Objective 1: To evaluate topical applications to the trunk of bactericides and Pentra-bark, a penetrant proven effective for trunk application of systemic insecticides. In the greenhouse, and field trials conducted in 2011, bark applications of bactericides with or without Pentra-bark were ineffective for uptake of the copper in the formulation and prevention of HLB infection in a field trial of nursery trees in Picos farm with very heavy infectious psyllid pressure. In contrast, preliminary trials conducted with potted nursery and young field trees indicate that soil drench is an effective and consistent application method for increasing copper status of leaves up to several fold over the baseline concentration in leaves. Hence, the trial in Picos Farm, was replanted with Hamlin on Swingle citrumelo trees that were root drenched in late spring with the copper bactericides EXP, Cop-R-Quik, (CQ) Magna-Bon (MB), and copper phosphite (CP) and a zinc phosphite (ZP). Spring flush leaves were collected in July to measure copper and zinc concentration in leaves to test for systemic movement of the metals. Leaf samples for PCR testing were also collected to track Las infection progress. To further evaluate soil drenches of the two commercial bactericides containing chelated copper (CQ and MB) three locations were selected. Two trials in blocks with 1 year old trees that are apparently healthy and a third trial in a block of 4-yr old trees with symptomatic and pre-symptomatic HLB infection as determined by PCR. Hence, the preventative and curative activity of the copper bactericides will be followed pre- and early stage infected trees.
For grapefruit, the objective was to evaluate formulations, rates, duration of residues for copper materials, combinations of copper materials and streptomycin, and application timing for effective canker control on young, fruiting grapefruit trees. Copper applications were made at 21-d intervals starting at spring flush in March until fruit were fully expanded in October. The period of fruit susceptibility to canker was established by applying sprays at 21-d intervals through the fruit growth period, with separate treatments ending spray application at each interval so that duration of protection varied and number of applications ranged from 3 to 11. 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. Copper sulfate pentahydrate (Magna-Bon), at a lower metallic copper rate/ha per application, provided equivalent control to other copper formulations. Streptomycin (FireWall, Agrosource, Inc.), alone or with a reduced rate of Kocide 3000, in July and early August gave equivalent control to Kocide 3000 alone. Copper phytotoxicity risk coincided with accelerated fruit growth after summer rains. Time was the most important factor affecting reduction in copper residue per fruit surface area. Th adjuvant Polymer Delivery System (PDS) had no effect on the residue. The objective for a three year trial with Hamlin orange in Hardee County, was to test formulations, rates and number of sprays for control of fruit infection and drop in 6- to 8 year-old ‘Hamlin’ trees. Copper sprays were applied at 21-d intervals after fruit reached 0.5 to 1.0 cm dia. Separate treatments ended at each 21-day interval so that there were four to seven applications per season. In 2008, early season infection occurred during rains before copper sprays commenced in late April. Subsequently, five sprays at rates exceeding 0.5 kg metallic copper/ha significantly reduced incidence of lesions on fruit. Fruit disease and cumulative fruit drop were co-ranked among copper treatments (r = 0.83). Although a tropical storm in early August promoted disease on fruit late in the season, most of the premature drop was due to infection occurring before July. In 2008 and 2009, sprays after the period of early season fruit susceptibility did not further reduce canker incidence or fruit drop. In 2009 and 2010, copper sprays were initiated before significant spring rainfall and the incidence of fruit disease and fruit drop were lower and less well-correlated among copper treatments (r = 0.57). In 2010, disease on fruit and premature drop were not significantly different from the untreated checks. Overall, there was little difference in efficacy among copper formulations, although copper sulfate pentahydrate at lower rates of metallic copper provided less control. In each season, copper treatments controlled fruit drop by ~50% compared to the untreated check, however as ‘Hamlin’ trees grew from 6 to 8 years of age, canker incidence dropped due to the development of hedgerows which reduced windblown rain penetration into the grove. A major concern is that excessive use of copper as a bactericide may lead to development of copper-resistant strains of Xcc. Streptomycin was tested as an alternative to copper bactericides. A semi-selective medium was developed to monitor the effect of a 21-day-interval copper or streptomycin spray program on Xcc for three consecutive seasons and on citrus epiphytic bacterial populations for two seasons. No copper- or streptomycin-resistant strains of Xcc were isolated after three seasons, however, the frequency of citrus epiphytic bacteria resistant to these chemicals increased. Improved canker management technology was transferred via updates of the recommendations in the Florida Citrus Pest Management Guide, reports in Citrus Industry magazine and annual presentations at the Florida Citrus Show and multi-county extension meetings.
