We conducted 3 assays to compare the effectiveness of a commercially available entomopathogenic nematode (EPN) species Heterorhabditis bacteriophora to that of Steinernema riobrave which is documented to be the most effective EPN pathogen of Diaprepes abbreviatus, but is not currently available commercially. In the basic assay, weevil larvae are preconditioned at 10 C or 27 C for 48 h. Then weevil larvae are exposed to very low rates (2 nematodes/cm2 soil surface) of EPNs at 18 C or 27 C for 6 days, during which mortality is evaluated at 2 day intervals. Thus, temperature regimes of 10C+18C simulate a wintertime cold event and 27C+27C simulates summertime conditions. Results of these trials revealed that: 1. H. bacteriphora was 50% as effective as S. riobrave in summer. 2. S. riobrave was 10% more effective in winter than it was with nonstressed weevils during summer 3. H. bacteriophora was 60% more effective in winter than it was with nonstressed weevils during summer 4. H. bacteriophora was 80% as effective in winter as Sr was with nonstressed weevils during summer We subsequently obtained an isolate of H. bacteriophora from upstate New York. In a single trial, not yet repeated, the New York isolate was somewhat more effective than the commercial isolate of H. bacteriophora during simulated winter cold events. We most recently obtained a commercial product containing Steinernema krauseii a temperate species capable of infecting hosts at temperatures as low as 8 C. In a single trial, not yet repeated, S. krauseii was ineffective against weevils under simulated summertime conditions. It was much more effective in the cold temperature regime, but inferior to H. bacteriophora and S. riobrave in its ability to kill weevil larvae.
Entomopathogenic nematodes: Amending soils to increase biological control of insect pests Because we found increased numbers of Steinernema diaprepesi in low pH treatments (as measured by qPCR of nematodes from soil samples) at the Bartow experiment (May 2013 report), we buried caged weevil larvae in all plots and evaluated the mortality rate after 7 days in the soil. In contrast to our predictions, weevil mortality and infection of weevils by S. diaprepesi were only 15% (74% vs 64%, ns) and 32% (33% vs 25%, ns) higher, respectively, in sulfur amended than non-amended treatments. Heterorhabditis indica infection of weevils was 8-fold higher (18% vs 2%, P<0.05) in the non-amended plots which conforms to the relationship measured in the Schumann ACPS trial in which H. indica were significantly more abundant in the high pH ACPS plots than in the low pH conventional citriculture plots. We Initiated a second round of buried sentinel weevils to confirm the results, to be reported in September 2013. In June 2013 the average fibrous root weight and numbers free living nematodes from sulfur-amended trees at Bartow were 60% (ns) and 56% (P<0.05), respectively, of those from non-amended trees. The abundance of Tylenchulus semipenetrans was 5-fold greater in non-amended than in sulfur amended plots (P<0.05). These results continue trends noted previously and suggest that sulfur is reducing fibrous root density somewhat (perhaps because roots are more efficient at lower pH), but is also affecting the citrus nematode independently of its affect on root availabilty. This is consistent with previous reports of the effects of pH on the citrus nematode and demonstrates that the potential for managing this nematode by pH adjustment is greater than previously thought. Completed a second manuscript (Cultural practices to manage a bacterial disease alter entomopathogenic nematode communities and increase the severity of a pest-disease complex) describing effects of ACPS and fabric mulch on citrus tree growth and yield, Diaprepes abbreviatus, Phytophthora nicotianae, EPNs and natural enemies of EPNs. First manuscript in this series (Campos-Herrera, R., et al. 2013. New citriculture system suppresses native and augmented entomopathogenic nematodes. Biological Control 66: 183-194.) published in June. Plant parasitic Nematodes: Characterizing a new nematode pest and the prevalence of resistance breaking populations of the citrus nematode. Evaluated nematicidal efficacy in the east coast, dagger nematode nematicide trial in June. No chemical treatment (oxamyl, and three experimental nematicides) reduced dagger nematode populations significantly. Plots will receive additional treatments at the end of the rainy season in early autumn and treatment effects measured in November. Dagger nematode spatial pattern at site on the central ridge was characterized and a second trial will be initiated this autumn.
