Ultra High Performance Liquid Chromatography – Pesticide Residue Analysis (Sept 2012 Update) Following scheduling delays by the company performing the installation, the new LC-MS-MS was installed in late August. Additional service calls have continued to be made through September to correct leaks in the lines so that the equipment functions properly. At the end of September, the installation technician returned and provided 2 days of instrumentation and software training and we have now begun running preliminary residue samples.
Research identifying enzymatic pathways that degrade the the salivary sheaths was advanced and multiple enzymes within the two classes known to degrade the salivary sheaths have been evaluated. Natural gene products already produced in plant systems have been shown to function in sheath degradation. This suggests it may be possible to engineer plants to block sheath formation, thus making them resistant to psyllid feeding. Novel method of pure sheath isolation has been perfected using a soluble membrane through which the psyllids feed. Subsequent purification of pure sheath material was shown to be possible through differential filtration. This method allows purification of sheath material that is not contaminated by any other chemicals and therefore provides more evidence showing the building blocks used by the psyllid to synthesize sheaths.
Two experiments were concluded by USDA-ARS on protecting young citrus from HLB using different ACP management programs. The results were reviewed in the July 2012 quarterly report. Briefly, an intensive insecticide program was evaluated in each experiment: eight annual calendar applications of traditional hard insecticides, hereafter referred to as the ‘complete program’. The results of the experiments indicated that up to eight monthly applications per year of hard pesticides applied on a calendar schedule were ineffective for getting young citrus into production without becoming diseased. Of probable importance is that the grove where the two experiments were conducted was subjected to a minimal psyllid management program and contained many trees infected by HLB, thus the ACP management programs we evaluated might have been more effective if psyllids in the surrounding areas had been more aggressively controlled and HLB-infected trees removed to reduce inoculum loads. It is possible that better ACP and resulting HLB control in the young trees could have been achieved under the complete program if it had included a scouting component – either as a substitute for timing sprays on calendar dates or for determining if additional insecticide sprays were needed. UF (Stansly) also concluded two experiments. In one test, the efficacy of four treatments for protecting young citrus resets from HLB was studied: (1) nutrition alone, (2) insecticides alone, (4) nutrition plus insecticides, and (4) untreated control. Resets (‘Valencia’) were planted in July 2010. At that time 92-95% of the surrounding trees were PCR positive for HLB. The nutritional regimen was adapted from that of production manager Maury Boyd. Insecticide treatments included dormant sprays during the winter, and additional sprays were made when numbers of ACP exceeded a threshold, initially 0.5 ACP but later 0.2 ACP per tap sample. Resets were subjected to regular drenches of the following insecticides: bifenthrin, thiamethoxam, and imidacloprid. The resets were drenched 3 times during 2010, 4 times during 2011, and 4 times during 2012. Foliar insecticides (spinetorum, chlorpyrifos, phosmet, fenpropathrin, dimethyl phosphate, spirotetramat, abamectin + thiamethoxam, or dimethoate) were applied to the resets 3 times during 2010, 7 times during 2011, and so far 2 times during 2012. The resets were PCR-assayed for Las (Li primers, Ct threshold of 32) 4 times in 2011 and most recently in Feb 2012. By 19 months after planting, averages of 16 to 45% of the resets tested positive for the pathogen (Ct-values of 27 to 33), and there were no significant difference among treatments with respect to percentages of trees infected and titers of the pathogen. In a second UF experiment, a new citrus planting (‘Hamlin’) was planted during May 2010 and subsequently drenched with insecticides (Verimark, Admire, Plantinum) at different rates and rotational schedules. The trees were treated 2 times in 2010, 4 times in 2011, and twice in 2012. All treatment regiments significantly reduced the number of adult and juvenile ACP on all sample dates with differences amongst the treatments only being observed with the nymph counts on 13 July 2011. HLB incidence has been lower in the treated plots with the lowest levels being seen when Verimark at the higher rate was used. At 24 months after planting, 63% trees tested positive for HLB in plots of trees not drenched with insecticides while fewer (from 11 to 26%) trees tested HLB-positive in plots of trees that were drenched.