Objective 1: To evaluate topical applications to the trunk of bactericides and Pentra-bark, a penetrant proven effective for trunk application of systemic insecticides. In the greenhouse, 0.5-1.0 cm dia trunks of Hamlin orange trees (1 yr old) were painted with a Magna-Bon (MB) (Copper sulfate pentahydrate), Cop-R-Quik (copper nitrate), a copper phosphite (CP), an experimental copper (EXP) or oxytetracycline (OTC) mixed with 0.1% Pentra-Bark or left non-treated. After for 2-3 weeks, the leaves were observed for phytotoxicity. No phytotoxicity was observed and systemic bactericidal activity in the plants was assayed with detached immature leaves inoculated with Xanthomonas citri subsp. citri (Xcc) as a Gram negative bacterial surrogate for non-culturable Canidatus Liberibacter asiaticus (Las). The canker disease control effect was measured as the number of the canker lesions in a detached leaf in vitro assay. Canker lesion no. per leaf was reduced for trees treated with EXP, but not OTC, CP or MB. When the canker assay was repeated on a second set of plants treated with EXP or MB and compared to another soluble copper Cop-R-Quik, EXP did not show canker control activity but Cop-R-Quik reduced lesions in the assay. Objective 2: In July 2011, four of the bactericides OTC, CP, MB and EXP were evaluated in a field trial by painting 1-2 yr-old nursery trees with a mixed with 0.1% Pentrabark. This planting, located at USDA-ARS Picos Farm in Ft. Pierce is highly exposed to infectious psyllids based on a previous study evaluating SARs located there (NAS-86). The trees were assayed for HLB status in January 2012 and mean Ct values for all treatments were between 22 and 23, i.e. all trees were highly infected with Las. Preliminary trials conducted with potted nursery and young filed trees indicate that soil drench is a more effective and consistent application method for increasing copper status of leaves than trunk painting. Henceforth at Picos Farm, replanted Hamlin on Swingle citrumelo trees will be root drenched. The bactericides chosen for further evaluation include EXP, Cop-R-Quik, MB, and a novel copper phosphite (CP) and zinc phosphite (ZP). These formulations will be applied as a root drench in the same volume of water used for application of neo-nicotinoid insecticides (250 ml). Terminal leaves will be collected periodically to measure copper or zinc concentration to test for systemic movement of the metals. Leaf samples for PCR testing will be collected at 3 month intervals to track Las infection progress.