Our long term goal is to develop a system for inoculating Asian citrus psyllid (ACP) with a native pathogenic fungus, Isaria fumosorosea (Ifr), and use these infected psyllids to rapidly ‘autodisseminate’ the pathogen to ACP populations in residential citrus. Specific research objectives for 2012-2013 were as follows: (1) Initiate Ifr-epizootics among ACP populations on dooryard citrus trees, (2) Evaluate seasonal and environmental effects on infection levels, (3) Determine the impact of pathogen on arthropod biological control agents. For objectives 1 and 2, we secured the permission of trailer park residents in the Rio Grande Valley to use their citrus trees for our field studies. To minimize the risk of spreading HLB, we agreed to: (1) inoculate and release only ACP adults collected from the study sites, and (2) use only trees infested by wild ACP. Since our last report submitted in April of 2013, the following trials were completed: “Quantify infection of Ifr-inoculated adults under field conditions and the effects of incubation treatments prior to field release”. To better assess what release rates of inoculated psyllids would be required to initiate epizootics within target trees, we conducted trials to quantify infection of Ifr-inoculated adults under field conditions and the effects of incubation treatments prior to field release. The rationale behind the incubation treatments were to develop a means of maximizing infection of inoculated psyllids after release on target trees. During June to September of 2013, we conducted field studies using orange trees at the ‘Victoria Palms’ trailer park in Donna, TX. Adult psyllids collected from orange trees at ‘Victoria Palms’ were inoculated with Ifr formulation and held (incubated) in humid vials with orange leaf disks for: 0 h, 24 h, and 48 h . Another set of adults were not inoculated and set aside as controls. Each psyllid was released into a ‘clip cage’ attached to a leaf on an orange tree at the trailer park. Groups of four clip cages (one cage for a control psyllid and one cage for each of the three types of inoculated psyllids) were attached to four apical leaves on the same stem. Ten groups of clip cages were setup on the North-East canopy of trees (total = 40 clip cages per tree). For eight consecutive days, we recorded the status of the psyllid within each clip cage. By the eighth day, all inoculated and incubated psyllids were dead and infected with Ifr. In comparison, 50 % of psyllids inoculated but not incubated were dead and only 20 % of these psyllids were infected with Ifr. None of the control psyllids were killed or infected by Ifr. These results demonstrated that incubation of Ifr-inoculated adults for at least 24 h will ensure 100 % mortality and infection within 8 days of release in residential citrus trees under summer weather conditions in Texas. We are currently repeating these studies under cooler and wetter fall conditions that should enhance infection of ACP by Ifr. “Effects of Ifr spores on lacewing larvae”. During June of 2013, we compared predation by lacewing larvae on healthy or Ifr-inoculated adults of ACP. We collected lacewing larvae from residential orange trees infested with ACP and held them for 12 h on orange leaf disks in plastic vials. After 12 h, we offered four healthy ACP adults and then four Ifr-inoculated ACP adults (inoculated by dusting with Ifr formulation 24 h earlier) to lacewing larvae that were similar in size and development. We observed each lacewing larva and found they accepted and fed on all the healthy ACP adults and also all the Ifr-inoculated adults. None of the lacewing larvae showed visible signs of infection by Ifr and appeared healthy after being held for five days in leaf-disk vials and fed additional healthy ACP adults. This study demonstrated that lacewing larvae do not appear to be adversely affected by feeding on ACP adults inoculated with Ifr formulation.
