Background information The objective of this project is to quantify the relative effect of copper (Cu), windbreak (Wb) and leafminer control (Lc) on the spatial and temporal progress of Asiatic citrus canker (ACC) under conducive conditions for epidemics and disease loss. The experiment is set up in a 10 ha plot planted with Valencia sweet orange grafted on Rangpur lime located in the municipality of Xambre, Parana, Brazil. The different treatments are the combination of up to three control measures (Cu, Wb, Lc) or none. The presence or absence of windbreak represents a plot. The presence or absence of copper sprays and leafminer control represents a subplot. Each subplot is composed of 112 trees. Each of the eight treatments has three replicates. Cu treated plots are being sprayed with Kocide (35% metallic copper) at 1 kg metallic copper/ha every 21 days. Lc is being performed with application of abamectin at 150 ml/ha every 21 days. Casuarina is used as a natural Wb around the plots. Disease evaluations started in December 2013 and include percentage of trees, leaves and fruits with ACC symptoms, and fruit yield. In the second season, the assessment of fruit drop was included. The present CRDF funding will cover the period of November 2015 to October 2016. Previous results Trees and leaves: Up to November 2015 (22 after ACC epidemics begun), incidences of diseased trees in the plots with complete management and no management reached 43.8 and 97.9%, respectively. The incidence of leaves with ACC in the canopy of affected trees dropped for all treatments and reached 0.6 and 2.5%. Fruits and yield: In the first harvest (September 2015), the incidences of symptomatic fruits from trees treated with the tree measures and none were 3.8 and 58.5%, respectively. Production of trees revealed the same trend observed for other assessments. Fruit yield of trees under complete management (40 kg/tree) was 186% higher than control trees (14 kg/tree). Latest results (February 2016 – 25 months of epidemics) Trees and leaves: Incidence of trees with citrus canker reached near 100%, except for trees with complete management (85%) or with the combination of copper sprays and leaf miner control (76%). Incidence of leaves increased since November 2015 and reached 5.6% for unmanaged trees and 1.1% for trees under complete management. Fruits and yield: Incidence of fruits with citrus canker on the trees reached 50.1% for the unmanaged trees and 5.8% for trees under complete management. Likewise, fruit drop per tree is, up to the present report, at 3.9 and 22.2 for unmanaged and managed trees, respectively. Harvest is planned for August-September 2016. All other treatments are showing intermediate results. Copper is more important for retarding disease dissemination among trees, whereas windbreaks are more important for reducing incidence of leaves with citrus canker on affected trees.
This project was initiated in 2014 and is focused on understanding the effect of nutrients applied through foliar fertilization programs (FFP) on HLB-affected trees in the Indian River marketing district. Two research trials have been established in commercial mature grapefruit groves in St. Lucie County and a young tree trial is being conducted at the UF-IRREC grove. Grove 1 has ~25 years old of ‘Flame’ grapefruit on Swingle rootstock. Grove 2 utilizes ~7-year-old ‘Ruby Red’ on Sour orange trees. Trial 3 is looking at the effect(s) that foliar fertilizers have on young tree growth and their ability to protract HLB disease symptoms in 2-year-old ‘Ray Ruby’ grapefruit on Kuharske rootstock. Combinations of macro and micronutrient treatments initiated on all three trials in February 2014 and applications have been made quarterly since. During the 2014 and 2015 production seasons, the population of the Asian Citrus Psyllid present in the groves were recorded using sticky traps. The monitoring shows a consistent decrease in the psyllid populations from 2014 until the recent counts in March 2016. The latest data had an average of only 0.02 psyllids per trap. However, the decrease in the psyllid population has not had an effect in HLB titer in the trees. The real time PCR analysis in trees exposed under each treatment has revealed a constant status of tree infection. The latest results (Jan 2016) showed a 100% presence of HLB in trees used in the experiments at the two commercial groves. There have not been any significant differences in the tree growth among treatments durig the 2 seasons in terms of tree volume or canopy density (a>0.05). Nonetheless, the canopy density (evaluated through Leaf Area Index (LAI) measurements) showed a trend of lower LAI in the control treatment compared to the rest of the treatments (receiving foliar applications) in one of the commercial groves. After two harvests, there has been no difference in juice quality parameters among treatments. There has, however, been a significant increrease in the percentage of medium size fruit (sizes 36 and 40) of trees treated with urea, di-potassium polyphosphate, and potassium phosphite compared to the control. This increment is reflected in an increase of 37% in the Gross Packed Value (GPV). (The GPV is the value of fruit when sold from a packinghouse and calculated by the number of fruit produced in each pack size and value of each size of fruit at the time of harvest). It is important to note that, although the other foliar treatments did not have significantly higher GPV compared with control (a>0.05), the GPV of these treatments were all 13%-33% higher and ranged from $85 to $103 per tree, compared to an average GPV of $75 in the untreated control trees.
