The overall objective of this research is to develop a push-pull system for the Asian citrus psyllid (ACP) that can complement integrated management systems in young citrus plantings. Towards that goal, visual factors that affect psyllid takeoff into flight and landing are being examined to guide development of an optimal pull component. A vertical flight attraction assay was developed to examine response of ACP resting or in flight towards visual targets that consist of different wavelengths of filtered light. Narrowband width filters (10 nm) were used to allow clear delineation between colors tested. This assay simulates the response of ACP to visual cues that are above them such as when an adult is settled on vegetation and looks up at the sky or when having fallen to the ground looks up and sees its host plant from the ground. ACP response was lowest to red and orange in the visible spectrum. Yellow was more attractive to ACP then orange or red, but less attractive then blue, green, or lime green. Green and lime green were the most attractive to ACP in the visible spectrum. In the ultraviolet spectrum the most attractive wavelength was long UV (405nm) compared to shorter wavelengths arranged in order of decreasing attractiveness 350nm, 380nm, and 365 nm (least attractive). The vertical bioassay differed from the horizontal bioassay, in that ACP responded as strongly to UV as they did to green and lime green. This may be evidence that the ACP orient differently to vertical and horizontal cues. For example, when ACP drop to the ground following a disturbance vertical cues of UV (sky) or green and lime green (leaves) are both used to return to a place of rest (the host plant). Whereas horizontal cues are more typically used when ACP are already situated on a plant and therefore only UV (sky) cues are used to navigate towards increasingly younger and more optimal portions of the host plant (young flush), which are near the edge of the plant (near UV) versus in the center of the plant (away from UV). Ultimately, the UV cues from the horizontal axis may be causing the ACP to move to another plant in search of new host locations. Further studies are on-going with the vertical bioassay to see if there is a difference between 0-1 day old and 4-7 day old ACP in this orientation. Additionally, studies are being undertaken to see if flying ACP will be attracted to different colors then walking/flying ACP by using specially designed walking preventing chambers coated with Fluon. A horizontal walking assay was developed to stimulate walking responses of ACP on vegetation and this assay measured direction of movement as well as speed of movement. Known age studies with ACP in the horizontal bioassay revealed that 1 day old ACP were positively attracted toward green light , whereas 4-7 day old ACP remained relatively neutral to green light. Both 1 day old and 4-7 day old ACP showed more positive attraction towards long UV light. These findings indicate that newly emerging ACP may be more attracted to green, because they need to acquire nutrients from feeding on a plant. Conversely, older ACP may be more interested in movement to other plants in search of mates and oviposition sites. Further studies with the horizontal walking assay will be made between newly emerged unmated female ACP and older gravid females. Examination of the effect of different visual stimuli on flight duration of ACP as measured on flight mills is on-going. Comparisons in the duration of flight and numbers of flight bouts are being made between different colored substrates, different quality of light overhead (colored, with UV, without UV, polarized), contrast between overhead lighting and substrate coloring and presence of visual targets.