Our long term goal is to develop a system for inoculating Asian citrus psyllid (ACP) with a native pathogenic fungus, Isaria fumosorosea (Ifr), and use these infected psyllids to rapidly ‘autodisseminate’ the pathogen to ACP populations in residential citrus. Specific research objectives for 2012-2013 were as follows: (1) Initiate Ifr-epizootics among ACP populations on dooryard citrus trees, (2) Evaluate seasonal and environmental effects on infection levels, (3) Determine the impact of pathogen on arthropod biological control agents. For objectives 1 and 2, we secured the permission of trailer park residents in the Rio Grande Valley to use their citrus trees for our field studies. To minimize the risk of spreading HLB, we agreed to: (1) inoculate and release only ACP adults collected from the study sites, and (2) use only trees infested by wild ACP. Since our last report submitted in April of 2013, the following trials were completed: “Quantify infection of Ifr-inoculated adults under field conditions and the effects of incubation treatments prior to field release”. To better assess what release rates of inoculated psyllids would be required to initiate epizootics within target trees, we conducted trials to quantify infection of Ifr-inoculated adults under field conditions and the effects of incubation treatments prior to field release. The rationale behind the incubation treatments were to develop a means of maximizing infection of inoculated psyllids after release on target trees. During June to September of 2013, we conducted field studies using orange trees at the ‘Victoria Palms’ trailer park in Donna, TX. Adult psyllids collected from orange trees at ‘Victoria Palms’ were inoculated with Ifr formulation and held (incubated) in humid vials with orange leaf disks for: 0 h, 24 h, and 48 h . Another set of adults were not inoculated and set aside as controls. Each psyllid was released into a ‘clip cage’ attached to a leaf on an orange tree at the trailer park. Groups of four clip cages (one cage for a control psyllid and one cage for each of the three types of inoculated psyllids) were attached to four apical leaves on the same stem. Ten groups of clip cages were setup on the North-East canopy of trees (total = 40 clip cages per tree). For eight consecutive days, we recorded the status of the psyllid within each clip cage. By the eighth day, all inoculated and incubated psyllids were dead and infected with Ifr. In comparison, 50 % of psyllids inoculated but not incubated were dead and only 20 % of these psyllids were infected with Ifr. None of the control psyllids were killed or infected by Ifr. These results demonstrated that incubation of Ifr-inoculated adults for at least 24 h will ensure 100 % mortality and infection within 8 days of release in residential citrus trees under summer weather conditions in Texas. We are currently repeating these studies under cooler and wetter fall conditions that should enhance infection of ACP by Ifr. “Effects of Ifr spores on lacewing larvae”. During June of 2013, we compared predation by lacewing larvae on healthy or Ifr-inoculated adults of ACP. We collected lacewing larvae from residential orange trees infested with ACP and held them for 12 h on orange leaf disks in plastic vials. After 12 h, we offered four healthy ACP adults and then four Ifr-inoculated ACP adults (inoculated by dusting with Ifr formulation 24 h earlier) to lacewing larvae that were similar in size and development. We observed each lacewing larva and found they accepted and fed on all the healthy ACP adults and also all the Ifr-inoculated adults. None of the lacewing larvae showed visible signs of infection by Ifr and appeared healthy after being held for five days in leaf-disk vials and fed additional healthy ACP adults. This study demonstrated that lacewing larvae do not appear to be adversely affected by feeding on ACP adults inoculated with Ifr formulation.
Five studies were conducted to investigate factors influencing acquisition and inoculation of Candidatus Liberibacter asiaticus (Las) by Diaphorina. citri, e.g vector developmental stage, feeding periods, leaf age, symptom expression/bacterial titer in infected trees and insecticide treatments, in order to improved Huanglongbing management strategies. In study 1, we compared the ability to acquire Las by different developmental stadia and adults of D. citri on Las-infected plants over a range of acquisition access periods (AAPs). Mean acquisition efficiencies by adults and 1st, 2nd, 3rd, 4th and 5th instars were 42.9, 68.4, 60, 66.6, 84 and 65.3%, respectively. Third-instar nymphs and adults acquired Las in AAPs as short as 30 min, but efficient acquisition (>90%) required longer AAPs (1 and 4 days, respectively). Transmission efficiency reached a maximum of 9.4 and 4.8% (per individual) with a 12-h AAP by nymphs and adults, respectively. By comparing electrical penetration graphs (EPG) of nymphs and adults, we found no significant variations in probing behavior that could explain differences in transmission efficiency. In study 2, we observed that efficient acquisition depends on the availability of young leaves