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.
During the past year, we have constructed four citrus tristeza virus (CTV) vectors containing four insecticidal peptides for management of the Asian citrus psyllid (ACP) and the brown citrus aphid (BCA). CTV expression vectors containing these peptides have been successfully bark flap-inoculated into plants to confirm systemic peptide expression and provide material for graft inoculation into citrus. To evaluate the effects of peptides on insect fitness, plants containing the CTV-expressed peptides have been used to graft-inoculated into citrus plants for psyllid bioassays. Since our last report, we have completed plant inoculations for each of the four CTV-peptide constructs originally proposed (henceforth A, B, C, and D). Most recently, fifteen plants have been grafted with peptide B and are being given latent period for the peptide to become established throughout the plants. The plants will be tested for the presence of CTV-peptide constructs using ELISA in a few days. Peptides C and D have been established in three and five plants, respectively, and additional plants will be grafted-inoculated to obtain a sufficient number of test plants for psyllid bioassays. Since the previous report, we have continued to conduct experiments to evaluate the lethal and sublethal effects of vector-expressed peptides A and B on development (egg and nymph), life history parameters (adult longevity, fecundity), and feeding of ACP and BCA. Bioassays with plants containing peptide A have been completed. Settling assays suggest that ACP adults prefer plants that do not contain either peptide A or B. Although adult survival was not significantly affected, development of eggs and nymphs were significantly longer when insects were exposed to plants containing peptide B compared with control plants. In addition, ACP feeding and fecundity were significantly reduced in the presence of peptide A compared with control plants. Similarly, the results of honeydew excretion assays suggest that peptide B reduces ACP feeding. In bioassays to evaluate the effect of peptides on BCA, survival of nymphs was significantly reduced when peptide A was present in citrus plants compared with control plants; however no other fitness parameters were significantly affected in response to peptide A. Longevity and fecundity of adult BCA were significantly reduced in response to peptide B plants compared with controls. The results from ACP and BCA bioassays with peptide B are based on four replicate plants only, due to limited availability of plants. Additional replications will be conducted as plants containing peptide B become available. Currently, artificial feeding bioassays are being conducted to evaluate the lethal concentration of a variety of insecticidal peptides, including the four originally proposed, against ACP. In addition, we have begun to conduct experiments to evaluate the effect of peptides on ACP endosymbionts, including Las. Insects from these ongoing bioassays are currently being collected and stored for subsequent analysis with qPCR analysis. In addition to the above ongoing experiments, our research plan for the next year is to conduct laboratory bioassays to evaluate the susceptibility of citrus leafminer, and T. radiata to citrus plants containing CTV-peptide constructs.
This project has 5 objectives: (1) evaluate efficiency of ACP control techniques in cooperation with growers, (2) develop efficient monitoring methods for ACP, (3) accelerate testing of new chemistries and techniques for ACP management, (4) evaluate the economic component of the comprehensive program, and (5) provide an information bridge between researchers, growers, and industry. The following is an update of ongoing field and laboratory experiments. The potential for ACP resistance is uppermost in many grower’s minds and management programs are based on rotation of modes of action. Nevertheless, many practical questions remain on how this is best accomplished. Experiments are underway to 1) compare selection rates for resistance using mixture (AgriFlex) versus rotation of its two components, and 2) evaluate stability of insecticide resistance and number of generations required to return tolerant populations to susceptibility. Following application of an LD80 dose (4 Jan), our colony experienced a crash. Because the untreated individuals were also affected, we are attributing this result to seasonal fluctuation of vigor. We are currently giving our murraya a 3-mo rest while we increase our laboratory psyllid populations. We continue to collaborate with the DPI CHRP program to evaluate results of the cooperative (area wide) ACP management program, in SW Florida (i.e. Gulf CHMA). We have presented this data for the last 10 cycles via interactive maps on our website (http://swfrec.ifas.ufl.edu/entomology/extension/chma/ for growers to use). These maps have allowed us to visualize ‘hot spots’ (i.e. those groves with high numbers of ACP for 3 consecutive cycles), and we are in the process of contacting growers to improve ACP management. Citrus leafminer (CLM) incidence and damage has been increasing, possibly due to increased use of broad spectrum insecticides to control ACP. Canker is also on the rise and growers are demanding assistance with management of CLM, thought to exacerbate the disease. We have been monitoring CLM using sticky card pheromone traps in citrus groves as well as a