Low volume (2-10 gallons per acre) applications have been increasingly popular in the citrus industry due to their low operating costs and flexible nature. The rationale for this investigation was to gain better understanding of limitations and suggest improvements to the implementation of low volume applications in mature citrus groves and compare them to traditional high volume (ca. 200 gallon) techniques. 1) Leaf residue toxicity studies. The residue left on citrus leaves following applications kills psyllids for up to several weeks. We investigated longevity of activity for Asian citrus psyllid, using leaves from field trials with fenopropathrin (16 oz/acre), phosmet (1.5 lb/acre) and imidacloprid (15 oz/acre) after low and high volume applications. A bioassay was then performed with citrus leaf discs in a Petri dishes. Approximately 15 adult psyllids were placed in dishes with leaf discs of either treated or untreated leaves. 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. 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. Fenpropathrin + Induce low volume and high volume were the only treatments to cause adult mortality: 65 and 80%, respectively. 2) Border row treatment as a tactic for ACP management. The purpose of this study was to investigate the application of border row treatments for psyllid management as compared with treating entire blocks. 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. 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 of the presence of the spray cloud produced by the low volume machine. 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, although rapid to deploy and characterized by low operating costs, results in lower penetration of the tree canopy as compared with high volume applications, which may explain the shorter longevity of efficacy of low volume applications as compared with standard sprays.
The objective of this project was to investigate three questions: 1) what is the seasonal pattern of Ca. Liberibacter asiaticus (Las) prevalence in leaf tissue on a grove scale; 2) what are the flushing patterns of citrus and do the flushing patterns affect the prevalence of Las in Diaphorina citri or citrus leaves; and 3) what is the prevalence of Diaphorina citri carrying Las 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 Las in the Asian citrus psyllid (ACP) 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 ACPs are feeding. This project aims to determine if there is a relationship between the frequency of disease on branches and ACPs. Data collection for Las prevalence in psyllids and branches continues in three sites (Lake Alfred, Conserv II, and Lake Wales) for the second year. Phenology is also being collected for all three sites. One complication is that the post-doc responsible for the project has left the program. At this time the samples are being frozen for processing. We have reduced the total number of psyllids per sampling date because we determined that there smaller samples were sufficient for a robust statistical test.
Our objective for this project was to evaluate botanical compounds as repellents of Asian Citrus Psyllid (ACP). Botanical oils and their constituent compounds are promising as repellents of ACP because many plant chemicals have shown repellency in other insect systems, and it is likely that as natural products these compounds will be ecologically sound. For the first part of our research we are using a custom-designed arena (T-olfactometer) where psyllids can choose between two odors. The olfactometer consists of a 30 cm glass tube that is bifurcated into two equal halves with a Teflon strip forming a T-maze. Each half serves as an arm of the olfactometer enabling the individual ACP to make a choice between two potential odor fields. In the previous quarter, a majority of the odors we screened for repellency were individual compounds. Unfortunately, our results suggest that these compounds are not likely to be useful for control of ACP in situ because the required dosages would be too high and cost prohibitive. Therefore, we selected additional botanical oils (citronella, camphor, litsea, fir needle, and clove) based on their availability and cost (less than $100/kg oil) to use in olfactometer and toxicity assays. We have completed olfactometer assays of 5 mg of each oil against clean air. We found fir oil to be significantly repellent while camphor and clove oils were significantly attractive. Litsea and citronella oils did not appear to attract or repel psyllids when assayed against clean air. We are in the process of assaying these oils in the presence of citrus flush to further characterize any potential repellency. In addition to olfactometer assays, we have started contact toxicology assays to determine the LCt50 for each oil. In preliminary experiments we coated the inside of 20mL glass vials with 0.1, 1.0, 10, 100 ng of each oil, then 10 psyllids were added to each vial and left for 48 hours. After 48 hours, the mortality at each concentration was evaluated. Our preliminary data shows that clove oil is the most toxic and is able to killed nearly 100% of psyllids at the 10ng/mL concentration. While both citronella and litsea oils cause 100% mortality at 100ng/mL, the lethal concentration may be lower and will be determined in future experiments. Fir and camphor oils exhibited minimal mortality at 100ng/mL suggesting that these oils are not very toxic to psyllids. Future contact toxicology experiments will be conducted so that there are at least two concentrations for each oil where the mortality is greater than zero but less than 100%. From these data, LCt50 values can be calculated for each oil. In the upcoming months, we will finish both olfactometer and toxicology experiments and follow up with a feeding bioassay to determine if these oils deter psyllids from feeding on citrus leaves. Briefly, 5-10 psyllids will be added to agar plates containing a citrus leaf disc and inverted onto a filter paper. As psyllids feed, the honeydew produced will fall onto the filter paper. After 48 hours, the filter paper will be removed and the honeydew droplets will be visualized using a 0.2% ninhydrin in acetone solution. Honeydew droplets will be quantified for abundance and will be considered an indicator of the amount of feeding that took place.