in Las-infected plants, apparently because phloem ingestion by D. citri adults is more frequent and last longer on younger leaves . In study 3, vector competence was assessed as the proportion of successful acquisition events by adult psyllids over a gradient in Las infection levels in citrus trees and over time after graft inoculation of this pathogen. We observed that plant infection levels (pathogen titer) increased rapidly over time, saturating at uniformly high levels (approximately 108 CN per g of plant tissue) near 200 days after inoculation ‘ the same time at which all infected trees first showed disease symptoms. Pathogen acquisition by vectors was positively associated with pathogen titer and time since inoculation, with acquisition occurring as early as the first measurement, at 60 days after inoculation. This result is problematic from a disease management perspective because it means that infected citrus trees may be sources of infectious vectors well before the disease symptoms become evident. Therefore, there is ample potential for psyllids to acquire the pathogen from trees during the asymptomatic (or latent) phase of infection, reducing the efficacy of diseased tree removal (rouging). In study 4, we conducted detailed transmission experiments coupled with EPG analysis of D. citri probing behavior in order to determine minimum time required for Las acquisition and inoculation, as well as the latent period. We observed Las transmission within an inoculation access period (IAP) as short as 45 min. EPG results showed that both acquisition and inoculation occur during the phloem phase, mainly during sustained sap ingestion (waveform E2). Nymphs and adults take an average of 63 min (16 – 241) and 75 min (16 – 241), respectively, to start E2. Thus, psyllids require ’15 min on citrus plants to reach citrus sieve elements and possibly acquire and inoculate Las. Once Las is acquired, D. citri is able to inoculate it in healthy plants after a latent period of at least 10 days at 25C. The mean latent period (LP50) is 16.5 and 18 days after acquisition by nymphs and adults, respectively. In Study 5, we evaluated the effects of insecticide mode of application (foliar vs. drench) on Las acquisition by D. citri nymphs and adults. Insecticides were not effective to avoid Las inoculation to healthy citrus trees, although they drastically affected bacterial acquisition. Therefore, insecticides should be more effective in preventing secondary spread, which requires bacterial acquisition by psyllids on infected plants, than primary spread by immigrating psyllids, which may be already infective when landing on healthy citrus trees in the orchard. The information on transmission biology of Las by D. citri generated in this project have direct implications on management of HLB and highlight the need of additional research to develop new control tools.
During this season, we are focusing our efforts on evaluating different formulations of imidacloprid. This research objective is in response to grower questions about the consistency of different imidacloprid formulations at a time when there are multiple generic products available. We are running two trials in commercial citrus groves – one trial on minneola tangelos and a second trial on grapefruits. We have completed 2 years of trials where we evaluated the uptake of clothianidin applied by soil drench and trunk spray. The results of the 2011 trials were very promising, whereas the results of the 2012 trials showed no residues in the trees. Due to the inconsistency of the results, we are conducting a third trial at Lindcove during the 2013 season. Soil drench and trunk spray applications at a single timing are currently being evaluated. In 2012, we evaluated the efficacy of thiamethoxam treatments on navel and Valencia oranges at several field sites in Redlands. At one of two sites where treatments were applied in October, thiamethoxam was only detected at 4 weeks. At a third site, where treatments were applied in mid-July, no thiamethoxam was detected up to 16 weeks after applications. At the latter site, monitoring was only begun at 8 weeks, so thiamethoxam residues may already have been established within the tree and then dissipated. Nevertheless, our data shows that thiamethoxam is not a persistent chemical in citrus trees. Our objective to conduct imidacloprid residue analysis on fruit from treated trees is now complete. Fruit from trees treated at 2 timings (Feb. and Mar.) with a 2X label rate of imidacloprid from 3 field sites in Bakersfield (Valencia oranges), Lindcove (navel oranges) and Hemet (grapefruit) have now been tested for residues. Samples were collected for up to 8 weeks after treatments at the Bakersfield and Lindcove sites and 16 weeks at the Hemet site. At the Bakersfield and Lindcove sites, residues were not detected (limit of detection of the assay was 0.01 ppm). At the Hemet site, residues were not detected in trees treated with a single application. However, in trees that were treated in 2 successive years with the 2X rate, residues of 0.01 ppm were detected, which is below the MRL established for citrus in the USA.