The overall objective of this research is to develop a push-pull system for the Asian citrus psyllid (ACP) that can complement integrated management systems in young citrus plantings. Towards that goal, visual factors that affect psyllid takeoff into flight and landing are being examined to guide development of an optimal pull component. A vertical flight attraction assay was developed to examine response of ACP resting or in flight towards visual targets that consist of different wavelengths of filtered light. Narrowband width filters (10 nm) were used to allow clear delineation between colors tested. This assay simulates the response of ACP to visual cues that are above them such as when an adult is settled on vegetation and looks up at the sky or when having fallen to the ground looks up and sees its host plant from the ground. ACP response was lowest to red and orange in the visible spectrum. Yellow was more attractive to ACP then orange or red, but less attractive then blue, green, or lime green. Green and lime green were the most attractive to ACP in the visible spectrum. In the ultraviolet spectrum the most attractive wavelength was long UV (405nm) compared to shorter wavelengths arranged in order of decreasing attractiveness 350nm, 380nm, and 365 nm (least attractive). The vertical bioassay differed from the horizontal bioassay, in that ACP responded as strongly to UV as they did to green and lime green. This may be evidence that the ACP orient differently to vertical and horizontal cues. For example, when ACP drop to the ground following a disturbance vertical cues of UV (sky) or green and lime green (leaves) are both used to return to a place of rest (the host plant). Whereas horizontal cues are more typically used when ACP are already situated on a plant and therefore only UV (sky) cues are used to navigate towards increasingly younger and more optimal portions of the host plant (young flush), which are near the edge of the plant (near UV) versus in the center of the plant (away from UV). Ultimately, the UV cues from the horizontal axis may be causing the ACP to move to another plant in search of new host locations. Further studies are on-going with the vertical bioassay to see if there is a difference between 0-1 day old and 4-7 day old ACP in this orientation. Additionally, studies are being undertaken to see if flying ACP will be attracted to different colors then walking/flying ACP by using specially designed walking preventing chambers coated with Fluon. A horizontal walking assay was developed to stimulate walking responses of ACP on vegetation and this assay measured direction of movement as well as speed of movement. Known age studies with ACP in the horizontal bioassay revealed that 1 day old ACP were positively attracted toward green light , whereas 4-7 day old ACP remained relatively neutral to green light. Both 1 day old and 4-7 day old ACP showed more positive attraction towards long UV light. These findings indicate that newly emerging ACP may be more attracted to green, because they need to acquire nutrients from feeding on a plant. Conversely, older ACP may be more interested in movement to other plants in search of mates and oviposition sites. Further studies with the horizontal walking assay will be made between newly emerged unmated female ACP and older gravid females. Examination of the effect of different visual stimuli on flight duration of ACP as measured on flight mills is on-going. Comparisons in the duration of flight and numbers of flight bouts are being made between different colored substrates, different quality of light overhead (colored, with UV, without UV, polarized), contrast between overhead lighting and substrate coloring and presence of visual targets.
The objective of this project is to optimize attractancy of visual targets and to determine which segments of the ACP population are responding to traps. Knowledge of the factors that enhance psyllid attraction to a target as well as enhance detection by psyllids of the target against the background will result in optimization of the design and placement of a visually targeted trap. Such as optimized trap can enhance surveillance efforts, provide a pull component for localized control of dispersing ACP or serve as the basis for a lethal pesticide-treated visual trap. Within canopies leaves are seen both as reflected light (from a leaf) and transmitted (translucent) light (through a leaf). Most traps focus on the use of reflected light and the role of transmitted light was examined to determine if this could enhance ACP attraction. A landing assay was developed in the laboratory using a high output light source emitting UV light to evaluate attraction of ACP released at the bottom of the chamber and landing on sticky translucent surfaces placed on the top of the chamber. In this assay, the numbers of ACP collected on two sticky surfaces were compared. ACP strongly preferred landing on translucent yellow rather than green translucent substrates. The effect of edges and lines to contrast and enhance detection of the colors was also evaluated with the translucent surfaces. Narrow vertical black lines enhanced attraction by about 20% to dark yellow translucent panels. Similar black lines did not significantly increase attraction to lighter yellow or green sticky translucent panels. Dark leaf silhouettes on green translucent panels only marginally enhanced collections. Collections on grey panels differed significantly with degree of polarization and these studies are on-going with different colors of polarized panels. Large cage choice assays conducted in the laboratory on the attraction of ACP to various sticky targets. Standard commercial sticky traps (yellow or green) which utilize reflected light were about twice as attractive as translucent sticky traps which allowed transmission of yellow or green light. When yellow sticky traps (reflected light) were modified by adding broad green or black vertical stripes to increase the contrast against the yellow, trap collections were reduced by one third. Use of a black border around a yellow sticky trap did not increase or reduce collections of ACP. Overall responses were about 10% greater to solidly colored traps than those with edges or stripes. On-going assays are further examining effects of polarization and background contrast on attraction.