The objective of this project is first to identify a Bacillus thuringiensis (Bt) crystal toxin with basal toxicity against Asian citrus psyllid (ACP). The toxicity of the selected toxin will then be enhanced by addition of a peptide that binds to the gut of ACP. This peptide addition to the toxin is expected to enhance both binding and toxicity against ACP. The identification of Bacillus thuringiensis strains with basal toxicity against ACP was conducted by means of a series of bioassays using trypsin-activated toxin as described in previous reports. A new logistic regression analysis indicated that seven isolates showed promise with ACP mortality at 500ug/ml relative to control treatments. A single strain was selected for further analysis and individual toxins expressed by this strain were identified by LC-MS/MS analysis. Two individual toxins shown to have toxicity to ACP in bioassays were selected for modification with gut binding peptide 18. These modifications are now underway. Honeydew production data collected during the course of ACP bioassays both with toxin mixtures from Bt strains and with individual toxins, were analyzed to determine whether ACP died from starvation. Toxin-mediated damage to the gut epithelium can result in an anti-feedant effect. Honeydew excretion was monitored on the third, seventh and eleventh day of ACP feeding with the relative quantity of ACP excretions present in each feeding chamber recorded. Based on these data, toxin mixtures derived from four of the Bt strains had an anti-feedant effect on ACP, resulting in mortality from starvation.
Using choice and no-choice probing behavioral assays, we studied the orientation of adult Asian citrus psyllids (ACP) to chemical odorants from a distance and the interaction between visual attraction to yellow and olfaction or gustation. We confirmed that the 3-component blend of 3.5 formic:1.6 acetic acid:1.0 p-cymene is the optimal blend of those compounds to maximize ACP probing behavior. The yellow color acts as a long range cue that attracts the psyllids to the point of alighting on a yellow wax substrate. Probing is thought to be a reflexive action that is initiated upon landing on any substrate. Once the psyllids initiated probing on wax beads containing odorant blends, the 3-component blend had a stimulatory effect that increased the number of probes along with the size and complexity of the salivary sheaths left behind in the wax substrate. To support the hypothesis that increased probing was due to phagostimulants perceived by mouthparts and not olfactory cues perceived by antennal receptors, a no-choice experiment was performed to study ACP probing behavior through plastic film into wax beads thereby isolating antennal receptors from the odorant or tastant cues. Yellow w wax beads were prepared without tastants or with the 3-component blend (3.5:1.6:1 formic acid: acetic acid: p-cymene). Wax beads were covered with a polyethylene/polybutylene plastic film (Saran Cling Plus Wrap, S. C. Johnson & Son, Inc., Racine, WI, USA) to minimize the potential for olfaction or contact chemoreception associated with antennal tapping behavior. The film is impermeable to water and we assume to the larger molecules of the phagostimulant blend. Fifty D. citri adults were placed in each of four cages for 21 h. Each cage contained 5 cover slips with yellow wax beads prepared with or without tastants and with or without a covering of plastic film. The wax beads were collected, stained with Commassie Blue and scored for salivary sheaths. Stained salivary sheaths were removed from the wax substrate by gently lifting the plastic film and separating it from the substrate. The length of the stained salivary sheaths adhering to the plastic film was measured under a stereo microscope. Ten salivary sheaths were measured for each treatment (plastic film over wax beads without tastants and plastic film over wax beads with the 3-component tastant blend). The number of salivary sheaths produced on the plastic film were counted. The length of salivary sheaths were measured using a Cell Sens Dimension software (Olympus Corporation, Tokyo, Japan). ACP adults probed more on yellow wax beads containing the 3 component blend compared with wax beads without tastants. There was no effect of plastic film on the number of salivary sheaths observed in the wax beads. The mean number (+ SEM, n = 10) of salivary sheaths observed on yellow beads without tastants was 47.5 + 5.3 and on yellow wax beads containing the 3-component blend was 94.5 + 8.5 sheaths. Microphotography of the salivary sheaths that adhered to the plastic film revealed differences between sheaths recovered from beads containing the 3-component tastant blend and sheaths recovered from beads without tastants. Salivary sheaths recovered from beads containing tastants were 4.5 times longer (208 + 22 m) compared with sheaths recovered from beads without tastants (46 + 7 m). Sheaths recovered from beads with tastants were longer with filamentous portions extending beyond the thicker initial sheath. We conclude that the blend of 3 tastants is a phagostimulant that acts through perception by chemoreceptors located on the psyllids mouthparts. George, J., P. S. Robbins, R. T. Alessandro, L. L. Stelinski and S. L. Lapointe. 