Objective 1 is to conduct a field evaluation of 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 located 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). Trees were 8 years old at the initiation of the trial. Treatments were 1) non-treated check; 2) Nutri-Phite sprayed 4 times 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. Four disease ratings have been taken so far and a slight decline in tree health has been observed, but no significant treatment effects have been observed. The 2011 harvest experienced a 27% yield increase in all treatments compared with the 2010 harvest, but no significant treatment effects were observed. Objective 2 is to determine the mechanism of HLB symptom suppression by foliar nutritional application, Rep 1 using Hamlin sweet orange trees inoculated with HLB and treated bimonthly with the nutritional sprays treatments 1, 2, 3, and 5 from objective 1 has finished. Monthly monitoring of infection rate and disease development did not show obvious treatment differences except a possible increased rate of decline in treatment 2 compared to all other treatments. Trees that were only PCR+ in root tissue showed an unexpectedly fast decline in tree health across treatments. After pruning trees at 6 MPI for canopy management, sampling at 7 months post inoculation (MPI) showed a slight reduction in titer in the new flush of all treatments except treatment 1, where no Las was detected until 8 MPI. This suggests that treatments 2,3, and 5 may potentiate movement of Las to new flush where psyllids are most likely to feed and acquire Las. Sectioned midrib samples were observed by light microscopy at 6 and 8 MPI and 9 MPI. At 6 MPI reduced phloem plugging and necrosis was observed in treatments 3 and 5, however these treatments had some symptomatic leaves without detectable Las. These leaves had abnormal starch buildup preferentially in phloem tissue instead of mesophyll cells. At 9 MPI there was significant variation in plugging between midribs within a treatment even with highly similar symptoms and Las titer. All treatments had a full range of phloem damage observable in midribs from similarly symptomatic leaves ranging from severe plugging and collapse to apparently healthy phloem. Rep 2 has been inoculated and monthly samplings of leaf and root tissue are underway. Root samples are split for qPCR Las quantification and starch analysis for a quantitative measure of phloem function throughout the plant. Microscopy will be continued, however the high variability of phloem plugging and collapse even within the same midrib from a symptomatic leaf makes interpretation of results difficult. 67 of the 75 inoculated trees are now positive with disease symptoms developing. No treatment effects have been observed, except that phosphite alone results in higher than expected infection of roots within 4 months of inoculation, and the effect is still present at 6 MPI. Now that leaf symptoms have developed and roots are consistently positive, sampling for microscopy will begin at the end of this month.
Under Objective 1 and 2: Soil applications of SAR inducers at various rates and application frequencies were evaluated for control of canker in field trial of 3- or 4-yr old ‘Ray Ruby’ grapefruit trees in southeastern Florida. Reduction of foliar incidence of canker produced by one, two or four soil applications of the neonicotinoids, IMID and thiamethoxam (THIA), or acibenzolar-S-methyl (ASM, Actigard) was compared with 11 foliar sprays of copper hydroxide and streptomycin applied at 21-day intervals. In 2011 crop season, all treatments significantly reduced the incidence of foliar canker on the combined Spring-Summer-Fall flushes compared to the untreated control, depending on rate, frequency and timing of application on young grapefruit trees under canker epidemic conditions. Soil application of systemic neo-nicotinoid insecticides has also been demonstrated to induce SAR and provide canker control for bearing trees but use of higher rates of these systemic insecticides for young fruiting trees is currently restricted. A preliminary trial in 2011 with 5 yr-old fruiting grapefruit trees trees demonstrated the efficacy of trunk application for IMID, THIA and ASM at 3.5X the label rate per season to compensate for the larger tree volume. Trunk application was as effective for canker control on foliage as soil application and control matched that of 11 sprays of copper. The objective for current field research is to develop more effective suppression of fruit infection using trunk applications of neonicotinoids and non-insecticidal SAR inducers (e.g. ASM). . Under Objective 3, the integrated use of ASM, THIA and IMID soil applications was evaluated to increase and/or extend canker control in 3-yr-old grapefruit and 2-yr-old Vernia orange trees. The highest incidence of disease trees and/or leaves was in the non-treated check in each trial compared with a very low incidence of canker in the integrated SAR treatments. 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 and Clothianidin. Clothianidin (Belay) is now registered for use on non-bearing citrus in Florida, hence all of neonicotinoids registered for non-bearing citrus in Florida have been shown to have SAR-inducing activity against canker. In 2012 spring, field trials the rates and and timing of soil drenches and trunk treatment with neonicotinoids are congruent with recommendations for use of neonicotinods for systemic control of psyllids . Novel non-neonicotinoid insecticides and fungicides with demonstrated systemic activity against canker in greenhouse trials are under evaluation in addition to ASM for integration with neonicotinoids and foliar copper sprays to optimize canker control on non-bearing and young bearing trees.
This report is for July/2011. 1) Evaluation of screens impregnated with insecticide barriers. As explained in previous reports, the experiment is being conducted in two farms located in the Sao Paulo State. On the farm located in Sao Manuel 14 evaluations were performed. In the area with screen impregnated with insecticide barriers 2 insects were collected, and in the area without screen nothing was collected. In Descalvado 12 evaluations were performed, in a total of 2 and 1 psyllids collected in areas with and without barrier, respectively.
