Work on this project was already in progress when funding was released in August 2011. Objectives 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. The colony at SWFREC of the previously established strain of T. radiata produced 53,398 wasps this quarter, increasing the 2011 total to 191,570. These wasps were used to maintain the colony and release in treated and untreated plots of commercial experimental blocks in Collier, Lee and Hendry counties. This quarter, 37,300 wasps were released, increasing the number released in 2011 to 124,970. Field releases this quarter of 20,600, 1,700, and 600 wasps from Pakistan, South China and North Vietnam colonies established at DPI, Gainesville join a total of 58,700, 4,185, and 4,700, wasps released this year. Wasps from the Pakistani colony continue to be released at the SWFREC, while wasps from south China and north Vietnam were released in commercial groves in Glades and Charlotte Counties, the latter being organic. Incidence of parasitism based on adult emergence from feral nymphs in the release block at SWFREC (Collier county) averaged 49% (N=565) and 45% (N=93) in July and August, respectively, compared to non release blocks averaging 3% (N=565) and 25% (N=327) in July and August, respectively. Parasitism of feral nymphs collected in August from a release block of a neighboring commercial grove averaged 3% (N = 175). Parasitism of nymphs recovered on sentinel plants placed in the release blocks in August averaged 98% (N=102) at SWFREC and 40% (N=5) in the commercial grove. No nymphs were recovered on sentinel plants placed in the non release blocks at SWFREC but 98% (N=174) were parasitized on sentinel plants placed in the commercial grove, probably indicating movement from the release block. In two sets of sentinel plants placed in September 35-100% (N=31-12) were parasitized at SWFREC and 13-97% (N=13-36) were parasitized in the commercial grove in release blocks. In non release blocks 13-65% (N=23-52) were parasitized at SWFREC and 38-42% (N=89-141) at commercial grove. Feral nymphs were also collected during August and September from experimental groves in Lee and Hendry counties, but less than 1% parasitism was observed. In general feral populations of psyllids were very low in the commercial groves during the report period. The recovered parasitoids are preserved in 95% ETOH and sent to Dr. Evan Braswell of USDA APHIS, Edinburg, TX, to identify genetic origins of these parasitoids using molecular markers. We also initiated the biparental colony of Diaphoencyrtus aligarhensis from Pakistan for release and evaluation at SWFREC. Addionally, we also visited Orange Co. to discuss their production and release system and some collaborative experiments involving release and evaluation of Tamarixia radiata.
Work on this project was already in progress when funding was released in August 2011. Objectives 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. The colony at SWFREC of the previously established strain of T. radiata produced 53,398 wasps this quarter, increasing the 2011 total to 191,570. These wasps were used to maintain the colony and release in treated and untreated plots of commercial experimental blocks in Collier, Lee and Hendry counties. This quarter, 37,300 wasps were released, increasing the number released in 2011 to 124,970. Field releases this quarter of 20,600, 1,700, and 600 wasps from Pakistan, South China and North Vietnam colonies established at DPI, Gainesville join a total of 58,700, 4,185, and 4,700, wasps released this year. Wasps from the Pakistani colony continue to be released at the SWFREC, while wasps from south China and north Vietnam were released in commercial groves in Glades and Charlotte Counties, the latter being organic. Incidence of parasitism based on adult emergence from feral nymphs in the release block at SWFREC (Collier county) averaged 49% (N=565) and 45% (N=93) in July and August, respectively, compared to non release blocks averaging 3% (N=565) and 25% (N=327) in July and August, respectively. Parasitism of feral nymphs collected in August from a release block of a neighboring commercial grove averaged 3% (N = 175). Parasitism of nymphs recovered on sentinel plants placed in the release blocks in August averaged 98% (N=102) at SWFREC and 40% (N=5) in the commercial grove. No nymphs were recovered on sentinel plants placed in the non release blocks at SWFREC but 98% (N=174) were parasitized on sentinel plants placed in the commercial grove, probably indicating movement from the release block. In two sets of sentinel plants placed in September 35-100% (N=31-12) were parasitized at SWFREC and 13-97% (N=13-36) were parasitized in the commercial grove in release blocks. In non release blocks 13-65% (N=23-52) were parasitized at SWFREC and 38-42% (N=89-141) at commercial grove. Feral nymphs were also collected during August and September from experimental groves in Lee and Hendry counties, but less than 1% parasitism was observed. In general feral populations of psyllids were very low in the commercial groves during the report period. The recovered parasitoids are preserved in 95% ETOH and sent to Dr. Evan Braswell of USDA APHIS, Edinburg, TX, to identify genetic origins of these parasitoids using molecular markers. We also initiated the biparental colony of Diaphoencyrtus aligarhensis from Pakistan for release and evaluation at SWFREC. Addionally, we also visited Orange Co. to discuss their production and release system and some collaborative experiments involving release and evaluation of Tamarixia radiata.
