One of the proposed objectives of this project has been to determine whether the use of chemical plant growth regulators (PGRs) affect acquisition of the citrus greening pathogen, Candidatus Liberibacter asiaticus (Las), by the Asian Citrus Psyllid (ACP). Previously, we reported on initial experiments conducted to evaluate the effect the PGR, prohexadione calcium, on Las acquisition after two weeks or one month of feeding. Subsequently, we have completed additional replicates of those trials. In these experiments, twenty adult psyllids of mixed gender were released onto healthy and Las-infected plants treated with prohexadione (sprayed until run-off) and allowed to dry. Treated plants and psyllids were enclosed in nylon mesh sleeve cages. As a control, twenty ACP were also released onto healthy and Las-infected plants treated with water + adjuvant. Each treatment was replicated 6 times on three separate dates. Plants and insects were maintained in a temperature-controlled environmental chamber for 28 d or 14 d acquisition access periods (AAPs) prior to collecting insects. The results from qPCR analysis of psyllids given 28 d AAP suggest that the PGR evaluated does not alter the rate of Las acquisition by ACP, suggesting that that the activity of prohexadione against psyllids does not extend to four weeks. In contrast, psyllids given 14 d AAPs were nearly 15% more likely to acquire Las when feeding on PGR-treated infected plants compared to untreated, Las-infected plants.
Since our last report, we have completed bioassays to evaluate the effect of prohexadione calcium on acquisition of Las by the Asian citrus psyllid over a range of acquisition access periods (AAPs). The psyllids collected from these bioassays are currently being processed (DNA extraction and qPCR) to determine the rate of Las acquisition from each treatment. Because our initial results from these studies indicated that acquisition was greater when psyllids fed on PGR-treated plants, experiments to evaluate the feeding efficiency of psyllids in response to PGR applications were conducted. Feeding efficiency on PGR-treated verses untreated plants was compared by quantifying excretion of honeydew by psyllids after 24, 48, 72, or 96 hr of feeding on treated citrus leaf discs placed in Petri dishes. Four concentrations of prohexadione calcium were evaluated. In addition to quantifying honeydew production, psyllids collected from each treatment have recently been tested to assess acquisition of Las from individual leaves used in experiments. Finally, to further understand the apparent increase in Las acquisition rates following PGR treatments, experiments are currently being conducted to evaluate psyllid settling preference on treated verses non-treated plants.
One of the objectives of this study has been to determine if the results found in previously published work from this project (Tsagkarakis et al., 2011, JASHS) were the result of direct toxicity of the PGRs to the Asian citrus psyllid or if they were the result of plant biochemical changes affecting psyllid fitness. To test this, work is currently being conducted to determine levels of the two most efficacious PGRs (uniconazole and prohexadione calcium) that are phytotoxic to citrus trees. These rates will be used as our upper threshold for conducting LD50 work on psyllids. In our initial rounds of testing we have found that uniconazole (formulated as Sumagic) is not phytotoxic to citrus at undiluted concentrations (500 ppm a.i.). Phytoxicity is assessed visually by looking for any discoloration, abnormal growth (e.g., distorted new leaves), or other obvious signs of plant distress. Prohexadione calcium has been tested to rates of 10,000 ppm (25x label rate) with no obvious signs of phytoxicity. Although the maximum rates tested far exceed label rates, since they were not phytotoxic to the citrus trees they will be used as our upper rate threshold for LD50 work with psyllids to be performed over the coming months.
1) Evaluation of screens impregnated with insecticide barriers. This experiment has already been completed (see annual report sent on 2/2/12). 2) Evaluate the impact of treatment of plants with systemic insecticides on the transmission of Ca. L. asiaticus by starved psyllids. The transmission trials have already been completed. A PCR test was performed to confirm the infectivity of psyllids used in this experiment and it was observed that about 75% of the samples were positive. The PCR test on plants to determine the inoculation is underway. 3) Determination of the concentration of pesticides present in the sap of the xylem and phloem of citrus plants and the lethal concentration to D. citri. The equipment for the extraction of plant sap has already been delivered and the experiment must be started in September (after Brazilian winter).
