0.8 between occurrence of flush and psyllids, which indicates that 80% of the ACP population present in these trees was explained by the occurrence of flush. The effectiveness of each pesticide used in the Grove 2 rotation was evaluated. We found that the Exirel spray to Valencia and Hamlin trees was the most effective insecticide used in the rotation program. The results indicated that Exirel eliminated ACP adults from treated trees for more than 30 days and ACP populations remained low (less than 0.1 ACP/tap) during 2020, except in one Valencia block. Significant differences were observed between the two insecticide rotation programs. High counts of ACP adults were associated with the presence of feather flush structures on Valencia and Hamlin citrus trees. Also, differences in vegetative growth intensity were observed between Valencia and Hamlin varieties, which could have an impact on ACP vector control programs if ACP adults are able to migrate to new groves where feather flush structures are present. Our results indicate that ACP management is most critical during the period between January to March, when citrus is characterized by flowering, fruit maturation (final stage), and the need for safe harvesting. When comparing the two rotation programs, significantly more ACP adults were observed in plots in Grove 1 that did not have an effective dormant season spray than plots in Groves 2, where an effective dormant season spray was applied. Our results highlight the importance of applying a highly effective insecticide, in this case Exirel, during the dormant winter period and soon after initial budbreak of the first seasonal flush.
1. Please state project objectives and what work was done this quarter to address them: The objectives for this proposal are 1) Conduct field trials of new products and fungicide programs for PFD management as well as validation trials for the Citrus Advisory System (CAS); 2) Investigate the reasons for the movement of Postbloom fruit drop (PFD) to new areas and recent major outbreaks; 3) Evaluate methods for initial inoculum reduction on leaves so that early fungicide applications could be more effective and identify the constituents of the flower extracts using omics techniques. We conducted 7 field trials to evaluate how well the Citrus Advisory System (CAS) predicted PFD outbreaks from 2017 to 2021. During this period there were very few PFD outbreaks. In all four years, only one fungicide application was recommended by CAS. This was in 2019 in Fort Meade. In most seasons, there was no significant difference among the treatments, applications recommended by CAS, the older model PFD-FAD, Weekly applications and an untreated control. This indicates that the recommendation of no fungicide application was correct. We also looked at the economic savings of using CAS over the other fungicide application recommendation methods and found there were considerable savings. We also conducted five fungicide trials from 2018 to 2021. Unfortunately, we were not able to make solid conclusions about fungicide efficacy from these trials because the disease was not at high enough levels to statistically separate the treatments reliably. We investigated how far the conidia of Colletotrichum acutatum (syn. C. abscissum) can travel under different conditions: 5, 10, and 20 m/s with and without rain in a laminar flow windtunnel. We also used a turbulent wind tunnel at 5 and 7 m/s with and without rain. We found that the secondary conidia formed on leaves could travel at least 15 m at the 15 and 20 m/s winds with and without rain. This has not been observed before. We were unable to test primary conidia from flowers in the laminar flow tunnel because of COVID-19 and a mechanical breakdown. In the turbulent wind tunnel, the conidia from the leaves did not travel as far but could still move further than if from simple splash with and without rain. We determined that the high polarity fraction of the sugars from citrus (flowers and leaves) can stimulate the germination of C. acutatum conidia nearly as well as the raw floral and leaf extracts. We did not expect leaf extracts to stimulate or stimulate as much as floral extracts, but surprisingly they did. We have tried most of the consituents of the high polarity sugar blend but no single consituent seems to work as well as the original extract. We tested the stimulation of conidia production on leaves with and without fungicide. Ferbam completely inhibits the production of conidia and Headline partially inhibited it. We are trying to figure out why the production of conidia are not stimulated by leaves in the field. Ultimately, we would like to test whether we could suppress inoculum by stimulating it and suppressing it with fungicide before it could infect flowers. 2. Please state what work is anticipated for next quarter: None. This is the final report 3. Please state budget status (underspend or overspend, and why): The budget is closed and no further spending will occur
In this project we are profiling the new scions and rootstocks for their tolerance to HLB by studying the metabolite content by GC-MS, and challenging new varieties with psyllids and HLB.Progress on Objectives: Objective 1.1. To understand the mechanism behind the tolerance of different varieties toward HLB. The comparison between the varietal responses will allow us to determine the mechanism of tolerance to CLas. This quarter we focused in three areas: 1) Marathon Mandarin analyses; 2) CUPS Mandarins, 3) new Valencia varieties.a. For the evaluation of the new mandarin hybrid Marathon, the leaf samples for analysis of volatiles and polar metabolites have been run on the GC-MS and integrated. The analysis found eucalyptol in Marathon, which we have not detected before in other citrus varieties. However, overall profile strongly suggests that Marathon is unfortunately susceptible and does not behave like Sugar belle. Challenging with CLas by grafting confirmed that. b. For the leaf samples from inside the CUPS taken in March 2021, we collected all of the varieties of Mandarins or mandarin hybrids that were available. The VOC analysis is completed for these. Findings: From the VOC analysis we found two distinct chemotaxonomic groups – those that produce thymol and those that don’t. Previously we found that leaves of Sugar Belle, a mandarin hybrid considered tolerant to HLB, contained thymol and its methyl ester, and leaves of most sweet orange (considered HLB susceptible) do not. The group that contained thymol and/or its methyl ester included Sugar Belle, Dancy tangerine (a parent of Sugar Belle), Minneola (also a parent of Sugar Belle), BB4-8-20, and UF711. We associated thymol with tolerance to HLB based on its well-known antimicrobial properties.The thymol non-producers were UF950 clementine, Murcott, Bingo, Early Pride, UF411, and Kinnow. These thymol non-producers also did not produce gamma-terpinene, and had high levels of sabinene. We will look at the ratios of thymol and other blends of VOCs to detect any trends that might indicate HLB tolerance. We expect that robust data analysis will help separate the varietal differences and identify key volatiles involved in ACP deterrence or action against CLas bacteria. We hope to be able to predict or screen for HLB tolerance based on the chemometric profiles of the new varieties if we can develop an accurate model.c. For Lucky and its parents Sugar Belle and Nava × Osceola, we repeated this experiment in June using CLas-infected ACPs. We will measure the response to ACP infestation and the acquisition of CLas over time. New work:d. We obtained Valencia and two new varieties from Southern Citrus (5 each of Valencia, Valquarius, and Vernia) for a small study. So far the VOC profile of the three varieties are nearly identical. We will look at non-volatile metabolites next and perform some ACP challenges. Objective 2.2. To understand the role of rootstocks in citrus tolerance to HLB. The comparison between rootstock metabolites will allow us to determine the best scion/rootstock combinations for tolerating CLas. a. The rootstock seeds from the USDA (US-802, 812, 897, 942, 1283, 1284, 1516) for metabolite profiling and HLB/nematode screening are about three months old and ready to be moved outside to encourage growth.b. We continue evaluating the previous rootstocks for growth habits and HLB tolerance.We greatly appreciate the Schumann Lab for granting access to the CUPS at CREC for sampling for this part of the study. They are presently one of the few sources of healthy mature citrus trees.