The objective of this project was to investigate three questions: 1) How long does a leaf needs to be infected by Guignardia citricarpa before ascospore production can be initiated; 2) How does infection and colonization of leaves by Guignardia citricarpa occur and potentially showing how pseudothecia, the sexual spore producing structures, are produced; and 3) what is the interaction between the common twig colonizing pathogen Diaporthe citri and the black spot pathogen Guignardia citricarpa and whether they can co-exist to successfully sporulate on dead twigs. This project was initiated in August. The graduate student, Nan-Yi Wang, whose Ph.D. project this is, started his studies in Gainesville at the end of August and progressing well in classes. He is also conducting research while in Gainesville. He has designed a first round primers for the mating genes so that we can determine if G. citricarpa needs more than one mating type to form ascospores. This will be helpful for later in the project when we are looking for pseudothecia production. Nothing with homology to known mating genes was found with these primers so he is redesigning primers for another try. He has also been attempting to transform G. citricarpa with GFP. He has found that the fungus is very sensitive to hygromycin, a selectable marker. In several attempts, he has not yet achieved a transformant but is continuing to modify his methods. Part of the difficulty is getting the conidia to germinate after the transformation process which is very difficult. He will be starting the greenhouse experiment in next couple months with leaves collected from infected groves in South Florida.
The objective of this project was to investigate three questions: 1) How long does a leaf needs to be infected by Guignardia citricarpa before ascospore production can be initiated; 2) How does infection and colonization of leaves by Guignardia citricarpa occur and potentially showing how pseudothecia, the sexual spore producing structures, are produced; and 3) what is the interaction between the common twig colonizing pathogen Diaporthe citri and the black spot pathogen Guignardia citricarpa and whether they can co-exist to successfully sporulate on dead twigs. This project was initiated in August. The graduate student, Nan-Yi Wang, whose Ph.D. project this is, continues his studies in Gainesville this term and is making good progress in his classes. He is also conducting research while in Gainesville. We have redesigned the mating gene primers several times but have not found any products with homology to known mating genes. We are evaluating new strategies to approach this program. He has also been attempting to transform G. citricarpa with GFP. He has found that the fungus is very sensitive to hygromycin, a selectable marker. In several attempts, he has not yet achieved a transformant but is continuing to modify his methods. We are beginning another method and hope to have success soon. He will be starting the greenhouse experiment in next couple months with leaves collected from infected groves in South Florida.
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). Citrus leafminer mine density was assessed at one site (St. Lucie Co.) and was found to be lower in SPLAT-CLM treated plots compared with untreated plots. A primary goal of our field work during 2012 is to correlate disruption of trap catch with actual damage by assessing mine density. We continue to analyze results from 2011 field trials at two locations to determine optimal coverage patterns with the goal of reducing the amount of SPLAT-CLM applied while maintaining adequate mating disruption. It appears that certain combinations of treated and untreated rows resulted in a significant savings (30% reduction of product) with minimal loss of mating disruption (4% loss of trap catch disruption). A manuscript is being prepared with the results from these trials. A field trial is planned for January, 2012 through the spring to test the effect of SPLAT-CLM on overwintering populations of citrus leafminer in a commercial citrus grove. Two SPLAT-CLM applications are planned, the first to be applied on January 24 and the second in early April. Mating disruption of the moth will be evaluated weekly or biweekly, and leaf mining will be evaluated following each application. A multi-site validation trial is planned starting in April to test the efficacy of SPLAT-CLM applied according to treatment recommendations incorporating intentional gaps in commercial citrus groves to control citrus leafminer. Three groves will be treated with SPLAT-CLM. At each site, leafminer damage will be evaluated and compared between SPLAT-CLM and conventionally treated hectares. These applications are planned for April. Two sites have been identified in Charlotte Co., and a third site may become available in Indian River Co.
