This study monitored Caribbean fruit fly populations counted in approximately 400 McPhail’s traps distributed across a 45 square-mile area receiving both fruit fly bait sprays and Mustang applications for Asian Citrus Psyilld. The study was performed in Vero Beach/Indian River County, north and south of Highway 60 and west of I-95 (also known as St. John’s Marsh area). The approximate distance between trap settings was 1050 feet, and they were checked about every 7 days for a total of approximately 2000 independent observations over the course of the study. The specific subject area included in this analysis encompassed a subset of the 2000 observations in 90 geographically-contiguous designated areas (each designated area is . square mile). The varieties in the groves in which traps were located included White Marsh, Pink Marsh, Star Ruby and Flame grapefruit and Navel, Hamlin, Valencia, Murcott and Temple oranges. This project was a pilot study designed to obtain observational information regarding whether or not Mustang applications applied for Asian Citrus Psyllid control might also suppress fruit fly populations. The construct of the study is that Mustang was applied in the Fall and again in the Spring for psyllid control to all areas monitored in the study. Coincident with that Fall/Spring time frame, Caribbean fruit fly populations were monitored and bait sprays applied as needed to maintain fruit fly certification for the target crops. The result of this arrangement was that all blocks observed in this study received two Mustang applications, but not all areas received bait sprays. The number of bait sprays applied ranged from none to 8, depending on the particular block. Fruit fly counts were monitored starting in August 2009 and continued through March 2010. Despite the considerable effort that went into performing field activities in this study, environmental and other circumstances resulted in very few non-zero values being obtained in the fly count data. This made quantitative statistical analysis difficult. As a result, graphical exploration of observed trends from the subject area was used to interpret these data. Caribbean fruit fly counts obtained from McPhail’s traps totaled across both time and space showed little or no relationship between the number of bait sprays applied and the total number of flies trapped per location. This result is consistent with the experimental supposition that Mustang sprays applied for psyllid control also suppress fruit fly populations. Specifically, fly counts were none to very low in areas both treated and untreated with bait sprays. Therefore, we suggest that factors other than bait sprays were responsible for the low counts observed. These other factors included: 1) Mustang applications applied in the Fall and Spring; 2) weather; and 3) undocumented factors. It is noteworthy that weather conditions over much of the course of this experiment were unfavorable for rapid fruit fly development. The results of this pilot trial do not contradict the premise of the study, but we believe a repetition of this experiment so that more complete numerical data can be obtained may be warranted. Since quantitative support of an experimental hypothesis that there is no difference between fly counts trapped in Mustang-sprayed vs. Mustang-non-sprayed conditions was not possible in this current pilot study, any follow-up experiment should be designed using the following criteria: 1) longer duration; 2) fewer locations; 3) try to get weather data for specific trap locations; 4) try to monitor fly counts in both Mustang-sprayed and Mustang-non-sprayed areas; 4) document other factors that may influence fly counts; and 5) reorganize data structure to facilitate on-going, real-time statistical analysis.
Although a successful trunk cutting, herbicide spray applicator device was constructed and mounted on a small tractor, little industry interest has evolved in its use. BASF Chemicals had expressed willingness to obtain a label for their formulation of the imazapur herbicide (Arsenal), but apparently no further work on labeling has occurred. Chemical Containers Corp had preliminary interest in commercial development of this equipment, but after all of the development and efficacy information was presented to the CRDF Committee the company apparently decided not to pursue development and no further discussions have occurred. This is probably because the foliar nutrition cocktail mixes appear to be maintaining HLB infected trees in a productive state for several years and fewer growers are scouting and removing infected trees. A simplified cutting and application machine was designed and is being constructed. This will be tested at least one time in the late winter in 2011.