natural preserve (Okaloacoochee Slough State Forest) in an attempt to determine effective distances from source to trap. We have been using bucket pheromone traps dispensed in citrus groves and the slough to collect identifiable specimens for identification. Gracillariid leaf mining moths are very small, and often very difficult to identify solely based on morphology. We have used a combination of traditional morphological methods and COI barcoding, based on a mitochondrial DNA sequence. A sample of specimens that were collected with bucket traps was sent to the Lepidoptera sequencing lab of collaborator Kawahara at the McGuire Center for Lepidoptera and Biodiversity in Gainesville Florida for analysis. Thus far results show that there are many different Phyllocnistis species coming to the pheromone traps; P. citrella, P. insignis, P. vitegenella, and a newly discovered leafminer species to Florida. We have submitted grant applications for additional funding. We feel it would be beneficial to publish a paper that discusses genetic variation/species boundaries of Phyllocnistis found in our citrus groves and natural areas. Within the next few months, these pheromone will be used in conjunction with mark and recapture experiments to determine distance traveled by CLM, and development of a preliminary degree-day model. We have started a colony of CLM to rear the parasitoid Citrastichus phyllocnistoides and support a program for monitoring CLM susceptibility to key insecticides. This summer we will use a diagnostic dose to monitor resistance in field populations of CLM exposed to intensive versus modest insecticide use.
Low volume (LV) aerial and ground sprays have become an important method of application in Florida citrus. Our eval- uations of LV application of 435 horticultural mineral oil (HMO) have shown promising results the last 3 years. Here we document overall results from the 5th trial begun Feb 2011 in a 10.9 acre plot of ‘Valencia’ orange in Lee County com- paring LV spray of 435 HMO with the Grower Standard (GS) and an Untreated check (UC). The grower has been applying a foliar nutritional program throughout the block. Three treatments were set out in 3×3 Latin square design. A Proptec rotary atomizer P400D spray machine was used for all treatments. HMO was applied alone (no water) every 2 wks at 2 gpa. Between Feb-Apr, 3 sprays of oil were applied, and the GS was Carbaryl and Azasol. Mean ACP counts were below the 0.2 adults/stem tap sample threshold in all treatments with no significant differences. Due to high freeze- induced fruit drop, harvest was early (Feb) and juice content averaged less than 50% (0.41). Total brix was within normal range of 9-14 for all samples, but the acid content was below normal (1.0 – 0.5) in 5 of 8 samples tested. There was no significant treatment effect on yield, but highest production was seen from trees treated with the GS (12.6 lbs solids/tree followed by HMO (10.5) and UC (6.1). Between May-July, 7 sprays of HMO with Actara and Agri-mek for GS plots were applied. During May, significantly fewer psyllids were seen on GS trees than HMO trees, but during June these differences disappeared. We then added citrus leafminer (CLM) assessments to determine if treatments were effective at reducing CLM numbers. A damage assessment of leaves using a modified Horsfall-Barratt scale found significant differences between the GS and oil treatments, with the GS having less CLM damage. Between Aug-Oct, 5 sprays of HMO oil and 1 spray ea of Dimethoate and Delegate for GS were applied. Mean adult psyllid populations were lowest for GS, followed by Oil and UC. Thus, LV oil treatments were suppressing ACP, though not as effectively as the GS. From Nov 2011-Jan 2012, 3 sprays of HMO were applied, and all plots received a dormant spray of Danitol (Jan). Mean psyllid populations for GS and HMO treatments were significantly less than UC, with HMO treatments suppressing ACP as effectively as GS. Resets sampled in Oct for HLB and Ct titer showed no significant differences between treatments and low (< 3%) HLB incidence. CLM trap catches in Nov were significantly lower with HMO compared to GS and UC even though highest flush density was seen on HMO-treated trees. probably due to egg and larval mortality. Between Feb-Apr 2012, 4 HMO sprays and 1 GS of Micromite were applied. Mean ACP counts for GS and HMO were similar and lower than UC. Resets were sampled for % HLB, most samples were not usable due to frost damage. The 2nd harvest (27 Feb) showed HMO treatment with greatest lb solids followed by UC and GS. Acid/brix results are pending. CLM flight began early this year (2 Mar) with first peak at 16 Mar showing no significant differences between treatments. An experiment initiated spring 2011 on an 80ac block divided into 12 large plots in a RCBD with 4 treatments and 3 reps (Jul) evaluated aerial applications of Intrepid 2F, and Delegate. Significant control was obtained with the aerial application of Intrepid, but not as much or as enduring as with the ground application. An experiment initiated Feb 2011 compared LV (5 or 10 GPA - Proptec) vs. HV(40 or 120 GPA - Airblast) apps. of Movento SC along with Mustang Max 1.5 EC (5 gpa), Baythroid XL 1 EC (5 gpa) and Provado 1.6 F+Agrimek 0.15 EC (120 gpa). All treatments provided significant reduction in psyllid adults through 5 wks and nymphs through 4 wks except Mustang, low rate of Movento (5 gpa) and Provado + Agrimek.