The intent of this study is to examine the effect of windbreaks, copper sprays to reduce infection, and leafminer treatments to determine there individual and combined effects on control of citrus canker in Brazilian commercial citrus and the applicability of this strategy to the US commercial citrus industry. A preliminary study was published in Crop Protection 27:807-813, that indicated that copper and insecticide applications significantly reduced canker infection but windbreaks did not have any effect. As described previously, a new series of plots with much more extensive windbreaks were established via a USDA/ARS specific cooperative agreement with the University of Sao Paulo, and the Brazilian cooperator at an IAPAR farm, in Xambr’, Parana state, using, 2-yr-old P’ra on Rangpur lime. Windbreaks were completed and plants were be established in Mid April 2010, but severe winds damaged the windbreaks during two storm events. These windbreaks have been reinforced and rebuilt. This delayed the experiment which is now scheduled to begin in March 2012. The following treatments will then be applied: 1) no sprays (control), 2) Cu++ sprays to reduce citrus canker incidence, and 3) insecticide sprays to inhibit infestations of Asian leafminer (secondary effects). Main effects are windbreak versus no windbreaks. Citrus canker incidence will be estimated on multiple branches on each tree treated as the number of leaves per branch infected. We anticipate running these plots for 2-3 more years to collect all necessary data. A subsequent field visit to Brazil plots is planed in late 2011. The development of the Programmable leaf wetness controller (PLWC) software was written, debugged, is complete, and the control program is working well. New leaf wetness sensors were designed and constructed and calibrated. An electronic glitch was determined in the leaf wetness sensors and new control circuitry was designed and constructed to overcome the glitch. New hydrophobic materials used as the sensor bridge allowing the detection of leaf moisture are being evaluated as well. The newly designed probes with various sensor bridge materials have been tested to determine their viability. A few electronic bugs still remain to work out. Publications: 167. Bock, C. H., Graham, J. H., Gottwald, T. R., Cook, A. Z., and Parker, P. E. 2010. Wind speed effects on the quantity of Xanthomonas citri subsp. citri dispersed downwind from canopies of grapefruit tree infected with citrus canker. Plant Di Bock C.H., Graham, J.H., Gottwald, T.R., Cook, A.Z., and Parker, P.E. 2010. Wind speed and wind-associated leaf injury affect severity of citrus canker on Swingle citrumelo. Eur J. Plant Path 128:21-38 Bock, CH, Parker, PE, Cook, AZ, Graham, JH and Gottwald, TR. 2001. Infection and decontamination of citrus canker and inoculated the surfaces. Crop Protection 30:259-264. Hall, D.G., Gottwald, T.R. and C.H. Bock. 2010. Exacerbation of citrus canker by citrus leafminer Phyllocnistis citrella in Florida. Florida Entomologist. Florida Entomologist 93:558-566. Bock, C.H., Gottwald, T.R. and Parker, P.E. 2011. Distribution of canker lesions on the surface of diseased grapefruit. Plant Pathology (Accepted).
Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), thought to be primarily a phloem-feeding insect, transmits the Huanglongbing pathogen, Candidatus Liberibacter asiaticus. Because this bacterium is restricted to the phloem and bacterial transmission is the result of psyllid feeding, investigation of the basic feeding behavior of D. citri is needed. In this study, an electrical penetration graph (EPG) monitor was used to: 1) determine whether gender-based differences in feeding behavior exist for D. citri and 2) examine the effects of photophase on D. citri feeding activities. In the first experiment, investigating gender-based differences in D. citri feeding behavior, overall, the number of male D. citri reaching the phloem was 20% higher compared to females. However, the mean duration of phloem ingestion (waveform E2) per insect was significantly higher for female D. citri compared to males. Analysis within treatments (gender) showed that, despite being considered a phloem feeder, the duration of xylem ingestion (waveform G) and phloem ingestion (waveform E2) were not significantly different. Prominent xylem ingestion was probably not caused by desiccation due to trauma, because insects were not anesthetized, starved or excessively handled during wiring. In the second experiment, examining the effects of photophase on D. citri feeding, within-treatment analysis showed that non-probing activities (waveform z and np), phloem penetration and salivation (waveform D and E1, respectively), and xylem ingestion (waveform G) were generally longer in duration per insect during the light photophase. In contrast, stylet pathway activities (waveform C) and phloem ingestion (waveform E2) were longer in duration during the dark photophase. Thus, results suggest that gender and photophase have an influence on D. citri feeding behavior, and are important variables that could affect the outcome of experiments investigating the transmission of Candidatus Liberibacter asiaticus by D. citri. Work has continued examining whether there are differences in the seasonality of psyllid movement of the HLB pathogen. This work has been ongoing for 3 field seasons. While there does appear to be some seasonal effect on the likelihood of psyllids to be carrying the HLB pathogen, our results suggest that the number of psyllids carrying the pathogen increases along with the incidence of diseased trees. At two locations in 2011, the incidence of psyllids testing positive for the HLB pathogen never dropped below 40% regardless of the time of year. This was a dramatic increase in the incidence of HLB positive psyllids from previous years at these locations and coincides with an increased abundance of trees showing symptoms of HLB. These results suggest that once HLB is well established in an area, the presence of any psyllids in an area presents a great risk for HLB spread.
Data collection from the 10-acre young tree protection multi-year trial continues. To date, foliar treatments have been applied as planned on 6 separate dates. Soil-applied neonicotinoids have been applied on three separate dates. Leaf samples from plots have been collected on 11 dates at two week intervals for pesticide residue analysis. These leaf samples have been ground in liquid nitrogen and stored in the freezer for residue analysis at a later date. Since planting, psyllid and leafminer counts have been made on 11 dates, performed every two weeks. Thus far, psyllid populations have remained below detectable levels. However, leafminer damage has occurred with high frequency (up to 90%), particularly in the control and foliar-applied broad spectrum insecticide treatments. Leafminer damage has remained low in the soil-applied neonicotinoid treatments as expected. PCR testing of leaf samples from our plots has failed to detect any Las positive trees in any of the treatments (including controls) to date. This is to be expected since we don’t anticipate getting positive Las test from plants in less than 6 months following infection; the plants have only been in the ground approximately 5 months. A field trial comparing application methods and rates of neonicotinoid insecticides, initiated in May and ended on August 30, has been completed. A trial similar to this one was conducted for the first time in 2010 and was repeated this year to determine if results from year 1 were accurate and repeatable. The primary goal of this trial was to confirm the efficacy of trunk applications compared to soil drench applications and also determine whether repeated trunk applications pose any phytotoxicity risk with regards to overall tree health. The trial consisted of fifteen treatments including varying rates of Admire Pro, Belay 50 WDG and Platinum 75 SG as both trunk applications and soil drenches. The results confirmed that the trunk applications were equivalent to soil drench applications in terms of psyllid control provided. No phytotoxicity was observed. In addition, leaf samples were collected every two weeks, ground in liquid nitrogen and stored in the freezer. These samples will be analyzed at a later date to determine neonic residue levels in leaf tissues and correlate those levels with the duration of control provided. Progress was made in our multi-year field experiment designed to test whether there is any benefit to continuing to control psyllids on trees that are already HLB infected. Inoculations of healthy field grown (caged) trees with selected numbers of presumptive Las(+) and Las(-) psyllids were conducted in May and again in June. Following recovery of the psyllids after a 2-week inoculation access period, psyllids were held in the freezer and then later analyzed using PCR to determine the exact number of Las(+) and Las(-) psyllids that fed and likely inoculated the plants. For the presumptive Las(+) psyllids, approximately 52% were Las(+), whereas all of the presumptive Las(-) psyllids were indeed negative. PCR analysis of leaf samples collected 3 months after the multiple inoculation access periods were Las (-). Growth measurements were also made on trees in each treatment at this time. Work on this objective continues.
A primary function of this grant is to hire a CHMA program assistant within IFAS to facilitate the CHMA outreach activities to further program development. To date, a committee has been formed and a position description drafted. Advertising to begin soon. No funds have been spent from this grant to date. No further action to report.