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. The test plants are being evaluated by PCR. 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 This experiment is delayed because the equipment for the extraction of plant sap is being imported. The device has already been bought, however the manufacturer has not delivered it yet. The experimental area has been selected and the experiment must be started in September (after Brazilian winter).
Exp.1 ‘ All test plants from the first trial were collected and submitted to real time PCR for the last time in January/2012. In the compartments where citrus plant were used as inoculum source of Las and Lam, the test plants were naturally more infected with Las than with Lam (0 and 3.8% of test plants infected with Lam and 9.6 and 19.2% of tested plants infected with Las). In the compartment with Murraya as source of inoculum of Lam, 8.2% of test plants got infected. The second trial is ongoing but there is no result yet. Also we had an infestation of Tamarixia radiata in our ACP breeding plants that completely devastated it and postponed the new releases of ACP into the compartments. We needed to restart our ACP HLB-free breeding. Exp. 2- Acquisition Period for Las and Lam. Different acquisition periods (AP) (30 min, 1h, 3h, 6h, 12h, 24h, 3 days, 7 days, 10 days and 14 days were tested. After these APs in sweet orange trees as source of inoculum, adults ACP were transferred to Rangpur lime seedlings for 21 days and after tested by PCR for Las and Lam. Both Lam and Las were detected by PCR in adult ACP after 1 hour AP (6.6%). For Las the efficiency of acquisition increased with the AP up to 7 days (16.6%) and decreased to 3.3% with 14 days AP. For Lam the efficiency of acquisition increased to 30% with 1 days AP and decreased after that to 3.3%. Inoculation Period for Las and Lam. Different inoculation periods (IP) were tested (30 min, 1h, 3h, 6h, 12h, 24h, 3 days, 7 days, 10 days and 14 days). Adults ACP had 21 days of AP in sweet orange as source of Las and Lam. After, they were put on test plants for different IPs. After 6 and 12 months, shoot samples were analyzed by PCR and all samples were negative for both Las and Lam. Exp. 3 ‘ Regardless the inoculation of trees at the screenhouses, some encaged trees showed symptoms just after building the screenhouses in December 2008 (probably they were already infected before be protected) and the severity progress of symptoms were assessed in those trees. About three year after that the average severity was 46.2 and 63.7%, respectively % for Hamlin/Rangpur lime planted in 1999 (6 trees) and planted in 2004 (2 trees). For Valencia/Rangpur lime planted in 1999 (5trees), the severity was 63.7% and for Pera/Rangpur lime planted in 2005 (1 tree) it was 37.5%. In the alternative experiment, comparing the disease severity on plants of Val’ncia/Swingle from January/March 2011 to January March 2012, the youngest trees (planted in 2007) showed the highest initial severity and also the highest final severity than older trees planted in 1999 and 1995. Comparing Valencia sweet orange at the same age but in different rootstocks, the severity increasing at the same period in trees grafted in Volkamerian lemon were double than in trees grafted in Swingle citrumelo. Comparing different scion varieties grafted on Swingle and at the same age, the severity increase were higher in Hamlin than in Valencia.
Immidicloprid applications and irrigation treatments started with the first spring flush on March 13, 2012 at the Southwest Florida Research and Education Center (SWFREC), of the University of Florida, in Immokalee, Collier County. The study will be conducted on citrus experimental groves, of Valencia orange of one and two years old, 5 to 6 years old and 8 to 10 years old. Field work will be timed with growth flushes in the spring and summer months. The soils in the SWFREC are poorly drained, with sandy textures, and they developed in ‘Flatwoods’ vegetation. Irrigation treatments were established 3 days prior to the initial application of Immidicloprid treatments and the Br tracer. The frequency of soil and leaf sampling were 3 times per week for two weeks following immidicloprid applications, twice per week for the next two weeks and then weekly for the remaining four weeks. A second application will be made with the next flush in mid May. The extraction procedures for immidicloprid in soil and leaf samples have been tested and will be used for samples now being taken. The analysis for soil degradation studies have not been completed, but will be available for the next report.