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. Yield data from various plots at one study site has been collected as an indicator of overall impact of HLB.
This project was designed to examine the potential disease control of citrus huanglongbing (HLB) by interplanting citrus with guava as previously demonstrated in Vietnam and Indonesia. Guava was shown to repel psyllid vectors and slow the disease, extending the economic life of plantings by several years. White guava trees were brought back to Florida from Vietnam under permit, propagated and both nursery and field citrus trees were assayed for HLB every 60 days, and have been assayed multiple times. Psyllid populations were monitored continuously ea. 2 weeks . Results: Guava/commercial citrus interplantings: with multiple replications were established but due to freezes and property sales these plantings were not viable and were discontinued. 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 2009/2010 winters affected the USHRL plots and caused a delay in the experiment. A final hard freeze during the 2010/2011 season killed most of the guava trees. Data analysis indicated no differences were observed among treatments, i.e., guava interplanted vs. non-interplanted plots prior to the final demise of the plots. Guava vs no guava nurseries: Two nursery sites, a guava protected citrus nursery versus an unprotected nursery, 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. HLB progressed more slowly in nursery plots interplanted with guava than in non-interplanted plots. The freezes discussed below did not adversely affect these nursery plots as they were more protected. Interpretation: Florida is actually a subtropical environment, prone to intermittent freezes and cool or cold temperatures. Whereas, Vietnam and Indonesia, where the guava effect seems to work, are truly tropical without such broad temperature swings. After freezes it takes a considerable time to either replant guava or for the freeze damage guava to recover. Even during cool weather guava trees are very sensitive and do not continue to flourish and grow. It is the new flush of guava which appears to be the best at producing ACP repellent volatiles. Cool or freezing temperatures inhibits volatile production and thus the citrus crop is left unprotected from ACP. While guava not be a viable deterrent as an intercrop, it still may be possible to identify individual volatiles from guava that might be useful under field applications as chemical applications. In mid-2011, we began examining more temperate, i.e., cold tolerant Myrtaceous plant species as citrus intercrops to determine If alternative Myrtaceous plants could be identified to be repellent to ACP. We abandoned this research when CRDF discontinued funding for this project.
We have continued to examine the latency period of Las in the psyllid by examining replication of Las in psyllid nymphs and adults. To examine latency in nymphs, ten adult ACP pairs (males + females) caged on young leaves of Las-infected ‘Valencia’ sweet orange plants. After a 5 d oviposition period, adult ACP were removed. Nymphs were allowed to develop on infected plants for varying acquisition access periods. Subsamples of nymphs were collected periodically and remaining nymphs were transferred to healthy or infected plants. Ten adults from each replicate were collected immediately after emergence and remaining adults were subsampled and transferred to healthy (uninfected) plants every 5 d, for 45 d. Similarly, latency in adult psyllids was assessed by enclosing one hundred newly emerged adults on Las-infected plants for various acquisition access periods. Subsamples of adults were collected every 5 d and remaining adults were and transferred to healthy (uninfected) plants. Quantitative real-time PCR (qPCR) is being used to to assess Las titers in all psyllids and recipient plants. Each experiment was replicated five times on different plants. Psyllid bioassays and testing are ongoing. In addition to examining psyllid latency and Las replication, we have continued experiments to assess psyllid suitability as a host for Las by examining the effect of endosymbionts on psyllid survival and transmission. Microinjections of psyllids with antibiotics are currently being used to clear psyllids of symbionts for fitness, acquisition, and inoculation bioassays comparing ‘natural’ verses aposymbiotic psyllids. Concurrently, we are developing breeding lines of psyllids to whether there is a genetic basis for vector efficiency.