In this project we are profiling the new scions and rootstocks for their tolerance to HLB by studying the metabolite content by GC-MS, and challenging new varieties with psyllids and HLB.Progress on Objectives: Objective 1.1. To understand the mechanism behind the tolerance of different varieties toward HLB. The comparison between the varietal responses will allow us to determine the mechanism of tolerance to CLas. This quarter we focused in three areas: 1) Marathon Mandarin analyses; 2) CUPS Mandarins, 3) new Valencia varieties.a. For the evaluation of the new mandarin hybrid Marathon, the leaf samples for analysis of volatiles and polar metabolites have been run on the GC-MS and integrated. The analysis found eucalyptol in Marathon, which we have not detected before in other citrus varieties. However, overall profile strongly suggests that Marathon is unfortunately susceptible and does not behave like Sugar belle. Challenging with CLas by grafting confirmed that. b. For the leaf samples from inside the CUPS taken in March 2021, we collected all of the varieties of Mandarins or mandarin hybrids that were available. The VOC analysis is completed for these. Findings: From the VOC analysis we found two distinct chemotaxonomic groups – those that produce thymol and those that don’t. Previously we found that leaves of Sugar Belle, a mandarin hybrid considered tolerant to HLB, contained thymol and its methyl ester, and leaves of most sweet orange (considered HLB susceptible) do not. The group that contained thymol and/or its methyl ester included Sugar Belle, Dancy tangerine (a parent of Sugar Belle), Minneola (also a parent of Sugar Belle), BB4-8-20, and UF711. We associated thymol with tolerance to HLB based on its well-known antimicrobial properties.The thymol non-producers were UF950 clementine, Murcott, Bingo, Early Pride, UF411, and Kinnow. These thymol non-producers also did not produce gamma-terpinene, and had high levels of sabinene. We will look at the ratios of thymol and other blends of VOCs to detect any trends that might indicate HLB tolerance. We expect that robust data analysis will help separate the varietal differences and identify key volatiles involved in ACP deterrence or action against CLas bacteria. We hope to be able to predict or screen for HLB tolerance based on the chemometric profiles of the new varieties if we can develop an accurate model.c. For Lucky and its parents Sugar Belle and Nava × Osceola, we repeated this experiment in June using CLas-infected ACPs. We will measure the response to ACP infestation and the acquisition of CLas over time. New work:d. We obtained Valencia and two new varieties from Southern Citrus (5 each of Valencia, Valquarius, and Vernia) for a small study. So far the VOC profile of the three varieties are nearly identical. We will look at non-volatile metabolites next and perform some ACP challenges. Objective 2.2. To understand the role of rootstocks in citrus tolerance to HLB. The comparison between rootstock metabolites will allow us to determine the best scion/rootstock combinations for tolerating CLas. a. The rootstock seeds from the USDA (US-802, 812, 897, 942, 1283, 1284, 1516) for metabolite profiling and HLB/nematode screening are about three months old and ready to be moved outside to encourage growth.b. We continue evaluating the previous rootstocks for growth habits and HLB tolerance.We greatly appreciate the Schumann Lab for granting access to the CUPS at CREC for sampling for this part of the study. They are presently one of the few sources of healthy mature citrus trees.
1. Please state project objectives and what work was done this quarter to address them: Objective 1. Assessing tree growth and absence of psyllids and HLB disease symptoms (including CLas bacteria titer) under protective covering (i.e., IPC). The most striking finding in this objective during the last quarter has been the finding that fruit retention was significantly improved in trees that were covered by IPCs, resulting in larger yields and improved internal quality. As a reminder, we removed covers in August 2020. These trees bloomed and set fruit for the first time in February 2020; therefore, this represented the first crop. Fruit drop was non-existent in trees that had been protected by the IPCs, whereas non-covered trees showed 60% fruit drop. Fruit quality was also dramatically improved by use of IPCs: Brix was 10.9 in IPC trees whereas in non covered trees Brix was 7.5. Objective 2. Assessment of alternative netting approaches involved in targeted, alternated or patterned setup of IPC in groves for more cost-effective protection. We have started analyzing samples to determine HLB incidence in the different layouts and if layout dictates different psyllid colonization. Objective 3. Monitoring the transition from vegetative to reproductive stage in the covered trees as compared to the non-covered trees.In the new plots, after having a good bloom in all three varieties (SugarBelle, Early Pride and Tango) covered by IPCs, we assessed fruit set and did not find significant differences compared to non-covered trees. This is promising, since it shows that these varieties do not need to be exposed to pollinators to set fruit, and IPC protection could potentially be prolonged to get the trees well into the productive age, producing high quality fruit, as we have shown in Objective 1. By applying brassinosteroids we expect to prolong further tree health and produce a commercial-size crop of good quality fruit. Objective 4. Comparing IPC with CUPS-like systems. We have collected data on bloom and fruit set on deficit irrigation plots for the second year, and we were able to confirm more bloom and fruit set in protected trees. We installed an automated irrigation system that is helping us to perform these treatments consistently. We have also installed several moisture probes to fine tune the treatments. Outreach for this quarter:-Alferez, F. Citrus Institute 2021. Virtual. April 6.Individual Protective Covers (IPCs) influence on tree performance, fruit production, pests, and diseases. -Alferez, F. Invited presentation at CRDF BOD meeting. April 26, Arcadia. -Alferez, F, Batuman, O, Gaire, S, Albrecht, U, Qureshi, J. Assesing spatial patterns of IPCs deployment in young citrus. Submitted to Citrus Industry -Batuman, Alferez, Qureshi: Assesing spatial patterns of IPCs deployment in young citrus. CRAFT TWG meetings and one-on-one grower meetings. 2. Please state what work is anticipated for next quarter:Objective 1. We will perform regular work on horticultural/pathology parameters in all plots.Objective 2. We will continue collecting data on psyllid populations and HLB incidence in the different netting layouts. Our idea here is to find any seasonal differences that can be affected by the different patterns.Objectives 3 and 4.We will continue collecting data on fruit set and fruit growth and maturation for this second season of deficit irrigation treatments. We will also monitor early fruit drop, if it occurs. Outreach:-Gaire, S, Alferez, F, Albrecht, U. Horticultural attributes of SugarBelle, Tango and Early Pride mandarin trees grafted on two different rootstocks grown with and without individual protective covers (IPCs). ASHS Annual meeting. August 5-9, 2021, Denver CO 3. Please state budget status (underspend or overspend, and why):We are on track with activities and spending. Budgeted amounts for salaries and student stipend and tuition are being spent as predicted. We expect to spent more this quarter, as we will be paying publication fees for our first paper accepted and registration for the ASHS annual meeting in Denver, CO.