During this season, we are focusing our efforts on evaluating different formulations of imidacloprid. This research objective is in response to grower questions about the consistency of different imidacloprid formulations at a time when there are multiple generic products available. We are running two trials in commercial citrus groves – one trial on minneola tangelos and a second trial on grapefruits. We have completed 2 years of trials where we evaluated the uptake of clothianidin applied by soil drench and trunk spray. The results of the 2011 trials were very promising, whereas the results of the 2012 trials showed no residues in the trees. Due to the inconsistency of the results, we are conducting a third trial at Lindcove during the 2013 season. Soil drench and trunk spray applications at a single timing are currently being evaluated. In 2012, we evaluated the efficacy of thiamethoxam treatments on navel and Valencia oranges at several field sites in Redlands. At one of two sites where treatments were applied in October, thiamethoxam was only detected at 4 weeks. At a third site, where treatments were applied in mid-July, no thiamethoxam was detected up to 16 weeks after applications. At the latter site, monitoring was only begun at 8 weeks, so thiamethoxam residues may already have been established within the tree and then dissipated. Nevertheless, our data shows that thiamethoxam is not a persistent chemical in citrus trees. Our objective to conduct imidacloprid residue analysis on fruit from treated trees is now complete. Fruit from trees treated at 2 timings (Feb. and Mar.) with a 2X label rate of imidacloprid from 3 field sites in Bakersfield (Valencia oranges), Lindcove (navel oranges) and Hemet (grapefruit) have now been tested for residues. Samples were collected for up to 8 weeks after treatments at the Bakersfield and Lindcove sites and 16 weeks at the Hemet site. At the Bakersfield and Lindcove sites, residues were not detected (limit of detection of the assay was 0.01 ppm). At the Hemet site, residues were not detected in trees treated with a single application. However, in trees that were treated in 2 successive years with the 2X rate, residues of 0.01 ppm were detected, which is below the MRL established for citrus in the USA.
We are currently pursuing our first objective to evaluate the effects of nursery practices (watering, citrus variety, potting media) on imidacloprid uptake and retention. Two citrus varieties were selected for this trial – Parent Washington navel and Limoneira 8A lemon, both on Carrizo rootstock. The trees were budded in June 2012 and grown in 5′ pots at LREC. Trees were transferred to UCR Agricultural Operations on June 13 2013 and transplanted on June 17 to no. 5 pots. Two potting media were chosen for the study that differed principally in the proportions of sand (10-30%) and redwood (40-60%). The evapotranspiration rate was determined for the two soil mixes and this data was used to select three watering levels for the study. The three levels were defined as ‘replacement watering’ (100-120% ET), ‘overwatering (150-200% ET) and ‘severe overwatering’ (300-400% ET). For the trial, trees were placed in a 12 x 25 grid pattern and randomized according to variety, soil mix and watering level. When the trees had adapted to their new potting media environment, they were treated with 0.33 mls Admire Pro per cu ft potting media. Monitoring for ACP on all trees is being conducted at monthly intervals for the duration of the trial, and imidacloprid residues are being determined for all trees by ELISA at 2, 4, 8, 16 and 32 weeks post-treatment.
This is a cooperative research project between Co-PIs Joseph Morse, Jim Bethke, Frank Byrne, Beth Grafton-Cardwell, and Kris Godfrey. One objective is to coordinate with researchers working on chemical control of ACP in Florida, Texas, Arizona, and elsewhere. Towards that end, Grafton-Cardwell, Godfrey, and Morse met with Jawwad Quershi, Phil Stansly, and 2 CA PCAs in Orlando 2-5-13 at the Third International HLB conference to discuss cooperative trials focusing on organic products; the same group toured the UF Immokalee Research Center 2-6-13 to see ongoing field trials; and Byrne and Morse traveled to the UF Lake Alfred Research Center with 3 CA PCAs 2-8-13 to discuss ongoing research and collaboration with Michael Rogers and Lukasz Stelinski. The Orlando HLB conference is an excellent opportunity to network with other scientists working on ACP and HLB and much was learned and discussed. In a similar fashion, many of the PIs will attend the CHRP meeting in Denver 15-17 October 2013. We are rearing ACP in a contained greenhouse at the Chula Vista Insectary (San Diego County; about 6 miles north of the Mexican border) under permit (#2847) from CDFA. To date, Jim Bethke et al. have run 24 screening trials (11 focusing on organic products). A second location where we are working with ACP is at UC Riverside, working under permit inside the UCR Insectary Facility. Frank Byrne is conducting trials on various neonicotinoid insecticides and Morse is evaluating the baseline susceptibility of CA ACP to various pesticides (30 trials to date) in comparison with studies done in Florida. Three field trials have been run to date evaluating organic products useful in control of ACP; the first 10-4-12 evaluated the impact of 5 treatments on adult ACP; the second trial 3-5-13 evaluated 8 treatments against young nymphs and eggs; the third 8-1-13 was recently concluded in San Juan Capistrano on organic lemons in cooperation with PCA Matt Hand and compared 7 treatments. Kris Godfrey obtained a permit to rear ACP inside UC Davis’ Contained Research Facility and now has a healthy colony going. She will focus on evaluating new organic products. One study has been concluded looking at Pest Out (combination of cottonseed, clove, and garlic oils) and she has initiated studies looking at the impacts of Grandevo on oviposition and development of ACP. Beth Grafton-Cardwell has updated online ACP pest management guidelines. She serves as a focal point for communicating with ongoing ACP management programs in the SJV, Ventura, and elsewhere. Both she and Morse also serve on CDFA’s recently convened Science Advisory Panel dealing with ACP and HLB; 2 conference calls of the SAP have been conducted to date. In summary, we continue to expand our ability to conduct ACP research in California with a clear focus on management of HLB (rather than ACP).