Data collection from the 10-acre young tree protection multi-year trial continues. Since the October 2011 update, foliar treatments have been applied as planned on 3 separate dates (9 total applications since planting). Soil-applied neonicotinoids have been applied on two separate dates (5 total applications since planting). Leaf samples from plots continue to be collected at two week intervals for pesticide residue analysis. Psyllid and leafminer counts have been continued every two weeks. Psyllid populations continue to remain below detectable levels. However, leafminer damage has remained extremely high, particularly in the control and foliar-applied broad spectrum insecticide treatments. As a result, significant differences were present in the trees growth data recently collected that is most likely attributable to the severe damage caused by leafminer in certain treatments. As a result, in November, the entire block was sprayed with abamectin once to help get the leafminer population under control. 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. Laboratory bioassays with the psyllid deterrent material used in two of the treatments in the field trial were conducted to determine the effect on psyllid host plant selection and psyllid feeding behavior. Effects on host plant selection were examined using choice test with treated and untreated plants in the same cage wherein psyllids were released. In choice tests, psyllids overwhelming chose to land on and subsequently feed on untreated plants by a factor of 6:1. Effects on feeding behavior were examined using an EPG monitor which showed that psyllid feeding behavior was disrupted on plants treated with the deterrent such that phloem feeding did not occur. Additional experiments were conducted that point to a likely mechanism (explanation) for how this feeding disruption occurred. A third field trial comparing application methods and rates of neonicotinoid insecticides, was initiated in January. Given the overall low psyllid population in the plots at this time of year, the primary goal was to compare pesticide rate of uptake of the different application methods in the winter months which was determined by collection of leaves for analysis of pesticide residue in the plant. We also began work looking at the effects of climate (time of year) on the efficacy of pesticide applications. In January, foliar applications were made in the field to replicated plots. Treatments included an organophosphate insecticide, a pyrethroid insecticide and a neonicotinoid. At 1, 7, 14, 21, and 28 days after application, adult psyllids will be caged on treated plants and then later recovered to determine the actual residual activity of these pesticides. This will be repeated throughout the year to determine if the duration of efficacy changes with the season.
The CHMA assistant position has been advertised twice to ensure all qualified applicants have been reached. Interviews for three candidates have been scheduled. No funds have been spent from this grant to date. No further action to report at this time.
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. We applied the first round of LD25 applications on 7 Dec. This month we are testing a sample of the population with the LD80 to determine if resistance has begun. If resistance is not present, we will again treat our psyllid populations with LD25 applications of their respective insecticide. The plan is to evaluate rate of resistance induction in caged psyllids using the LC25 dose, then using discriminating dose bioassays to monitor response to 5 treatments: the premix, rotation, each insecticide alone, and a check. Later, insecticides will be withdrawn and return to susceptibility evaluated. 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. In the process we have found what we believe to be 5 different leafminer species attracted to the pheromone lure. Therefore we embarked on an investigation using of bucket pheromone traps to collect identifiable specimens in different locations. Representative moths will then be keyed to species by a taxonomist and subject to DNA bar coding. A botanist has identified the species of plants where mines are found, so that we have a better indication of the species present near the pheromone traps. 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 to rear the parasitoid Citrastichus phyllocnistoides and support a program for monitoring CLM susceptibility to key insecticides. And, this spring we will use a diagnostic dose to monitor resistance in field populations of CLM exposed to intensive versus modest insecticide use. We are collaborating with the DPI CHRP program to evaluate results of the cooperative (area wide) ACP management program, in SW Florida, now the Gulf CHMA which uses a sampling protocol of 50 taps/block. We now present this data spatially and temporally by way of interactive GIS maps available on our website http://swfrec.ifas.ufl.edu/entomology/extension/chma/ for growers to use.
Low volume (LV) aerial and ground sprays have become an important method of application in Florida citrus. We continue our evaluations of LV application of 435 horticultural mineral oil (HMO) which has shown promising results the last 3 years. This report documents updated results from the fifth trial begun on February 2011 in a 10.9 acre plot of ‘Valencia’ orange in Lee County. The efficacy of low volume spray spray of 435 horticultural spray oil (HMO) with the Grower Standard and an Untreated control are being compared. This trial is the first with sufficiently high ACP populations to assess the ability of LV oil sprays to provide suppression. Three sprays of 435 oil (12, 20 Oct @ 2gal/ac; 3 Nov @ 2gal/ac) have been completed since the last report. No insecticide sprays have been applied to the Grower Standard plots since the last report. All plots will receive a dormant spray this month of Danital on 9 Jan in conformance with IFAS recommendations. Mean adult psyllid populations over the last 3 months were 0.11 +/- 0.023, 0.07+/- 0.023 and 0.203+/-0.023 for the Grower Standard, Oil, and Untreated Check respectively. The Grower Standard (p = 0.005) and Oil treatments (p < 0.0001) had significantly fewer psyllids than the Untreated Check. Thus, the low volume oil treatments are suppressing ACP as effectively as the Grower Standard. Resets were sampled in Oct for percent HLB (n= 40, Grower Standard; n = 34, Oil; n = 39 Untreated). Results showed no significant differences between treatments and incidence of infection was low (<3%). There was also no difference in Ct titer with values ranging from 35 for Untreated to 37 for Oil treatments. Citrus leafminer damage assessments for Oct were unobtainable due to low density of flush. There were two peak flights since the last report (13 Oct and 15 Nov). Moth flight in the Oil treated plots was significantly (p < 0.05) lower than the Grower Standard and Untreated plots for the sixth generation (10 Nov) in spite of higher flush density. This result indicates that oil is contributing to CLM egg and larvae mortality. Monitoring of traps is continuing over winter to follow moth phenology and determine the effect of treatments on CLM populations.