In the past quarter, we have identified four chemical compounds that Asian citrus psyllid antennae are capable of recognizing physiologically at the level of the antenna. Identification of two of these compounds was verified through the use of coupled gas chromatographic-electroantennogram detection (GC-EAD) and we as GC-mas spectroscopy. We believe, this is the first instance of successful electrophysiological recordings by the coupled GC-EAD method for any psyllid species. The four compounds are currently being tested in the laboratory in both Lake Alfred and Fort Pierce using olfactometers and in field trapping trials at both locations. Initial results suggest that these antennally active compounds may also elicit psyllid behavior, but are ongoing tests are focused on confirming this hypothesis. Our initial field test in February was inconclusive, because psyllid populations were low. Laboratory tests are ongoing and subsequent field testing is planned.
In this research, we have been developing a repellent formulation for Asian citrus psyllid (ACP). A DMDS-based SPLAT formulation has been developed. It is currently formulated and produced by ISCA technologies. Our recent results have produced inconsistent results; however, there have been cases where the formulation has effectively reduced psyllid populations both in Florida and in trials in another state. In the final year of the project, we have tested new active ingredients that may be more effective than DMDS for several reasons. First, these newly identified active ingredients are less noxious than DMDS and simply do not smell as bad to humans. This makes them much easier to work with. Also, these chemicals are less phytotoxic and easier to formulate. Therefore, these new formulations may not have the drawbacks that are associated with DMDS-SPLAT. In this previous quarter, we have been working to evaluate these new formulations and we have determined that two of the newly identified active ingredients are effective in repelling psyllids when deployed in SPLAT. We are currently finishing up these tests to hopefully determine whether a more practical SPLAT-based repellent formulation can be developed than our current DMDS-based standard.
Our studies from 2009-2011 have shown that ACP populations in Florida have developed varying levels of resistance to several insecticide chemistries. Baseline susceptibility data for both adult and immature ACP to commonly used insecticides was collected in 2009 and 2010. These data were collected for five ACP populations from various parts of Florida. In 2009, the highest level of resistance for adult ACP, as compared with the laboratory susceptible (LS) population, was found with imidacloprid with an LD50 resistance ratio (RR50) of 35 in one population. This was followed by chlorpyriphos (RR50 = 17.9, 13.3, 11.8 and 6.9), thiamethoxam (RR50 = 15 and 13), malathion (RR50 = 5.4 and 5.0) and fenpropathrin (RR50 = 4.8). In 2010, mortality of adults from all five sites sampled was lower than with the LS population at three diagnostic concentrations of each insecticide tested. Among nymph populations, indications of resistance were observed with carbaryl (RR50 = 2.9), chlorpyriphos (RR50 = 3.2), imidacloprid (RR50 = 2.3 and 3.9) and spinetoram (RR50 = 4.8 and 5.9). General esterase, glutathione S-transferase and monooxygenase levels were also elevated in field-collected adult and nymph ACP as compared with the LS population. Also, we tested whether changes in susceptibility of organophosphate and carbamate insecticides was due to target site (acetocholynesterate) inactivity. We proved that the levels of resistance we were observing were due to increased levels of detoxifying enzymes as opposed to target site insensitivity. In 2011, 3 diagnostic doses (LD50, LD75 and LD95), obtained using the laboratory susceptible population in 2009, were used to compare susceptibility levels among field-collected and laboratory populations. Susceptibility data obtained in 2011 show marked reduction in the susceptibility levels of ACP to chlorpyriphos and fenpropathrin, when compared to the susceptibility data obtained in 2010. Mean percent mortality obtained from all five locations was significantly lower than that of the laboratory susceptible population for all tested insecticides in 2011. Additionally, we have identified five CYP4 genes that were inducible with insecticide treatment in ACP. In 2011, gene expression analysis indicated significant overexpression of all CYP4 genes in field-collected populations when normalized against laboratory susceptible population. SDS-PAGE showed few differences in the total protein profiles among six populations, particularly for proteins of 25 and 200 kDa molecular masses. Western blot analysis indicated increased signal of a band corresponding to 60 kDa protein in Fort Pierce population when compared with the laboratory susceptible population. These results provide insight on the CYP4 mediated insecticide resistance in field populations of ACP, which has led us to study the effects of silencing such CYP4 genes in ACP through RNAi. Our preliminary results on RNAi show that silencing of CYP4 genes was achieved with as low as 25 ng dsRNA, which was confirmed through gene expression and western blot. The above results suggest that insecticide rotation that includes existing registered modes of action as well as incorporation of new modes of action or non neurotoxic products and molecular tools, such as RNAi could potentially be used to prolong resistance development in ACP. We have recently finished investigating various pesticide rotation modules in the field and we are currently analyzing those data. We are hoping to determine if there is an optimal strategy for rotating our currently available modes of action.