we have completed the harvest for the fourth year of the Hamlin and Valencia trials with the Boyd Nutrient/SAR treatments. The ‘Hamlin’ orange block at SWFREC receiving the Boyd cocktail treatments was harvested in December before the freeze on January 4, 2011 with temperatures in Immokalee of 25 degrees F. Fruit yield on 8.2 foot tall trees from the better treatments averaged about 2+ boxes per tree. The better treatments contained Macro nutrients as DKP + KNO3, micro-nutrients Mg, Mn, Zn, Mo, B, and a Phosphite. Juice quality from the ‘Hamlin’ trees with HLB trial has not been affected. Citrus canker was a significant factor in our ‘Hamlin’ trial for the first time this year. Fruit loss due to canker varied from 40% in less vigorous trees to between 60% to 75% fruit loss in treatments stimulating more vigorous growth. Treatments with spray grade KNO3 + micro-nutrients had less fruit loss to canker. The less vigorous trees with less flush carried the larger fruit load with less fruit drop in the presence of citrus canker. Fruit yield from our 30 acre commercial ‘Valencia’ block experienced frozen fruit in the January freeze with some fruit loss, and still produced 1.6+ boxes per tree on 7 to 8 foot tall trees. This trial was harvested in March and juice quality data is not yet available. The highest yield per tree for ‘Hamlin’ and ‘Valencia’ continues to be treatments 2 (complete Boyd cocktail minus the SARs), treatment 9 (complete Boyd cocktail minus hydrogen peroxide, and treatment 1 (complete Boyd cocktail. These three treatments consistently are among the four highest yielding during the past three years. Treatment 3 (KNO3 + micro- nutrinets) has moved into the top three performers. Treatments 4, 5, 6, and 8 which do not contain the foliar applied nutrients Mg, Mn, Zn, Mo, and B are among the lower yielding trees. We are well into the 4th year of a replicated experiment in a 12-acre experiment commercial block of 8-year-old ‘Valencia’ oranges on Swingle to test effects two factors: (1) micro-nutrients + systemic acquired resistance inducers, and (2) Asian citrus psyllid (ACP) chemical control on ACP populations on Can. Libericacter asiaticus (CLas) titer, and plant yield. While we are continuing with the experiment, results from the first 3 years are being written up for publication. Psyllid populations for all treatments remained below the 0.20 threshold during each sampling period (13 Jan ‘ 21 Mar) except for 13 Jan when the nutritional only plots reached 0.23. Insecticide and Insecticide+nutritional had significantly (P< 0.05) fewer adult ACP than control or nutritional only on dates 13, 27 Jan; 10, 24 Feb; 7, 21 Mar. All three treatments had significantly (P < 0.05) fewer ACP than control on 21 Mar. Since our last report we applied a dormant spray of Danitol 4EC (12oz/ac) on 2 Feb in plots designated for insecticide treatment. Resets planted (June 2010) were tested for HLB detection (13 Jan) but showed no significant treatment effect on percent PCR positive for HLB (16% - 60% infection). All mature trees (10 years old) tested positive for HLB. Ct values were significantly less for Untreated (21.2) than the Insecticide only plots (22.5). However, there were no significant differences between the insecticide plus nutritional plots (21.6) and nutritional only plots (21.6). For the resets, there were no significant differences in Ct values (range 25.0 ' 33.4). All trees were harvested and all fruit weighed 8 Mar. Trees receiving the Insecticide + nutrition treatment produced greatest average yield (199.7 lbs/tree ' A) followed by nutritional only (182.3 - AB) Insecticide only (171.6 B) and Untreated (147.0 - C). We are waiting for results of brix/acid ratios.