The goal of this investigation has been to identify Asian citrus psyllid (ACP) attractants for development of practical management tools. We have identified a cuticular hydrocarbon that appears to function as a pheromone-type attractant. With this result, we have developed a prototype ACP trap that incorporates the attractant and as a result catches more ACP than unbaited traps. We have also identified a number of plant volatiles that attract ACP and which can also increase of of psylllids on traps as compared with unbaited controls. Male ACP were attracted to the cuticular extracts of conspecific females. Furthermore, removal of cuticular hydrocarbons by solvent washing rendered females non-attractive to males; while normally, recently killed females are known to attract male psyllids. The primary role of insect cuticular hydrocarbons is to provide a hydrophobic barrier to minimize transpiration and desiccation. However, cuticular hydrocarbons are also known to mediate chemical communication in many insect species, including psyllids. The behavioral and chemical laboratory results indicated a sex-specific function of female cuticular hydrocarbons, but our field results did not exclude a possible aggregative function. In field trials, female cuticular extracts attracted more male ACP on clear traps; however, this difference did not occur on yellow traps. Visual cues are known to strongly influence the orientation of ACP to olfactory cues. ACP adults are strongly attracted to yellow color. Therefore, at the dosage of cuticular extracts tested here, it is possible that response to an olfactory cue was obscured by the visual stimulus of yellow traps. Both clear and yellow traps baited with five or 10 equivalent units of either male or female cuticular extract captured more total D. citri than unbaited controls. These results suggest a possible aggregative function of the cuticular hydrocarbons. Dodecanoic acid was one of the few components detected in higher amounts from female than male extracts that also elicited a behavioral response from males in laboratory assays. Initial testing showed that dodecanoic acid alone did not increase total catch of psyllids on traps as compared with a blank control; however, it did skew the sex ratio of captured psyllids towards male bias at the highest dosage tested. Later tests that were conducted with a new generation trap that released much higher amounts of this chemical indicated that the attractant could increase catch of psyllids on traps as compared to unbaited controls. In addition to identifying psyllid-based attractants, we have made significant progress in identifying plant-based psyllid attractants. We have identified several of the key volatiles from citrus that attract psyllids. Also, we have discovered that break-down products of citrus volatiles may be important components of an ACP attractant rather than the actual volatiles that are initially given off by citrus. Specific tools (both traps and attract and kill devices) are under development that will incorporate these attractants for use as practical tools.
The objective of this research has been to identify repellents for Asian citrus psyllid (ACP) and also to develop practical tools from these identifications that may eventually be used for ACP management. Throughout the project we have engaged in partnerships with private industry; therefore, our focus has remained on practical end-products that have been under development. The pest management company, ISCA Technologies, was one private company that made significant progress with their SPLAT dispenser, in terms of developing a practical repellent tool for ACP using our discoveries. However, other companies, such as Alpha Scents also made progress in the development of tools for ACP repellency during this project. We determined that volatiles from guava leaves signi’cantly inhibited attraction of ACP to normally attractive host-plant (citrus) volatiles. A similar level of inhibition was recorded when synthetic DMDS was co-released with volatiles from citrus leaves. In addition, the volatile mixture emanating from a combination of intact citrus and intact guava leaves induced a knock-down effect on adult ACP. Compounds similar to DMDS including dipropyl disulphide, ethyl-1-propyl disulphide, and diethyl disulphide did not affect the behavioral response of ACP to attractive citrus host plant volatiles. Head-space volatile analyses were conducted to compare sulphur volatile pro’les of citrus and guava, used in our behavioral assays, with a gas chromatography-pulsed ‘ame photometric detector. DMDS, produced by wounded guava in our olfactometer assays, was not produced by similarly wounded citrus. The airborne concentration of DMDS that induced the behavioral effect in the 4-choice olfactometer was 107 pg/ml. In a small plot ‘eld experiment, populations of ACP were signi’cantly reduced by deployment of synthetic