Low volume (2-10 gallons per acre) are currently routinely used by many Florida citrus growers. The cost savings as compared with standard higher volume applications (100-200 gallons/acre) make low volume applications a potential useful tool given the need for additional sprays that target Asian citrus psyllid (ACP). The objective of this investigation was to study potential alternative methods for implementing low volume technology, as well as, to understand the potential limitations of the technology. 1) Duration of residual toxicity. Insecticide residue on citrus leaves following applications may kill psyllids for up to several weeks. We investigated longevity of activity of low volume sprays, using leaves from field trials with fenopropathrin (16 oz/acre), phosmet (1.5 lb/acre) and imidacloprid (15 oz/acre) and compared with high volume applications. A bioassay was then performed with citrus leaf discs in a Petri dishes. Mortality was recorded at 24 h and 48 h intervals. The mortality of adult psyllids after 4 days was between 60 and 100% after high volume applications, but <10% after low volume applications. By day eight, only the high volume fenpropathrin treatment caused high mortality (80%). All other treatments tested showed <10% mortality. These results indicate very limited residual activity of low volume treatments. Essentially, the majority of psyllids are killed during the initial 24 hours following a low volume application and this is likely due to both fumigation and direct contact activity. 2) Border row treatment as a tactic for ACP management. The purpose of this study was to investigate the potential of border row treatments for psyllid management as compared with treating entire blocks with low volume sprays. Psyllid numbers in both fully and border only treated blocks were significantly reduced by the applications three and seven days after application. On day 14, the border row treatment was not different from the control, while psyllid populations were still reduced in the fully treated blocks. These results indicate that border row treatment by low volume may have some use for up to two weeks after treatment, but is not as effective as treating entire blocks of citrus at the five acre replicate plot sizes that we tested. These results indicate that border row applications of low volume sprays may be limited in effectiveness, but results may be different in larger-plot tests. 3) The vertical distribution of adult psyllids in mature citrus. Adult psyllid distribution within the canopy of citrus has has not been investigated thoroughly following applications of insecticides. Our season-long study revealed that there are up to three times more adult psyllids at ~3 m as compared with 1 m height within the canopy following insecticide treatment. Leaf disks from the top most leaves were previously shown not to be toxic to adult psyllids. A spray droplet penetration study was performed, using water sensitive paper (WSP) strips as an indicator. These strips were placed at three heights within the canopy of trees: 1.2, 2.1 and 3.2 m. Results revealed that droplets penetrated both sides of the leaf at 2.1 m only. At 1.2 m, only the upper surface received significant numbers of droplets. At 3.2 m, no droplets were detected. In summary the low volume technique results in lower penetration of the tree canopy as compared with high volume applications, which may in part explain the shorter longevity of efficacy of low volume applications as compared with standard sprays. Also, our tests indicated that adjuvants did not significantly improve longevity of effectiveness of our low volume applications.