Imidacloprid (IMD) fate and transport in Immokalee Fine Sand (IFS) soils for three citrus tree ages was studied in SW Florida Flatwoods at selected irrigation rates. Sorption and degradation studies have shown That IMD is a weakly-sorbed (log Koc, 1.1-2.4) and non-persistent chemical (half-lives 0.9-2.3 years) with high potential for leaching. We also established field experiments in three age classes of Hamlin trees with micro-sprinkler irrigation at three irrigation rates, during growing seasons between 2011 and 2013. IMD was soil-drench applied in the root zone (PA), and in a control zone not affected by roots (NPA). IMD concentrations (.g g soil-1) were higher for the NPA than PA as a function of time due to uptake by the citrus trees. IMD leached out of the root zone about 3 to 4 weeks after application in the summer, and about 6 to 8 weeks after application during spring. Nonetheless, there was effective systemic control of the CG vector Diaphorina citri Kuwayama (ACP) at about 2 weeks after application, where treated trees showed consistently lower ACP adults and immatures infestation, continuing for at least 8 weeks. A method to analyze IMD from citrus tissue (ng g-1) was developed using HPLC-MS/MS detection, and preliminary data are in close agreement with our findings in soils and insect counts on trees. Leaf tissue concentrations of IMD increase for the initial two weeks and stay constant for an additional 6 to 8 weeks. Leaf IMD concentrations are significantly greater with increased irrigation amount. Close irrigation and rainfall monitoring during IMD application is of the utmost importance to avoid leaching problems in groundwater resources of SW Florida, and to ensure systemic control of the ACP.
Progress on development of an acoustic trap to capture male Asian citrus psyllids (ACP) that are searching for females on citrus tree branches continued in the first second of 2013. In early stages of the research, we had programmed an Arduino Uno microcomputer system to detect and record psyllid-produced vibrations from a microphone attached to a citrus tree branch. In the second phase of the research, we programmed the system to play back ACP communicatory signals whenever it detects a male calling on the branch. The signal playback is done through an inexpensive piezoelectric buzzer system. During this last quarter, we have begun incorporated the microphone-buzzer microcomputer-controlled system into traps that were tested in field environments. Several technical issues were identified in the field tests that restricted the trapping efficiency and the duration of time that the traps could be used in the field. Both the traps and the microprocessor systems are being modified to address these issues. In March, we presented some of the initial findings of the research at the 3rd International Research Conference on Huanglongbing in Orlando, FL. One paper on the initial phase of the study has been published in the Annals of the Entomological Society of America, and two papers discussing a later phase of research have been submitted to the Florida Entomological Society. A fourth paper is in progress on the results of laboratory tests using the new system that plays back ACP communicatory signals whenever it detects a male calling on the branch.
