Ultra low-volume and Aerial Application of Insecticides and Horticultural Mineral to Control Asian Citrus Psyllid in Commercial Orchards. Low volume (LV) aerial sprays have become the principal method of application during the dormant season in SW Florida. More than 70,000 acres have been sprayed at least once during the last two years in the Gulf ‘CHMA’ cooperative dormant spray program, and this is likely to be repeated this season. Meanwhile, we continue our evaluations of LV application of 435 horticultural mineral oil (HMO) which has shown promising results the last 2 years. This year we chose a 40-acre block of mature ‘pineapple’ oranges in Glades County that had not received a dormant spray and consequently was expected to have high psyllid populations. We used a Proptec rotary atomizer P400D spray machine which has provided better results than the modified London Fogger 18-20 and also allowed for higher volumes necessary to combine oil with a foliar nutrient package that is being widely used to mitigate effects of HLB. Applications at 10 gpa were made every two weeks in a randomized complete block (RCB) design with four replications. Asian Citrus Psyllid (ACP) populations were monitored on alternate weeks using stem tap sampling, and leaf samples were submitted to the HLB laboratory at the Southwest Florida Research and Education Center (SWFREC) for PCR analysis. Initial incidence of PCR positive trees was 11%. Contrary to expectations, ACP populations were low, although the accumulated number of adult x days in treated plots was about half (3.4′ 1.1 ACP x day) that in untreated plots (6.3’2.1 ACP x day). In a second trial employing an RCB design with three replicates, the response of ACP populations was evaluated to biweekly applications of oil applied at 2% (v/v) spraying 100 GPA with an aiblast sprayer in an 85-acre block of organic ‘Valencia’ oranges in Charlotte County. However populations were again low and no differences were observed between the treated and the untreated plots. Thus, it seemed that LV at 20% v/v was more effective than HV at 2% v/v the difference in concentration. A third trial evaluating coverage, deposition, and absorption of micronutrients applied at high and low volume was conducted in a 16 acre block of Valencia oranges in Collier County. Comparison was made between the Proptec sprayer spraying @ 10 GPA every two weeks and an air blast sprayer applying the same total amount of material at 100 GPA during summer and falls flush. Leaf samples were collected and are being analyzed at the foliar analysis laboratory at the University of Florida’s Everglades Research and Education Center. Coverage of blue dye on paper targets in the foliage is being analyzed using digitized images and samples are being processed at the Soil and Water Laboratory at the SWFREC to evaluate deposition using a spectrophotometer. In a fourth trial we evaluated psyllid suppression following application of spirotetramat (Movento ‘) at 10 oz/ac applied at 5, 10 GPA with the Proptec or 40, and 120 GPA with a speed sprayer. While sprayer type did not produce clear differences, a trend toward better performance was seen with the greater of the two volumes applied by each sprayer. Stansly, P.A., H. A. Arevalo and M. Zekri. 2010. Area-wide psyllid sprays in Southwest Florida: An update on the cooperative program aimed at controlling the HLB vector. Citrus Industry, 91(10):6-8
Progress on a new special regulatory trap for capturing and preserving citrus psyllids in situ has been advanced enough to develop some prototypes for further field testing and refinement. The capture and preservation components of the trap were developed from laboratory bioassays that examined psyllid behavior in detail. An industry partner has been identified and contracted with to construct the new traps and future work will be focused on evaluating and improving visual and odor components along with the total trap efficiency in the field.