We have initiated a trial in the Indian River Production Region with grapefruit growers with whom we are establishing foliar nutritional trials similar to what we have done in southwest Florida with oranges using the Boyd cocktail. we are looking specifically at the nitrogen source in combination with individual micro-nutrients. Harvest data the past 5 years from our replicated trial in a 32 acre commercial grove of ‘Valencia’ in southwest Florida evaluating foliar nutrition has shown yield in HLB infected trees have increased each year and juice quality has been maintained. Economic analysis is showing the treatments with highest yield are the most expensive and yield is not significantly different from treatments with less expensive products that are more productive in dollar returns. The common ingredients in the most cost productive treatments are micro- and macro-nutrients, some with salicylate and phosphite. B9: This quarter we completed the 6th harvest in a 13 acre block of ‘Valencia’ on ‘Swingle’ set out in an RCB factorial design with 4 replicates and 4 treatments: insecticide alone, enhanced foliar nutrition along, insecticides + foliar nutrition and untreated control. Both factors significantly affected yields (F = 75.25; df = 1, 9; P < 0.0001 and F = 5.44; df = 1, 9; P = 0.0446 for 'insecticides' and 'nutritionals' respectively). Again, highest yields were obtained in plots receiving both insecticide for ACP plus foliar nutrition (205 ' 7.9 lb of fruit per tree) followed by insecticides only (188 ' 7.5 lb per tree). Yields in plots without insecticide were the least (158 ' 8.3 and 154 ' 9.2 lb per tree in 'nutritional' and 'untreated plots' respectively). Economic analysis will evaluate cost effectiveness. Thresholds: The fourth consecutive year of treatments was completed in two commercial blocks ('Earlygold' and 'Valencia') using a RCB design with 4 reps and 4 ACP management treatments, (1) monthly insecticide sprays, (2) two dormant sprays plus sprays based on a 0.2 ACP adults per stem tap threshold, (3) one dormant spray plus sprays on a 0.7 threshold, and (4) no insecticide sprays. Yields this season were significantly different among treatments (F = 2.53; df = 3, 9; P = 0.0192 and F = 4.77; df = 3, 9; P = 0.0295 for 'Earlygold' and 'Valencia' blocks respectively). Plots receiving calendar sprays (1) had the highest yields followed by treatment (2), and (3) and (4) respectively. No treatment effects on juice quality parameters were found in 'Earlygold' (F = 0.64; df = 3, 25; P = 0.599 and F = 0.64; df = 3, 25; P = 0.599 for brix/acid ratio and lbs solids per box respectively). Yields correlated with ACP numbers assess by biweekly stem tap samples (F = 13.14; df = 2, 14; P = 0.0009; r2 = 0.69 and F = 24.48; d.f. = 2, 14; P = 0.0001 r2 = 0.68, in the 'Earlygold' block and 'Valencia' block respectively). All our results confirm the importance of vector control even when most trees are HLB infected. The correlation between yield losses and ACP densities found in this study is being used in the elaboration of an economic injury level model that permits optimizing the number of insecticides sprays during the growing season based on ACP monitoring. Work continued with the developed fluorescent leaf assay to determine if phloem translocation was enhanced by the use of extra nutritional supplements. We tried this technique using fruit with stems to compare the phloem translocation on normal sized fruit and small fruit. This work was done on fruit from trees that tested positive by qPCR for HLB. We were unable to determine if uptake occurred. Other work consisted in using the fluorescent assay in an organic grove operation where good fruit size was being produced on HLB qPCR positive trees. Visual assays showed that the leaves from the HLB affected trees had uptake similar to healthy leaves.
The objective of this project is to identify the location and movement patterns of Asian citrus psyllids during their winter dormant period. We have previously identified potential overwintering sites based on management practices and surrounding landscape characteristics. Significantly more psyllids were captured in intermittently managed groves during the 2012/2013 and 2013/2014 winter season than in groves under any other management regime. We are currently testing the hypothesis that psyllids move to and ‘shelter’ in intermittently managed groves during winter months, and subsequently disperse in the spring. We have conducted movement studies using capture sticky traps set up at canopy height in concentric buffers surrounding groves to understand movement and directionality of psyllid populations within citrus growing areas. During the winter season of 2013/2014, we evaluated three local citrus area landscapes, each containing three differentially managed grove types; organic, conventional, and intermittent management. Psyllid abundance was evaluated using tap sampling, sticky trap sampling and vacuum insect collection methods. As in the previous year, psyllid abundance was associated with the type grove management conducted at each site. There was no evidence for psyllid movement between groves within our experimental areas. This experiment will continue into the spring season to assess whether movement between groves increases during the spring season. Initial results from this experiment suggest that survival of psyllids in groves is the main factor contributing to population densities in groves under differential management, rather than psyllid movement between groves.