A total of 6 applications of SPLAT-CLM were made at two locations during 2011: 3 applications each to 90 acres in a grapefruit grove in St. Lucie county (Emerald Grove, The Packers of Indian River) and 82 acres in an orange grove in Charlotte county (TRB Groves). These two field trials represent complementary experiments to determine the potential for reducing the cost of SPLAT-CLM applications by leaving untreated beds (gaps). During the period since our previous report, we continue to collect weekly counts of male leafminers attracted to pheromone-baited traps (a measure of mating disruption) and periodic assessments of mining damage. End of year analysis of results of various gap treatments will attempt to identify coverage patterns that optimize mating disruption and minimize the amount of product applied. The prototype applicator fabricated by International Fly Masters Inc. of Ft. Pierce continues to function well. Final compilation and analysis of data from these field trials will occur at the end of the season when leafminer populations decline to winter levels. A manuscript describing results from SPLAT-CLM trials conducted in 2010 was accepted for publication during the period: Lapointe, S. L. and L. L. Stelinski. 2011. A GPS-guided applicator for high viscosity semiochemical products and optimizing cost of mating disruption for Phyllocnistis citrella with intentional treatment gaps. Entomologia Experimentalis et Applicata (accepted 8/16/2011). Dr. Craig Keathley joined ARS and assumed his position as postdoctoral research entomologist at USHRL, Ft. Pierce on 12 September. Craig has quickly come up to speed on the project and will be taking a greater leadership role in the on-farm validation trials expected to commence in the spring of 2012.
Spatial and Temporal Incidence of Ca. Liberibacter in Citrus and Psyllids Detected Using Real Time PCR, October 2011. 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 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 100%, in the plots. 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. 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. Yield data from various plots has been collected as a indicator of overall impact of HLB, at one site of these studies.
Two 3-year field experiments are being conducted in two commercial orange blocks in Hendry County (southwest Florida). One of the groves is planted with ‘Earlygold’ oranges and the other with ‘Valencia’ oranges. Average HLB incidence estimated in both groves at the beginning of the experiment based on PCR analysis of a random sample of 160 trees was 98% in ‘Earlygold’ and 42% in ‘Valencia’. Experimental design is randomized complete block with 4 replicates and 4 treatments: (1) No insecticide, (2) Calendar applications, in order to drive vector populations close to 0, (3) nominal threshold of 0.2 psyllids per tap, and (4) nominal threshold of 0.7 psyllids per tap. Calendar applications are being applied every month. The insecticides used for these applications in the last three months were fenopropathrin (Danitol 2.4 EC) at 16 fl oz/ac in September, spirotetramat (Movento MPC) at 16 fl oz/ac plus horticultural mineral oil 2% in October and carbaryl (Sevin XLR plus) in November at 0.65 gallons/acre. In December, treatments (2) and (3) received the first dormant spray with phosmet (Imidan 70-W) at 1 lb per acre. In the third week of November the “Earlygold” block was harvested and yields, yield increments with respect to the 2010 harvest as well as several fruit quality parameters were measured for each treatment. Values obtained were correlated to cumulative number of ACP adults obtained by tap sampling during the last season. A significant effect of treatments on yields was found (F = 4.03; df = 3, 15; P = 0.045). Treatment (2) had significantly higher yields (266.9 ‘ 10.9 boxes per acre) than the rest of the treatments (208.9 ‘ 11.7, 213.4 ‘ 22.5 and 220.7 ‘ 14.6 boxes per acre for treatments (1), (3) and (4) respectively). Similarly, yields with treatment (2) significantly increased (45.25 ‘ 15.73 boxes per acre) compared to 2010, in contrast to the rest of the treatments (-7.00 ‘ 15.59, 14.60 ‘ 13.34 and 10.14 ‘ 15.19 boxes per acre from 20110 to 2011 for treatments (1), (3) and (4) respectively). There was also a significant treatment effect on fruit diameter (F = 4.27; df = 3, 639; P = 0.0053), fruit weight (F = 5.23; df = 3, 639; P = 0.0014) and the fruit weight/volume ratio (F = 6.07 df = 3, 639; P = 0.0004) with higher values for the three parameters in treatment (2). Despite the fact that we also found significantly ACP treatment (2) compared to the rest of the treatments (F = 6.13; df = 3, 15; P = 0.0148), no significant correlation was found between cumulative ACP numbers and yield losses (P = 0.8353). Future harvests are expected to increase differences among treatments. In a preliminary cost-benefits economic analysis the estimated additional cost of the calendar insecticide program was $555.6 per acre and the estimated yield increment from 2010 to 2011 due to the insecticide calendar applications was 39.3 boxes per acre. According to this, the juice price that would return the insecticide investment would be $2.28 per pound solids. Currently, markets price are under this number, around $2.00 per pound solids. Therefore, after the first year of applying the ACP insecticide calendar program, increase profits due to this program in last harvest would not cover the extra costs of the program.