Objectives of this project are to: (1) import, release and evaluate new strains and species of parasitoid specific to D. citri. (2) identify genetic markers that can be used to track T. radiata in the environment, (3) develop efficient methods for mass rearing and release of T. radiata and possibly other species to increase biological control through augmentation of natural populations, and (4) transfer technology to industry clientele. Objectives 1 and 3: Colonies of Tamarixia radiata from Vietnam, China, and Pakistan that we established at DPI- Gainesville as well as the colony at SWFREC of what could now be termed the ‘Florida’ strain continue to provide wasps for release, investigation and distribution. Field releases this quarter of 7,952, 10,839, and 7,354 wasps from the respective Gainesville colonies join 56,031, 60,334, and 45,898, wasps released earlier this year. Wasps from the Pakistani colony continue to be released at the SWFREC while wasps from south China and N. Vietnam were integrated with biweekly sprays of horticultural oil in replicated trials at two commercial groves, in Glades and Charlotte Counties, the latter being organic. Incidence of parasitism in October based on adult emergence from feral nymphs averaged 45% (N=126) and 34% (N=523) from oil-treated and untreated plots at the Glades county site while no nymphs were found at the Charlotte Co. location. Parasitism averaged 35% at SWFREC (N=69) in a release block compared to 0.9% (N=323) in control blocks. An additional 20,000 wasps were produced at SWFREC, increasing the 2010 total to 76,645. These were used to refresh the colony at OrangeCo, conduct laboratory experiments, and release in experimental, organic and conventional groves. We also collaborated with the California Department of Food and Agriculture, USDA-ARS, USDA-APHIS and FDACS-DPI to arrange and conduct a Tamaraxia Workshop this November in Florida, attended by private and public sector researchers from Fl. TX. CA. Mexico, Costa Rica and Belize. Rearing methods are being improved and we hope to see new DPI facilities for mass rearing of Tamarixia in Dundee this year. Objective 2: We have initiated a collaborative follow-up study to (1) with Dr. Evan Braswell of USDA APHIS, Edinburg, TX, aimed at identifying genetic origins parasitoids sampled from release sites and other locations using molecular markers. A. study on the searching behavior of T. radiata was also published (2). Objective 4: An extension document (3) on T. radiata was published at the Cornell Univeristy website “A Guide to Natural Enemies in North America”. Sixty one percent of SW Florida citrus growers surveyed this quarter on what additional coordinated activities they would you like to see applied area wide chose mass release of parasitoids for biological control of ACP. 1) Barr, N.B., D.G. Hall, A. Weathersbee, R. Nguyen, P. A. Stansly, J. A. Qureshi, and D. Flores. 2009. Comparison of laboratory colonies and field populations of Tamarixia radiata, an ecto-parasitoid of the Asian Citrus Psyllid, using ITS and COI DNA sequences. J. Econ Entomol. 102: 2325-2332. 2) Mann, R.S., J. A. Qureshi, P. A. Stansly and L.L. Stelinski. 2010. Behavioral responses of Tamarixia radiata (Hymenoptera: Eulophidae) to volatiles emanating from Diaphorina citri Kuwayama (Hemiptera: Psyllidae) and citrus. Journal of Insect Behavior. 23: 447-458. 3) Qureshi, J. A., and P. A. Stansly. 2010. Tamarixia radiata Waterston [Hymenoptera: Eulophidae], an ectoparasitoid of Diaphorina citri Kuwayama [Hemiptera: Psyllidae]: http://www.nysaes.cornell.edu/ent/biocontrol/parasitoids/Tamarixia.html
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 of methods for assessing psyllid density, shoot density, and infestation rates and their integration into a user friendly system accessible to consultants and managers. Accomplishments are described for each objective. 1) We continue to evaluate and refine different sampling methods. Based on our comparisons of stem-tap, sweep-net, and sticky cards and using an amount $ 10 for per hour labor and per day depreciation cost for an ATV, the cost of sampling a 50 acre block of citrus for ACP control averaged $ 17.40 with use of stem-tap or sweep net and $ 213.60 with sticky cards. An additional disadvantage with sticky cards is the delay in obtaining data to make informed decisions treatment decisions or evaluate applications. We found no difference in efficiency between single taps or single sweeps in detecting 0.2-0.3 ‘ 0.1 adults per sample. Below this range, an inordinate number of taps are necessary. However, the net can be used to cover more area than the tap by sweeping multiple times and therefore is able to detect lower ACP populations. On the other hand, sweeping is tiring, collects a lot of trash, and incurs a risk of canker spread. Detailed descriptions with pros and cons of each method are reported in an extension (EDIS, ENY857/IN867) publication which is in press. We have also initiated comparisons of stem-tap with vacuum sampling, which like the sweep net can cover more area than the tap. In a conventional block of ‘Valencia’ oranges adults averaged 0.3 ‘ 0.07 and 0.9 ‘ 0.12 for a sample duration of 6.7 ‘ 0.2 and 8.3 ‘ 0.3 seconds per tap and vacuum sample, respectively. 