Entomopathogenic nematodes: Amending soils to increase biological control of insect pests Developed molecular probe to quantify Phytophthora nicotiana. Measured 6-fold greater amounts of the pathogen (P=0.0001) in samples obtained from Advanced Citrus Production System (ACPS) plots compared to conventional plots. Samples were obtained quarterly between July 2011-May 2012. This result is consistent with 2-fold more D. abbreviatus trapped in ACPS plots (P=0.02) during the same period, because D. abbreviatus exacerbates root infection by Phytophthora spp. We confirmed in soil assays, results from aqueous tests showing that spores of Paenibacillus sp. detach readily from Steinernema diaprepesi at pH<6.0, but not at neutral pH. Initiated laboratory bioassays to investigate effects of soils from ACPS and conventional plots on nematophagy by fungi and subsequent EPN efficacy against D. abbreviatus larvae. Plant parasitic Nematodes: Characterizing a new nematode pest and the prevalence of resistance breaking populations of the citrus nematode. Developed molecular probe to distinguish Xiphinema citricolum vs X. laevistriatum, two morphologically indistinguishable dagger nematodes encountered in citrus orchards. Began producing plasmids that will serve as positive controls for those primers. Sampled 6 orchards near Ft. Pierce and detected trace amounts of X. vulgarum in just two samples, juvenile Xiphinema sp. which cannot be identified to species in 4 samples. All samples had Phytophthora nicotianae and P. palmivora propagules above treatment thresholds and all samples were positive for the EPN Heterorhabditis indica. Discussed results with Denise Dunn who processes large numbers of samples for DuPont and was informed that X. vulgarum had declined greatly in DuPont samples, during this period. Will resume sampling in mid-autumn when populations are likely to increase.
Citrus production is facing increasing acreage losses due to disease threats arising from pests like the Asian Citrus Psyllid and Citrus Greening (Huanglongbing, HLB) Disease. Some growers in Florida have experienced positive results at combating the physiological damage and yield loss commonly associated with HLB, even in fields with up to 95% of trees with confirmed HLB disease. A mixture of micro- and macro-nutrient, along with some agents to fight against pathological diseases, applied in a oil-based foliar spray solution may have promise at boosting citrus tree vigor to assist in the combating HLB disease. Preliminary field and laboratory studies performed at TAMU-Kingsville Citrus Center focused on the impacts of Ca applications at reducing Asian Citrus Psyllid (ACP) populations. In the field, composts higher in calcium (Ca) levels led to higher Ca content in citrus leaves, and subsequently reduced ACP populations feeding on these trees compared to other compost sources. In a controlled lab study, foliar sprays containing Ca led to fewer ACP eggs laid and decreased adult ACP survival on ‘Rio Red’ grapefruit leaves. From these initial investigations a large field study was initiated in May 2011 on 6-7 year old ‘Rio Red’ grapefruit trees located at the Citrus Center South Farm. Varying foliar micro- and macro-nutrients treatment mixtures were applied as a means to supplying increase tree vigor to fight against citrus pest disease symptoms. Objectives: The purpose of this project was to determine the effect of using various micro- and macro-nutrient foliar sprays, in combination with nitrogen and oil spray treatment, on the physiological growth parameters of young grapefruit trees, their pest load, and subsequent impacts on fruit yield and quality. Foliar treatments contained various chelated nutrient sources in solutions that were formulated by Metalosate’: Trt 1= Control (N and oil only); Trt 2 = K; Trt 3 = Ca; Trt 4 = Crop Up: (Mg, B, Cu, Fe, Mg, Zn); Trt 5 = Crop Up+ K; Trt 6 = Crop Up + Ca; Trt 7 = K + Ca; Trt 8 = Crop Up + K + Ca. All treatments received 2% 435 Oil; 50 lb/Acre N; RequieM 25 EC; and Serenade (strain of Bacillus). Results: We observed a positive correlation between lower ACP infestations in trees receiving additional calcium application, regardless of whether the macro-nutrient is applied to the soil or to foliage. However, all foliar treatments that included supplemental calcium additions significantly reduced the ACP population in field trials from 16 to 25% compared to equivalent treatment excluding Ca. The lowest ACP infestation levels on citrus leaves were observed in foliar spray treatments that included the Crop-Up plus Ca treatment, followed by the Ca only treatment. Benefits to Citrus Industry: With an increased threat of HLB disease and other insect related diseases facing Texas citrus growers, we anticipate that this data may allow us to find another aspect of decreasing this threat to the industry with minimal use of bio-pesticides.