The objectives of this study are: 1) to develop a series of flexible stochastic models to predict the temporal increase and spatial spread of citrus disease. The models were initially designed for citrus canker but have subsequently been extended to HLB. They can be used in a number of ways: to predict spread and to analyze the effectiveness of control strategies both in plantations and State-wide. 2) Test various control methods under field conditions to evaluate effects and collect data to parameterize models As previously described, an SEIDR model was developed that uses Markov-chain Monte Carlo methods, and extensive data from South Florida. This model portrays successive snapshots of the occurrence of symptomatic detected trees in known populations of susceptible trees. To date we have been able to estimate the transmission rates and dispersal kernel for HLB by interrogating this prior data center. currently we are working on differential effects of host age on epidemiological parameters and variability across the plantation. this allows us to explore the uncertainty how the predictions which is then incorporated in models to predict spread and to allow for uncertainty in the efficiency and comparison of control methods. A web based version of the model is in the final stages of development. This web-based model is for non-researcher users you can utilize it as a tool to understand how the disease will increase and spread both residential and commercial situations. It can also be used to test a wide variety of epidemiological and climate/weather variables and their effects on an HLB epidemic as well as various disease control/mitigation parameters to see the effect of these various control strategies. we’ve been using the data from southern gardens citrus that includes both young and mature trees, since host age is likely to be an important consideration for HLB. The model continues to be improved upon to capture more and more of the true features of the data and the disease. The model is being extended to estimate spread in diverse situations, should HLB be introduced into new areas such as TX, CA or AZ. Field plots were established at the USDA, ARS Picos Farm to examine the effects of insecticide control and roguing in various combinations, both to evaluate treatment effects and to collect epidemiological data for model development. These field studies are underway as well however, at the time of this writing there are no detectable statistical differences among various control strategies.
This project was designed to examine the potential disease control of citrus huanglongbing (HLB) by interplanting citrus with guava. In Vietnam guava has been shown to be an effective deterrent to HLB, slowing the disease and keeping plantings alive for up to 15 years that normally succumb in 2-3 year. For all plots and experiments, Guava trees, (Vietnamese white cultivar) were propagated and grown to appropriate size requiring ~1 year. Both nursery and field citrus trees are assayed for HLB every 60 days, and have been assayed multiple times. Psyllid populations are also being monitored continuously every 2 weeks within interplanted plots to document any repulsion of the vector due to guava. Results: Guava vs no guava nurseries: Two nursery sites, a guava protected citrus nursery versus an unprotected nursery, have were established with disease free, PCR-negative citrus trees (2 sweet orange and 1 grapefruit cultivars) in June 2009 and were located in the protected and unprotected plots. The guava trees were grown to appropriate size as indicated in Vietnam prior to outplanintg. To date HLB appears to be progressing more slowly in nursery plots interplanted with guava that non interplanted plots. Citrus/guava interplantings: 3 commercial plantings with multiple replications were established. This required 1 year to grow the guava transplants and a second year to become established in the field before interplanting with citrus per Vietnam protocols. One trial was established in a commercial orchard with collaborators in Southern Gardens Citrus, but two years of freezes and replanting prompted the grower/collaborator to abandon the planting. A second was established in grove in Martin county but the plantation was sold and removed before data could be collected. A third trial planting was established at the USHRL Picos Farm in Fort Pierce. The Picos plot was interplanted with citrus in August 2009. Severe frosts during 2008/2009 and again during Dec 2010 winters continue to affect the USHRL plots and have caused a delay in the experiment. To date, several HLB+ (PCR+) plants have been identified in the USHRL plots after multiple assays. The majority of these positives have occurred as the result of an edge effect. That is, treatment plots closest to an existing HLB+ planting of Valencia were affected. There continues to be no significant difference among the treatments thus far, however this data is insufficient to draw any conclusions at this point. Research using a Y-tube olfactometer to investigate guava volatiles as repellents of the psyllid has been challenging and resulted in no clear psyllid attraction or repulsion. The best response was 1-wk-old psyllids with C. macrophylla shoots, although psyllid attraction to this odor source was weak. Research with white guava (germplasm from Vietnam) did not lead to any improvement. We will continue to investigate repellency of guava alone or in combination with citrus and refined methods to achieve more sensitivity.