2) We are working on comparing different sampling methods over large data sets using regression analysis and bootstrapping procedure at precision targets of 0.25 and 0.01 SEM:mean in order to determine the number of samples required using these methods for routine monitoring and analytical modeling respectively. We have already reported some of these estimates in our earlier reports and in several of our presentations and workshops and extension publication mentioned above 3) We recommend 100 tap samples per block divided into 10 stops, five along the perimeter where ACP tends to congregate, and five inside the block. At each stop 10 tap samples are conducted at one per tree, counting ACP, as well as natural enemies and other pests. Then 10 young shoots, each containing ‘feather flush’ are examined with a hand lens to determine if they are infested with psyllid immatures. The search is terminated if 10 young shoots cannot be found after examining 20 trees. The detection ability of this system is more than adequate for most commercial purposes. The system is explained and forms and spreadsheets provided in the EDIS publication and our website: swfrec.ifas.ufl.edu/entlab. We also provide tap sampling kits to growers in our workshops or on demand. In a recent survey, 75% of growers in SW Florida said they used the tap sample and 63% monitored ACP more than 12 time a year, an increase of 26% over last year. We are also working on the development of a website with ZedX Inc. where growers will be able to enter their sampling data on the incidence of pest and disease in order to assess the need and recommendation of appropriate treatments. Arevalo, A., J. Qureshi and P. Stansly. 2011. Sampling Asian citrus psyllid (ACP) in Florida citrus groves. EDIS (In press) Stansly, P., A. Arevalo and J. Qureshi. 2010. Monitoring methods for Asian citrus psyllid. Citrus Industry 91(4) 20-22.
This study monitored Caribbean fruit fly populations counted in approximately 400 McPhail’s traps distributed across a 45 square-mile area receiving both fruit fly bait sprays and Mustang applications for Asian Citrus Psyilld. The study was performed in Vero Beach/Indian River County, north and south of Highway 60 and west of I-95 (also known as St. John’s Marsh area). The approximate distance between trap settings was 1050 feet, and they were checked about every 7 days for a total of approximately 2000 independent observations over the course of the study. The specific subject area included in this analysis encompassed a subset of the 2000 observations in 90 geographically-contiguous designated areas (each designated area is . square mile). The varieties in the groves in which traps were located included White Marsh, Pink Marsh, Star Ruby and Flame grapefruit and Navel, Hamlin, Valencia, Murcott and Temple oranges. This project was a pilot study designed to obtain observational information regarding whether or not Mustang applications applied for Asian Citrus Psyllid control might also suppress fruit fly populations. The construct of the study is that Mustang was applied in the Fall and again in the Spring for psyllid control to all areas monitored in the study. Coincident with that Fall/Spring time frame, Caribbean fruit fly populations were monitored and bait sprays applied as needed to maintain fruit fly certification for the target crops. The result of this arrangement was that all blocks observed in this study received two Mustang applications, but not all areas received bait sprays. The number of bait sprays applied ranged from none to 8, depending on the particular block. Fruit fly counts were monitored starting in August 2009 and continued through March 2010. Despite the considerable effort that went into performing field activities in this study, environmental and other circumstances resulted in very few non-zero values being obtained in the fly count data. This made quantitative statistical analysis difficult. As a result, graphical exploration of observed trends from the subject area was used to interpret these data. Caribbean fruit fly counts obtained from McPhail’s traps totaled across both time and space showed little or no relationship between the number of bait sprays applied and the total number of flies trapped per location. This result is consistent with the experimental supposition that Mustang sprays applied for psyllid control also suppress fruit fly populations. Specifically, fly counts were none to very low in areas both treated and untreated with bait sprays. Therefore, we suggest that factors other than bait sprays were responsible for the low counts observed. These other factors included: 1) Mustang applications applied in the Fall and Spring; 2) weather; and 3) undocumented factors. It is noteworthy that weather conditions over much of the course of this experiment were unfavorable for rapid fruit fly development. The results of this pilot trial do not contradict the premise of the study, but we believe a repetition of this experiment so that more complete numerical data can be obtained may be warranted. Since quantitative support of an experimental hypothesis that there is no difference between fly counts trapped in Mustang-sprayed vs. Mustang-non-sprayed conditions was not possible in this current pilot study, any follow-up experiment should be designed using the following criteria: 1) longer duration; 2) fewer locations; 3) try to get weather data for specific trap locations; 4) try to monitor fly counts in both Mustang-sprayed and Mustang-non-sprayed areas; 4) document other factors that may influence fly counts; and 5) reorganize data structure to facilitate on-going, real-time statistical analysis.