The questions to be addressed by this research project are 1) how does Imidicloprid move in the sandy soils of south Florida, 2) how long does imidicloprid persist in sandy soils, and 3) how much Imidicloprid leaches below the root zone of citrus trees. Isotherms relating soil Imidicloprid concentrations in soil solutions with Imidicloprid concentrations in the solid phase of sandy soil were conducted using Immokalee fine sand. The concentrations added to the soil were 2, 4, 6 and 8 mg ml-1 and represent the range of concentrations in the soil estimated after soil drenching. Imidicloprid was found to penetrate to a depth of 45 cm and have greatest affinity in the 0-15 cm soil depth due to higher soil organic matter at that depth. These data were supported by soil partition coefficients (Kd) of 1.68 mg of Imidicloprid. in one liter of soil solution at the 0-15 cm depth and decreases to 0.33 and 0.25 mg l-1 at 15-30 and 30-45 cm, respectively. A laboratory study found that Imidicloprid decreased in soil concentrations due to biodegradation at a rate of 0.013 .g g-1 d-1, thus one milligram of Imidicloprid would persist in the soil for more than 27 years. Two field studies were conducted the spring and summer of 2012. Initial analysis of soil samples from the spring study indicate that Imidicloprid concentrations decreased by 90% in 10 days at the 0-15 cm depth by tree uptake and recommended microsprinkler irrigation. At the 0-15 cm depth. Imidicloprid concentrations reached the 15-30 cm depth in 5 days after application and persisted at that depth for approximately 15 days. During this initial application study, adult psyllid populations per tree decreased from approximately 1.7 for both treated and non-treated trees to 0.1 psyllids per tree for the treated trees at 22 days after application. Psyllid populations on treated trees were below 0.1 psyllids per tree from 22 to 50 days after application.
In this project we are studying the influence of various factors on transmission efficiency of Candidatus Liberibacter asiaticus (CLas) by the Asian citrus psyllid (ACP), Diaphorina citri. Here we report partial results of the last study, on the effects of systemic insecticides on pathogen acquisition and or inoculation. In this final study, we are testing if widely-used neonicotinoid insecticides can prevent CLas acquisition and/or inoculation on citrus plants. In a first experiment, we evaluated the effects of insecticide mode of application and citrus branch age on pathogen acquisition by ACP nymphs and adults. CLas-infected sweet orange nursery trees [Citrus sinensis (L.) Osbeck grafted on ‘Rangpur’ lime] with and without young shoots were submitted to the following treatments: a) foliar application of imidacloprid (200 SC ‘ 0,24 ml c.p/1 L water), for contact action; b) drench application of thiametoxam (250 WG ‘ 1 g c.p./plant, diluted in 50 ml water), for systemic action; and c) untreated plants (water only; positive control for estimating acquisition efficiency after exposure to source plants). Two hours after treatments a) and c), and 10 days after treatment b), about 50 3rd-instar ACP nymphs were confined on the youngest branch of each nursery tree using sleeve cages, during a 72-h acquisition access period (AAP). As a negative control for checking possible vector infectivity before exposure to the treated nursery trees, ACP nymphs and adults from the same rearing batch were submitted to a similar AAP on untreated healthy nursery trees. Insect mortality was assessed right after the AAP; the surviving insects were kept on healthy citrus seedlings for 10 days and then tested by real-time (RT) PCR for infectivity with CLas. The experiment had a completely-randomized block design, with 2 factors (‘application mode’ and ‘citrus branch age’) (4×2) and 3 replications per treatment. Each replication was represented by a group of 50 nymphs confined on the youngest branch of a nursery tree. A similar experiment was carried out with 1-week old adults. No infective psyllids were detected by RT-PCR after the AAP on infected nursery citrus trees that had been treated with either foliar or drench applications