Understanding the interactions between the Asian citrus psyllid (ACP) Diaphorina citri and Candidatus Liberibacter asiaticus (Las), is key in identifying potential controls and management of citrus greening. Recently we found that exposure and pre-exposure to different temperature alters ACP acquisition and inoculation of Las. Thus, variable climatic conditions in Florida are likely to influence ACP transmission of Las. In addition, in cool temperatures ACPs exhibit altered coloration indicating up-regulation of melanization genes. This response is a typical insect response to fungal pathogens. In order to investigate the effect of melanization further, we are conducting fitness assays on melanized ACPs to determine how this change in morphology affects developments, longevity, and fecundity. We are also currently conducting qRT-PCR assays to quantify regulation of a number of heat shock proteins and melanization genes such as phenoloxidases and genes within the rhodopsin pathway. It is possible that expression of these genes may also play a role in ACP-Las interactions within the insects, and to this end we are currently conducting transmission assays on melanized ACP nymphs and adults. Experiments to assess ACP gene expression in response to simultaneous challenges of cool temperature and entomopathogenic fungi are underway. We expected these additional data will 1) identify potential targets for disrupting ACP vector competence, and 2) yield a better understanding of the potential for use of entomopathogenic fungi as an overwinter biocontrol agent of ACPs.
Based on results from the previous Contest Project (CRDF#400), eleven compounds have been screened by the contest committee as candidates for further research to determine their efficacy for control of HLB based on their ability to substantially reduce the titers of the bacterium Candidatus Liberibacter in our grafted citrus assay, lack of phytotoxicity to citrus and potential for registration. After first evaluating combinations of these molecules using the graft-based chemotherapy method under a separate agreement, this project extension will evaluate these 11 compounds as control agents for the HLB bacterium individually and in combination using infected, container-grown citrus and HLB-affected scions. The objective of this project is to determine an optimum chemical formulation that may be registered for field control of HLB. In this quarter (Jan. 2014 to March, 2014),all graft-based tests have been done in 16 treatments of 11 compounds alone and in combination. Some treatments were effective in reducing the Las bacterium to undetectable levels by qPCR. However, some treatments had serious phytotoxicity to citrus, such as ACT and its combinations. We continued the third-round test of the potted-plant experiment including 72 treatments of 11 compounds and their combinations. Based on our delivery research, we changed the application from root-soaking to bark-application using nano formulation of the antimicrobial agents. No bacterium was detected in the new leaves but was present in the old leaves two months after treatment with some of the compounds. Six months after treatment, several treatments were effective in reducing the Las bacterium both in the new and the old leaves, especially SDX, AMP. The research is ongoing.
Ultra High Performance Liquid Chromatography – Pesticide Residue Analysis (Final Report) The purpose of this proposal was to purchase a LC-MS-MS in order to facilitate ongoing CRDF funded research requiring the analysis of pesticide residues in citrus leaf tissue. Funding provided by CRDF paid for a portion of this equipment which was cost-shared by UF-IFAS. The LC-MS-MS was delivered at setup in the Rogers’ lab at the Citrus Research & Education Center. Despite lengthy delays in getting the equipment to function properly due to installation of faulty parts, the LC-MS-MS is functional and is being used to meet the goals of other CRDF funded research projects. During the course of our method development period, we split research samples being analyzed for independent verification with the research labs of Bayer, Syngenta and Valent. Such interaction with these companies help use refine and perfect our methods being used for pesticide residue analysis. To date, the LC-MS-MS has been used to quantify parent compounds and metabolites of imidacloprid, thiamethoxam and clothianidin in citrus nectar collected as part of CRDF funded projects. The goal of these nectar analyses is to support pesticide label changes needed to help protect young trees from becoming infected with HLB. Our results from this project have played an important role in a larger group effort which has resulted in changes in the Admire Pro label, for which a 24C SLN was granted to increase the annual rate of product applied from 0.5 lbs a.i. per acre to 1.0 lbs a.i. per acre, and Belay Insecticide which now has a bearing label permitting use for trees in the 5-9′ size class. This equipment will continue to be used in similar efforts and additional studies looking at maximizing the effectiveness of currently used pesticides for psyllid control.
