Jan 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. The small plot work of the leaf litter was completed and the data processing has begun. Molecular data is being collected to match with counts. A large field trial was initiated and leaf litter was collected from the plots for evaluation. The evaluations are completed and being compiled. To look at the effect of bagasse, a controlled experiment portion was conducted twice. It involved an in vitro study of the decomposition of citrus leaves and inactivation of G. citricarpa by various amendments including bagasse including the microbial consortium of fungal and bacterial strains to aid in the decomposition of bagasse and of citrus leaves. After inoculation of the leaves, G. citricarpa conidia were observed on D1 but not D15 and no isolations were successful either day. There was a significant difference in the amount of leaf decomposition but not the rate with the control have the least decomposition and the bagasse treatment the most. Collection of leaf litter material continues in Florida and is being collected every two weeks from a grove with moderate black spot incidence in the previous season. Some data summary has begun and we are finding much lower structure numbers and incidence in the leaf litter. This is likely because the disease pressure is much lower and more scattered in Florida than it has been in Australia historically. We expect to find the same trends but since our climate is very wet, there may be differences in leaf litter cycle. Phyllosticta capitalensis and G. citricarpa isolates were collected in Australia to look at the competitive interaction of the two fungi. They are also evaluating the relative sensitivity to fungicides of the two species. They did lower germination rates for P. capitalensis than G. citricarpa. Preparations are being made for the leaf litter dynamics studies. The same Valencia block will be used but the second block in a new location to be determined. Also preparing for a second round of germplasm inoculations. A leaf litter degradation trial is in the planning stages that will closely follow the Florida experiments.
September 2014 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: Tests with with the DMIs are nearing completion with assays with a QoI/SDHI on-going. Molecular characterization of CYP51 was initiated. Manuscript preparation has begun. Objective 2: Trials have been initiated and treatments are on going. Objective 3: Preliminary analysis has been carried out on Groves I through III. Where Grove I shows total infectivity of the rows scouted clustering analysis cannot be done. In Grove with emerging disease (Grove II) and intermediate grove (Grove III) both show clustering according to spatial analysis in R (Ripley’s K, Binomial distribution etc’). We are still waiting for color change in fruits to re-map Grove II and III for assessment of spread, and severity. Objective 4: Two sets of in vivo experiments were conducted using large numbers of naturally infected fruit. Fresh Valencia oranges from a block infected with citrus black spot were harvested and evaluated for presence/absence of CBS lesions and equal numbers of randomized fruit were distributed among the different treatments. Fruit were treated with one of seven fungicides at ambient or heated (10 or 13’C) temperatures. The fungicides include azoxystrobin, fludioxonil, pyrimethanil, phosphorous acid, Imazalil, thiabendazole, and sodium-o-phenylphenate. Each of these have formulations that are registered for postharvest use on citrus. Control fruit were either left dry or dipped in water alone. After treatments, the fruits were air dried and kept at 25’C, 70% relative humidity, 3 ppm ethylene, and continuous light condition to promote CBS lesion development. Fruit treated with 1,000 mg/l thiabendazole at 25, 50, or 56 significantly inhibited subsequent lesion development. Fruit treated with 1,200 mg/l azoxystrobin at either 50 or 56’C also significantly inhibited lesion development, while treatments at 25’C were not significant. Treatments with SOPP solution (20000 mg/l; 25’C, 50’C, or 56’C) were usually not significant, except for an occasional significant reduction in lesion development in experiment #2. Fruit treated with 1,200 mg/l fludioxonil, 1,000 mg/l pyrimethanil 10,000 mg/l KPhos, or 1,000 mg/l imazalil were not effective at any temperature.
Dec 19, 2014 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. Guignardia mangiferae sequencing is complete and the assembly is continuing. To get better resolution with the G. citricarpa genome, the organism was resequenced, giving far better resolution from the genome data. Analysis of the gene structure is being continued. A manuscript on mating type genes is in preparation. The data has been finalized and a third draft of the materials and methods completed. Introduction, results have a first draft and the discussion has begun. Sample collection for the greenhouse inoculation experiment continues and the samples are being fixed and embedded. Monthly collections continue from the greenhouse. Sectioning has continued at a faster pace. We found that D. citri overwhelmed the population of G. citricarpa on twigs under the conditions we were working with. The twigs that were incubating from the last experiment are being processed and a new experiment has begun to look at the effect of RH conditions on G. citricarpa sporulation on twigs.
Dec 19, 2014 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. Guignardia mangiferae sequencing is complete and the assembly is continuing. To get better resolution with the G. citricarpa genome, the organism was resequenced, giving far better resolution from the genome data. Analysis of the gene structure is being continued. A manuscript on mating type genes is in preparation. It was decided that we needed further confirmatory evidence to strengthen our work so a new experiment was initiated. Sample collection for the greenhouse inoculation experiment continues and the samples are being fixed and embedded. Monthly collections from the greenhouse have begun. Sectioning continues at a slow pace. We found that D. citri overwhelmed the population of G. citricarpa on twigs under the conditions we were working with. We have began an experiment to look at the environmental conditions of G. citricarpa sporulation on twigs. It is incubating.