of the insecticides, or on the untreated healthy trees (negative control), in both experiments. In contrast, 47.2% of the nymphs and 32.5% of the ACP adults were able to acquire the pathogen during the same AAP on untreated infected citrus trees with young shoots. On untreated infected nursery trees without young shoots, lower but relatively high acquisition rates were detected for adults (23.7%), whereas no nymphs acquired the pathogen. The average mortality rates of psyllid adults (<30%) and nymphs ('50%) were surprisingly low after the 72-AAP on treated plants, although significantly higher than those observed on untreated plants ('8%) in the experiments with adults (F=10.9, P=0.002) and nymphs (F=13.6, P=0.001). Citrus branch age did not influence the mortality rates caused by the insecticides for adults (F=1.99, P=0.19) and nymphs (F=2.98, P=0.11). Despite the low mortality rates, these results show that both insecticide treatments (foliar and drench applications) prevent pathogen acquisition by the vector, possibly because of sub-lethal effects on feeding behavior. We will now check for the presence of CLAS (by RT-PCR) in the test seedlings exposed to the surviving psyllids after the AAP, to make sure that no transmission event occurred in these insecticide treatments. A second experiment is being carried out to test if the same insecticide treatments (foliar and drench applications of neonicotinoids) can prevent CLas inoculation by ACP on citrus nursery trees with or without young shoots. Results and conclusions of this second experiment will be presented in the final report.
We have previously conducted experiments to evaluate the effect of chemical plant growth regulators (PGRs) on acquisition of the citrus greening pathogen, Candidatus Liberibacter asiaticus (Las), by the Asian Citrus Psyllid (ACP). Previously, we reported the results of bioassays in which psyllids were allowed to feed on Las-infected or healthy citrus plants treated with the PGR, prohexadione calcium, for 28 or 14 d acquisition access periods (AAPs). Subsequently, we have conducted assays to evaluate the effect of prohexadione calcium acquisition during a 7 d AAP. Three independent experiments were conducted in temperature-controlled environmental chamber as described previously. ACP from each treatment were then collected and analyzed with qPCR. Results of these analyses indicated that ACP feeding on PGR-treated, infected plants acquired Las at a higher rate than did ACP held on untreated, Las-infected plants. Subsequent experiments will be conducted to determine the rate of acquisition following a 24 h AAP with adult ACP and during nymph development.
One of the proposed objectives of this project has been to determine whether the use of chemical plant growth regulators (PGRs) affect acquisition of the citrus greening pathogen, Candidatus Liberibacter asiaticus (Las), by the Asian Citrus Psyllid (ACP). Previously, we reported on initial experiments conducted to evaluate the effect the PGR, prohexadione calcium, on Las acquisition after two weeks or one month of feeding. Subsequently, we have completed additional replicates of those trials. In these experiments, twenty adult psyllids of mixed gender were released onto healthy and Las-infected plants treated with prohexadione (sprayed until run-off) and allowed to dry. Treated plants and psyllids were enclosed in nylon mesh sleeve cages. As a control, twenty ACP were also released onto healthy and Las-infected plants treated with water + adjuvant. Each treatment was replicated 6 times on three separate dates. Plants and insects were maintained in a temperature-controlled environmental chamber for 28 d or 14 d acquisition access periods (AAPs) prior to collecting insects. The results from qPCR analysis of psyllids given 28 d AAP suggest that the PGR evaluated does not alter the rate of Las acquisition by ACP, suggesting that that the activity of prohexadione against psyllids does not extend to four weeks. In contrast, psyllids given 14 d AAPs were nearly 15% more likely to acquire Las when feeding on PGR-treated infected plants compared to untreated, Las-infected plants.