Although a successful trunk cutting, herbicide spray applicator device was constructed and mounted on a small tractor, little industry interest has evolved in its use. BASF Chemicals had expressed willingness to obtain a label for their formulation of the imazapur herbicide (Arsenal), but apparently no further work on labeling has occurred. Chemical Containers Corp had preliminary interest in commercial development of this equipment, but after all of the development and efficacy information was presented to the CRDF Committee the company apparently decided not to pursue development and no further discussions have occurred. This is probably because the foliar nutrition cocktail mixes appear to be maintaining HLB infected trees in a productive state for several years and fewer growers are scouting and removing infected trees. A simplified cutting and application machine was designed and is being constructed. This will be tested at least one time in the late winter in 2011.
The objectives of this study are: 1) to develop a series of flexible stochastic models to predict the temporal increase and spatial spread of citrus disease. The models were initially designed for citrus canker but have subsequently been extended to HLB. They can be used in a number of ways: to predict spread and to analyze the effectiveness of control strategies both in plantations and State-wide. 2) Test various control methods under field conditions to evaluate effects and collect data to parameterize models As previously described, an SEIDR model was developed that uses Markov-chain Monte Carlo methods, and extensive data from South Florida. This model portrays successive snapshots of the occurrence of symptomatic detected trees in known populations of susceptible trees. To date we have been able to estimate the transmission rates and dispersal kernel for HLB by interrogating this prior data center. currently we are working on differential effects of host age on epidemiological parameters and variability across the plantation. this allows us to explore the uncertainty how the predictions which is then incorporated in models to predict spread and to allow for uncertainty in the efficiency and comparison of control methods. A web based version of the model is in the final stages of development. This web-based model is for non-researcher users you can utilize it as a tool to understand how the disease will increase and spread both residential and commercial situations. It can also be used to test a wide variety of epidemiological and climate/weather variables and their effects on an HLB epidemic as well as various disease control/mitigation parameters to see the effect of these various control strategies. we’ve been using the data from southern gardens citrus that includes both young and mature trees, since host age is likely to be an important consideration for HLB. The model continues to be improved upon to capture more and more of the true features of the data and the disease. The model is being extended to estimate spread in diverse situations, should HLB be introduced into new areas such as TX, CA or AZ. Field plots were established at the USDA, ARS Picos Farm to examine the effects of insecticide control and roguing in various combinations, both to evaluate treatment effects and to collect epidemiological data for model development. These field studies are underway as well however, at the time of this writing there are no detectable statistical differences among various control strategies.