Objectives of this project include 1) refinement of sampling methods, 2) testing the influence of adult density and shoot infestation on precision of estimated means and distribution of population within blocks, and 3) evaluation and integration of methods for assessing psyllid density, shoot density, and infestation rates into a user friendly system accessible to consultants and managers. Counts of psyllid adults by stem tap and sticky traps were compared for two years in a 12-acre commercial block planted with Valencia x Carrizo oranges subjected to four treatments (1) Nutritional (2) Insecticides (3) Insecticides + Nutritionals and (4) Untreated. This block was divided into 16 plots, equally distributed among four treatments. Plots under treatment 2 and 3 were treated with insecticides when psyllid adults exceeded 0.2 per tap sample. The remaining eight plots were also continuously monitored, but were not treated with insecticides although four received nutritional sprays. In each plot six trees were selected and in each selected tree, one ‘sticky trap’ was deployed inside the canopy. Traps were replaced biweekly, at which time two tap samples were conducted in each tree. A ‘tap sample’ count consisted of adult psyllids falling on a white clipboard placed under randomly chosen branches which were then struck 3 times with the PVC pipe. Sticky traps were examined under the stereoscopic microscope in the laboratory and adult psyllids counted. Biweekly captures of adults on sticky traps averaged 2, 3, 13 and 15 in treatments 3, 2, 4 and 1, respectively. Adults per tap sample conducted only at trap replacement averaged 0.1, 0.2, 0.7 and 0.7 in treatments 3, 2, 4 and 1, respectively. The relationship between the two sampling methods was analyzed using Pearson Correlation Coefficient. Analysis of cumulative data showed that two methods were highly correlated in treatments 1 (r = 0.66, P = < 0.0001) and 4 (r = 0.69, P = < 0.0001) not treated with insecticides but weak in treatments 2 (r = 0.21, P = 0.12) and 3 (r = 0.18, P = 0.20) that were treated. Analysis of data on individual dates showed that out of 37 comparisons 10, 16, 17 and 23 were statistically significant in treatments 3, 2, 4 and 1, respectively. Examination of data plots showed that although both methods were detecting psyllids at low and high densities, either one or the other was detecting more psyllids at low density at different times, particularly in treatment 3 averaging lowest population. These findings once again indicate that tap sampling is an effective and efficient method which provides reliable and instant information for management decisions. Detailed comparisons of different sampling methods are provided in the EDIS document listed below. We are now comparing stem tap sampling with vacuum sampling in commercial citrus. The vacuum sampler is made from a leaf blower and collects many psyllids even at low populations. A single strike captured an average of about twice what a single tap sample would catch and the two samples were significantly correlated. Use and effectiveness of the tap sampling method was promoted through several meetings and workshops including the one arranged by FAO on "Taller subregional 'Control Biol'gico en HLB': Recomendaciones para Centroam'rica". It was encouraging to see that stem tap method is already being used in some concerned countries such as Costa Rica and Belize. Arevalo, A. H, J. A. Qureshi and P. A. Stansly. 2011. Sampling Asian citrus psyllid (ACP) in Florida citrus groves. EDIS, http://edis.ifas.ufl.edu/in867.