Mid Florida Citrus Foundation (MFCF) currently supports the research efforts of scientists from the University of Florida, USDA and private industry. The majority of research projects are conducted by UF scientists at the approximately 112 acre citrus grove. The MFCF supports citrus research through the employment of a full time grove manager whom works closely with researchers to ensure that their projects are handled properly and that the grove is an excellent condition. The management of this grove requires extra financial commitment as grove care cost tend to be higher than a commercial grove due to the nature of many of the research projects. Current projects being conducted at the MFCF are Asian citrus psyllid (ACP) pesticide evaluation control trials, low volume applicator trials, windbreak evaluation, HLB nutritional programs, new and existing herbicide trials, variety and rootstock evaluation trials. The MFCF is in the process of expanding grove to allow more research work to be conducted. This was made possible due to the fact that the MFCF received an EQIP grant from the NRCS. This past summer 13 acres were planted for new research trials, which included an HLB trial, multiple new herbicide trials and new variety evaluations. Additionally windbreaks were established for new and future citrus research blocks. Current plans call for the establishment of 30 additional acres of research citrus trials for the purpose of young tree psyllid control research, evaluation of new psyllid control products, economic study on rooted cuttings, evaluation of miticides and herbicides and large block planting of experimental early orange.
We are still assessing new symptoms appearance in all established experiments. Exp.1 – In the compartments 1 and 2 where citrus plants served as primary source of inoculum of CLas or CLam we are still observing a predominance of infective psyllids and diseased plants with positive conventional PCR for CLas. In average 30.4% of psyllids collected from inoculum source plants and 8.4% collected from test plants were positive for CLas and no one for CLam. In average 12.8% of test plant were positive for CLas and only 0.9% for CLam. From the three Clam citrus infected plants, two had also CLas in a mix infection. Average Ct value for leaves with CLas were 24.7 and for CLam 33.7, indicating a higher titer for CLas than for CLam. In compartment 4, where Murraya exotica served as source of inoculum, 46.0% and 9.4% of psyllids collected respectively in source plants and test plants were PCR positive for CLam, whereas in compartment 3, where Citrus sinensis served as source of inoculum, 6.35 and 4.7% of psyllids collected respectively in source plants and test plants were PCR positive for CLam. 8.2% of test plants were PCR positive for CLam when inoculum source was Murraya exotica and no positive test plant was detected when inoculum source was Citrus. All plants were in other insect-proof screenhouse and will be there for symptoms observation and leaf sampling for PCR analysis at least until December 2011. A new leaf sampling will be done in March to check the presence of both liberibacters in new test plants. A replication of this experiment was started to repeat this experiment. These results will be present in the 2nd International Research Conference on Huanglongbing in Orlando January 10-14th. Exp. 2- All test plants used to HLB-insect transmission are under evaluation for the symptom expression and the presence/concentration of the HLB bacterium by qPCR. Exp. 3 – No HLB-symptoms and infection were observed yet on inoculated trees at different sweet orange varieties and ages that were encaged under insect proof screenhouses. The disease severity (% of symptomatic canopy) of each tree from the alternative experiment under field conditions is being periodically assessed. Because of the heavy defoliation during the drought season and the recovery of tree canopy with new flushes during the spring, the average disease severity in all assessed trees seems to decrease at this time of year. New assessments after leaves maturation will be done.