We have continued this investigation by conducting a second year of replication. Specifically, we sampled Asian citrus psyllid (ACP) populations during the winter season at various heights within tress and with respect to the cardinal direction of trees within Florida citrus groves. We sampled two locations and each one was divided into two plots: one oriented north-south and the other east-west. For each plot, we sampled the citrus canopy at three different heights within trees and the four cardinal orientations within the grove using a custom-made, high powered insect vacuum sampler to collect ACP. Our goal was to develop a two dimensional picture of ACP distribution within citrus groves during winter. Hobo data loggers (which collect environmental data such as temperature) were placed at these various locations to correlate temperature and relative humidity with ACP distribution within groves. The data are currently still being analyzed. However, preliminarily, it appears that ACP populations were high within the groves sampled. We collected 2 psyllids per sample with a maximum sample with 33 psyllids per sample during our winter collections from individual portions of trees. We compared our results with those obtained and posted by personnel from USDA-APHIS that sampled the same plots for the CHMA project and who used the tap sampling method. While tap sampling conducted by USDA-APHIS did not find psyllids in these particular areas during February and March, we collected over 100 psyllids in a single day using the vacuum method in these areas.
One objective of this project is to determine how cold and heat acclimation and temperature-mediated gene expression influence Las transmission by Asian citrus psyllids (ACP). We previously reported that climatic conditions appear to influence the likelihood of Las transmission. Moreover, at some temperatures ACPs exhibit altered coloration indicating up-regulation of melanization genes. We continue to identify additional cryoptotective gene targets for quantification using qRT-PCR. Currently, qRT-PCR assays to quantify several heat shock protein and melanization genes expressed by psyllids under varying temperatures are ongoing. Understanding how cold and heat acclimation, and underlying temperature-mediated gene expression, influence transmission of Las should provide novel targets for managing transmission by ACP populations. We continue to develop isofemale lines of Wolbachia and Wolbachia-free psyllids derived from 10 distinct geographic locations in Florida. Currently, replicate isofemale lines from seven distinct regions of the state have been established. Additional collections will be conducted during the next month to establish additional psyllid lines. Phenotypic screening of isofemale lines is expected to begin in the next quarter. Recently, personnel have been hired by Handler to optimize rearing and egg collection protocols needed to support for germ-line transformation of ACP from these isofemale lines.
The objective of the current project is the identification of a Bacillus thuringiensis (Bt) crystal toxin with basal toxicity against Asian Citrus Psyllid (ACP) and enhancement of this toxin by addition of an ACP gut binding peptide. A phage display library will be screened to identify peptides that bind to the gut of the ACP. Addition of the gut binding peptide to the Bt toxin will increase toxin binding and associated toxicity against the ACP. During the current reporting period partially purified Bt toxins from selected Bt strains provided by Dr. Michael Blackburn, USDA, Maryland were trypsin activated. Proteolytic activation of Bt toxins was carried out at Iowa State University. Briefly, Bt toxins were solubilized using sodium carbonate pH 10.5 + 10mM DTT for three to 16 h at 37’C and dialyzed against 50 mM Tris-Cl pH 8.5. Bt toxins were then incubated with bovine trypsin at a final concentration of 10% of the toxin concentration at 37 ‘C for 1 h. Removal of trypsin was carried out using benzamidine sepharose. The samples were boiled in denaturing SDS sample buffer for 5 min, separated on 10% (wt/vol) SDS/PAGE and stained with Coomassie blue. The SDS-PAGE profiles of trypsin-treated Bt toxins indicated the presence of two different toxin groups with different molecular mass protein bands in the protoxin samples. Samples in the first protoxin group consisted of one toxin band of ~39 kDa, while samples in the second protoxin group consisted of two protein bands of ~40 and ~38 kDa. In contrast, all Bt strains had a single toxin band of ~35 kDa in the trypsin activated state. Samples of 1.8 to 2.3 milligrams of five trypsin-activated Bt toxins were sent to Dr. David G. Hall, USDA-ARS for ACP membrane feeding assays for toxicity analysis.