1. Please state project objectives and what work was done this quarter to address them:Objectives1. Quantify the effect of citrus antimicrobials on vector fitness. 2. Determine the effect of antimicrobials on Las transmission. 3. Determine the effect of antimicrobials on plant response and associated ACP behavior. The goal of this proposal was to determine whether antimicrobial treatments interfere with Asian citrus psyllid (ACP) populations and their capacity to transmit Candidatus Liberibacter asiaticus (Las), the causal agent of citrus greening (HLB). The premise of this technique is to kill Las with application of registered antimicrobials, streptomycin (Firewall) and oxytetracyline (Fireline) to the tree beyond the pathogens capacity to survive. These data suggest that antimicrobials used for CLas management, particularly oxytetracycline, elicit lethal and sublethal effects in D. citri. We determined that antibiotic use has a negative impact on ACP, therefore there is utility of these applications for ACP management in addition to any effects on Las in trees. ACP feeding on bactericide treated trees could be less capable of transmitting CLas to healthy trees. This can be due to 1) trees treated with bactericides are more likely to have lower CLas titers for acquisition and 2) CLas in infected will be reduced or eliminated when ACP feeds on bactericides, and 3) trees treated with bactericides prior to ACP will be protected from CLas inoculation. Given the limited efficacy of antimicrobial treatments to eliminate CLas completely in infected trees, it appears that their greatest benefit may due to their negative effects on the ACP vector and CLas transmission. 2. Please state what work is anticipated for next quarter: The project is complete. The final work will consist of completing data analysis and submitting manuscripts for publication. 3. Please state budget status (underspend or overspend, and why): Our budget was slightly underspent due to orders for materials to extract DNa not received by the project end date.
Work done this quarter (continued on Word document)(1a) Develop monitoring methods to time management actionsWe have developed methods for following the seasonal populations of lebbeck mealybugs and are working with 7 growers throughout central Florida to monitor populations. Based on data collection through the end of May 2021, there is some consistency in the onset of population development, with mealybug populations increasing in March and April concurrent with early fruit development. Lebbeck mealybugs appear to be highly attracted to developing fruit and establish populations around the calyx at fruit set. In our study and in a fruit drop study by a colleague, we are seeing high levels of fruit drop related to the mealybugs not related to physiological fruit drop. While we are not quantifying it in our phenology study, Dr. Vashisth has added this quantification to her fruit drop trials.Along with population monitoring, we are evaluating the potential use of virgin females as a lure for males with the intention of using these data to develop a targeted lure in the future to help reduce field populations and detect cryptic populations before they increase to damaging populations. No data yet, this method is in the trouble shooting stage.(1b) Adjuvant screeningPreliminary trials have been conducted with adjuvants alone to determine their lethality to lebbeck mealybug. A total of 10 adjuvants, including and 4 from Helena Agri Enterprises were mixed with DI water at label rates and sprayed until dripping on Volk lemon leaves with mealybugs attached. 9 of the adjuvants resulted in significantly greater mealybug mortality over a 7-day period compared to a DI water control. (1c) Evaluate promising materials in open grove setting: We began a field trial at a 10-acre commercial citrus planting that was heavily infested in 2020. First insecticide applications occurred as a pre-bloom prophylactic spray of a systemic material, with a second spray planned in the end of April.(1d) Ant Management We are testing a variety of methods to remove red imported fire ants (Solenopsis invicta) from citrus groves. Four experimental treatments were tested and compared to an untreated control: Chlorpyrifos drench, Clinch ant bait (Abamectin), Extinguish ant bait (S-methoprene), and spot treating ant colonies with hot water. Fire ant abundance was assessed by counting the number of surviving colonies, and by determining presence/absence of foragers with pecan sandie baits. Natural enemy abundance was assessed by dissecting mealybug clusters for predator larvae. Sampling for each of these methods took place every 2 weeks.Currently, all treatments have been applied and we are conducting follow-up surveys to determine their efficacy. Preliminary data shows that both insecticidal baits and hot water treatments significantly reduced fire ant colony abundance, while the chlorpyrifos drench had no effect on colony abundance.Impacts on mealybug predator population development is currently being quantified now that populations are starting to establish.(1e) Evaluate management options for IPCsEntomopathenognic Fungi (EPF) data shared last quarter. More work to come.(2a) Predator assessmentsPredators who directly consume prey:The commercially available predators Cryptolaemus montrouzieri, Orius insidiosus, Adalia bipuctata, Hippodamia convergens, and Chrysoperla carnea have been screened using no-choice assays to determine if they will feed on larval lebbeck mealybugs, and on mealybug ovisacs. Additionally, several wild-caught and lab reared predators have also been screened, including Harmonia axyridis, larva of the genus Ceraeochrysa (colloquially called trash bugs), Diomus austrinus, and Coccinella septempunctata. Both adult and larval C. montrouzieri readily feed on lebbeck mealybug larvae and ovisacs, as do larval Ceraeochrysa. Larval Chrysoperla carnea and adult Diomus austrinus consistently consume mealybug larvae, but do not consume ovisacs. Adult Orius insidiosus, early instar Adalia bipunctata, and adult and larval Harmonia axyridis do not feed on lebbeck mealybug larvae or ovisacs. Adult Hippodamia convergens, Coccinella septempunctata, and Adalia bipunctata do feed on some lebbeck mealybug larvae, but appear to attack and kill the larvae more than fully consuming them. Neither feed on ovisacs. From our results, only Cryptolaemus montrouzieri shows promise as a commercially available biological control agent for lebbeck mealybug, although Ceraeochrysa larvae may act as natural biological control in the grove. Chrysoperla carnea may be useful for controlling mealybug larvae, but not reproductive adult females.Parasitoids:Limited numbers of Anagyrus pseudococci, a commonly used parasitoid for mealybugs in greenhouses, were tested to determine if they would parasitize lebbeck mealybug adults and ovisacs. A. pseudococci adults were placed in arenas with adult lebbeck mealybugs, or ovisacs and left for 40-48 hrs. Surviving parasitoids were then transferred to adult Citrus mealybugs and given an opportunity to parasitize them, to act as a positive control. Mealybugs were checked for parasitism after 16 days. The majority of parasitoids died in arenas with lebbeck mealybugs, and none parasitized adults or ovisacs. However, half of those that survived went on to parasitize Citrus mealybug