The objective of this project is to investigate three questions: 1) whether HLB symptoms or boron/zinc deficiencies alone affect how ACP responds to citrus; 2) whether feeding patterns by adults, length and location of feeding, are altered by HLB infection or boron/zinc deficiencies; and 3) whether different strains of Ca. Liberibacter asiaticus (Las) differentially affect the response of ACP to citrus. In other pathogen/host/vectors systems, such as that with Ca. Phytoplasma mali and Cacopsylla picta (the apple psyllid), the pathogen manipulates the plant host metabolism so that diseased plants become more attractive to the psyllid vector, thereby spreading the pathogen more rapidly than if no plant host manipulation occurred. Since nutrient deficiencies are often associated with HLB in citrus, we wished to confirm that the reported attraction of Diaphorina citri to HLB symptomatic plants over uninfected plants was due to changes in host metabolism by the pathogen rather than physiological changes due to poor nutrition. The production of greenhouse-grown citrus trees with nutrient deficiency symptoms for both zinc and boron continues. Deficiency symptoms are expected to take a few months to develop. This is especially the case for zinc because of the high mobility of zinc within the plant allowing redistribution of existing zinc to new flush, delaying the development of symptoms. Multiplication of our stocks of HLB infected citrus is also underway to provide a constant source of symptomatic tissue for experimentation once the nutrient deficiency symptoms have developed. We are also interested to determine if strains of Las will have any effect on the attractiveness of trees to D. citri. It has been reported that Las strains have varying levels of virulence and symptomatology (Tsai et al. 2008). We have analyzed DNA samples from HLB positive trees from Polk and Highlands counties as well as the ‘Smoak Grove’ CREC greenhouse strain by PCR and sequencing. Three putative strains of Ca. Liberibacter asiaticus (Las) were found with 5 (CREC greenhouse isolate), 13, and 15 tandem repeats of DNA in the LAPGP locus described by Chen et al. 2010 and have identified sources of budwood. We are currently using the identified budwood sources to acquire greenhouse isolates of the three strains. Cloning and sequencing of loci including the b-operon, OMP (outer membrane protein) gene and phage DNA polymerase to support the differentiation of the three strains is underway (Bastianel et al. 2005; Lin et al. 2008; Okuda et al. 2005; Tomimura et al. 2009).
The objective of this project was to investigate three questions: 1) what is the seasonal pattern of Ca. Liberibacter asiaticus prevalence in leaf tissue on a grove scale; 2) what are the flushing patterns of citrus and whether these flushing patterns affect the prevalence of Ca. Liberibacter asiaticus in Diaphorina citri or citrus leaves; and 3) what is the prevalence of Diaphorina citri carrying Ca. Liberibacter asiaticus on a grove scale and how does it compare the results from the citrus trees in the same grove. In 2008 and 2009 Ebert and Rogers demonstrated that the prevalence of Ca. Liberibacter asiaticus in the Asian citrus psyllid varied seasonally but the pattern between seasons was not consistent. It was suggested that perhaps the reason for the differences between the years related to the flushing patterns of citrus and the prevalence of the bacterium in the leaves where psyllids are feeding. This project aims to determine if there is a relationship between the frequency of disease on branches and psyllids. The postdoc has been hired for this project and is currently processing the backlog of samples but we have some preliminary results from 1 grove. An ‘Earlygold’ grove in Orange county Florida was selected to examine seasonal prevalence of HLB over a 3-year period. Two hundred trees were selected from 10 consecutive rows. One leaf/tree was randomly picked every fortnight. Sample collection began at the end of June 2010 with collections ongoing. For qPCR detection of Las, the midribs of five random leaves were pooled to obtain 40 samples/date. An estimated Las prevalence in the branches was generated from the pools with PooledInfRate v3. Simultaneously, ACPs were collected from the same location to compare the seasonal prevalence of Las in citrus branches and ACPs. Las prevalence increased (from 0.14, 0.20, 0.21 to 0.27) from June to September. The data from ACPs are still being processed. Comparing the data from ACPs and citrus trees could provide more information on seasonal variation in Las prevalence in both the vector and the host, and thereby enhancing our management strategies by identifying the essential periods for ACP control to prevent HLB transmission.