Research targeting the development of a new Asian citrus psyllid control strategy based on blocking salivary sheath formation was advanced in two areas. First, Compositional analysis has shown that this sheath is synthesized as a two part structure each with different composition. The first part is a flange that is initially secreted on the surface of the leaf. This secretion is highly autofluorescent and sensitive to alkaline treatment. Once the leaf is penetrated, the sheath composition changes to a non-autofluorescent structure that is more resistant to alkaline hydrolysis. This sheath section is primarily carbohydrate in structure. Compositional and structural research will be completed during the next year and this information will be used to identify ways in which to inhibit its formation. Second, an artificial diet bioassay has been used to screen a positional scanning peptide library to identify peptide inhibitors of salivary sheath formation and/or psyllid feeding behavior. Initial screenings with highly complex decapeptide mixtures has shown activity against feeding and salivary sheath formation. Using a positional scanning method developed by Torrey Pines Institute for Molecular Studies, the complexity of these decapetide libraries is being deconvoluted to identify the specific peptides responsible for the biological activity. During the next year, specific peptides will be identified. Once this is identified, this sequence will be used to construct a synthetic gene encoding this peptide for use in transgenic plant construction and will be used to test topical application strategies to block this feeding process
The ‘Hamlin’ orange block at SWFREC receiving the Boyd cocktail treatments was harvested in December before Christmas. By harvesting in December we avoided the January 4, 2012 Freeze in Immokalee that we experienced 25 degrees F. Fruit yield on 8.2 foot tall trees from the better treatments averaged about 2 boxes per tree. The better treatments were those that contained Macro nutrients as DKP + KNO3, micro-nutrients Mg, Mn, Zn, Mo, B, and a Phosphite. Fruit and juice quality from the ‘Hamlin’ trial at SWFREC has been sampled and will be reported in the next quarterly report. Citrus canker was a significant factor in our trial this year for the first time. Fruit loss among treatments varied from 40% in less vigorous trees to between 60% to 75% fruit loss in treatments stimulating more vigorous growth. Treatments with macro-nutrients from only spray grade foliar applied KNO3 + the micro-nutrients had less loss of fruit to canker. The less vigorous trees with less flush carried the larger fruit load with less fruit drop in the presence of citrus canker. The highest yield per tree for Hamlin 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. 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 of 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. Except for 14 Dec, psyllid populations in the nutritional only plots reached the 0.20 threshold during each sampling period 6Oct – 29Dec. Insecticide and Insecticide+nutritional had significantly (P< 0.05) fewer adult ACP than control or nutritional only on dates 6, 20 Oct; 3 Nov, and 29 Dec. All three treatments had significantly (P < 0.05) fewer ACP than control on 1, 14 Dec. Since our last report we have not sprayed any treatments, but will be applying a dormant spray of Danitol in plots designated for insecticide treatment on 15 Jan. Resets planted (June 2010) were tested for HLB detection (19 Oct) but showed no significant treatment effect on percentage PCR positive for HLB (20% - 52% infection). For adult trees (9 years old), a lower incidence of HLB (80 and 86%) was seen for nutritional and insecticide plus nutritional treatments compared to the untreated (98%) or insecticide only (94%) plots. For adult trees, Ct values were significantly lower for Untreated (24.34) and Insecticide only plots (24.83). However, there were no significant differences between the insecticide plus nutritional plots (24.83) and nutritional only plots (26.81). For the resets, there were no significant differences in Ct values (range 28.88 - 31.80).
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