The overall goal of this 3-year research project is to efficiently deliver antimicrobial molecules into citrus phloem against HLB bacteria. This quarter’s (from Jan. to April 2014) research continued to evaluate the penetrants based on our cuticle assay and to prepare the nano-formulations coupled with penetrant for foliar spray or bark-application. Zone of Inhibition Tests (Kirby-Bauer Test), one of the fast, qualitative assays, was used to measure the ability of nano formulations of antimicrobial agents coupled with the penetrant to inhibit the growth of microorganisms (bacillus subtilis). The chemicals penetrated easily in the cuticles from HLB-affected citrus and the old-mature leaves when compared to those from young cuticles; Nano-formulation of the antimicrobial agents coupled with penetrant significantly inhibited the growth of microorganisms. The ideal nano-formulation, based on the cuticle assay, has been applied to potted plants by bark-application of O/W and foliar spray of W/O. Compared to root-soaking application, nano-formulation promoted the uptake of the antimicrobial agents and resulted in the higher concentrations of antimicrobial agents in phloem for more 15 days. No Las bacterium was detected in any of the plants treated with Ampicillin using either the foliar or bark application nano formulation 6 months from the initial treatment. The future work will be focused on: 1) Continuing to optimize the final formulations by combinations of the penetrants and high drug loading capacity formulations; 2) Evaluating drug loading capacity using the optimized nano formulations; 3) Treating the HLB-affected citrus by foliar-spray and bark-application in the field.
Optimization of CLM pheromone trap deployment was evaluated at 3 densities (1 trap per acre, 1 trap per 3 acres and 1 trap per 5 acres). The total number of CLM captures was similar at all densities tested (F = 0.26; df = 2, 52; P = 0.77). CLM flight activity followed similar patterns among the three trap densities tested (1 trap per 0.40 ha and 1 trap per 1.21 ha: R = 0.93, P < 0.0001; 1 trap per 0.40 ha and 1 trap per 2.02 ha: R = 0.85, P < 0.0001; 1 trap per 1.21 ha and 1 trap per 2.02 ha: R = 0.89, P < 0.0001). These results showed that 1 trap per 5 acres is sufficient to obtain reliable moth counts upon which to base management decisions. A manuscript was submitted to the Journal of Economic Entomology. LD50 and LD80s for some commonly used insecticides for management of citrus pests in Florida were calculated for a susceptible CLM colony. These values are being used to evaluate possible resistance to the tested insecticides in CLM field populations. Larvae and adults from the susceptible colony were exposed for 48 h to different doses (0; 0.01; 0.03; 0.1; 0.3; 1; 3; 10; 30; 50; 100, 300, 600 and 1000 ppm) of the following insecticides: Actara 25WG, Agri-Mek 0.15EC, Cyazypyr, Danitol, Delegate WG, Dimethoate, Intrepid 2F and Micromite 80WGS. The following baselines have been obtained so far for their active ingredients against larvae: Actara (thiamethoxam) LD50=2.813 (CL95: 1.07-6.46) ppm, LD80=619.176 (CL95 199.10-3100.06) (n = 681; .2 = 3.81; d.f = 7; Heterogeneity = 0.76); Agri-Mek (abamectin): LD50= 0.097 ppm (CL95: 0.05-0.16), LD80=2.61 ppm (CL95: 1.41-6.04) (n = 743; .2 = 2.03; d.f = 5; Heterogeneity = 0.41); Cyazypyr (cyantraniliprole): LD50=49.55 ppm (CL95: 18.36-129.61), LD80=27,94 (CL95: 6,19.4-0,29E+06) ppm, (n = 1,021; .2 = 2.22; d.f = 5; Heterogeneity = 0.44); Delegate (spinetoram): LD50=3.56 (CL95: 0.16-20.92), LD80= 201.83 (CL95: 31.70-53761.1) ppm (n = 859; .2 = 19.43; d.f = 5; Heterogeneity = 3.88); for Dimethoate (dimethoate) LD50=1.56 ppm (CL95: 0.15-56.31) and LD80=497.45 ppm (CL95: 22.27-0.37E+09) (n = 546; .2 = 13.07; d.f = 6; Heterogeneity = 2.18); and Micromite (diflubenzuron): LD50=88.32 (CL95: 20.69-246.69) LD80=1800.5 ppm (CL95: 522.84-75810.00), (n = 714; .2 = 10.31; d.f = 5; Heterogeneity = 2.06). A different bioassay technique