DMDS from polyethylene vials compared with untreated control plots. Our results verified that guava leaf volatiles inhibit the response of ACP to citrus host plant volatiles and suggested that the induced compound, DMDS, may be partially responsible for this effect. Also, we showed that ‘eld deployment of DMDS reduces densities of ACP and thus may have potential as a novel control strategy. Also, we found that volatiles from crushed garlic chive leaves, garlic chive essential oil, garlic chive plants, wild onion plants and crushed wild onion leaves all repelled ACP adults when compared with clean air, with the ‘rst two being signi’cantly more repellent than the others. However, when tested with citrus volatiles, only crushed garlic chive leaves and garlic chive essential oil were repellent, and crushed wild onions leaves were not. Analysis of the headspace components of crushed garlic chive leaves and garlic chive essential oil by gas chromatography-mass spectrometry revealed that monosul’des, disul’des and trisul’des were the primary sulfur volatiles present. In general, trisul’des (dimethyl trisul’de) inhibited the response of ACP to citrus volatiles more than disul’des (dimethyl disul’de, allyl methyl disul’de, allyl disul’de). Monosul’des did not affect the behavior of ACP adults. A blend of dimethyl trisul’de and dimethyl disul’de in 1 : 1 ratio showed an additive effect on inhibition of ACP response to citrus volatiles. The plant volatiles from Allium spp. did not affect the behaviour of the D. citri ecto-parasitoid Tamarixia radiata. Thus, Allium spp. or the tri- and di-sulphides could be integrated into management programmes for ACP without affecting natural enemies. In addition, we investigated volatiles from essential oils of coriander, lavender, rose, thyme, tea tree oil and 2-undecanone, a major constituent of rue oil repelled ACP adults compared with clean air. Also, coriander, lavender, rose and thyme oil inhibited the response of ACP when co-presented with citrus leaves. Volatiles from eugenol, eucalyptol, carvacrol, b-caryophyllene, a-pinene, a-gurjunene and linalool did not repel ACP adults compared with clean air. Practical tools from this under development.
During the last 3 years, 2 factorial field experiments, E1 and E2, initiated in October/05 and May/06, respectively, in new plantations of sweet orange in a HLB epidemic region of Sao Paulo-Brazil, were carried out, assessed and analyzed. The objective of this study was to assess the effectiveness and the importance of bacterial inoculum reduction and ACP vector control strategies applied within young citrus plots (Local management), in different frequencies and combinations, on HLB temporal progress. Local inoculum reduction levels for E1 were every 4, 8 and 16 weeks, and for E2, every 2, 4, 12, and 26 weeks. Local vector control levels for E1 were no control, program A (PA) and program B (PB), and for E2, no control and program C (PC), as follows. Psyllid control was done with two 56-day-interval soil or drench applications of systemic insecticides concurrently with the rainy season each year; and during the rest of the year, with insecticide sprays every 28 days for PA, and every 14 days for PB and PC. Regional HLB management was present for E1 and absent for E2. The main results were: i) The beginning of the HLB epidemic was delayed for 10 months in E1, but wasn’t affected by different local strategies for both experiments; ii) After 60 (E1) and 53 (E2) months, the HLB incidence and progress rates were not affected by different frequencies of local inoculum reduction in either experiment, and were different only in plots with and without local vector control in E2; iii) In E1 the disease incidence was reduced by 90% and the disease progress rate by 50% in both plots with and without vector control. These reductions were explained by smaller psyllid populations (4-5x less and smaller year after year) and lower frequency of bacterialiferous psyllids (6-7x less) in E1 compared to E2; iv) Annual productivity remained increasing over time in E1 as expected for young plantings, whereas remained stable or decreased in E2 (E2 was completelly eliminated 4.5 year old because became economically unprofitable); v) Area-wide HLB management reduces the control costs because with less intensive vector control program in E1 it was possible to be more efficient than the high intensive vector control program applied locally within a region without regional management (E2). These results scientifically confirmed, for the first time in the world, the great importance of primary infection by migrating bacterialiferous ACP populations on HLB epidemics and suggest that an area-wide inoculum and ACP management heavily affects the efficiency and cost of HLB control. The results of this project were also presented to many citrus growers and crop protection agents in many events in South, Central and North America