This project was designed to examine the potential disease control of citrus huanglongbing (HLB) by interplanting citrus with guava. In Vietnam guava has been shown to be an effective deterrent to HLB, slowing the disease and keeping plantings alive for up to 15 years that normally succumb in 2-3 year. For all plots and experiments, Guava trees, (Vietnamese white cultivar) were propagated and grown to appropriate size requiring ~1 year. Both nursery and field citrus trees are assayed for HLB every 60 days, and have been assayed multiple times. Psyllid populations are also being monitored continuously every 2 weeks within interplanted plots to document any repulsion of the vector due to guava. Results: Guava vs no guava nurseries: Two nursery sites, a guava protected citrus nursery versus an unprotected nursery, have were established with disease free, PCR-negative citrus trees (2 sweet orange and 1 grapefruit cultivars) in June 2009 and were located in the protected and unprotected plots. The guava trees were grown to appropriate size as indicated in Vietnam prior to outplanintg. To date HLB appears to be progressing more slowly in nursery plots interplanted with guava that non interplanted plots. Citrus/guava interplantings: 3 commercial plantings with multiple replications were established. This required 1 year to grow the guava transplants and a second year to become established in the field before interplanting with citrus per Vietnam protocols. One trial was established in a commercial orchard with collaborators in Southern Gardens Citrus, but two years of freezes and replanting prompted the grower/collaborator to abandon the planting. A second was established in grove in Martin county but the plantation was sold and removed before data could be collected. A third trial planting was established at the USHRL Picos Farm in Fort Pierce. The Picos plot was interplanted with citrus in August 2009. Severe frosts during 2008/2009 and again during Dec 2010 winters continue to affect the USHRL plots and have caused a delay in the experiment. To date, several HLB+ (PCR+) plants have been identified in the USHRL plots after multiple assays. The majority of these positives have occurred as the result of an edge effect. That is, treatment plots closest to an existing HLB+ planting of Valencia were affected. There continues to be no significant difference among the treatments thus far, however this data is insufficient to draw any conclusions at this point. Research using a Y-tube olfactometer to investigate guava volatiles as repellents of the psyllid has been challenging and resulted in no clear psyllid attraction or repulsion. The best response was 1-wk-old psyllids with C. macrophylla shoots, although psyllid attraction to this odor source was weak. Research with white guava (germplasm from Vietnam) did not lead to any improvement. We will continue to investigate repellency of guava alone or in combination with citrus and refined methods to achieve more sensitivity.
Mid Florida Citrus Foundation (MFCF) currently supports the research efforts of scientists from the University of Florida, USDA and private industry. The majority of research projects are conducted by UF scientists at the approximately 112 acre citrus grove. The MFCF supports citrus research through the employment of a full time grove manager whom works closely with researchers to ensure that their projects are handled properly and that the grove is an excellent condition. The management of this grove requires extra financial commitment as grove care cost tend to be higher than a commercial grove due to the nature of many of the research projects. Current projects being conducted at the MFCF are Asian citrus psyllid (ACP) pesticide evaluation control trials, low volume applicator trials, windbreak evaluation, HLB nutritional programs, new and existing herbicide trials, variety and rootstock evaluation trials. The MFCF is in the process of expanding grove to allow more research work to be conducted. This was made possible due to the fact that the MFCF received an EQIP grant from the NRCS. This past summer 13 acres were planted for new research trials, which included an HLB trial, multiple new herbicide trials and new variety evaluations. Additionally windbreaks were established for new and future citrus research blocks. Current plans call for the establishment of 30 additional acres of research citrus trials for the purpose of young tree psyllid control research, evaluation of new psyllid control products, economic study on rooted cuttings, evaluation of miticides and herbicides and large block planting of experimental early orange.
We are still assessing new symptoms appearance in all established experiments. Exp.1 – In the compartments 1 and 2 where citrus plants served as primary source of inoculum of CLas or CLam we are still observing a predominance of infective psyllids and diseased plants with positive conventional PCR for CLas. In average 30.4% of psyllids collected from inoculum source plants and 8.4% collected from test plants were positive for CLas and no one for CLam. In average 12.8% of test plant were positive for CLas and only 0.9% for CLam. From the three Clam citrus infected plants, two had also CLas in a mix infection. Average Ct value for leaves with CLas were 24.7 and for CLam 33.7, indicating a higher titer for CLas than for CLam. In compartment 4, where Murraya exotica served as source of inoculum, 46.0% and 9.4% of psyllids collected respectively in source plants and test plants were PCR positive for CLam, whereas in compartment 3, where Citrus sinensis served as source of inoculum, 6.35 and 4.7% of psyllids collected respectively in source plants and test plants were PCR positive for CLam. 8.2% of test plants were PCR positive for CLam when inoculum source was Murraya exotica and no positive test plant was detected when inoculum source was Citrus. All plants were in other insect-proof screenhouse and will be there for symptoms observation and leaf sampling for PCR analysis at least until December 2011. A new leaf sampling will be done in March to check the presence of both liberibacters in new test plants. A replication of this experiment was started to repeat this experiment. These results will be present in the 2nd International Research Conference on Huanglongbing in Orlando January 10-14th. Exp. 2- All test plants used to HLB-insect transmission are under evaluation for the symptom expression and the presence/concentration of the HLB bacterium by qPCR. Exp. 3 – No HLB-symptoms and infection were observed yet on inoculated trees at different sweet orange varieties and ages that were encaged under insect proof screenhouses. The disease severity (% of symptomatic canopy) of each tree from the alternative experiment under field conditions is being periodically assessed. Because of the heavy defoliation during the drought season and the recovery of tree canopy with new flushes during the spring, the average disease severity in all assessed trees seems to decrease at this time of year. New assessments after leaves maturation will be done.