2016. Formic and acetic acids in degradation products of plant volatiles elicit olfactory and behavioral responses from an insect vector. Chem. Senses doi: 10.1093/chemse/bjw005
Objective 1, investigating the specificity and efficacy of immune priming response in ACP to pathogenic bacteria, is nearing completion and will be analyzed during the next quarter. Subsequent experiments to address the effects of non-pathogen immune priming to pathogenic bacteria are underway, and should be nearly complete by this summer. The second project objective, to determine whether double strand RNA (dsRNA) uptake can result in immune priming in D. citri, we will be conducting RNAi experiments on D. citri adults of a CLas-free laboratory colony. dsRNA of genes that exist (e.g., V-type proton ATPase) or do not exist in D. citri (a bacterial GFP gene) will be used for this experiment. Briefly, primers targeting GFP fragments in plasmid pCMV-GFP (Matsuda and Cepko 2004) or a vATPase gene fragment of D. citri [based on sequences determined in a published work (Vyas et al. 2015)] wereover time. Insect mortality will be recorded every 24 h. Depending on the results, we may also attempt to determine the effects of RNAi-treatments on D. citri transmission of CLas in the coming months. designed. The primers were synthesized with T7 promoters added to the 5′ ends (Table 2). Amplification products obtained by using these primers and their template DNA will be purified using the QIAquick PCR purification kit (Qiagen, Valencia, CA). Purified amplicons will be used for dsRNA synthesis using the MEGAscript RNAi kit (Ambion, Austin, TX). RNAi treatments will be conducted by feeding D. citri with 30% sucrose solutions including 100 ng/ul of each type of dsRNA, using previously described methods (Wuriyanghan, Rosa, and Falk 2011) with slight modification. For the negative control, products of a non-template RNAi synthesis reaction will be used. The insects will be kept on the diets for 24 h. RNAi-treated insects will be moved to caged citrus plants (var. “Swingle”) for one week. The insects will then be challenged with Serratia marcescens by microinjection of bacterial suspensions (~107 cells/ml) using a FemtoJet Microinjector (Eppendorf, Inc., Fremont. CA). Effects of RNAi-treatments on Serratia marcescens growth will be determined by qPCR using primers specific to this bacteria (Joyner et al. 2014). Insects will be sampled every 48 h, over two weeks. A separate cohort of the challenged insects will be kept on the citrus plant and monitored for their survivorship
A second thermal treatment was applied to trees in our field assay during late November 2015. Adults and nymphs were enclosed in mesh sleeves on trees for acquisition feeding approximately 5 weeks following treatments during early January and March 2016. Insect and leaf samples were collected after 10d of acquisition feeding or upon adult emergence to assess adult and nymph acquisition, respectively. These samples are currently undergoing nucleic acid extraction and PCR to determine CLas titers. A second field site, consisting of a commercial grove in Lake Wales, was added to our project this quarter. We collected leaf samples this site for quantification of CLas titers. Trees are expected to be treated with thermal therapy in the next couple of weeks, and we’ll do an adult acquisition trial on those in about 2 months. led environmental chamber will be used to apply heat treatments to trees for use in subsequent acquisition experiments For the lab assay, we evaluated a fungicide treatment to improve the survival of the potted trees. Trees in the greenhouse tend to get secondary infection following thermal therapy, so once we have a method for improving the tree lifespan post treatment, laboratory thermal therapy assays will begin. Trees were inoculated with CLas three months ago, and will be tested using PCR during late March to confirm that they are positive prior to use in the lab assay.