to alert for the difficulties in HLB control in small geographicall scale (small farms) and help the establishment of growers’ groups for HLB area-wide management. This management strategy has become the predominant intermediate strategy recommended to growers both in South and North America. Two papers were submitted for publication: “Efficacy of area-wide inoculum reduction and vector control on temporal progress of huanglongbing in young sweet orange plantings” presenting all results of both experiments was submitted to Plant Disease; and “Frequency of local inoculum reduction on citrus Huanglongbing epidemics” with results of 8 experiments, including E1 and E2, was submitted to Crop Protection. We would like to acknoledge all CRDF support for the conclusion of this project.
The objectives were: 1) to compare the temporal progress of HLB caused by C. L. asiaticus (CLas) and by C. L. americanus (CLam), both transmitted by D. citri (ACP), having infected Citrus or Murraya as primary inoculum sources; 2) to compare the acquisition efficiency of both species by ACP in Citrus and Murraya; 3) to determine incubation and latency periods of HLB after transmission of CLas or CLam by ACP; 4) to determine when citrus plants infected by CLas or CLam become an effective source of inoculum for ACP; 5) to quantify and compare the HLB symptoms progress in sweet orange cultivars infected with CLas or CLam by ACP at different ages. After 3 yrs of experiments under insect-proof and field conditions the main results were: i) CLas was better acquired from infected citrus plants and transmitted to new citrus plants by ACP than CLam (In average 30.4% of psyllids collected from inoculum source plants and 8.4% collected from test plants were CLas+ and no one for CLam. 9.6-19.2% of test plant were CLas+ and only 0-3.8% CLam+. From the three Clam citrus infected plants, two had also CLas in a mix infection); ii) CLas titer in citrus infected plants was higher than CLam titer (Average Ct value for leaves with CLas were 24.7 and for CLam 33.7); iii) CLam induces more severe HLB symptoms in citrus plants than CLas; iv) CLam and CLas were detected by PCR in adult ACP after 1 h of acquisition period (AP) in citrus infected plants, but not with 30 min AP. For CLas the efficiency of acquisition increased with the AP up to 7 days and decreased with 14 days AP. For CLam the efficiency of acquisition increased with 1 days AP and decreased after that; v) CLas incubation period seems to be shorter than CLam’s (The first CLas and CLam citrus infected plant were detected respectively 6 and 27 months after the beginning of the experiment); vi) CLam was better established in Murraya than CLas (many attempts by grafting or natural inoculations were done trying to get Murraya plants infected with CLas but all failed); vii) For the first time, it was observed the transmission of CLam from Murraya to citrus by ACP (The note “First Report of ‘Candidatus Liberibacter americanus’ Transmission from Murraya paniculata (L.) Jack to Sweet Orange (Citrus sinensis Osbeck) by Asian Citrus Psyllid (Diaphorina citri Kuwayama)” was published in Journal of Plant Pathology); viii) CLam was better acquired and transmitted by ACP to citrus plants from Murraya than from citrus sources of inoculum (where Murraya served as source of inoculum, 46.0% and 9.4% of ACP collected respectively in source plants and test plants were CLam+, whereas where citrus served as source of inoculum, 6.4 and 4.7% of ACP collected respectively in source plants and test plants were CLam+. 8.2% of test plants were CLam+ when inoculum source was Murraya and no positive test plant was detected when inoculum source was citrus); ix) ACP population was better established on Murraya than in citrus plants; x) ACP population was better established and bacteria transmission was higher in compartments with more sun light; xi) HLB severity was variable during the year. Usually, lower disease severities were observed after the recovery of tree canopy spring and summer new vegetative flushes. Higher disease severities were observed at the end of autumn and the middle of winter and beginning of summer; xii) HLB severity progress was variable among years, not being always cumulative; xiii) Unfortunately, only two years of assessments were not enough for modeling disease severity progress, and no conclusions about the relation of disease severity progress with scion/rootstock combination or tree age at the appearance of first symptoms could be made; xiv) Yield reduction (%) was higher for diseased trees of younger plots. During this project we had difficulties related to infestation of Tamarixia radiata in our ACP breeding plants that completely devastated it and postponed the new releases of ACP, and inoculation of CLas by adult ACP. Some of these results were presented in the 2nd International Research Conference on Huanglongbing in Orlando January 10-14th.