This is the third and final year of a project on protecting newly planted citrus trees from Asian citrus psyllid (ACP) and huanglongbing (HLB). The project is collaborative between USDA-ARS (Hall) and University of Florida (Stansly). Update on USDA-ARS activities. Two experiments are being concluded by USDA-ARS in the Indian River citrus area at a grove just west of Fort Pierce. For research purposes, most of the grove is under a minimal ACP management program and HLB-infected trees are not removed. A detailed summary of the two experiments (as of late summer 2011) was presented in the September 2011 Annual Report. Since that time, notable is that regardless of the particular psyllid management program studied in each experiment, the percentage of trees infected by HLB increased to 90% within 42 months after planting in one experiment (infected trees removed as they were found and not replanted) and to nearly 100% within only 26 months after planting in the second experiment (infected trees not removed). This was based on qPCR of trees using the Wenbin Li primers and a cT threshold of 32. The results support that a grower will have difficulty protecting new plantings from HLB if concerted efforts are not made to control ACP not only in a young planting but also on an area-wide basis in the vicinity of a new planting. Simple calendar sprays were ineffective for completely preventing ACP infestations, even when hard pesticides were applied monthly. It may be more productive to use calendar sprays in conjunction with scouting to ensure infestations of eggs and nymphs are controlled, although such an approach may inflate the use of insecticides to more than once a month during some times of the year. In an experiment in which infected trees were not removed, the trees were ‘Valencia’ on ‘Carrizo’ rootstock and harvest data were collected during March 2012 (31 months after planting). An average of 10% trees per plot had died by March 2012. Across all three psyllid control treatments, an average of 72.5% of the trees produced fruit including fruit remaining on the trees plus fruit that had dropped to the ground. Harvestable fruit remained on 62.5% of the trees. Over all trees, we picked an average of 7.5 fruit per tree with an average of 137 grams per fruit (1,028 g of fruit per tree). Although yield of the 31 month old trees was low, yield was generally highest in plots of trees subjected to a complete insecticide program, intermediate in plots of trees subjected to a reduced insecticide program, and lowest in plots of trees subjected to oil sprays every three weeks. UF Update – A comparison of young trees treated four times annually with different rotational schedules of Admire, Platinum and Cyazypyr indicates that, regardless of the order that the insecticides were applied, significant control of ACP was achieved as compared to ACP levels in untreated trees. Cyazlypyr is a new insecticide very effective against ACP, and a label for citrus is anticipated. As the trees have grown the rate of this insecticide has had to be increased to maintain control of ACP but application frequency will be maintained at 3 times a year to adhere to expected label directions. This insecticide is of a novel MOA (diamide chemical class) and is effective against a number of important types of pests including fruit flies, leafminers, leaf-feeding beetles, whiteflies, hoppers, thrips and weevils. Lower percentages of trees tested HLB positive after almost two years in plots receiving insecticides (0 to 11% trees infected) than in plots of trees untreated (greater than 30 % of trees infected).