is being developed for Intrepid. After testing 309 larvae with Danitol, a dose of 600 ppm only resulted in larval mortality of 52%. Due to the high a.i. rates used and low mortality values, no higher doses will be tested with this product. LD50 and LD80 for Delegate, Intrepid and Micromite are being currently being estimated for adults (n = 487, n = 703, n = 381 individuals already tested respectively). CLM larvae were collected for testing from 5 commercial citrus groves with different ACP and CLM insecticide management programs: Bob Paul, Moreno Tanner Road, Silver Strand B9, Duda and PTG. Potential resistance to Agri-Mek in these field populations was assessed by obtaining mortality rates from exposure to the previously obtained LD80 for this product, 0.097 ppm. Larval mortalities thus obtained were 0.76 (n = 33), at Bob Paul, 0.76 (n = 44) Tanner Road, 0.70 (n = 80) at B9, 0.82 (n = 44) at Duda, and 0.80 (n = 50) at PTG. Thus, mortality In all cases was similar to that observed in the laboratory susceptible colony (0.80) indicating no measurable resistance to this product yet in the field populations tested. More individuals and sites will be tested for Agri-Mek and other insecticides this spring and summer.
This is one-year enhanced project of CRDF#584. The goal of this enhanced project is to evaluate the effective compounds, which were formulated for nano-emulsion delivery, in the field. This quarter (from Jan. 2014 to April 2014) research continued greenhouse tests and began field trials. The preliminary results from the greenhouse experiment showed that bark application of the O/W or foliar spray of the W/O were the best application methods to deliver the compound into phloem against Las bacterium, when compared to root-soaking. Nano-formulation of the effective compounds coupled with the screened penetrants increased the uptake of antimicrobial compounds. More than 30 HLB-affected citrus trees were pruned, fertilized and treated with the tested nano formulation of effective compounds in Dec. 2013. Two antimicrobial compounds were loaded into the nano formulation of W/O (Water in Oil) coupled with insecticide oil for foliar spray or O/W (Oil in Water) for bark application. Trunk injection and treatment without antimicrobials were used as controls. Each treatment was repeated for three times. Chemical treatment applications will be made every one month when flush is present starting with the spring flush in 2014. All trees involved in this experiment were confirmed to be Las-positive via a real-time quantitative polymerase chain reaction (qPCR) assay. ACP populations will be recorded by stem-tap sampling. Citrus effects of the treatments will be investigated, including: a) reduction in fruit drop; b) increased canopy density; c) reduced HLB symptoms; d) increased root uptake; e) residues and phytotoxicity. Las titers will be monitored via qPCR.
In order to speed up their application and registration for use by the citrus industry, this one-year enhancement project will immediately test these antimicrobial compounds in the field. The proposed research will focus on evaluating the efficiency of compounds against the Las bacterium in HLB-affected field citrus. In this quarter (Jan to March, 2014), we continued the field trial. The pruned trees were treated with six antimicrobial molecules that have been shown to be effective against Las in graft assays and potted plant experiments using three delivery methods. The treatments will be repeated once a month. The samples will be taken every two months and analyzed for Las and HLB disease. Phytotoxicity was observed in some of the trunk-injection treatments. In these cases, treatment was suspended. We will track this temporal phytotoxicity in next quarter. If the treated trees recovered normal growth in next quarter, we will continue the trunk-injection at lower concentration of the compounds.
(863) 956-8817
(863) 956-5894
700 Experiment Station Road
Lake Alfred, FL 33850
Email Us