Spatial and Temporal Incidence of Ca. Liberibacter in Citrus and Psyllids Detected Using Real Time PCR, January 2012. Objective 1. Assess seasonal patterns of pathogen incidence in citrus trees and psyllid vector populations in an infected experimental block. Since March 2008, the pathology and entomology researchers have been working at a site located within a commercial grove that initiated nutritional and/or insecticidal sprays on 7-year-old Valencia-on-Swingle trees. Initially, disease incidence of HLB in trees in the various plots average around 25%. One year later, disease incidence was greater than 80%, and in the nutritional treatment plots, 100%. Determining the titer of HLB in symptomatic leaf samples and in collected psyllids was possible by training and resources provided by collaborator, M. Keremane. Citrus leaf samples and psyllids, stored from initiation of the trial and sampled at approximately 6 month intervals, are being processed. Sampling continues on schedule, with processing and analysis remaining up-to-date. Data reveal that while some fluctuations in the titer of bacteria in occur at sampling dates, preliminary conclusions are limited. The data is skewed toward a detectable population of HLB by the selection of symptomatic tissue, therefore it may not be that differences in populations will be detected in symptomatic tissue. Other studies are using other sampling techniques to try to get around this bias. Objective 2. Evaluate the influence of cultural factors that affect incidence and titer of Liberibacter in citrus trees and psyllid populations including tree age, variety, rootstock, block size, surroundings and management practices such as vector control and tree removal. In another location where HLB incidence and tree health is being monitored on grapefruit and Hamlins receiving various treatments, including initially, tree removal, S. Halbert has been conducting trapping of psyllids. Psyllids from the traps are being analyzed for HLB titer by K. Hendricks, SWFREC. Four suction traps were operated at the SW Florida Research & Extension Center from July 2009 to present. These included an 8 meter tall trap and three 2 meter traps. Of the latter, one was in managed citrus, one was in unsprayed citrus, and the other was in an open field. Samples were collected approximately weekly. The psyllids were removed and identified in Gainesville. Beginning in 2011, all Diaphorina citri Kuwayama were tested singly for presence or absence of the HLB pathogen. All three short traps collected D. citri. Both traps located in citrus collected at least occasional D. citri throughout the year, but the trap in the unsprayed citrus collected the most. The trap in the open field showed peak activity in March, coinciding with the spring flush. These collections could indicate that longer distance flights away from the crop occur at that time of the year. Overall, there were five samples positive for Las and three questionable samples in 2011. There were positive samples collected from all three short traps. There was no difference in the numbers of positives by trap. This can be attributed to the fact that citrus greening disease is widespread and common in the Immokalee area. Preliminary data indicates that neither nutritional nor insecticidal sprays impacted the disease progress of HLB, because either the treatments were initiated during the long lag time between inoculation/symptom expression or another reason. Recent yield data indicates that trees in plot receiving nutritionals and insecticide are benefiting by increased yields.
Experiment 2 (within HLB-Area-Wide Management AWM). The incidence of HLB increased very few in the last 3 months during summer season (January to Masrch/12), in plots without insecticide application (from 7.3% in December/11 to 7.4% in March/12) and did not increased in plots with inseticide application (5.3%). Even during the summer, the ACP population density was very low (almost zero) and deccelerated in the last two years, even in the plots without ACP control. The paper “Efficacy area-wide of inoculum reduction and vector control on temporal progress of huanglongbing in young sweet orange plantings” by Bassanezi, R. B., Montesino, L. H., Gimenes-Fernandes, N., Yamamoto, P. T.; Gottwald, T. R., Amorim, L., and Bergamin Filho, A. were submitted to Plant Disease for publication. The full paper were sent to CRDF and the Abstract is: Huanglongbing (HLB), caused by Candidatus Liberibacter spp. and transmitted by the Asian citrus psyllid Diaphorina citri (ACP), is an important threat to citrus industries worldwide, causing significant yield loss. The current recommended strategies to manage HLB are to (i) eliminate HLB symptomatic trees to reduce sources of bacterial inoculum, and (ii) apply insecticides to reduce psyllid vector populations. The objective of this study was to assess the effectiveness and the importance of both strategies applied within young citrus plots (Local management), in different frequencies and combinations, on HLB temporal progress. Two factorial field experiments, E1 and E2, were initiated in a new plantation of sweet orange in a HLB epidemic region of Sao Paulo, Brazil, in October/05 and May/06, respectively. 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 beginning of the HLB epidemic was delayed for 10 months in E1, but wasn’t affected by different local strategies for both experiments. 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. 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 and lower frequency of bacterialiferous psyllids in E1 compared to E2. Annual productivity remained increasing over time in E1 as expected for young plantings, whereas remained stable or decreased in E2. These results confirmed 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 HLB control.
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