We continue to conduct replicated experiments and measure the impact of psyllid control programs on non target pests and beneficial insects. During this quarter, experimental blocks at commercial and SWFREC groves were sampled for psyllids, citrus rust mites, citrus red mite, predatory mites, snow scale, chaff scale, Glover scale, purple scale, citrus blackflies, whiteflies, mealy bugs, as well as their natural enemies. Only more common species are reported. The experiment in Collier county compares 4 treatments (1) Nutritional (2) Insecticides (3) Insecticides + Nutritionals and (4) Untreated control. Insecticides currently recommended for psyllid control are used when adults exceed 0.2 per tap sample and nutritional products and their application timing follow a program developed by McKinnon Corporation averaging three sprays per year. CRM were high on fruits in the treatments using insecticides (0.2-0.3/lens field) compared to nutritionals and control (0.02-0.03/lens field). However, chaff scale was not observed in the samples conducted in insecticide treatments compared to 0.1/lens field in the nutritional and control treatments. Shoots infested with woolly whitefly averaged 9-12% in insecticide treatments compared to 19-27% in nutritional and control treatments. Threshold levels of psyllid population were not reached this quarter in two experiments in Hendry county, one in a 35 acre block of ‘Early Gold’ and the other in a 16 acre block of ‘Valencia’. However plots designated for calendar sprays received of a rotation of insecticides recommended for ACP control applied every month: abamectine (Agri-Mek SC) at 3.5 fl oz/ac + horticultural mineral oil 2% in July, malathion (Gowan Malathion 8F) at 2.5 pt/ac in August and fenpropathrin (Danitol 2.4 EC) at 16 fl oz/ac in September. Psyllid adults per tap sample averaged 0-0.01 in the treated plots and 0-0.08 and 0-0.2 in the control of Early Gold and Valencia, respectively. Citrus rust mites and chaff scale did not differ between treated and untreated plots. However, only 2% shoots were infested with woolly whitefly in treated plots compared to 34% in control plots of ‘Valencia’. 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 a10.9 acre block of ‘Valencia’ in Lee county. Citrus rust mite and chaff scale averaged 1.9 and 0.35 per lens field, respectively, and did not differ between the three treatments. Psyllids in the grower standard, oil and control treatments averaged 0.03, 0.24 and 0.35 per tap sample, respectively. A study conducted at the SWFREC used 16 yr old Valencia orange trees and tested 13 treatments of Danitol 2.4 EC, Actara 25 WG, Agri-flex, Voliam Flexi, Dibrom 8 E, Portal 0.4 EC and MBI203 DF1. All treatments provided significant reduction in psyllid populations for one month. However, treatment effects against citrus leafminer were very short lived. Significant reduction was observed at 3 days after treatment (DAT) with Danitol 2.4 EC, Actara 25 WG, Agri-flex, and Dibrom 8 E all applied with 435 oil and Voliam Flexi and Portal 0.4 EC applied alone. Only Agri-flex + 435 oil and Voliam Flexi were providing significant reduction at 10 DAT. It seems that 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. Psyllid populations were very low during the reported period and fewer or no sprays were warranted based on thresholds.
The objective of this project is to investigate three questions: 1) whether HLB symptoms or boron/zinc deficiencies alone affect how ACP responds to citrus; 2) whether feeding patterns by adults, length and location of feeding, are altered by HLB infection or boron/zinc deficiencies; and 3) whether different strains of Ca. Liberibacter asiaticus (Las) differentially affect the response of ACP to citrus. In other pathogen/host/vectors systems, such as that with Ca. Phytoplasma mali and Cacopsylla picta (the apple psyllid), the pathogen manipulates the plant host metabolism so that diseased plants become more attractive to the psyllid vector, thereby spreading the pathogen more rapidly than if no plant host manipulation occurred. Since nutrient deficiencies are often associated with HLB in citrus, we wished to confirm that the reported attraction of Diaphorina citri to HLB symptomatic plants over uninfected plants was due to changes in host metabolism by the pathogen rather than physiological changes due to poor nutrition. The production of greenhouse-grown citrus trees with nutrient deficiency symptoms for both zinc and boron continues. Deficiency symptoms continue to develop for boron and zinc deficiencies have started to be apparent. The high mobility of zinc within the plant allows redistribution of existing zinc to new flush, delaying the development of deficiency and the associated symptoms. HLB symptom development continues in our plants with the different HLB strains. As soon as strong deficiency symptoms develop, then psyllid testing for objective 1 and 2 will commence and is expected to move rapidly. We are also interested to determine if strains of Las will have any effect on the attractiveness of trees to D. citri. It has been reported that Las strains have varying levels of virulence and symptomatology (Tsai et al. 2008). We have analyzed DNA samples from HLB positive trees from Polk and Highlands counties as well as the ‘Smoak Grove’ CREC greenhouse strain by PCR and sequencing. Three putative strains of Ca. Liberibacter asiaticus (Las) were found with 5 (CREC greenhouse isolate), 13, and 15 tandem repeats of DNA in the LAPGP locus described by Chen et al. 2010 and have identified sources of budwood. Cloning and sequencing of loci including the b-operon, OMP (outer membrane protein) gene and phage DNA polymerase to support the differentiation of the three strains is complete (Bastianel et al. 2005; Lin et al. 2008; Okuda et al. 2005; Tomimura et al. 2009). Results from sequence analysis clearly defines two strains based on conserved mutations in the b-operon sequence, matching strains from Japan and Vietnam and a strain from Vietnam for the northern and southern Florida strains, respectively.