This project aims to 1) refine sampling methods for ACP, 2) test the influence of adult density and shoot infestation on precision of estimated means and distribution of population within blocks, and 3) evaluate methods for assessing psyllid density, shoot density, and infestation rates and their integration into a user friendly system accessible to consultants and managers. 1-2) An EDIS document describing the use and comparison of stem-tap sampling, sweet-net sampling and sticky traps for monitoring ACP adults in citrus groves was published (http://edis.ifas.ufl.edu/in867). Data showed that a little more than 100 tap samples would be necessary to detect with confidence 15 psyllids with 75% precision, a reasonable threshold during the growing season when trees are producing new growth. Young shoots are required for psyllid oviposition and immature development. Therefore, routine monitoring protocol developed for ACP integrates adult sampling, shoot density and infestation rates. For adults 100 tap samples per bock divided into 10 stops 5 along the perimeter to cover for edge effect and 5 inside the block are recommended. This scheme could lead to decision to spray only the block perimeter. At each stop 10 shoots containing feather flush are examined using hand lens to look for infestation with psyllid immature and search is terminated if 10 shoots are not found after 20 trees. Number of shoots examined, found infested and number of trees searched to find the examined shoots is recorded. Cost for materials and labor was almost same for stem-tap and sweep-net methods but 28 times more for sticky traps. Stem tap method is rapid, works under either dry or wet conditions and has proven to be reliable and consistent. Sweep net collect a lot of trash and incur a risk of canker spread. Whereas, sticky traps would cause delay in making management decisions and allowing psyllids more time to reproduce and acquire or transmit causal pathogen of HLB. Comparison of stem-tap- with vacuum sampling to detect ACP adults in two conventional blocks of citrus showed a strong positive relationship between the two methods explained by a linear equation y = 9.816x + 1.522 (r2 = 0.61) in ‘Earlygold’ and y = 14.79x + 0.044 (r2 = 0.74) in ‘Valencia’. Vacuum sampler detected psyllids in 53-55% samples compared to stem-tap which detected in 29-34% (n = 109-96). Additional data are being collected and analyzed. 3) Psyllid monitoring guidelines are provided at our website: http://www.imok.ufl.edu/entomology/extension/ including instructions and sampling sheets to conduct tap sampling to detect psylilds, other pests and beneficials http://www.imok.ufl.edu/docs/pdf/ento_ext_acp_sampling_english.pdf. This year approx. 3,000 tap sampling kits have been distributed to clientele through workshops conducted at SWFREC and IFAS extension. Two pest scouting workshops one each in 2011 and 2012 were conducted at SWFREC in which citrus growers were trained in monitoring psyllids and other pests and beneficials. In collaboration with the Protect US, Community Invasive Species Network a demonstration of tap sampling and shoot examination was posted at Protect US youtube channel. Stem-tap method has been widely adopted by the citrus industry and also by APHIS and DPI CHRP to monitor 6,000 blocks of citrus in Florida every 3 weeks in support of CHMA program. Tap sampling method was also used to evaluate several experimental and recommended insecticides at SWFREC and large scale studies in commercial citrus designed to control psyllids using insecticides, horticultural oils and nutritionals.
This project is focused on evaluating the impact of psyllid control programs on non-target pests, beneficial insects and mites. Four replicated studies comparing 43 foliar treatments of recommended and experimental insecticides against ACP and citrus leafminer were conducted at SWFREC and submitted for publication in the Journal of Arthropod Management Tests of the Entomological Society of America. Additionally, large replicated blocks of mature citrus in conventional groves untreated or treated with foliar sprays of insecticides, horticultural oils, and nutritionals were sampled for psyllids, citrus leafminer (CLM), citrus rust mites (CRM), citrus red mite, predatory mites, snow scale, chaff scale, Glover scale, purple scale, citrus blackflies, whiteflies, mealy bugs, as well as their natural enemies and fruit damage at two conventional groves in Hendry County and one each in Lee and Collier Counties. Studies conducted at SWFREC showed that most commonly used and experimental insecticides cause significant reduction in psyllid populations compared to the untreated control for three to four weeks. A few products, such as Delegate, Movento, Agri-flex and Voliam flexi, provided reduction in CLM populations which nevertheless, hardly lasted for two weeks. Most insecticidal sprays against ACP were seen impact beneficial insects and therefore reduce their effects on secondary pests. For example, arboreal ants thought to be critical for CLM were most affected in large plots treated with a calendar spray program for ACP control in Hendry county using selective and broad spectrum products compared to untreated control. Predation on CLM was reduced from 