Activities of the CHMA program assistant (Brandon Page) April-July 2012: During this reporting period, the CHMA assistant provided support to the CHMA effort by attending various local CHMA meetings as well as statewide meetings. At these meeting, Mr. Page participated by setting up displays and/or giving talks on ongoing efforts and successes of the CHMA program to encourage more participation. Particularly in the case of local CHMA meetings, Mr. Page returned from these meetings and posted updates for these CHMAs on the website to help growers stay up to date with the activities and plans for these CHMAs. The following is a list of meetings attended: All Florida Ag Show (4/23-4/26), Hardee County CHMA meeting (5/1), Citrus OJ Squeezer in Ft. Pierce (5/10), Citrus Advisory meeting ‘Volusia CHMA (5/11), Immokalee meeting (5/22), Hillbillies (5/22), Dundee CHMA meeting (5/30), FSHS meeting (6/3-6/5), Pasco county (6/11), Citrus Mutual Annual meeting (6/13-6/14), South Hillsborough CHMA (6/20), Immokalee (6/21), FFA State Convention (6/26-6/28), and Hardee county CHMA (7/13). In conjunction with the grower leaders for the CHMAs, numerous CHMA meetings have been scheduled for late summer/early fall. Announcements have been posted on the CHMA website for those with firm dates at this time. In addition to attending meetings, Mr. Page has spent a considerable amount of time working on improvements to the CHMA website and communication efforts. An email listserv has been created for each of the CHMAs for growers who wish, can sign up and receive notifications of updates for their CHMA. A CHMA questionnaire was created and posted on the CHMA website too get feedback from growers on the CHMA communication efforts to determine how best to meet the needs of the growers. A new logo for the CHMA program was created to help brand the Florida CHMA program, this logo will be unveiled soon. As a result of requests by grower team leaders, we are in the process of creating a series of psyllid scouting report maps that show results broken down by TRS to help growers more readily identify the trouble areas within a CHMA. Mr. Page has been creating the frame work for these maps manually and providing these to CHMAs upon request. This is a time consuming process however. Thus, a computer programmer has been hired and is currently working with Mr. Page to create a program that will automatically create such maps which can then be posted on the website for each of the CHMAs. This work has only recently begun and the timetable for completion is not yet determined.