One of the most recent challenges with deploying DMDS in the ISCA release device called SPLAT (specialized pheromone lure application technology) has been the phytotoxicity of the treatment to leaves and branches. A substantial amount of the DMDS active ingredient is needed in order to affect psyllid population densities. Unfortunately, we have found the DMDS active ingredient burns tree foliage and can even kill entire small tree branches, if applied directly to the wood surface. Therefore, we have been developing alternative release devices that would allow deploying the DMDS active ingredient within trees without touching tree surfaces. Our most recent prototype is a sachet that is hung in trees with a wire hanger. The sachet contains the SPLAT-DMDS, which is allowed to evaporate through a porous membrane. Therefore, the DMDS dispenser is deployed in trees; however, the active ingredient does not come in direct contact with tree branches or leaves. We are currently investigating whether these devices will be effective. The experiment was initiated in September and we are still analyzing data. The results of an earlier experiment conducted in August with a newer formulation of SPLAT-DMDS have been analyzed. The results of this test did not replicate the success we observed with the same formulation last fall. Psyllid populations were not significantly reduced by deployment of this formulation in this mid-summer test (as compared with control plots)as was observed last fall. We are unsure why we were unable to replicate the earlier success. We are trying to determine if the inconsistent results are because of differences in psyllid population densities between these tests or differences in environmental conditions when the different tests were conducted. It is possible that the formulation is not holding up to the intense temperatures and rainfall experienced in the summer as compared with cooler and dryer conditions in the fall. Finally, we have initiated testing of three new formulations of SPLAT that contain repellents other than DMDS that have proven effective against psyllids in laboratory tests. These experiments have only recently been initiated and we should have initial results in 3-4 months.
The purpose this investigation has been to evaluate and improve low volume spray technology for psyllid control. We have been investigating how low volume treatments (2-10 gallons per acre) compare with standard applications using airblast sprayers at 200 gallons of finished spray per acre. We have been investigating longevity of residual activity of the sprays against Asian citrus psyllid (ACP). Also, we have been investigating alternative application practices, such as border row treatments with low volume technology. 1) Leaf residue toxicity studies that compare standard high volume with low volume spray applications in the field. In these experiments, we investigated the longevity of residual activity of low volume spray residues against adult ACP by comparing low and high volume treated leaves. Trees were treated in the field with commercial airblast or low volume sprayers. Leaves were removed from the plots where fenopropathrin (16 oz/acre), phosmet (1.5 lb/acre) or imidacloprid (15 oz/acre) were applied by low (12 gpa) or high volume (200 gpa) applications. Leaves were removed at four and eight days post-application. A bioassay was then performed on leaf discs held in Petri dishes. Approximately 15 adult Asian citrus psyllids were placed per assay dish with leaf discs of either the treated leaves (low volume versus standard) or untreated control leaves. Adult mortality was assessed at 24 h and 48 h post exposure. The results showed that mortality of adult psyllids on 4-day old insecticide residues was between 60 and 100% for high volume application, but <10% for low volume treatments. For residues on day eight, only the high volume fenpropathrin treatment caused mortality (80%). The other treatments caused <10% mortality. A residue trial of the adjuvant, Induce, was conducted with the insecticides fenpropathrin and chlorpyrifos at both low and high volume applications. At day three, discs from all treatments caused 100% mortality. On day seven; however, fenpropathrin + Induce low volume and high volume were the only treatments to cause adult mortality: 65 and 80% respectively. 2) Effectiveness of the border row treatment tactic for ACP control. The objective of this experiment is to investigate the reduction in numbers of ACP adults caused by treating the two border rows of grove plots as compared with blocks in which every row was treated. An untreated control of three plots was included for comparison. Numbers in both fully and border only treated blocks were significantly reduced by applications three and seven days after applications were made. On day 14, the effects were not significant in the border row-treated plots as compared with the controls. The three scheduled low volume applications of 16 oz/acre of fenpropathrin with with 2% V/V 435 crop oil added as a LV application of 12 gpa have now been made and spatial analysis of the data is underway. Leaf disk bioassays were also performed on leaves taken from the upper canopy (~2.5 m) of mature trees and and compared to leaves collected from 1 m. At three days after treatment, the 1 m leaf disks caused 100% mortality versus 0% for the upper canopy leaves. Results from day seven indicate that neither low (1m) or high (2.5m) leaves were significantly toxic to the adults after low volume treatment. Overall, these results indicate that low volume treatment applications have very short residual activity and most of the ACP kill occurs during or very shortly after treatment.