The objective of this project is to investigate three questions: 1) whether HLB symptoms or boron/zinc deficiencies alone affect how ACP responds to citrus; 2) whether feeding patterns by adults, length and location of feeding, are altered by HLB infection or boron/zinc deficiencies; and 3) whether different strains of Ca. Liberibacter asiaticus (Las) differentially affect the response of ACP to citrus. In other pathogen/host/vectors systems, such as that with Ca. Phytoplasma mali and Cacopsylla picta (the apple psyllid), the pathogen manipulates the plant host metabolism so that diseased plants become more attractive to the psyllid vector, thereby spreading the pathogen more rapidly than if no plant host manipulation occurred. Since nutrient deficiencies are often associated with HLB in citrus, we wished to confirm that the reported attraction of Diaphorina citri to HLB symptomatic plants over uninfected plants was due to changes in host metabolism by the pathogen rather than physiological changes due to poor nutrition. The production of greenhouse-grown citrus trees with nutrient deficiency symptoms for both zinc and boron continues. Deficiency symptoms are expected to take a few months to develop. This is especially the case for zinc because of the high mobility of zinc within the plant allowing redistribution of existing zinc to new flush, delaying the development of symptoms. Multiplication of our stocks of HLB infected citrus is also underway to provide a constant source of symptomatic tissue for experimentation once the nutrient deficiency symptoms have developed. We are also interested to determine if strains of Las will have any effect on the attractiveness of trees to D. citri. It has been reported that Las strains have varying levels of virulence and symptomatology (Tsai et al. 2008). We have analyzed DNA samples from HLB positive trees from Polk and Highlands counties as well as the ‘Smoak Grove’ CREC greenhouse strain by PCR and sequencing. Three putative strains of Ca. Liberibacter asiaticus (Las) were found with 5 (CREC greenhouse isolate), 13, and 15 tandem repeats of DNA in the LAPGP locus described by Chen et al. 2010 and have identified sources of budwood. We are currently using the identified budwood sources to acquire greenhouse isolates of the three strains. Cloning and sequencing of loci including the b-operon, OMP (outer membrane protein) gene and phage DNA polymerase to support the differentiation of the three strains is underway (Bastianel et al. 2005; Lin et al. 2008; Okuda et al. 2005; Tomimura et al. 2009).