Work on the influence of season (climate) on longevity of pesticide applications for psyllid control was continued. In April, using standard tractor driven airblast spray equipment, foliar applications of an organophosphate, pyrethroid and neonicotinoid were made. Caging studies showed in general that treatments were effective until 14 days after application. Compared to field trials conducted in January, the results were fairly similar with the exception of the pyrethroid which had provided reductions for up to 21d. However, despite the reduction in duration of efficacy provided, the pyrethroid still provided control equal to or better than the other classes of chemistry during this evaluation period. A field trial investigating the effects of different classes of adjuvants on residual activity of pesticides was initiated in early July. In this trial, an organophosphate (contact insecticide) and a foliar-applied neonicotinoid (translaminar activity) were applied alone and in combination with either a petroleum oil, organosilicone surfactant, crop oil concentrate, or a non-ionic surfactant. Following applications, caging studies were conducted to determine the length of residual control provided based on product/adjuvant combination. In addition, the mortality provided is being compared with the actual pesticide residue levels on the leaf surface to determine what level is needed to provide control. This particular field trial is still underway and will be summarized next report. Data collection from the 10-acre multi-year young tree protection trial continues. Psyllid populations began to increase for the first time above detectable levels in April. Bi-weekly psyllid counts continue with significant differences in the psyllid population found between some treatments. Also for the first time, Las+ trees were detected in the block. Thus far, the numbers of infected trees are too small for meaningful comparison, but there exists a definite bias for infected trees in the untreated control. In addition to the leafminer and psyllid counts, and collection of leaves for residue analysis, we have also begun monitoring for any shifts in pesticide susceptibility.
During spring/summer 2012, we established 2 field trials in St. Lucie County. We completed 2 grower validation trials in St. Lucie and Okeechobee counties and participated in 2 others in Charlotte and DeSoto counties in collaboration with ISCA, Fly Masters International, grove managers, owners, and crop consultants. These trials address timing, coverage, formulation, longevity, and efficacy of mating disruption (MD) under various crop phenologies. 1. Effect of winter applications. The first application was made 6 February followed by a second application 24 April. The February application had no effect on trap catch disruption after the April application. The April application reduced trap catch for >4 weeks. CLM flight preceded leaf mining. Leaf mines were evaluated 6 times. Data are being evaluated. 2. Effect of formulation on longevity and efficacy across treatment gaps. Established 27 April to compare current SPLAT CLM pheromone formulation with a formulation that incorporates the ‘natural’ 3:1 triene:diene blend of two pheromone components. Treatments were applied 29 May and 3 June. Mines were evaluated 18 June when widespread early-stage leaf mines were present on young flush. 3. Validation trial, 200 g/acre nominal rate with treatment gaps (effective rate 140 g/acre). Cooperator: The Packers of Indian River. SPLAT CLM purchased by grower. 40 acres of grapefruit were treated in mid-April (1300′ rows, 10T 4S 8T 6S 8T 4S 11T where T=treated row, S=skipped row). The trial continued for 10 weeks. Mating disruption was evaluated weekly. Mating disruption lasted 6 weeks. Three leaf mine evaluations were made. Data are still being evaluated. 4. Validation trial, 200 g/acre, no treatment gaps, DeSoto county. SPLAT CLM purchased by grower. Approximately 100 acres of pomelos treated, late February, second application made 18 April. Longevity of MD, mining activity and canker incidence will be documented. Data are being evaluated. 5. Validation trial, 200 g/acre, no gaps. Okeechobee County. SPLAT applied by hand to ~12 acres of an irregularly-shaped grove of 3-yr-old grapefruit. Effective disruption lasted 8 weeks. Two leaf mine evaluations were made. Data from the second mine evaluation (8 weeks) showed that mines were not significantly lower in the treated block. 6. Validation trial in 100 acres of grapefruit, 200 g/acre nominal rate with treatment gaps (effective rate 140 g/acre). Charlotte county. Mating disruption lasted 6 weeks. Leaf mine incidence and severity were lower in the treated block 4 weeks after first application, but there was no difference in mines by 10 weeks. Second application made 22 May 2012. 7. Effect of SPLAT formulation, application method, and rate. Cooperator: Scott Lambeth, St. Lucie County. Grower validation trial installed in July to test the efficacy of large scale application of 3:1 triene:diene pheromone blend. A small-scale companion trial will test the efficacy of the current formulation with the ‘natural’ 3:1 triene:diene blend. Machine application will be compared with hand application. Mating disruption and leaf mines will be evaluated.