This proposal aims to continue improvement to a novel psyllid trap and to use the trap to gather new information on the behavior, biology, population dynamics and biological control of ACP/Candidatus Liberibacter asiaticus. Lab and field testing was and continues to be conducted to increase trap efficiency by exploiting unique vector behaviors in response to traps and behaviorally active components. We continue to conduct field and laboratory studies toward obtaining an understanding of ACP trap response behavior by manipulating psyllid behavior around the trap or farther away so that they are moved close enough to the trap to perceive it (i.e., increase trap active distance). We have a number of positive results from our bioassays with which to attempt to increase trap efficiency but have yet to reach a level of trap capture rate which is a satisfactory representation of ACP populations in the vicinity of the trap or equal to the capture rate of the current industry standard, the AlphaScents green-yellow sticky trap . During this quarter we have cooperated with several USDA-ARS personnel to develop, test and incorporate other trap features that affect psyllid visual response but also involve other sensory modalities including sound productions during psyllid courtship. This work is ongoing and more experiments are being conducted. We have run in the last 45 days an extensive field test of our trap prototypes in Ft Pierce groves to discern what trap features are key to exploiting psyllid behavior to increase capture rate. We have also used combinations of semiochemical lures that supposedly attract psyllids provided by other scientists. So far these have not made a large difference in capture rates of any traps tested. Following another round of field tests with new traps improved based on the field data gathered this quarter, we will initiate the areawide psyllid sampling objective.
Xambr’ Paran’ Brazil Plots: The experiment is designed to quantify the effect of windbreaks, copper sprays, and insecticide sprays individual and combined effects on citrus canker management. In 2010 replicated field plots were established. I was soon evident that the screens used as windbreaks were not strong enough to provide the required effect. Thus in addition to the screens, we established natural windbreaks using Casuarina. Casuarina trees that are currently ~7 m high. There were a few new canker-affected plants in the experimental area that will be pruned every 3 weeks. Trees are well established now and have developed enough canopy to allow inoculation and to start the experiment in September/October 2013. During 2013 inspections, 25 plants were discovered with HLB symptoms. Florida Windbreak plots: The final data taken through September 2012 from the preliminary experiments last season confirmed that the number of wind gusts >11 mph increased with distance from the windbreak whether measured within the north-to-south rows or across the rows from east to west. Consequently, the highest fruit disease recorded in September in the cv. Valencia orange orchard (10 percent fruit cankered) was in the center of the 11-acre block and the lowest incidence (<2 percent fruit cankered) was in the east-west row location nearest the windbreak. The weather stations at the two locations (cv. Valencia orange, Estes Farm, Indian River Co. and cv. Rubyred grapefruit, Scott Farms, St. Lucie Co.) continue to be monitored this season with weather data being recorded and downloaded on a monthly basis. The disease data on leaves and the first sample on fruit have been taken and will be related to the wind and leaf wetness conditions from the weather data recorded in these orchards during the 2013 season. Programmable leaf wettnes controller: Further tests on the 'pin sensor' have proven problematic, as water retention control is difficult. First, to facilitate putting the silk onto the pins, the pins were lengthened off the board (approximately 1 cm). This allowed for 'cavities' between the pins, which allows too much water to be held, which lead to drying times being too long. We also determined that the board itself that the pins are mounted in will hold water, especially with the silk on top of it, which again led to longer water retention times. So, the next series of tests will include coating this board to prevent water uptake (we will attempt to use wax to coat the board to emulate the leaf surface a bit), followed by trying to keep the pins long enough to put through the silk, yet not be so long as to create cavities. Finally, a future test would be to NOT push the pins through the silk, but to keep the silk taunt across the tops of the pins, thus using the silk as not only a water absorption layer, but also a 'blocker' to prevent the water from sitting anywhere else within the sensor. Project publications: (In addition to the 7 previously reported publications relative to this project, the following was recently submitted as well) Bock, C. H., Gottwald, T. R. and Graham, J. H. 2013. A comparison of the bioassay test and culture to detect Xanthomonas citri subsp. citri . Plant Pathology 62: xx-xx.