adults. These preliminary results suggest that A. pseudococci will not readily parasitize lebbeck mealybug, however further trials with more individuals and life stages of mealybugs are needed.Gut content assays of field-collected potential predatorsSpecies-specific primers for lebbeck mealybugs and a DNA extraction protocol have been established and used in feeding bioassays with the predator mealybug destroyers (Cryptolaemus montrouzieri). Using DNA extracted from the predators after they fed on the mealybug in PCR, we were able to model the length of time that the mealybug DNA fragment associated with our primers is detectable in mealybug destroyers. We found that the lebbeck mealybugs amplicon was detectable in 100% of mealybug destroyers for 4 hours after feeding, in 40% of mealybug destroyers up to 56 hours after feeding and was no longer detectable in mealybug destroyers 60 hours after feeding. Field collections were executed in mealybug infested groves August 2019 through December 2020. Species identified as potential predators of lebbeck mealybugs were selected for DNA extraction and PCR using the lebbeck mealybugs primers. So far we have found that green lacewings have the lowest abundance but the highest rate of positive detection of lebbeck mealybugs DNA. Field-collected mealybug destroyers has the next lowest abundance and the next highest rate of positive detection of lebbeck mealybugs DNA. The most abundant predators are spiders, but which have a far lower rate of positive detection of N. lebbeck mealybugs DNA. The spider which tests positive most frequently is the jumping spider, Hentzia palmarum. Predatory flies in the family Dolichopodidae will also be screened for lebbeck mealybugs DNA using our primers. (2b) Determine how to implement mealybug management concurrent with other pest management programsStarting in July 2021 for field efficacy then planning to test programs in Spring 2022(2c) Determine what insecticide chemistries inhibit feedingWe have completed EPG documentation of lebbeck mealybug to determine wavelength correlations on one host plant and will be starting on a second host plant once plants are voided of insecticides (3-4 month holding process in the greenhouse to). Baseline feeding interaction data are necessary for a minimum of 3 host plants prior to including insecticides to look at feeding inhibition and the ability to kill the adult female in her ovisac. (2d) Develop tools to minimize spreadKilling crawlers with isopropyl alcoholWe tested different concentrations of isopropyl alcohol to determine how lethal they are to 1st instar lebbeck mealybugs. 50%, 70%, and 90% solutions of isopropanol were sprayed onto mealybug crawlers placed on cloth swatches, and compared to a DI water control. Both 1 spray at each concentration, and 2 sprays at each concentration were tested. Mortality was assessed after 5, 10, and 15 minutes. The test was repeated, this time assessing mortality at 30 min, 1hr, and 2hrs. For all concentrations of isopropanol, 1 spray resulted in significantly greater mealybug mortality compared to the control. However, several mealybug crawlers remained alive and active after a single spray for all concentrations. 2 sprays of each concentration resulted in almost 100% mortality or incapacitation at all time points. Using steam to kill adult mealybugs and ovisacsAdult mealybugs and ovisacs may be accidentally transferred from infested groves on tools and equipment. Steam treatments may be an effective method of sanitizing equipment and killing both adults and ovisacs. Using a steam cabinet on-station, we steam treated adults and ovisacs at 100, 120, and 130 degrees Fahrenheit for 5, 10, and 15 minutes to determine mortality. Previous preliminary experiments showed steam treatments at 130 degrees Fahrenheit for 15 and 30 minutes resulted in 100% mortality. Mortality was assessed at 0, 3, and 5 days after treatment, and ovisacs were held for an additional 2 weeks to see if crawlers emerged. At 100 degrees F for all times points, adult mealybug and ovisac mortality was not significantly different than the control. At 120 degrees F for 5 minutes, mortality was also functionally 0%. However, mortality rose to 100% at 120 degrees F for 10 and 15 minutes. At 130 degrees F, mortality was 100% for all time points. This week we have begin testing ovisacs embedded in IPCs, which are insulating the ovisacs, requiring higher temperatures and longer time points. 2. Please state what work is anticipated for next quarter:(1a) Seasonal population monitoring will occur at 7 groves for one calendar year. Virgin female lure traps will be deployed once seasonal rains end.(1b) Adjuvant screening will continue to determine optimal adjuvants to work in synergism with insecticide sprays. We plan to take the most effective adjuvants and add them to an insecticide with good, but not great, efficacy on its own.(1c) We will continue treating and scouting the grove we have started a management comparison trial at.(1d) The ant management project will continue throughout the upcoming quarter with the addition of monitoring for predatory insect establishment.(1e) IPC management trials will continue, incorporating conventional materials for management and spray penetration by tractor mounted sprayers (this was delayed from our work plan last quarter by unexpected challenges in establishing infestation).(2a) Working with FDACS, we have permission to deploy sentinel infested materials to screen more broadly for predators that may be present in the system which we missed with haphazard rearing from infested grove sites. We plan to do this starting in late summer 2021, once higher populations have established, which would attract a higher abundance and diversity of predatory insects.(2c) Feeding mechanisms will continue to be worked out using EPG with the future plan to determine if we can interfere with their feeding via chemical intervention leading to reduced offspring production.(2d) We will continue evaluating sanitation options and are planning to look at vehicle & equipment sanitation in the next quarter. 3. Please state budget status (underspend or overspend, and why): on target
The objective of this experiment is to determine the effect of incorporating action thresholds for ACP on populations of natural enemies as well as secondary pests of citrus. ACP vector control is a basic component of HLB management even in situations where disease incidence is high. The use of action thresholds is a possible strategy to reduce unnecessary insecticide input to improve economic return, and reduce potential for insecticide resistance. The idea is to spray only when one reaches a population level of ACP that cause economic damage rather than spraying for ACP all the time. We suspect that an ancillary benefit of using action thresholds will be to reduce the negative impact of insecticides on populations of natural enemies and/or reduce secondary pest infestations because we spray less for ACP control. This may provide further benefit by improving activity of biological control. While the main goal of this investigation is to establish economic thresholds for ACP control to optimize returns on investment, we investigated this ancillary question of whether reducing insecticide input for ACP control may affect populations of beneficial natural enemies in citrus groves. A