Under Objective 1 (define rates and formulations of copper sprays for more effective control) one trial with Red grapefruit is on-going in Ft. Pierce, FL and likewise one trial with Hamlin orange in Hardee County, each with 14 treatments of formulations, rates and combinations with other chemical treatments of interest. This season, trials have low to moderate disease epidemics as a result of a periodically wet spring, moderately wet summer and an absence of tropical storm events. Evaluations of fruit infection in these trials will begin in November 2010. Under Objective 2 (establish the period of fruit susceptibility, residual activity and phytotoxicity of copper) These results have been summarized for publication in Florida State Hort. Society (FSHS) Proceedings 2010. Major findings reported are: 1) Copper formulations containing copper hydroxide or basic copper sulfate (metallic rates of 0.67 to 1.12 kg/ha), varied from low to moderately effective for canker control depending on late-season, wind-blown rains. 2) Copper pentahydrate, with a lower metallic copper rate/ha per application, provided equivalent control to other copper formulations. 3) Streptomycin, alone or with a reduced rate of Kocide 3000, in July and early August gave equivalent control to Kocide 3000 alone. 4) Copper phytotoxicity risk coincided with accelerated fruit growth after summer rains. 5) Greater canker susceptibility of fruit in later season is likely because of increased opening of stomates for bacterial infection coincident with more numerous windblown rain events. 6) The only factor that led to significant reductions in copper residue per fruit surface area over time was the Kocide 3000 concentration. PDS had no effect on the residue. Under Objective 3 ( evaluate the use of streptomycin [Firewall]) Two trials, one non-bearing and one bearing, in grapefruit are underway to further evaluate FireWall for canker control. The package to obtain an EPA Section 18 Emergency Exemption for FireWall has been submitted to FFVA based on data from Florida trials conducted in 2008-2009. Under Objective 4 (To define risk for development of bacterial resistance to copper and streptomycin in FL citrus groves) a number of factors favorable for the development of copper resistance in Xcc were identified, but further investigation is necessary to fully assess the risk for streptomycin resistance. Previously reported findings are being summarized for publication. Under Objective 5 (rapid transfer improved canker management technology to the Florida citrus industry), 2010-11 canker management recommendations have been published in the Florida Citrus Pest Management Guide and Citrus Industry Magazine. Oral presentations have been delivered to the Florida Citrus Production Managers, at county extension meetings, and at the FSHS annual meeting.
The objective is to evaluate soil-applied neo-nicotinoids and other SAR inducers on HLB disease progress in newly planted citrus trees subjected to psyllid-mediated infection or graft-inoculation. One yr-old Hamlin trees were planted in May 2009 and treated as follows: 1) non-treated check (UTC), 2) foliar insecticide to control psyllids, 3) soil-applied imidacloprid/thiamethoxam (IMID/THIA) to induce SAR, 4) soil-applied IMID/THIA plus foliar insecticides, 5) graft-inoculated UTC, 6) graft-inoculated with IMID/THIA. There were 40 trees per treatment (5 blocks of 8 trees). In 2009, the effect of SAR inducers on HLB infection progress was inconclusive perhaps attributable to the interaction of IMID/THIA with psyllid control which may have an uncontrolled effect on psyllid transmission. In 2010, the SAR inducer acibenzolar-S-methyl (ASM, Actigard 50WP) which does not control psyllids was substituted in treatments 3, 4 and 6. At 15 months after treatments began, 56 trees were PCR+ (23%) in the trial. Higher number of PCR+ occurred in the UTC (14), the UTC with graft inoculation (13), and the IMID/THIA/ASM with graft-inoculation (13). Lower number of PCR+ trees occurred without graft inoculation in treatments with SAR inducers (7), foliar insecticides (6), and foliar insecticide plus SAR inducers (3). An HLB-SAR experiment has set up in Parana, Brazil. The trial utilizes soil applied ASM (Bion) for the SAR treatments and is proximal to tree in a farm with HLB. The first tree to show HLB symptoms after six months is a tree treated with ASM. While effect of SAR on HLB disease progress is still inconclusive, thus far these trials and other evidences indicate lack of promise for SAR in HLB management.