The objective of this project was to investigate three questions: 1) what is the seasonal pattern of Ca. Liberibacter asiaticus prevalence in leaf tissue on a grove scale; 2) what are the flushing patterns of citrus and whether these flushing patterns affect the prevalence of Ca. Liberibacter asiaticus in Diaphorina citri or citrus leaves; and 3) what is the prevalence of Diaphorina citri carrying Ca. Liberibacter asiaticus on a grove scale and how does it compare the results from the citrus trees in the same grove. In 2008 and 2009 Ebert and Rogers demonstrated that the prevalence of Ca. Liberibacter asiaticus in the Asian citrus psyllid varied seasonally but the pattern between seasons was not consistent. It was suggested that perhaps the reason for the differences between the years related to the flushing patterns of citrus and the prevalence of the bacterium in the leaves where psyllids are feeding. This project aims to determine if there is a relationship between the frequency of disease on branches and psyllids. The postdoc has been hired for this project and is currently processing the backlog of samples but we have some preliminary results from 1 grove. An ‘Earlygold’ grove in Orange county Florida was selected to examine seasonal prevalence of HLB over a 3-year period. Two hundred trees were selected from 10 consecutive rows. One leaf/tree was randomly picked every fortnight. Sample collection began at the end of June 2010 with collections ongoing. For qPCR detection of Las, the midribs of five random leaves were pooled to obtain 40 samples/date. An estimated Las prevalence in the branches was generated from the pools with PooledInfRate v3. Simultaneously, ACPs were collected from the same location to compare the seasonal prevalence of Las in citrus branches and ACPs. Las prevalence increased (from 0.14, 0.20, 0.21 to 0.27) from June to September. The data from ACPs are still being processed. Comparing the data from ACPs and citrus trees could provide more information on seasonal variation in Las prevalence in both the vector and the host, and thereby enhancing our management strategies by identifying the essential periods for ACP control to prevent HLB transmission.
Under Objective 1 (define rates and formulations of copper sprays for more effective control) one trial with Red grapefruit is on-going in Ft. Pierce, FL and likewise one trial with Hamlin orange in Hardee County, each with 14 treatments of formulations, rates and combinations with other chemical treatments of interest. This season, trials have low to moderate disease epidemics as a result of a periodically wet spring, moderately wet summer and an absence of tropical storm events. Evaluations of fruit infection in these trials will begin in November 2010. Under Objective 2 (establish the period of fruit susceptibility, residual activity and phytotoxicity of copper) These results have been summarized for publication in Florida State Hort. Society (FSHS) Proceedings 2010. Major findings reported are: 1) Copper formulations containing copper hydroxide or basic copper sulfate (metallic rates of 0.67 to 1.12 kg/ha), varied from low to moderately effective for canker control depending on late-season, wind-blown rains. 2) Copper pentahydrate, with a lower metallic copper rate/ha per application, provided equivalent control to other copper formulations. 3) Streptomycin, alone or with a reduced rate of Kocide 3000, in July and early August gave equivalent control to Kocide 3000 alone. 4) Copper phytotoxicity risk coincided with accelerated fruit growth after summer rains. 5) Greater canker susceptibility of fruit in later season is likely because of increased opening of stomates for bacterial infection coincident with more numerous windblown rain events. 6) The only factor that led to significant reductions in copper residue per fruit surface area over time was the Kocide 3000 concentration. PDS had no effect on the residue. Under Objective 3 ( evaluate the use of streptomycin [Firewall]) Two trials, one non-bearing and one bearing, in grapefruit are underway to further evaluate FireWall for canker control. The package to obtain an EPA Section 18 Emergency Exemption for FireWall has been submitted to FFVA based on data from Florida trials conducted in 2008-2009. Under Objective 4 (To define risk for development of bacterial resistance to copper and streptomycin in FL citrus groves) a number of factors favorable for the development of copper resistance in Xcc were identified, but further investigation is necessary to fully assess the risk for streptomycin resistance. Previously reported findings are being summarized for publication. Under Objective 5 (rapid transfer improved canker management technology to the Florida citrus industry), 2010-11 canker management recommendations have been published in the Florida Citrus Pest Management Guide and Citrus Industry Magazine. Oral presentations have been delivered to the Florida Citrus Production Managers, at county extension meetings, and at the FSHS annual meeting.