year-long study was initiated on March 5, 2021 in an experimental sweet orange grove under standard cultural practices located in Lake Alfred and with an estimated initial HLB infection level of 100 %. Prior to the start of the experiment, the entire site was sprayed with pyrethroid. Four replicates were established for each threshold treatment. Insecticide sprays for ACP were based on nominal thresholds of 0.2, 0.5, or 1.0 adult per stem tap and ACP treatment sprays were made of different insecticide modes of action in rotations. There were seven applications for the 0.2 adults per tap threshold treatment, five applications for the 0.5 adults per tap threshold treatment, and two applications for the 1.0 adult per tap threshold treatment. Also, a calendar based positive control treatment was established where ACP sprays were applied once per month, irrespective of ACP population density. ACP were monitored by calculating the mean number of adults per tap from ten randomly selected trees across all four plots for each treatment. Tap samples were made by holding a 22 × 28 cm plastic laminated white paper sheet horizontally underneath a randomly chosen branch, which was then struck sharply three times with a 40 cm length of PVC pipe. ACP adults falling on the sheet were quickly counted to obtain the number of ACP adults per stem-tap and tree. If the means reached or exceeded the target economic threshold, all replicate plots assigned to that treatment threshold were sprayed. ACP sampling occurred every 7 to 15 d. Populations of ACP and natural enemies were assessed every week from March 19 to April 28, 2021 using the stem tap sample described above. Spiders (Araneae), arboreal ants (Hymnoptera: Formicidae), lady beetles (Coleoptera: Coccinellidae) and lacewings (Neuroptera) previously identified as key natural enemies of ACP or other important citrus pests were counted. Counts were made by visually inspecting randomly selected tree branches in earch plot for 2 minutes per sampling period and counting all arthropods found during that period. Inspections were conducted weekly. Arthropods were identified to species level where possible. Ants were collected with pointed round paint brushes and preserved in 70% ethanol and identifications were made subsequently. Cumulative numbers for Asian citrus psyllid were 156, 129, 143 and 135 for the 0.2, 0.5, and 1.0 psyllid per tap, and calendar treatments, respectively. There were 8, 11, 8 and 4 spiders found for the 0.2, 0.5, and 1.0 psyllid per tap, and calendar treatments, respectively. We counted 25, 50, 41, and 51 arboreal ants for the 0.2, 0.5, and 1.0 psyllid per tap, and calendar treatments, respectively. There were 3, 1, 0. and 0 lacewings for the 0.2, 0.5, and 1.0 psyllid per tap, and calendar treatments, respectively. There were 10, 16, 16, 22 ladybird beetles for the 0.2, 0.5, and 1.0 psyllid per tap, and calendar treatments, respectively. Finally, there were 1, 4, 2 and 1 citrus root weevils for the 0.2, 0.5, and 1.0 psyllid per tap, and calendar treatments, respectively. This experiment will run throughout the remainder of the summer. At this early point in the esperiment, we have not yet observed an effect of reducing sprays by employing treatment thresholds on populations of natural enemies as compared with plots treated with calendar sprays. However, we predict that differences may emerge as the investigation progresses, based on our previous experience. The possible improvement in the effect of biological control as a consequence of using treatment thresholds for timing sprays against ACP may prove to be a means of integrating insecticides with biological control for psyllid management.
In this quarter, monitoring and management activities continued in all of the Integrated Pest Management (IPM) programs for ACP which include: 1. conventional and organic insecticides plus biological control, 2. organic insecticides, and Horticultural Mineral Oil (HMO) plus biological control, 3. conventional insecticides plus biological control 4. HMO plus biological control. 5. biological control only. The dormant spray applications in February included Danitol in programs 1 and 3, Pyganic + 435 oil (2%) in program 2, and 435 oil (2%) in program 4. The March sprays included Microthiol in program 1, 435 oil (2%) in program 2 and 4, and Movento in program 3. Nine samplings were conducted to monitor for ACP and beneficial arthropods. February sprays conducted in the middle of the month kept psyllids below treatment threshold of 0.1 adults per tap sample across all programs until the second week of March. After March sprays a decreasing trend in the populations of ACP was seen in all programs and numbers dropping from 0.2-0.3 adults per tap sample to 0.1 adults per tap sample by the end of the month. Within the predator guild, spiders and lacewings continue to be the dominant groups and among lacewings Ceraeochrysa cubana most dominant. In the laboratory, C. cubana larvae were more tolerant to imidacloprid than C. claveri or D. citri. Ceraeochrysa cubana seems to have a significant potential to be used in biological control against D. citri. A preliminary laboratory study testing a predator prey ratio of 1:1 (mite: ACP egg) showed that the predatory mite Amblyseius swirskii provided 50% reduction in ACP. Follow up experiments were initiated in the greenhouse using different densities of this predator against ACP. Residual toxicity of March sprays was evaluated against A. swirskii. Three days after sprays leaves were collected from the treated trees and exposed to the predatory mite in the experimental arenas in the laboratory. After, 24 h of exposure 12% mortality was observed in the Movento treatment, and 8% in the Microthiol and 435 oil treatments. Amblyseius swirskii were also released in the field within a week of March sprays. Approximately 5,000 mites per plot and total of 20,000 per program were released. No predatory mites were observed in a sample conducted before the release. After release, 20% of the sampled trees in program 3 sprayed with Movento were found to contain predatory mites, 30-32.5% in the program 2 and 4% sprayed with 435 oil, 35% in program 1 sprayed with Microthiol and 40% in the program 5 which is untreated control. Colonies of field collected ACP from all programs were established in the laboratory and their subsequent generations tested for tolerance to dimethoate, fenpropathrin, and imidacloprid in comparison with a laboratory colony. The concentration required to kill 50% of the field population averaged 2, 4 and 8 times more for dimethoate, fenpropathrin, and imidacloprid, respectively, than the concentration required to kill same percentage of ACP from the laboratory colony. Leaf samples were collected from all programs and submitted for HLB analysis in March. Analysis of the leaves collected in Fall 2020 showed that 80-95% samples collected across all programs were HLB positive. Although, no Tamarixia radiata was released in the programs during this quarter due to the problems with the colonies at the FDACS-DPI, Dundee, facility, the previous work on the parasitism activity of T. radiata tested at different times of the day and temperatures was written and a presentation on the same work given at the Southeastern Branch Meeting of the Entomological Society of America and Florida Citrus Grower Institute.