90% to 70% by calendar sprays and parasitism by the formally dominant introduced wasp Ageniaspis citricola was reduced to 3% of the total compared to other less specialized species. Calendar or grower standard sprays also impacted other non target pests and beneficial insects in large scale studies. For example, citrus red mite increased markedly in calendar sprays plots in Hendry county, presumably in response to suppression of predaceous mites. Similarly, more scales, particularly purple and chaff, were observed on fruits in the insecticide-treated plots in Hendry and Collier counties. CRM were also high on fruits in the treatments using insecticides in Collier county compared to treatments of only nutritionals and the untreated control. In contrast, only 2% of shoots on ‘Valencia’ orange were infested with woolly whitefly in plots treated with calendar sprays compared to 34% in control plots in Hendry county. However, shoot infestation with woolly whitefly averaged 36% and did not differ between plots treated with grower standard sprays, biweekly spray of 435 oil or untreated check in a block of ‘Valencia’ in Lee county. It seems that most calendar or grower standard treatments and experimental treatments suppressed psyllids but did not reduce non target pests in most situations, creating need for additional applications and negative impacts on predators and parasitoids. However, psyllid populations were very low during most of the reported period and fewer or no sprays were warranted based on thresholds. Publications: Ferrer, C. M., J. A. Qureshi and P. A. Stansly. 2012. Insecticidal control of Asian citrus psyllid: effects on secondary pests and natural enemies. Citrus Industry. 93 (4): 12-16. Qureshi, J. A., B. C. Kostyk and P. A. Stansly. 2011. Effectiveness of selective insecticides to control Asian citrus psyllid and citrus leafminer during leaf flushing. Proc. Fla. State Hort. Soc. 124: (In press).
Objectives of this project include: 1) scale up production of Tamarixia radiata to levels that will allow better assessment of the potential impact an augmentation program may have on the ACP population and ultimately the spread of HLB, 2) use genetic techniques to identify parasitoids recovered from the field to demonstrate establishment and effectiveness of released strains, and 3) pass on rearing technology to both private and public sectors to encourage production and an adequate supply of these parasitoids into the future. Funding for this project was released in August 2011. 1) This year 303,973, 300,627, 346,778 and 338,881 Tamarixia radiata were produced in colonies from South China, Pakistan, North Vietnam and Florida strain previously established from Taiwan and South Vietnam and maintained at DPI, Gainesville. About 4, 000 wasps from Pakistan colony were also sent to California for their colony and host specificity studies. An additional colony of Florida strain maintained at SWFREC produced 172,112 T. radiata. Wasps from these colonies were used for research, to maintain the colonies and to release in conventional citrus mostly in southwest Florida and organic citrus, mostly in North Florida. We have observed parasitism rates of up to 60% or more at release sites in conventional citrus in southwest Florida during spring and summer compared to < 20% at sites with no releases, showing that augmentative release can potentially increase incidence of parasitism by T. radiata in the field. Similarly, parasitism rates averaged 50% in May and 80% in November in one of the organic groves in North Florida where parasitoids were released. However, in three other groves parasitism rates averaged below 25%. We also initiated two new colonies of the biparental colony of Diaphoencyrtus aligarhensis from Pakistan maintained at DPI and SWFREC and released a few in southwest Florida. 2) Collections are made at all release sites and recovered parasitoids were preserved in 95% ETOH and sent to Dr. Evan Braswell of USDA APHIS, Edinburg, TX, to characterize using molecular markers. 3) We have been assisting OrangeCo in their efforts to mass rear, release and evaluate T. radiata. Recently, we initiated with them collaborative experiments to determine the effects of release rates on psyllid populations and to look at the effects of soft and hard insecticide programs on incidence of T. radiata in citrus. Part of this research will be undertaken with the assistance of a self-financed master's student Ziyi Zhang AKA "Mike" with whom we had committee meeting at OrangeCo in Arcadia. chaired by Dr. Norm Leppla. Another master's student, Xulin Chen, whose assistantship is being paid for by this project, has been taking courses in Gainesville since August and has already undertaken a study of the use of CO2 for anesthetizing T. radiata to assist with manipulations during wasp rearing. Findings on the production, field release and evaluation of the parasitic wasp T. radiata against ACP in Florida were presented at two workshops at SWFREC and the annual meeting of the Entomological Society of America held in Reno, Nevada, and at the Subregional Workshop "Biological Control in Huanglongbing Recommendations for Central America" held in San Carlos, Costa Rica.
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