The objective is to evaluate soil-applied neo-nicotinoids and other SAR inducers on HLB disease progress in newly planted citrus trees subjected to psyllid-mediated infection or graft-inoculation. One yr-old Hamlin trees were planted in May 2009 and treated as follows: 1) non-treated check (UTC), 2) foliar insecticide to control psyllids, 3) soil-applied imidacloprid/thiamethoxam (IMID/THIA) to induce SAR, 4) soil-applied IMID/THIA plus foliar insecticides, 5) graft-inoculated UTC, 6) graft-inoculated with IMID/THIA. There were 40 trees per treatment (5 blocks of 8 trees). In 2009, the effect of SAR inducers on HLB infection progress was inconclusive perhaps attributable to the interaction of IMID/THIA with psyllid control which may have an uncontrolled effect on psyllid transmission. In 2010, the SAR inducer acibenzolar-S-methyl (ASM, Actigard 50WP) which does not control psyllids was substituted in treatments 3, 4 and 6. At 15 months after treatments began, 56 trees were PCR+ (23%) in the trial. Higher number of PCR+ occurred in the UTC (14), the UTC with graft inoculation (13), and the IMID/THIA/ASM with graft-inoculation (13). Lower number of PCR+ trees occurred without graft inoculation in treatments with SAR inducers (7), foliar insecticides (6), and foliar insecticide plus SAR inducers (3). An HLB-SAR experiment has set up in Parana, Brazil. The trial utilizes soil applied ASM (Bion) for the SAR treatments and is proximal to tree in a farm with HLB. The first tree to show HLB symptoms after six months is a tree treated with ASM. While effect of SAR on HLB disease progress is still inconclusive, thus far these trials and other evidences indicate lack of promise for SAR in HLB management.
Objective 1: Potential for soil application of the neonicotinoids, Admire (imidacloprid, IMID)and Platinum (thiamethoxam, THIA), and Actigard (acibenzolar-S-methyl, ASM), to provide long-lived SAR control of canker was evaluated. In the field trial of 3- and 4-year-old ‘Ray Ruby’ grapefruit trees in Ft. Pierce, Florida, soil drenches of IMID, THIA, and ASM were compared with contact activity of Kocide 3000 (copper hydroxide, CH) and/or Firewall (streptomycin, STREP) applied as a foliar spray at 21-day interval for canker control on foliage. Canker on each set of vegetative flushes was assessed as the percentage of leaves with lesions. In 2008, despite above average rainfall and a tropical storm event, all treatments significantly reduced incidence of foliar canker. Spray of CH was the most effective treatment. As a group, soil drenches of SAR inducers reduced foliar disease incidence depending on rate and frequency of application. In 2009, all treatments significantly reduced incidence of foliar canker compared to the untreated check. IMID, THIA, and ASM as soil drenches were each effective for sustained control of canker on young trees under epidemic conditions. Control with SAR inducers was highest for four applications of ASM in 2008 and 2009 seasons which demonstrated the value for maintenance of SAR with repeated soil applications. Objective 2 Integration of soil applied IMID with foliar applications of copper sprays for control of canker. IMID applied once at the beginning of the season followed by 11 CH sprays gave the best control in the 2009 trial. This suggests that SAR and copper could be used in an integrated program for augmenting canker control for young fruiting trees. In 2010, a trial integrating ASM at different frequency of soil application with THIA and CH sprays at 21 day interval was set up on 1-yr-old Vernia sweet orange in Ashland, FL. Incidence of newly infected trees is just starting to increase in the various treatments this summer. This highest incidence of disease trees and leaves is in the nontreated check. Objective 3 is to evaluate of the complementary use of ASM, THIA and IMID soil applications to increase and/or extend canker control in 2-yr-old grapefruit trees. Canker was first observed in the trial area in September 2009 after a very high rainfall period in August (17 inches). The pattern of disease spread was across the trial area from southwest to northeast. Incidence of trees with canker was 56% in the non-treated check trees, whereas in most of the SAR treatment combinations the incidence was less than 10%. Incidence of canker in this trial continues to increase in 2010. A field trial with soil applied neonicotinoids in Parana, Brazil was evaluated. IMID(Confidor) as a soil drench and IMID (Winner) applied to trunk gave comparable in disease control activity on 2-yr old Valencia orange trees, as well as, the other neonicotinoids tested, THIA (Actara) and Clothianidin (Poncho). In Brazil a greenhouse evaluation, soil drenches of these neonicotinoids and ASM were effective for reducing lesion and Xcc population development in leaves. ASM was the best treatment among those evaluated. Thus, SAR not only prevented infection but also acted post-infection to reduce the level of bacterial populations in lesions. This confirms the best activity that the inducers of SAR have for reducing canker incidence and epidemic development of disease on leaves and fruit.
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