We built a new wind tunnel adapted for Asian citrus psyllid; this wind tunnel has been controlled for regular air flow and absence of air disturbance. We tested the effect of wind direction on psyllid ability to find a young emerging leaves ( flush ) introduced in the wind tunnel. In the absence of wind, or when they have to move in the same direction than the wind (downwind) psyllids found the introduced flush at a 30% rate. On the contrary, when psyllids had to move against the wind (upwind) only 11% settled on the flush. This may indicate that psyllids are reluctant to move upwind. Also the damaged flush in the wind tunnel may not release enough volatiles to attract psyllids. We will pursue our work with the wind tunnel with higher dosage of volatiles and different wind speeds to better understand psyllid movement depending of wind direction. Additionally, we developed a pressure chamber to measure psyllid dispersion depending of controlled pressure changes. Our pressure chamber consists of a glass chamber with controlled air flows. Psyllid are placed in the box within the chamber, and the pressure of the chamber is manipulated by changing the flow of air pushed in the chamber. When the pressure stabilized the box is open with a remote system and the number of psyllid captured by a small band of yellow sticky trap hanged on the top of the pressure chamber are counted. With this system, we were able to study the effect of barometric pressure changes on psyllid dispersal abilities. We found that psyllids responded to barometric changes rather than to different stable pressure. Psyllids were not more active at 1009 mbar or at 1022 mbar. However, we found that psyllids tend to disperse more as barometric pressure increased, and were less mobile when barometric chamber dropped. For instance, with an increase of 2.4 mbar per hour we captured 7.2 psyllid per hour, whereas with a decrease of -2.4 mbar per hour we only captured 4 psyllids per hour.
The objective of this study was to determine the contact toxicity data for flupyradifurone to Asian citrus psyllid Diaphorina citri using a vial bioassay. The insect population of D. citri used was reared in a greenhouse at the Citrus Research and Education Center, University of Florida, Lake Alfred, FL. The strain has been reared without exposure to insecticide. The tested insecticide was analytical grade flupyradifurone (99.5%) obtained from Chem Service Inc. For contact toxicity, female and male D. citri adults were placed in 20ml scintillation vials that had been treated with six concentration and replicated five times of flupyradifurone. The 24 hour contact toxicity LC10, LC25, LC50, LC75 and LC90 were 0.001, 0.02, 0.38, 8.25, 130.13 ng/ l, respectively. We also investigated the effect of lethal and sublethal doses of flupyradifurone on the feeding behavior of D. citri adults. Five adult psyllids were placed in petri dishes with citrus leaf discs treated with the LC10, LC25, LC50, LC75 and LC90 concentrations of flupyradifurone. Each concentration was replicated five times. The amount of feeding was evaluated by the amount of honeydew produced as visualized by exposure to nynhydrin at 48 hours post treatment. D. citri that fed on citrus leaves treated with lethal and sublethal concentrations of flupyradifurone excreted significantly less honeydew (8%-83%) comparted with control in a concentration dependent manner suggesting an antifeedant effect of flupyradifurone. Finally we conducted settling bioassay to determine if citrus treated with flupyradifurone effects host choice. Citrus flush was sprayed with a solution of flupyradifurone at concentrations equivalent to the LC10, LC25, LC50, LC75 and LC90 and placed in cages. One hundred psyllid adults were then introduced into the cage and number of psyllid on treated and untreated flush were counted at 24, 48 and 72 hours post-treatment. There was no significant difference in the number of psyllid on treated flush compared to untreated flush at 24 and 48 hours. However, there were significantly fewer adults on treated flush at 72 hours compared to untreated flush. The results of these experiment suggest that Asian citrus psyllid have reduced feeding on plants treated with sublethal concentrations of flupyradifurone and this may potentially decrease the capacity of D. citri to successfully acquire and transmit the HLB causal pathogen. Flupyradifurone could be an effective tool for rotation in insecticide resistant management programs.