Xambr’ Brazil Plots: Designed to examine the effect of windbreaks, copper sprays to reduce infection, and leafminer treatments to determine their individual and combined effects on control of citrus canker. Windbreaks were completed and plants were be established in Mid April 2010, but severe winds damaged the windbreaks during two storm events. These windbreaks have been reinforced and rebuilt. From April through June 2012, we continued planting of Casuarina resets to replace damaged windbreak plants and removal of damaged screens and poles. The damage delayed the experiment. Established citrus will be of sufficient size to begin the experiment in March 2013. New windbreak trials established in Saint Lucie County. A location to explore gradients of citrus canker in wind-breaked fields identified (cv. Valencia orange, Estes Farm, Indian River Co.). Ten Hobo-brand weather stations were purchased to record wind speed, leaf wetness and rainfall. Weather stations were deployed equidistantly in an East-West and North-South orientation in the citrus block. Preliminary data collection was begun. Programmable leaf wetness controller (PLWC) to examine canker bacterial survival in the field. Software was written, debugged, is complete, and the control program is working well. Development of leaf wetness sensors that function across the full range of wetness has eluded scientists for many years. We have designed and constructed sensors based on completely new technology and continue to debug them prior to deployment. The sensor is designed to use various materials with superior capillary action and restricts contact between the two probe wires only to material used within the area of sensor. We are currently addressing plateauing issues when completely saturated. Project publications: Bock, C. H., Graham, J. H., Gottwald, T. R., Cook, A. Z., and Parker, P. E. 2010. Wind speed effects on the quantity of Xanthomonas citri subsp. citri dispersed downwind from canopies of grapefruit tree infected with citrus canker. Plant Di Bock C.H., Graham, J.H., Gottwald, T.R., Cook, A.Z., and Parker, P.E. 2010. Wind speed and wind-associated leaf injury affect severity of citrus canker on Swingle citrumelo. Eur J. Plant Path 128:21-38 Bock, CH, Parker, PE, Cook, AZ, Graham, JH and Gottwald, TR. 2001. Infection and decontamination of citrus canker and inoculated the surfaces. Crop Protection 30:259-264. Hall, D.G., Gottwald, T.R. and C.H. Bock. 2010. Exacerbation of citrus canker by citrus leafminer Phyllocnistis citrella in Florida. Florida Entomologist. Florida Entomologist 93:558-566. Bock, C.H., Gottwald, T.R. and Parker, P.E. 2011. Distribution of canker lesions on the surface of diseased grapefruit. Plant Pathology (Accepted). Bock, C.H., Cook, A.Z., Parker, P.E., Gottwald, T.R., and Graham, J.H. 2011. Some characteristics of the dispersal plume of bacteria of Xanthomonas citri subsp citri in wind-driven splash downwind of canker-infected grapefruit tree canopies. (Plant Disease). Bock C.H., Graham J.H., Cook A. Z., Parker P.E., and Gottwald T.R.. 2012. Predisposition of citrus foliage to infection with Xanthomonas citri subsp. citri. (Submitted to Plant Disease )
Current management strategies for citrus huanglongbing disease (HLB) are focused on effective control of the Asian citrus psyllid (ACP) primarily through use of broad-spectrum insecticides. However, the repeated use of a limited number of insecticides poses a serious risk of resistance development. We have documented that resistance levels of ACP to certain insecticides have reached 30-35 fold as of two year ago. There is an urgent need to investigate biorational tactics that involve non-neurotoxic compounds or compounds with novel mode of actions as a tool for managing ACP. In the current project, we aim to evaluate and optimize candidate non-neurotoxic compounds including nonprotein amino acids, phytolectins, kinins, alllatostatins and insect growth regulators for ACP management. In the current project, these compounds will be evaluated for their effects on overall mortality, development, fecundity and feeding of ACP. Such compounds will broaden current ACP and resistance management programs. We have begun evaluating the role of allatostatin (juvenile hormone inhibitor), novaluron (chitin synthesis inhibitor), L-canavanine (causes several physiological and morphological abnormalities), and methoprene (juvenile hormone mimic) in the management of ACP. These compounds are currently being evaluated for their effects on mortality, feeding behavior, longevity, host selection and development of ACP. Feeding behavior assessment is being conducted using the electrical penetration graph (EPG) technique. Currently, we are also assessing the role of a novel non-neurotoxic insecticide, cyanotraniliprole (CyazypyrTM), a new anthranilic diamide compound that affects insect muscles, as an alternative to the classic neurotoxic insecticides for the management of ACP. Our results have shown that cyanotraniliprole not only adversely affects the feeding behavior of ACP but also adversely affects the settling behavior of ACP adults on cyanotraniliprole-treated plants. Further investigations on the effects of cyanotraniliprole on growth and development of ACP are currently in progress. We anticipate that inclusion of promising non neurotoxic compounds will broaden current ACP and resistance management programs.