Since our last report, we have completed bioassays to evaluate the effect of prohexadione calcium on acquisition of Las by the Asian citrus psyllid over a range of acquisition access periods (AAPs). The psyllids collected from these bioassays are currently being processed (DNA extraction and qPCR) to determine the rate of Las acquisition from each treatment. Because our initial results from these studies indicated that acquisition was greater when psyllids fed on PGR-treated plants, experiments to evaluate the feeding efficiency of psyllids in response to PGR applications were conducted. Feeding efficiency on PGR-treated verses untreated plants was compared by quantifying excretion of honeydew by psyllids after 24, 48, 72, or 96 hr of feeding on treated citrus leaf discs placed in Petri dishes. Four concentrations of prohexadione calcium were evaluated. In addition to quantifying honeydew production, psyllids collected from each treatment have recently been tested to assess acquisition of Las from individual leaves used in experiments. Finally, to further understand the apparent increase in Las acquisition rates following PGR treatments, experiments are currently being conducted to evaluate psyllid settling preference on treated verses non-treated plants.
One of the objectives of this study has been to determine if the results found in previously published work from this project (Tsagkarakis et al., 2011, JASHS) were the result of direct toxicity of the PGRs to the Asian citrus psyllid or if they were the result of plant biochemical changes affecting psyllid fitness. To test this, work is currently being conducted to determine levels of the two most efficacious PGRs (uniconazole and prohexadione calcium) that are phytotoxic to citrus trees. These rates will be used as our upper threshold for conducting LD50 work on psyllids. In our initial rounds of testing we have found that uniconazole (formulated as Sumagic) is not phytotoxic to citrus at undiluted concentrations (500 ppm a.i.). Phytoxicity is assessed visually by looking for any discoloration, abnormal growth (e.g., distorted new leaves), or other obvious signs of plant distress. Prohexadione calcium has been tested to rates of 10,000 ppm (25x label rate) with no obvious signs of phytoxicity. Although the maximum rates tested far exceed label rates, since they were not phytotoxic to the citrus trees they will be used as our upper rate threshold for LD50 work with psyllids to be performed over the coming months.
1) Evaluation of screens impregnated with insecticide barriers. This experiment has already been completed (see annual report sent on 2/2/12). 2) Evaluate the impact of treatment of plants with systemic insecticides on the transmission of Ca. L. asiaticus by starved psyllids. The transmission trials have already been completed. A PCR test was performed to confirm the infectivity of psyllids used in this experiment and it was observed that about 75% of the samples were positive. The PCR test on plants to determine the inoculation is underway. 3) Determination of the concentration of pesticides present in the sap of the xylem and phloem of citrus plants and the lethal concentration to D. citri. The equipment for the extraction of plant sap has already been delivered and the experiment must be started in September (after Brazilian winter).