December 2015 The objectives of this proposal are 1) To determine the temperature and relative humidity optima for Guignardia citricarpa pycnidiospore infection and production on citrus twigs, leaf litter, and fruit; 2) To determine the relative potential of Guignardia citricarpa to form pycnidiospores on citrus twigs, leaf litter, and fruit; 3) To determine whether Guignardia citricarpa can survive and reproduce on citrus debris on grove equipment. Experiments to confirm initial relative humidity findings continue. The most recent set of twigs inoculated gave inconclusive results. Very few conidia were formed and mostly spermatia were formed. Pycnidia did not form as expected. We are trouble shooting and expect to try again in the near future. Planning of further experiments is underway. A site has tentatively been found to conduct field experiments of inoculum potential and some preliminary work is underway. We are testing ideas for collecting spores in the lab and in the field Two types of disinfectants approved by the Florida Department of Agriculture and Consumer Services/Citrus Health Response Program (FDACS/CHRP) were tested for their effect on spore germination in Phyllosticta citricarpa. These disinfectants are quaternary ammonium and sodium hypochlorite. All of the FDACS/CHRP approved quaternary ammonium products contained the same active ingredients in the same concentrations. Therefore two representatives of the approved products were tested. Our preliminary tests for quarternary ammonium indicated that spore germination was reduced to zero at rates as low as 5 ppm. In our study treatments used are: 20, 10, 5.0, 2.5, 1.0, 0.1, and 0 ppm. Preliminary tests with bleach indicated that spore germination was reduced to almost zero at a concentration of 82.5 ppm. Concentrations being evaluated are: 8250 ppm, 825 ppm, 82.5 ppm 8.25 ppm and 0.825 ppm. Trials for both products are currently in process and each product has been tested at least once on five different P. citricarpa isolates. Testing is done using three psuedo-replications per treatment and all treatments will be repeated twice.
December 2015 The objectives of this proposal are 1) to determine if a) leaf litter biodegradation treatments reduce Guignardia spp. pseudothecia and improve control afforded by routine fungicide applications; b) if biodegradation is affected by the current fungicide application practices; and c) whether the biodegradation treatments will affect current citrus best management practices (BMP); 2) to determine the seasonal dynamics of leaf litter inoculum load in varying management regime intensities and how environment affects pseudothecia production in the leaf litter; 3) to test if the resistance to black spot in the leaves and fruit in sour orange is correlated and under simple genetic control through laboratory and field testing of progeny of sour orange crosses in both Florida and Australia. In the large field trial, there was a greater amount of G. citricarpa DNA found in 2015 leaf litter so that while there was more G. mangiferae than G. citricarpa, it was less than 10 times. In 2014, there was no pattern in the number of leaves with Guignardia structures over time in any treatment but in 2015, the % leaves with structures increased until the third collection date and the started to decline. In 2015, the treatment with the least number of leaves with structures was urea over all. In 2015, the pattern of structure formation was consistent across treatments and over all the treatment with the fewest structures was urea. There was greater G. citricarpa DNA in the control whereas for G. mangiferae there was more DNA in the soilset treatment. The bagasse field trials confirmed the laboratory experiments that bagasse increased the leaf decomposition rate compared to nothing or urea. Greater soil moisture also accelerate leaf decomposition. The manuscript preparation is still continuing. Collection of leaf samples from the grove in Immokalee has continued biweekly. Each batch of samples contained 40 samples of 25 leaves collected below 40 trees. Leaves were examined under microscope to check for fructification of Phyllosticta spp. Leaf portions without fructification were discarded and the remainder were immersed in 0.02% tween20 to collect conidia and ascospores. Conidia and ascospores produced in leaf litter were quantified, weather data were collected from FAWN. Data collection is continuing and some of the qPCR data has been processed. In 2014, very little G. citricarpa DNA was found overall while G. mangiferea was high but, substantially more G. citricarpa DNA was detected in the 2015 collections. In Australia, confirmation of the ascospore production results continues. Inoculations of fruit are underway in the field but no symptoms from this year. From the 2014 inoculations, there are some promising crosses that did not form any lesions and no Guignardia citricarpa was isolated. They are repeating the fungicide work to confirm previous results. They are also continuing to sample leaf litter in two groves in Queensland mandarin growing region.