Our objectives are to determine how psyllid behavior and life history are affected by tree nutrition supplement programs. These programs have been developed to maintain the health and productivity of HLB-infected citrus trees. However, their impact on Asian citrus psyllid biology and pathogen transmission is unknown. We have begun with a laboratory experiment, for which, forty 2’year old Valencia trees have been selected. Half of them are HLB-infected, the others are uninfected. We collected volatiles from these plants and sent leaf samples to Waters Agricultural Laboratories (Camille, GA) in order to obtain nutrient analysis of the leaves before starting the different treatments (baseline). Subsequently we have divided these plants in 4 treatments: 1. uninfected / Control (no nutrient regime) 2. uninfected / Nutritional treatment 3. HLB-infected / Control (no nutrient regime) 4. HLB-infected / Nutritional treatment Treatments consist of bi-weekly application of 500ml of a solution of KeyPlex’ 1200 (2.5ml/L) and N-Sure’ (2.5 ml/L) for the nutrient regime, and of 500ml of tap water for the control. The nutrient regime has been selected with the help of Timothy Spann, assistant professor in horticultural science at the CREC. After 2 months, we expect that the nutrient regime will show significant differences compared to the control. To estimate this difference, leaf samples will be sent for nutrient analysis and compared to those from the baseline. Subsequently, we will perform behavioral tests with these plants. We hypothesize that the nutritionally supplemented plants will be more attractive to the psyllid, and therefore the insects will remain longer on nutrient supplemented plants than on controls. Volatiles from citrus plants will be collected and analyzed to correlate volatile release with behavioral response of psyllids. We will also evaluate the oviposition preference of psyllids as well as nymph development, to study if psyllids develop differently on nutrient supplemented citrus as compared with non-supplemented controls.
Little is known about alternate hosts of the Asian citrus psyllid (ACP) during overwintering months in Florida. It is often stated that ACP overwinter as adults within the canopy of citrus trees, but this hypothesis has never been verified through scientific study. To better understand how ACP survives during winter in Florida, we plan to establish an extensive sampling program during the fall and winter. We already have identified the citrus arboretum in Winter Haven, FL (http://www.freshfromflorida.com/pi/budwood/arb.html) as a research sampling location and begun a sampling protocol for this location. In this arboretum, almost 200 citrus species and related species are grown, and during our first visit we observed a significant number of psyllids on citrus plants. Moreover we have started to identify other commercial citrus growing locations for sampling. We plan to sample organic groves, abandoned groves, and trees surrounding conventional groves. Particular attention will be given to conifer trees, as we found several studies showing that in Europe, psyllids usually overwinter in conifers. We are currently planing laboratory experiments in a climatic chamber. For these experiments, we will examine the effects of temperature and photoperiod that will be similar to those observed during winter in Florida. We will perform choice and survival tests between different plants selected based on their potential for overwintering. These laboratory experiments will be compared to our results from the field and help us to identify potential alternative hosts during winter for ACP.
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