This project evaluates young tree protection from ACP/HLB using approaches to integrate ground cover, insecticides, and irrigation management at three locations 1) Southwest Florida Research and Education Center (SWFREC), Immokalee, FL, 2) Citrus Research and Education Center (CREC), Lake Alfred, FL, and 3) Florida Research Center for Agricultural Sustainability, Vero Beach, FL. Treatments of 1) soil-applied neonicotinoids interspersed with sprays of a different mode of action insecticides on a calendar basis, and 2) rotation of insecticide modes of action sprayed twice on each major flush are being implemented to the trees on UV reflective and bare ground. The irrigation deficit treatments are also functional at the SWFREC and CREC locations to trees on UV reflective and bare ground to synchronize flush to target spray applications on major flushes. Sampling was conducted to monitor flush abundance and psyllid populations at three experimental sites. At the Vero Beach location, significantly more flush was observed in the trees on mulch compared to the trees on bare ground averaging 4.09 and 3.47 per plant, respectively. The diameter of the trunk of the rootstock and scion of the trees on the mulch was significantly more than the trees on the bare ground. An average rootstock diameter of 33.79 mm on the mulch and 28.20 mm on the bare ground was observed. Scion diameter averaged 24.04 mm on the mulch and 21.12 mm on the bare ground. At the CREC location, on average, there was also significantly more flush observed on mulched trees than on bare ground trees. Analysis of data from September 2020 to March 2021 showed significantly fewer adults on trees with mulch than with no mulch. Trees with insecticides applied based on a calendar schedule also had fewer adult ACP than those that experienced insecticide applications based on flush. ACP adult abundance was weakly but positively dependent on flush abundance. Peaks of adult counts occurred between March to June as well as September to October in 2020 and this is where treatment differences were starkest. Significantly fewer eggs and nymphs were observed on the trees with mulch than those on the bare ground. At SWFREC, trends on flush abundance across treatments and ACP response to the treatments were similar to other two locations. During this quarter, the mulched and non-mulched treatments soil moisture contents varied between 0.11±0.02 m3 m-3 and 0.10±0.01 m3 m-3 showing not much difference in water storage with the root zone. Overall, canopy density appears to be greater on mulched than non-mulched trees. In the next quarter, we will do leaf and soil nutrient analysis and canopy size determinations to see changes if any in the treatment effects. At SWFREC, several experiments were conducted using the remote-controlled and manual ground-penetrating radar (GPR) operation to evaluate the effort needed to perform the GPR scanning, measure the required time to complete the scanning process, evaluate precision and accuracy of the scanning circles, and determine if the remote-controlled system can perform better for non-invasive root detection than the manual process. The scan line data collected from both the remote-controlled and manual process were compared after processing the data using an auto root detection software (Tree Radar Inc., Maryland, USA.) The results of root detection for both processes were almost the same, and there were no significant differences between them. The depth of the detected roots in the remote-controlled process was same as of the manual process. These experiments show that the remote-controlled process can reduce the required application time by 3 times when compared to a manual process. It can also reduce the human effort required and increase the precision of the data collection process. A Qualtrics survey to obtain growers input on the reflective mulch technology was developed and distributed through several channels.
In this quarter, monitoring and management activities continued in all of the Integrated Pest Management (IPM) programs for ACP which include: 1. conventional and organic insecticides plus biological control, 2. organic insecticides, and Horticultural Mineral Oil (HMO) plus biological control, 3. conventional insecticides plus biological control 4. HMO plus biological control. 5. biological control only. The dormant spray applications in February included Danitol in programs 1 and 3, Pyganic + 435 oil (2%) in program 2, and 435 oil (2%) in program 4. The March sprays included Microthiol in program 1, 435 oil (2%) in program 2 and 4, and Movento in program 3. Nine samplings were conducted to monitor for ACP and beneficial arthropods. February sprays conducted in the middle of the month kept psyllids below treatment threshold of 0.1 adults per tap sample across all programs until the second week of March. After March sprays a decreasing trend in the populations of ACP was seen in all programs and numbers dropping from 0.2-0.3 adults per tap sample to 0.1 adults per tap sample by the end of the month. Within the predator guild, spiders and lacewings continue to be the dominant groups and among lacewings Ceraeochrysa cubana most dominant. In the laboratory, C. cubana larvae were more tolerant to imidacloprid than C. claveri or D. citri. Ceraeochrysa cubana seems to have a significant potential to be used in biological control against D. citri. A preliminary laboratory study testing a predator prey ratio of 1:1 (mite: ACP egg) showed that the predatory mite Amblyseius swirskii provided 50% reduction in ACP. Follow up experiments were initiated in the greenhouse using different densities of this predator against ACP. Residual toxicity of March sprays was evaluated against A. swirskii. Three days after sprays leaves were collected from the treated trees and exposed to the predatory mite in the experimental arenas in the laboratory. After, 24 h of exposure 12% mortality was observed in the Movento treatment, and 8% in the Microthiol and 435 oil treatments. Amblyseius swirskii were also released in the field within a week of March sprays. Approximately 5,000 mites per plot and total of 20,000 per program were released. No predatory mites were observed in a sample conducted before the release. After release, 20% of the sampled trees in program 3 sprayed with Movento were found to contain predatory mites, 30-32.5% in the program 2 and 4% sprayed with 435 oil, 35% in program 1 sprayed with Microthiol and 40% in the program 5 which is untreated control. Colonies of field collected ACP from all programs were established in the laboratory and their subsequent generations tested for tolerance to dimethoate, fenpropathrin, and imidacloprid in comparison with a laboratory colony. The concentration required to kill 50% of the field population averaged 2, 4 and 8 times more for dimethoate, fenpropathrin, and imidacloprid, respectively, than the concentration required to kill same percentage of ACP from the laboratory colony. Leaf samples were collected from all programs and submitted for HLB analysis in March. Analysis of the leaves collected in Fall 2020 showed that 80-95% samples collected across all programs were HLB positive. Although, no Tamarixia radiata was released in the programs during this quarter due to the problems with the colonies at the FDACS-DPI, Dundee, facility, the previous work on the parasitism activity of T. radiata tested at different times of the day and temperatures was written and a presentation on the same work given at the Southeastern Branch Meeting of the Entomological Society of America and Florida Citrus Grower Institute.