The goal of this investigation has been to identify Asian citrus psyllid (ACP) attractants for development of practical management tools. We have identified a cuticular hydrocarbon that appears to function as a pheromone-type attractant. With this result, we have developed a prototype ACP trap that incorporates the attractant and as a result catches more ACP than unbaited traps. We have also identified a number of plant volatiles that attract ACP and which can also increase of of psylllids on traps as compared with unbaited controls. Male ACP were attracted to the cuticular extracts of conspecific females. Furthermore, removal of cuticular hydrocarbons by solvent washing rendered females non-attractive to males; while normally, recently killed females are known to attract male psyllids. The primary role of insect cuticular hydrocarbons is to provide a hydrophobic barrier to minimize transpiration and desiccation. However, cuticular hydrocarbons are also known to mediate chemical communication in many insect species, including psyllids. The behavioral and chemical laboratory results indicated a sex-specific function of female cuticular hydrocarbons, but our field results did not exclude a possible aggregative function. In field trials, female cuticular extracts attracted more male ACP on clear traps; however, this difference did not occur on yellow traps. Visual cues are known to strongly influence the orientation of ACP to olfactory cues. ACP adults are strongly attracted to yellow color. Therefore, at the dosage of cuticular extracts tested here, it is possible that response to an olfactory cue was obscured by the visual stimulus of yellow traps. Both clear and yellow traps baited with five or 10 equivalent units of either male or female cuticular extract captured more total D. citri than unbaited controls. These results suggest a possible aggregative function of the cuticular hydrocarbons. Dodecanoic acid was one of the few components detected in higher amounts from female than male extracts that also elicited a behavioral response from males in laboratory assays. Initial testing showed that dodecanoic acid alone did not increase total catch of psyllids on traps as compared with a blank control; however, it did skew the sex ratio of captured psyllids towards male bias at the highest dosage tested. Later tests that were conducted with a new generation trap that released much higher amounts of this chemical indicated that the attractant could increase catch of psyllids on traps as compared to unbaited controls. In addition to identifying psyllid-based attractants, we have made significant progress in identifying plant-based psyllid attractants. We have identified several of the key volatiles from citrus that attract psyllids. Also, we have discovered that break-down products of citrus volatiles may be important components of an ACP attractant rather than the actual volatiles that are initially given off by citrus. Specific tools (both traps and attract and kill devices) are under development that will incorporate these attractants for use as practical tools.
The objective of this research has been to identify repellents for Asian citrus psyllid (ACP) and also to develop practical tools from these identifications that may eventually be used for ACP management. Throughout the project we have engaged in partnerships with private industry; therefore, our focus has remained on practical end-products that have been under development. The pest management company, ISCA Technologies, was one private company that made significant progress with their SPLAT dispenser, in terms of developing a practical repellent tool for ACP using our discoveries. However, other companies, such as Alpha Scents also made progress in the development of tools for ACP repellency during this project. We determined that volatiles from guava leaves signi’cantly inhibited attraction of ACP to normally attractive host-plant (citrus) volatiles. A similar level of inhibition was recorded when synthetic DMDS was co-released with volatiles from citrus leaves. In addition, the volatile mixture emanating from a combination of intact citrus and intact guava leaves induced a knock-down effect on adult ACP. Compounds similar to DMDS including dipropyl disulphide, ethyl-1-propyl disulphide, and diethyl disulphide did not affect the behavioral response of ACP to attractive citrus host plant volatiles. Head-space volatile analyses were conducted to compare sulphur volatile pro’les of citrus and guava, used in our behavioral assays, with a gas chromatography-pulsed ‘ame photometric detector. DMDS, produced by wounded guava in our olfactometer assays, was not produced by similarly wounded citrus. The airborne concentration of DMDS that induced the behavioral effect in the 4-choice olfactometer was 107 pg/ml. In a small plot ‘eld experiment, populations of ACP were signi’cantly reduced by deployment of synthetic DMDS from polyethylene vials compared with untreated control plots. Our results verified that guava leaf volatiles inhibit the response of ACP to citrus host plant volatiles and suggested that the induced compound, DMDS, may be partially responsible for this effect. Also, we showed that ‘eld deployment of DMDS reduces densities of ACP and thus may have potential as a novel control strategy. Also, we found that volatiles from crushed garlic chive leaves, garlic chive essential oil, garlic chive plants, wild onion plants and crushed wild onion leaves all repelled ACP adults when compared with clean air, with the ‘rst two being signi’cantly more repellent than the others. However, when tested with citrus volatiles, only crushed garlic chive leaves and garlic chive essential oil were repellent, and crushed wild onions leaves were not. Analysis of the headspace components of crushed garlic chive leaves and garlic chive essential oil by gas chromatography-mass spectrometry revealed that monosul’des, disul’des and trisul’des were the primary sulfur volatiles present. In general, trisul’des (dimethyl trisul’de) inhibited the response of ACP to citrus volatiles more than disul’des (dimethyl disul’de, allyl methyl disul’de, allyl disul’de). Monosul’des did not affect the behavior of ACP adults. A blend of dimethyl trisul’de and dimethyl disul’de in 1 : 1 ratio showed an additive effect on inhibition of ACP response to citrus volatiles. The plant volatiles from Allium spp. did not affect the behaviour of the D. citri ecto-parasitoid Tamarixia radiata. Thus, Allium spp. or the tri- and di-sulphides could be integrated into management programmes for ACP without affecting natural enemies. In addition, we investigated volatiles from essential oils of coriander, lavender, rose, thyme, tea tree oil and 2-undecanone, a major constituent of rue oil repelled ACP adults compared with clean air. Also, coriander, lavender, rose and thyme oil inhibited the response of ACP when co-presented with citrus leaves. Volatiles from eugenol, eucalyptol, carvacrol, b-caryophyllene, a-pinene, a-gurjunene and linalool did not repel ACP adults compared with clean air. Practical tools from this under development.