One of the main objectives of this research is to identify attractants for Asian citrus psyllid (ACP) that could be used for monitoring, as well as, developing attract-and-kill technologies for ACP. Although we have focused on identification of ACP pheromones considerably, we have also made substantial progress recently with respect to identifying citrus-based volatiles as ACP attractants. Recently, we examined host plant volatiles from uninfested flush and young leaves of citrus genotypes that were reported to vary in susceptibility as measured by colonization by ACP in the field (Westbrook et al. 2011). Five species of Rutaceae were selected for plant volatile analysis from a list of genotypes assayed for colonization by Westbrook et al. (2011). In that study, 87 genotypes were examined in the field for presence of eggs, nymphs and/or adults. We collected and analyzed volatiles from three genotypes on which adults were abundant, including Bergera koenigii L. (curry leaf tree), Murraya paniculata (L.) (orange jasmine) and Citrus macrophylla Wester. Volatiles were also analyzed from Citrus jambhiri Lush. (rough lemon), a genotype on which the ACP population was nearly midway between the highest and lowest recorded, and Poncirus trifoliata L. (trifoliate orange), whose population of adults was near the lowest recorded in the study. C. sinensis (L.) Osbeck ‘Valencia’ was also included because of its widespread commercial use and susceptibility to ACP. Plant volatiles were collected by placing freshly excised 15 g bouquets consisting of shoots of terminal leaves and flush of each genotype into separate 50 ml beakers containing distilled water. Bouquets from B. koenigii were collected from field-grown plants whereas bouquets from the other five genotypes were collected from potted greenhouse-grown plants. The beaker was then placed into a closed ca. 1-liter glass container. Charcoal-filtered humidified air was pushed through the container at a rate of 500 ml/min for 24 h. Plant volatiles were trapped in glass tubes packed with Porapak Q. The collected volatiles analyzed by GC-MS using a ThermoElectron Trace GC coupled to a DSQII quadrupole MS, all controlled by Xcalibur software. Limonene and (E)- .-ocimene were the only volatiles that occurred in the headspace over all six genotypes. Whereas limonene was present at high percentages in headspace collected from C. jambhiri and C. macrophylla collections (55.4% and 60.7%, respectively), it constituted 5.0% of volatiles from C. sinensis ‘Valencia’ and <1% from B. koenigii, M. paniculata and P. trifoliata. Similarly, (E)- .-ocimene was found at levels of 10.1% and 14.0% in C. jambhiri and C. sinensis 'Valencia' headspace, respectively, but only at 2.4% of volatiles collected from B. koenigii; <1% of this compound was found in extracts of C. macrophylla, M. paniculata and P. trifoliata headspace. The collection from B. koenigii, the genotype with the second highest susceptibility to adult ACP in the Westbrook et al. (2011) study, contained 48.3% '-phellandrene. Our most recent data report the proportions of various compounds found in the headspace volatiles among six species in the family Rutaceae differing in their susceptibility to ACP. Some compounds occurred exclusively while others were common to several species. In genotypes such as P. trifoliata, it will be important to assess whether it is a lack of key attractive components that renders it unsuitable for ACP or whether it is the presence of repellent compounds. Behavioral analysis of individual compounds as well as blends of compounds are underway and should produce useful information for psyllid management and plant breeding strategies.
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