Objective 1: Potential for soil application of the neonicotinoids, Admire (imidacloprid, IMID)and Platinum (thiamethoxam, THIA), and Actigard (acibenzolar-S-methyl, ASM), to provide long-lived SAR control of canker was evaluated. In the field trial of 3- and 4-year-old ‘Ray Ruby’ grapefruit trees in Ft. Pierce, Florida, soil drenches of IMID, THIA, and ASM were compared with contact activity of Kocide 3000 (copper hydroxide, CH) and/or Firewall (streptomycin, STREP) applied as a foliar spray at 21-day interval for canker control on foliage. Canker on each set of vegetative flushes was assessed as the percentage of leaves with lesions. In 2008, despite above average rainfall and a tropical storm event, all treatments significantly reduced incidence of foliar canker. Spray of CH was the most effective treatment. As a group, soil drenches of SAR inducers reduced foliar disease incidence depending on rate and frequency of application. In 2009, all treatments significantly reduced incidence of foliar canker compared to the untreated check. IMID, THIA, and ASM as soil drenches were each effective for sustained control of canker on young trees under epidemic conditions. Control with SAR inducers was highest for four applications of ASM in 2008 and 2009 seasons which demonstrated the value for maintenance of SAR with repeated soil applications. Objective 2 Integration of soil applied IMID with foliar applications of copper sprays for control of canker. IMID applied once at the beginning of the season followed by 11 CH sprays gave the best control in the 2009 trial. This suggests that SAR and copper could be used in an integrated program for augmenting canker control for young fruiting trees. In 2010, a trial integrating ASM at different frequency of soil application with THIA and CH sprays at 21 day interval was set up on 1-yr-old Vernia sweet orange in Ashland, FL. Incidence of newly infected trees is just starting to increase in the various treatments this summer. This highest incidence of disease trees and leaves is in the nontreated check. Objective 3 is to evaluate of the complementary use of ASM, THIA and IMID soil applications to increase and/or extend canker control in 2-yr-old grapefruit trees. Canker was first observed in the trial area in September 2009 after a very high rainfall period in August (17 inches). The pattern of disease spread was across the trial area from southwest to northeast. Incidence of trees with canker was 56% in the non-treated check trees, whereas in most of the SAR treatment combinations the incidence was less than 10%. Incidence of canker in this trial continues to increase in 2010. A field trial with soil applied neonicotinoids in Parana, Brazil was evaluated. IMID(Confidor) as a soil drench and IMID (Winner) applied to trunk gave comparable in disease control activity on 2-yr old Valencia orange trees, as well as, the other neonicotinoids tested, THIA (Actara) and Clothianidin (Poncho). In Brazil a greenhouse evaluation, soil drenches of these neonicotinoids and ASM were effective for reducing lesion and Xcc population development in leaves. ASM was the best treatment among those evaluated. Thus, SAR not only prevented infection but also acted post-infection to reduce the level of bacterial populations in lesions. This confirms the best activity that the inducers of SAR have for reducing canker incidence and epidemic development of disease on leaves and fruit.
Objective 1 is to conduct a field evaluation nutritional sprays for control of HLB and HLB symptom expression and yield. The field study was set up May 2010 in Southern Grove, Hendry Co., FL. Six treatments were set in 4 plots of 150 trees per treatment (interior 10 trees in each block were identified for PCR, leaf nutrition sampling, tree health and yield evaluation). Treatments were 1) non-treated check; 2) Nutri-Phite sprayed 3times bimonthly; 3) N-Sure sprayed bimonthly; 4) Agra Sol Mn/Zn/Fe plus Nutri-Phite plus triazone urea sprayed bimonthly; 5) Keyplex 1400 DP plus Nutriphite plus triazone urea sprayed bimonthly; 6) Wettable powder nutrients (Diamond R #2) plus Nutri-Phite P+K sprayed bimonthly. The materials were applied to both sides of the tree in 125 gallons per acre with an airblast sprayer driven at 2 mph to obtain thorough coverage. Three applications have been completed as of October 2010. Ratings of tree health, leaf nutritional status and PCR status will commence in November 2010. Objective 2 is to determine the mechanism of HLB symptom suppression by foliar nutritional application. Hamlin sweet orange trees have been inoculated and are being treated bimonthly with the nutritional sprays. Infection rate and progress are being monitored by qPCR monthly. One month after inoculation, the new flush on a few of graft inoculated trees was weakly positive for Las. Two months after inoculation, new flush on some trees is strongly positive for Las; however, too few of the trees are positive to determine any treatment effects. Three month post inoculation samples are currently being processed. Sampling and fixing of plant material for microscopy of phloem and leaf blade tissue began at two months and continues monthly. Fixed samples will be observed by microscopy once strongly symptomatic tissue is available for comparison.