During the last 3 years, 2 factorial field experiments, E1 and E2, initiated in October/05 and May/06, respectively, in new plantations of sweet orange in a HLB epidemic region of Sao Paulo-Brazil, were carried out, assessed and analyzed. The objective of this study was to assess the effectiveness and the importance of bacterial inoculum reduction and ACP vector control strategies applied within young citrus plots (Local management), in different frequencies and combinations, on HLB temporal progress. Local inoculum reduction levels for E1 were every 4, 8 and 16 weeks, and for E2, every 2, 4, 12, and 26 weeks. Local vector control levels for E1 were no control, program A (PA) and program B (PB), and for E2, no control and program C (PC), as follows. Psyllid control was done with two 56-day-interval soil or drench applications of systemic insecticides concurrently with the rainy season each year; and during the rest of the year, with insecticide sprays every 28 days for PA, and every 14 days for PB and PC. Regional HLB management was present for E1 and absent for E2. The main results were: i) The beginning of the HLB epidemic was delayed for 10 months in E1, but wasn’t affected by different local strategies for both experiments; ii) After 60 (E1) and 53 (E2) months, the HLB incidence and progress rates were not affected by different frequencies of local inoculum reduction in either experiment, and were different only in plots with and without local vector control in E2; iii) In E1 the disease incidence was reduced by 90% and the disease progress rate by 50% in both plots with and without vector control. These reductions were explained by smaller psyllid populations (4-5x less and smaller year after year) and lower frequency of bacterialiferous psyllids (6-7x less) in E1 compared to E2; iv) Annual productivity remained increasing over time in E1 as expected for young plantings, whereas remained stable or decreased in E2 (E2 was completelly eliminated 4.5 year old because became economically unprofitable); v) Area-wide HLB management reduces the control costs because with less intensive vector control program in E1 it was possible to be more efficient than the high intensive vector control program applied locally within a region without regional management (E2). These results scientifically confirmed, for the first time in the world, the great importance of primary infection by migrating bacterialiferous ACP populations on HLB epidemics and suggest that an area-wide inoculum and ACP management heavily affects the efficiency and cost of HLB control. The results of this project were also presented to many citrus growers and crop protection agents in many events in South, Central and North America to alert for the difficulties in HLB control in small geographicall scale (small farms) and help the establishment of growers’ groups for HLB area-wide management. This management strategy has become the predominant intermediate strategy recommended to growers both in South and North America. Two papers were submitted for publication: “Efficacy of area-wide inoculum reduction and vector control on temporal progress of huanglongbing in young sweet orange plantings” presenting all results of both experiments was submitted to Plant Disease; and “Frequency of local inoculum reduction on citrus Huanglongbing epidemics” with results of 8 experiments, including E1 and E2, was submitted to Crop Protection. We would like to acknoledge all CRDF support for the conclusion of this project.
(863) 956-8817
(863) 956-5894
700 Experiment Station Road
Lake Alfred, FL 33850
Email Us