1. Development and testing of efficient methods of statistical inference to estimate epidemiological parameters from maps of emerging epidemic.) Using citrus canker as a test system, we are developing and testing quantitative models to link weather variables to the rate of disease spread. We are also analysing models for anisotropic dispersal of the pathogen, in order to correlate the direction and extent of pathogen dispersal with wind direction/strength during extreme weather events (rainstorms). The outcome will be a set of epidemiological parameters that can be used as inputs for predictive modelling, with (at least) two different final goals: i. To produce risk maps for disease spread for large (state-wide) geographical areas and long time scales (several years), under different “what if” scenarios for favorable and unfavorable weather conditions; and ii. To produce a risk map on a smaller (county-wide) scale in response to a local storm. With knowledge of the distribution of disease prior to the storm, it should be possible to estimate the new distribution of disease using the strength and direction of wind, and other relevant weather parameters. This would help directing a post-storm sampling procedure (e.g. which areas surveyors should target for new symptoms). We have developed and tested a set of advanced spatial statistical methods for goodness of fit. The methods are based on the comparison of simulated and observed spatial patterns of infection. They have been successfully tested using model estimates for the Miami outbreak, and they were able to discriminate between good and less good dispersal models. Such methods are also a fundamental ingredient, hence a significant step forward, for the ABC (simulation-based) estimation algorithms that are currently being developed. The methodology being tested with citrus canker can be generalized to HLB. A paper on Markov chain Monte Carlo for estimation of epidemiological parameters in the Miami area has been submitted. 2. Develop a generic epidemiological model that can be used to compare control scenarios and to optimize the probability of controlling and managing high-risk pathogens of agricultural significance. We have built a model that represents the spread of HLB within an individual tree. Successful spread of the pathogen depends on transmission both within the vascular system of the tree and between leaves via psyllid vectors. The relative importance of these transmission routes is being explored, with the speed of spread of the pathogen dependent on whether transmission via psyllid vectors is frequency- or density- dependent: this depends on the population density of psyllids relative to the number of leaves. A novel feature of our modelling approach is that it explicitly incorporates the ability of Las bacteria to survive in the vascular system of the plant. Control: We are using this model for a variety of purposes. Firstly, we are investigating and comparing the efficacy of roguing, application of insecticide and the use of nutritional products and thermotherapy for disease control and mitigation. Secondly, we are using it to inform grove scale models for the spread of HLB. Grove scale models typically assume that each citrus plant is either entirely infected or not (instead of considering the proportion of the tree that is infected). This model is being used to inform the force of infection of each infected citrus tree in grove scale models. 3. Develop user friendly model ‘front ends’ that can be used by researchers and regulatory agencies. We are finalising the publication on Webidemics (http://www.webidemics.com/), the user-friendly front-end for control of citrus disease.
Soil application of systemic neonicotinoid insecticides for control of psyllid vectors of Huanglongbing disease on young citrus trees also produces season-long SAR control of citrus canker caused by Xanthomonas citri subsp. citri. The neonicotinoids imidacloprid (IMID; Admire Pro, Bayer) and thiamethoxam (THIA;Platinum, Syngenta) were compared with soil or sprinkler applications of the commercial SAR inducer acibenzolar-S-methyl (ASM, Actigard, Syngenta) and foliar sprays of copper hydroxide (CH) and/or streptomycin (STREP) to evaluate their effects on the percentage of canker-infected leaves on 2-yr-old ‘Vernia’ orange and 3-yr-old ‘Ray Ruby’ grapefruit trees in Southeast Florida. All treatments significantly reduced incidence of foliar canker compared to the untreated check. Soil drenches of ASM and season long rotations with IMID and THIA were highly effective for suppressing foliar canker on young grapefruit and orange trees under weather conditions absent of high intensity rains or tropical storms. Sprinkler application of ASM was less effective than soil drench. The level of control for SAR treatments was comparable to eleven 21-day interval sprays of CH and/or STREP. SAR induced by soil-applied insecticides provides substantial benefits for canker disease management on young citrus trees that may be augmented with ASM. Currently, use of neo-nicotinoids insecticides for control of the psyllids and leafminer is limited to trees less than 2.75 m tall in part due to the potential risk for leaching of soil applied materials into the groundwater at the higher rates required for pest control on larger size trees. An alternative approach is spray application of the chemicals on the trunk. Four soil drench or trunk applications of IMID and THIA and ASM were compared to untreated controls and 9 or 10 standard 21-day interval copper sprays for protection of foliage and fruit on 5 to 6-yr old ‘Ray Ruby’ grapefruit trees. Soil drench and trunk applications similarly reduced the incidence of canker lesions on foliage and fruit but were less effective than copper sprays. SAR inducers appeared to protect fruit by reducing incidence of foliar disease, and thereby, when integrated with 21-day interval copper sprays may improve control canker on young, fruiting trees. Currently, we are collaborating with Syngenta in an EPA-approved Experimental Use Program (EUP) in two east coast grapefruit groves to support the labeling of Actigard (ASM) integrated with copper sprays for control of canker on bearing grapefruit.
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