Transmission of Candidatus Liberibacter asiaticus by the Asian citrus psyllid (ACP), Diaphorina citri, probably involves complex psyllid-pathogen interactions, which should be understood in order to improve management strategies to control HLB. The goal of this research is to determine factors that influence the risks of acquisition or inoculation of the pathogen (Candidatus Liberibacter asiaticus – CLas) by D. citri, e.g vector developmental stage, feeding periods, leaf age and symptom expression/bacterial population in disease plants, in order to optimize strategies to avoid or reduce disease spread within and between citrus groves. We already set up the first four of five proposed studies and the project is progressing as planned originally. Partial results of previous studies showed that bacterial acquisition can occur when ACP adults feed on asymptomatic infected plants, although acquisition efficiency is higher on citrus plants with higher bacterial titers, usually symptomatic. We also have reported that acquisition efficiency by psyllid adults is markedly affected by citrus leaf age and duration of acquisition access periods (AAP). Efficient acquisition depends on the availability of young leaves in infected plants and long AAPs (>2 days). In this quarterly report, we present details of the first study, concluded in September/2010, which was carried out to determine how acquisition efficiency of CLas varies in relation to ACP developmental stages. Health insects of known age were obtained from a lab colony maintained on Murraya paniculata. In each experiment trial, groups of 40 adults with 3-5 days post-emergence and newly-molted nymphs of all development stadia (1st, 2nd, 3rd, 4th and 5th instars) were confined on young leaves of a same symptomatic branch of an infected plant, during a 48-h AAP. Psyllids of each treatment (developmental stage) were confined on a separate leaf. After the AAP, the insects were maintained on healthy sweet orange seedlings for 21 days (healthy seedlings were replaced after the first 14 days). Surviving psyllids were then fixed in 100% ethanol and individually tested for the presence of CLas by real-time quantitative PCR (qPCR). As a negative control, a group of 40 psyllids of the same rearing batch was transferred directly to the healthy seedlings (without previous AAP on infected plants). The experiment was repeated three times using distinct pathogen source plants. Acquisition efficiencies by 1st, 2nd, 3rd, 4th and 5th instars, as measured by the proportion of infective psyllids by qPCR, were 68.4, 60, 66.6, 84 and 65.3%, respectively. In contrast, only 42.9% individuals were infective when acquisition took place during the adult stage. Interestingly, a higher concentration of CLas was observed in psyllids that acquired the bacterium during the 4th or 5th instar. These results show that all developmental stages of ACP are able to acquire the bacterium with moderate to high efficiencies during a 48-h AAP on infected plants, but nymphs are more efficient than adults. We are now concluding PCR assays for detection of CLas in the test seedlings exposed to the psyllids of each treatment, to check if the higher acquisition rates by nymphs result in higher transmission rates of this pathogen.