December 2015 The objectives of this proposal are 1) Determine the base line level of Guignardia citricarpa sensitivity to fungicides registered for disease control in citrus and evaluate new products for efficacy against G. citricarpa in vitro; 2) Conduct and improve implementation of spray trials for efficacy of registered products for citrus and to evaluate novel compounds in the field; 3) Optimize field evaluation of control measures through analysis of the spatiotemporal disease progress utilizing past and current field data of the outbreaks to gain knowledge on the incidence, severity and rate of the epidemic and assess the fungal population to increase the likelihood of successful field research and 4) Evaluate products and treatment conditions for postharvest control of citrus black spot. This quarter we accomplished: Objective 1: Manuscript preparation continues for the DMI fungicides. The assays with two SDHIs (fluxapyroxad and fluopyram) are on-going. Spore germination experiments with Cannonball and Vanguard are continuing. Manuscript preparation for the mycelial assays is on-going. Objective 2: Fungicide trials were initiated in 2015. Since July 2 applications were made for the fungicide trial. Data collection is underway Objective 3: Data collection is underway. Objective 4: Manuscript preparation is in progress; potentially with minor follow-up experiments to address any weaknesses in the data.
The objective of this project is to determine if various combinations of ground and foliar applied fertilizer nutrients, coupled with psyllid control, can rejuvenate young 3-year old HLB-symptomatic trees in a grove with 14% HLB incidence, allowing them to grow and bear an economically viable yield of quality fruit for juice processing. The field experiment was established in a commercial 58 acre-grove of 3-year-old ‘Valencia’ / Kuharske Carrizo trees using a combination of three different foliar and three different ground applied nutritional programs. Factorial AxB treatments consist of A) ground-applied: 1) Liquid/dry+Ca (‘BHG standard’), 2) Liquid+Ca, 3) Liquid/dry-Ca B) foliar-applied: 1) ‘BHG standard’-Ca, 2) ‘BHG standard’+Ca, 3) ‘Prescription'(+Ca). The prescription treatment was designed to be dynamic, customized for optimization, with feedback for development based on frequent leaf tissue analyses, visual symptoms, and the growth of the tree canopies and yield. There are six replications of the treatments, with two being pure replications. By the time the project was approved and we began treatments, the HLB incidence was already approximately 30%, and all HLB-symptomatic trees showed severe canopy decline. In the three following years, HLB incidence rapidly increased to near 100% by the third year of the experiment, and yet the severity of HLB symptoms decreased steadily so that by year two, HLB symptoms were difficult to identify in the grove. At the end of the project period, all treatments continued to perform equally well, which was quite difficult to comprehend given that the grove is practically 100% HLB-affected. Yields per tree have increased from year to year, averaging 1.14 boxes/tree for the 2014/15 season, and passing the juice quality requirements for harvest. Unfortunately the commercial block was set widely at only 151 trees/acre, resulting in only 172 boxes/acre at age 6 years. Future higher density plantings (300-500 trees/acre) of similar HLB-affected trees responding favorably in the same way could potentially realize a respectable 342-570 boxes/acre. The lack of experimental treatment response in this project was unexpected and disappointing. However it did serve a very important purpose in demonstrating that the reason for the inconsistent performance of HLB-affected young groves in Florida lies more in the soil and water of the site or the basal management level used in the grove than in the multiple applied enhanced nutritional programs being used. The most advanced nutritional treatments often will not elicit a response on HLB-affected trees on one (unresponsive) site and yet the simplest standard grove fertilization will be sufficient on another (responsive) site. Obviously complete absence of grove fertilization will cause rapid decline and collapse of HLB-affected trees on any site. In this study site we could not identify any special soil amendment, pesticide or fertilizer that had been used before or during the experiment, that could explain the complete recovery of HLB-affected trees in the Valencia block. It is noteworthy that the grove is irrigated primarily with surface (pond) water, but that does not account for the initial poor condition of HLB-affected trees in year 1 of the project, and in the three preceding years before the project began. This experiment site and others with similar rehabilitation success of HLB-affected trees may contain important information waiting to be discovered, specifically the site conditions (soil and /or water) that permitted the sustainable recovery and reversal of HLB symptoms, putting the grove back on track to economic production. The Blumberg grove will be one of the 24 survey sites to be used in subsequent studies. By spreading the survey over a wide range of responsive and unresponsive grove sites, we aim to identify the key components responsible and then home in on developing a remedy that can be replicated in any HLB-affected grove in Florida.