This project evaluates young tree protection from ACP/HLB using approaches to integrate ground cover, insecticides, and irrigation management at three locations 1) Southwest Florida Research and Education Center (SWFREC), Immokalee, FL, 2) Citrus Research and Education Center (CREC), Lake Alfred, FL, and 3) Florida Research Center for Agricultural Sustainability, Vero Beach, FL. Treatments of 1) soil-applied neonicotinoids interspersed with sprays of a different mode of action insecticides on a calendar basis, and 2) rotation of insecticide modes of action sprayed twice on each major flush are being implemented to the trees on UV reflective and bare ground. The irrigation deficit treatments are also functional at the SWFREC and CREC locations to trees on UV reflective and bare ground to synchronize flush to target spray applications on major flushes. Sampling was conducted to monitor flush abundance and psyllid populations at three experimental sites. At the Vero Beach location, significantly more flush was observed in the trees on mulch compared to the trees on bare ground averaging 4.09 and 3.47 per plant, respectively. The diameter of the trunk of the rootstock and scion of the trees on the mulch was significantly more than the trees on the bare ground. An average rootstock diameter of 33.79 mm on the mulch and 28.20 mm on the bare ground was observed. Scion diameter averaged 24.04 mm on the mulch and 21.12 mm on the bare ground. At the CREC location, on average, there was also significantly more flush observed on mulched trees than on bare ground trees. Analysis of data from September 2020 to March 2021 showed significantly fewer adults on trees with mulch than with no mulch. Trees with insecticides applied based on a calendar schedule also had fewer adult ACP than those that experienced insecticide applications based on flush. ACP adult abundance was weakly but positively dependent on flush abundance. Peaks of adult counts occurred between March to June as well as September to October in 2020 and this is where treatment differences were starkest. Significantly fewer eggs and nymphs were observed on the trees with mulch than those on the bare ground. At SWFREC, trends on flush abundance across treatments and ACP response to the treatments were similar to other two locations. During this quarter, the mulched and non-mulched treatments soil moisture contents varied between 0.11±0.02 m3 m-3 and 0.10±0.01 m3 m-3 showing not much difference in water storage with the root zone. Overall, canopy density appears to be greater on mulched than non-mulched trees. In the next quarter, we will do leaf and soil nutrient analysis and canopy size determinations to see changes if any in the treatment effects. At SWFREC, several experiments were conducted using the remote-controlled and manual ground-penetrating radar (GPR) operation to evaluate the effort needed to perform the GPR scanning, measure the required time to complete the scanning process, evaluate precision and accuracy of the scanning circles, and determine if the remote-controlled system can perform better for non-invasive root detection than the manual process. The scan line data collected from both the remote-controlled and manual process were compared after processing the data using an auto root detection software (Tree Radar Inc., Maryland, USA.) The results of root detection for both processes were almost the same, and there were no significant differences between them. The depth of the detected roots in the remote-controlled process was same as of the manual process. These experiments show that the remote-controlled process can reduce the required application time by 3 times when compared to a manual process. It can also reduce the human effort required and increase the precision of the data collection process. A Qualtrics survey to obtain growers input on the reflective mulch technology was developed and distributed through several channels.
1. Please state project objectives and what work was done this quarter to address them: Objective 1. Assessing tree growth and absence of psyllids and HLB disease symptoms (including CLas bacteria titer) under protective covering (i.e., IPC). As in the last quarter, we have continued monitoring trunk diameter and canopy area as well as flushing and blooming dynamics in the new plots (700 trees planted last year). After IPC removal in the original plot in August 2020, we have been monitoring CLas infection of the uncovered trees in real time. We are now processing these samples for real time PCR CLas detection so we can document the rate of infection once IPCs are removed from trees. Objective 2. Assessment of alternative netting approaches involved in targeted, alternated or patterned setup of IPC in groves for more cost-effective protection. We have continued monitoring the new 700 trees mentioned in the Objective 1 planted last year that are arranged in an alternated pattern we are monitoring for CLas in trees adjacent to the IPC-covered trees. Also, we have continued working with several commercial collaborators who are also evaluating different netting layouts under the CRAFT program. Objective 3. Monitoring the transition from vegetative to reproductive stage in the covered trees as compared to the uncovered. We are continuing data collection on Bingo, Early Pride, and Tango trees. This is the second year in documenting blooming on these varieties. We have also documented different blooming rate in the trees from our first experiment that were uncovered last August. These trees are blooming more profusely than the always-uncovered trees. We are counting flowers and we will assess fruit set in the coming weeks. Objective 4. Comparing IPC with CUPS-like systems. We have performed for the second year deficit irrigation. As in last year, we have induced more bloom. We are also finishing regular quality analysis from fruit that matured this year. Outreach for this quarter: -Batuman, O. Individual and direct contact with CRAFT applicants to establish and evaluate IPC trials for psyllid and HLB control. -Gaire, S., Albrecht, U., Batuman, O., Qureshi, J., Zekri, M., Alferez, F. 2020. Horticultural performance of citrus trees grown under Individual Protective Covers (IPCs). Crop Protection, under review. -Individual Protective Covers’ by Alferez, F, Gaire, S., Albrecht, U., Batuman, O., Qureshi, J., Zekri, M., 2021-2022 Citrus Production Guide, EDIS. Under Review. -Gaire, S. Evaluation of individual protective covers for preventing vector transmission of Candidatus Liberibacter asiaticus and effects on growth and physiology of young citrus trees. Master’s Thesis Defense, March 11 2021, UF, Horticultural Sciences Dept. -Gaire, S. Evaluation of individual protective covers for preventing vector transmission of Candidatus Liberibacter asiaticus and effects on growth and physiology of young citrus trees. Oral Presentation at the Southern Fruit Workers 3 Minute Thesis Competition, ASHS, 2nd Prize winner. 2. Please state what work is anticipated for next quarter: Objective 1.We will continue monitoring parameters described in the first section. Also we will continue monitoring HLB progression after IPC removal in the first experiment.and fruit yield and quality to compare fruit from IPC and non-IPC trees.Objective 2. We will continue collecting data on psyllid populations and HLB incidence in the different netting layouts.Objectives 3 and 4.We will start collecting data on on bloom and fruit set for this second season of deficit irrigation treatments. Outreach:-Alferez, F. Invited speaker at the Citrus Institute 2021. Virtual. April 6.Individual Protective Covers (IPCs) influence on tree performance, fruit production, pests, and diseases. 3. Please state budget status (underspend or overspend, and why): As mentioned in the last report, we are on track with activities and spending after the COVID pause. Budgeted amounts for salaries and student stipend and tuition are being spent as predicted.