Imidacloprid (Confidor 700 GrDA), 0.35 g AI/plant and thiamethoxam (Actara 250 WG) 0.25 g AI/plant, applied in the nursery tree bags, before planting, was efficient to control ACP until 60 days after application. The time to cause 100% of ACP mortality was between 5 to 7 days after the confinement of adults in treated plants. However, researches using electrical penetration graph (EPG) showed that in plants treated with imidacloprid and thiamethoxam, after the first feeding on phloem, the adults do not do more probing. We carried out the first PCR of the plants in this experiment and the results were negative, no plants have been detected the presence of the bacterium L. Ca asiaticus. No transmission results yet. We finish the second experiment that was performed to determine if the systemic insecticides are effective until 90 days after application and its effect on transmission of the bacteria. In this experiment, the time to reach 100% of mortality ranged from 3 to 7 days for both systemic insecticides tested (imidacloprid and thiamethoxam). The insecticides were effective up to 90 days after application. The results of PCR carried out for the ACP, in some periods, were positive for 100% of the samples, consisting of 10 insects tested, but in the confinement held at 46 days after application, in any sample was detected the presence of the bacteria. No acquisition in this period. In bioassays performed at 75 and 90 days after application, the percentage of positive samples was 50 to 70% and 10 to 40%, respectively. We finish the experiment 2, the difference from the experiment 1 is the application of varying doses of the systemic insecticides and confinement of the ACP in plants treated only 7 days after application. To thiamethoxam (Actara 250 WG), the doses tested were: 1, 0.5, 0.1 and 0.05 g/nursery tree and imidacloprid (Provado 200 SC) were: 1.75, 0.9, 0.2 and 0.08 mL/nursery tree. We also finish the experiment 3, using different insecticide spraying to determine if they prevent the transmission and for how long. In both experiments the systemic insecticides were effective in control of ACP, but have no result of transmission. Plants treated with insecticide, the proportion of insects reaching the phloem was similar between plants treated with imidacloprid (0.35 g AI/tree), thiamethoxam (0.25 g AI/tree) and control (untreated plants), being respectively 74, 72 and 76%. The time to perform the first ACP salivation was also similar between treatments, 118.4, 103.2, and 112.6 minutes, respectively. However, the time of phloem ingestion is drastically reduced compared to untreated plants. Apparently, ACP can only distinguish between plants with and without treatment from the moment that start ingesting the phloem sap. In this case, it was observed that after ingestion of sap with insecticide, the ACP removes the stylet from the plant and rarely returns to start a new probe on the same plant. With systemic insecticides, the main interference on probing behavior occurred during the phloem phase; phloem sap ingestion, as measured by duration of waveform E2, is significantly reduced (approximately 91%), and the insect subsequently withdrawals the stylets from the plant and rarely restarts a new probe. We finish the experiment to evaluate the effect of oil on the feeding behavior of ACP and its effect on repellency of the vector. The results showed that up to 21 days after application, mineral oil, 1.5% and 1.0%, shows repellency to adults of D. citri. Using electrical penetration graphs (EPG) techniques, we are studying the probing behavior of ACP in plants that were applied mineral oil. Plants sprayed with insecticides and M.O. affect mainly the initial phase of probing (pathway). In the case of insecticides, D. citri was able to perform probes 1 DAA, but it was able to reach the phloem only in the evaluation of 15 DAA. However, on plants treated with M.O. around 32% of insects were able to reach the phloem 1 DAA. We started the EPG experiment using pymetrozine.
Work on Objective 1 was initiated this season. The purpose of this objective was to determine how best to apply systemic insecticides to young trees to gain the longest lasting duration of psyllid control possible. Three neonicotinoid insecticides were evaluated in replicated field plots on trees approximately two years of age. These three products were imidacloprid (Admire), thiamethoxam (Platinum) and clothianidin (a product expected to be registered for use in citrus in the coming year). Each of these products were evaluated using three different application methods; soil drench, soil band spray and trunk application with multiple application rates for each method tested. For the trunk applications with imidacloprid, in addition to evaluating Admire, trunk applications were also made using Confidor 200SL which is the formulation reportedly used in the past for trunk applications in South Africa. Using the same material and rate as used in South Africa where several months of control are touted, we will be able to determine if we can obtain the same level of control reported from South Africa and also determine if by altering application method can we use our currently labeled products to obtain a level of control similar to that reported from S. Africa under Florida growing conditions. Currently, this trial is still ongoing with weekly evaluations of psyllid adults and nymphs being made. We are also collecting data on control of citrus leafminer to ensure that changing application methods does not have any negative effects on control of this pest as well. Results should be reported in the next quarterly progress report.
(863) 956-8817
(863) 956-5894
700 Experiment Station Road
Lake Alfred, FL 33850
Email Us