The low concentrations (1/4 rate) of Citrus Fix (2, 4-D) and MaxCel (Cytokinin) with or without ProGibb (GA) every 45 days to Hamlin orange trees in central Florida for the 2015-16 growing season did not reduce fall leaf drop nor preharvest fruit drop of HLB infected trees. Total leaf drop per tree averaged 249 leaves for the Control trees and the treated trees had 3 % more for the MaxCel + 2, 4-D or GA treatments and the combined treatment of all three had 4 % less loss of leaves. Percentage fruit drop was equal to the Control (22.5 %) or higher by one or four %. Two additional tests on Hamlin trees of 2, 4-D + GA compared top Headline, Priaxor or a Control did not affect fruit drop at either site. Average fruit drop for both 1 and 3 (decline) rated trees for all treatments ranged from 27.1 to 29.6 % at one site and 22.5 to 24 % at the other site. Highest rates of fruit loss occurred in October (2 week periods) and decreased to about 1/3rd to 1/4 of these after November 4th at both sites. The test comparing GA rates on root growth of HLB infected Valencia trees was completed and had less effect on root growth than the test on healthy trees. New growth of roots from the bottom third of the pots averaged 25 and 35 cm at 4 and 8 weeks for the highest GA level (.1 gm) while the controls averaged 14 and 20 cm. For the middle of the pot the best growth was for the lower concentration (0.00125) but only at 8 weeks, 18/27 versus 23/23 for the control. For the top third of the pot, there was little differnce between GA concentrations and the control (22/30 versus 20/36). At the end of 8 weeks the healthy trees has 160 gm of roots while the HLB control plants had 100. The best GA treatment (.0025 gm) had 132 gm versus 100 for the control. For dry wt the 0.00125 gm/plant was best and had 22, 18 and 26 % more root, stem and leaf weigth, respectively, than the control. Results were not as consistent as the previous test with healthy plants, but variability due to level of HLB infection probably is responsible. It does appear that there was a tendency for GA to improve root growth within the first 4 to 8 weeks of treatment.
The up-graded on-line ‘Citrus Flowering Monitor System’ has been tested extensively by grower and extension use, plus in making advisories to growers. Five advisories were prepared based on the models predictions by the end of December 2015. The totally abnormal weather pattern this past fall and early winter, essentially no cold induction before January 1st, has made advising and deciding on flower bud enhancement a large challenge for the Florida citrus industry. The fist estimates of vegetative flush will be added to advisories in February along with 5-10 % open flower estimates. In analyzing the data from last years bloom, some deficiencies in data collection were discovered that will be corrected in this springs data collection.
Collection of trap catch and leafminer infestation data continued apace in citrus groves at three locations that received a second year of application of DCEPT CLM . Groves were monitored for disruption of trap catch and for citrus leafminer damage and populations. Citrus flush was sampled twice during 2015 and exhaustively evaluated for the number of mines present and the developmental stage of the leafminer larvae present within the mines. We also tabulated the degree of infestation by leaf and shoot. Analysis of these data was delayed due to hiring difficulties at USDA headquarters. Results will appear in the next quarterly report for this project. In general, it is clear from field inspections that biological control of the citrus leafminer by the introduced parasitoid Ageniaspis citricola has been eliminated from the three test locations . We assume this is due to the elevated number of insecticide applications made to control the Asian citrus psyllid, vector of the citrus greening pathogen. It is now rare to observe parasitized leafminer larvae at those locations. The unfortunate result for growers is that populations of citrus leafminers have increased dramatically, making the successful implementation of mating disruption more difficult. Nonetheless, tat least one grove manager in our test study has been impressed with the suppression of leafminer populations in blocks receiving the DCEPT CLM product and has expressed interest in continuing to participate in future trials if the cost of the product is reasonable. At another location, the decline of mature groves due to greening is seen to eclipse the benefit of CLM control.
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