We investigated the potential of a usable economic threshold to increase sustainability of Asian citrus psyllid (ACP) management in citrus under conditions of high huanglongbing (HLB) incidence. A year-long study was initiated in the spring of 2020 in a young planting of Hamlin sweet orange grove under standard agricultural practices for citrus, including mowing and fertilization, located in Lake Alfred, Florida. ACP management strategies were tested in a randomized complete block design with four replicates. Insecticidal sprays for ACP were based on either of three nominal thresholds of 0.2, 0.5, and 1 adult per stem tap and ACP treatment sprays were comprised of two rotations of different MoAs designated as rotations A and B. There were seven applications for the 0.2 adults per tap threshold treatment; five applications for the 0.5 adults per tap threshold treatment; and two applications for the 1.0 adult per tap threshold treatment (Table 1). ACP were monitored by calculating the mean number of adults per tap across all four plots for each treatment. If the means reached or exceeded the target economic threshold, all replicate plots assigned to that treatment were sprayed. ACP sampling occurred every 7 to 15 d. If the mean ACP density for a threshold treatment was within ± 0.05 per tap below the target threshold, a decision was often made to spray that treatment rather than waiting until the following week. Sprays were made after plots were sampled, and insecticide susceptibility to thiamethoxam was determined. Thiamethoxam was chosen as bellwether to test for resistance development given that resistance in ACP is predominantly metabolic and this MoA typically predicts subsequent multiple resistance within populations of this pest. An insecticide program was designed to maintain ACP numbers as close to zero as possible in the treatments considering potential impacts on resistance risks. Broad-spectrum insecticides were restricted to the dormant season, and when activity of natural enemies was expected to be reduced, whereas more selective insecticides were used during the primary growing season. Table 1. Description of insecticide rotation programs according to different economic thresholds to manage Asian citrus psyllid Rotation A Rotation B App Date 0.2* 0.5 1.0 0.2 0.5 1.0 5-May-20 dimethoate ———— ———— fenpropathrin ———— ———— Jun 9 10, 2020 cyantraniliprole dimethoate ———— dimethoate fenpropathrin ———— Jul 7-10, 2020 fenpropathrin cyantraniliprole dimethoate cyantraniliprole dimethoate fenpropathrin 12-Aug-20 thiamethoxam fenpropathrin ———— diflubenzuron cyantraniliprole ———— 24-Sep-20 spinetoram thiamethoxam cyantraniliprole thiamethoxam diflubenzuron dimethoate 28-Oct-20 diflubenzuron ————- ———— spinetoram ———— ———— 18-Dec-20 abamectin spinetopram ———— abamectin thiamethoxam ———— *: 0.2, 0.5 and 1.0 was the designated action (economic) threshold that triggered treatment with insecticide The average number ACP eggs, nymphs, and adults counted was higher in plots where the 1 adult/tap threshold was implemented than in plots where the 0.2 or 0.5 D. citri/tap economic thresholds were implemented for both rotation A and rotation B. There were no differences in treatment efficacy between the two rotations. Overall, there were no statistically significant changes in susceptibility of D. citri following the completion of the either rotation schedule triggered by either of the three treatment thresholds tested. Furthermore, GSTE1, GST1, EST6, CYP4D1, and CYP4C67 gene expression levels were not significantly different in ACP collected from different threshold treatment populations as compared with the susceptible control. These results allow us to conclude with confidence that resistance was effectively kept in check throughout the trial. The incidence of HLB was determined by the level of CLas pathogen in each of the economic threshold treatment plots. There was 100 % infection of trees before the first application in the early spring. Therefore, the scoring and decline index of HLB was observed after harvesting and nutritional applications. All 480 trees were scored for each economic threshold treatment after harvest on a 0-4 scale, where category 0 = no HLB symptoms, normal growth flushes; category 1 = some HLB symptoms, mostly normal growth of flush; category 2 = some HLB symptoms, some normal growth; category 3 = obvious symptoms with no flush growth. category 4 = obvious HLB symptoms, including small leaves and dead wood and no new growth. The decline index was calculated for each treatment. Furthermore, for rotation A, greater input of insecticides (lower action threshold) was correlated with lower incidence of HLB. We determined insecticide application costs and fruit drop rate for each economic threshold treatment. Insecticide costs were compiled from the University of Florida extension reports and the 2020-2021 Florida Citrus Production Guide. All prices were based on the products used in our tests. For fruit drop counts, each treatment threshold, 20 trees were counted per replicate plot and 80 trees total were counted per economic threshold treatment to determine mature fruit drop. Dropped fruit numbers were counted weekly for four weeks before harvesting. To estimate the level of CLas pathogen infection among treatment plots, three trees were randomly chosen for sampling per plot for a total of 24 trees for each rotation x treatment threshold treatment combination. Every tree sampled from each treatment plot was CLas positive. Similarly, all trees exhibited HLB symptoms, The results indicated that trees had similar symptoms of HLB in all treatment plots and ranged between categories 1-4. The input costs of spraying at the 0.2 adults per tap economic threshold were estimated at $451.50 and $ 451.93/hectare for rotations A and B, respectively. The costs associated with the 0.5 adults per tap economic threshold were estimated at $ 288.88 and $ 284.38 per hectare for rotations A and B, respectively. Finally, at the 1.0 adult per tap economic threshold treatment, costs were estimated at $ 101.12 and $ 35.62 per hectare for rotations A and B, respectively (Table 6 and Supplementary data Table 7 and 8). There were no significant differences in fruit drop between each economic threshold treatment compared. However, we have no yet finished analyzing the yield data that were collected. In summary, our results indicate that an economic threshold could be implemented as a decision tool for timing insecticide applications in Florida and is compatible with a range of possible rotations of available insecticides for ACP management. Such rotational programs can maintain psyllids below population levels that negatively impact yield but can reduce the number of insecticide sprays needed per season. In the current investigation, although psyllid populations were reduced more effectively with the lower threshold that necessitated the most insecticide sprays per year (7), there was no difference observed in fruit drop or tree health between plots treated 2 times / year using the 1.0 psyllid / tap threshold and those sprayed 7 times/ year using the 0.2 psyllids/ tap threshold. As we continue this research, we will continue to validate use of economic thresholds in mature trees and determine how use of economic thresholds impacts secondary pest and beneficial arthropod populations. Also, we plan on compating profits between the management programs evaluated by including the yield component into our calculations.
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