Report for period ending 6/30/14 Acitivites of the CHMA program assistant (4/1/14 – 6/30/14): During this reporting period, the CHMA assistant provided support to the CHMA program by attending various local CHMA meetings as well as statewide and multi state meetings. Specifically, Mr. Page attended 12 meetings including the following: Growers institute meeting (4/8/14), Volusia CHMA Meeting (4/11/14), Gulf CHMAs meeting (4/14/14), Conserve Field day presention (4/22/14), Hardee CHMA meeting (5/5/14), meeting with Noel Troxclair from texas citrus mutual (5/12/14), CHMA working group meeting (5/23/14), presentation for Hillbillies meeting (5/27/14), Florida State Horticulture Society Annual Meeting (6/1-6/2), Mountain Lake / Dundee CHMA meeting (6/3), Florida Citrus Mutual Conference (6/10-6/12), and attended meeting at SWFREC (6/25/14). In addition to attending meetings, Mr. Page continued to spend time working with CHMA captains and other interested growers on a daily basis identifying trouble areas, planning programs, and updating website information.
Report for period ending 9/30/14 Acitivites of the CHMA program assistant (7/1/14 – 9/30/14): During this reporting period, the CHMA assistant provided support to the CHMA program by attending various local CHMA meetings as well as statewide and multi state meetings. Specifically, Mr. Page attended 12 meetings including the following: FFA Meeting (7/2-7/3), American Sociey for Horticultural Sciences meeting (7/25-7/29), Small farms Conference (8/1-8/2), Citrus Expo (8/12-8/14), Gulf CHMA meeting (8/28/14), Grower meeting in Sebring (9/3/14), Hardee CHMA meeting (9/5/14), meeting with county agents (9/12/14), county agent Oj break (9/24/14), Landscape tradeshow (9/25-9/26), FDACS CHMA planning meeting (9/29/14), Hardee county CHMA roundtable (9/30/14). In addition to attending meetings, Mr. Page continued to spend time working with CHMA captains and other interested growers on a daily basis identifying trouble areas, planning programs, and updating website information. Mr. Page also worte an article for Citrus Industry Magazine to update growers on the success of CHMAs statewide and also began working with the new UF/IFAS Citrus Extension Economist to gather data from the CHMA program to conduct an economic analysis of the benefits of CHMA participation.
Report for period ending 6/30/14 Previously we reported on greenhouse -based trials examining the ability of soil applied insecticides to disrupt psyllid feeding such that incoulation of the plant with the HLB bacterium is prevented. In that work, treated plants were challenged with approximately 50 ACP (the majoirty of which tested postivie for Las) and then held for several months to test the plants for Las. Thus far after more than 9 months, none of the plants, including the untreated controls, have tested positive. These results demonstrate the difficulties in conducting such transmission studies with larger plants and suggest that perhaps developmental stage of leaves and variety used may play a role in successful transmission studies. We examined the effects of leaf struture to determine how this may affect psyllid feeding and ultimately pathogen transmission. Using an electrical penetration feeding graph (EPG) monitor, we compared psyllid feeding on leaves of different ages and varieties. Across treatments we found significant differences in the amount of time required to access both phloem and xylelm for psyllid feeding. We then conducted a histological examination of leaf tissues from these treatments, examining the pathway of the stylets. Here we found a certain defensive structure within certain leaf tissues that was present in leaf samples where psyllids had difficulty in accessing both phloeom and xylem. The presence of these structures will likely delay both inoculation and acquisiton of the Las pathogen by psyllids. These findings will not only be of use in designing future insecticide feeding studies, but may also be a potential factor for apparent host-plant resistance to ACP we have previously reported in other plants such as Cleopatra mandarin.
Report for period ending 9/30/14 Field trials were established to compare the amount of imidacloprid, thiamethoxam and clothianidin in leaf tissues based on tree size and rate of product applied. Plots were established at the CREC where no other soil-applied insecticides were being applied. Three rates of product were applied to trees in one initial size class. On a weekly basis, leaf samples were collected and taken back to the lab and processed for residue analysis and then placed into the freezer. Concurrently, work on validating the residue analysis methods being used in our lab is underway (see project 616). Upon completeion of that work, these samples will be analyzed to compare concentration of residues in leaf tissue over time at each rate applied. Additionally, we examined psyllid feeding behavior in the lab by removing branches from treated trees and determining if psyllid woulf still feed (and thus possibly be able to inoculate those plants with Las). Residue analysis of this leaf tissue will be conducted to compare levels of insecticide present and the lieklihood that psyllids fed on the plant. This work is preliminary but will provide a better starting point for work whcih will be conducted in the following reporting period wherein we plan to begin more controlled studies to determine what level of insecticide is needed in the leaf tissues to prevent psyllid feeding behavior.
Report for period ending 6/30/14 During the period of 4/1/14 to 6/30/14 we finished the analysis of nectar samples collected during the bloom of 2014. More than 300 samples were collected, albeit not all were able to be analyzed due to variation in quantity of nectar collected. It was observed that trees diseased with HLB produced far less nectar than healthier trees whcih complicated the standardization of samples. Samples were collected from 110 plots treated with different soil applied insecticides on varying dates up to 4 months prior to bloom. For each of the plots, bloom samples were collected on 3 separate dates to ensure rigourous sampling. The analysis of nectar from one date was reported in a previous reporting cycle. During the current reporting period, we completed the nectar analysis from the remaining samples. The remaining samples provided results similar to those rpeviously reported. Samples collected from trees treated more than 2 months (or more) prior to actual bloom did not contain appreciable levels of inseciticide in the plant nectar.These results support the hypothesis that soil-applied insecticide applications made 2 months or more prior to bloom will result in residue levels in nectar belwo the level of concern for pollinators. Work will now shift to focusing on analysis of insecticide residue levels in leaf tissues.
Report for period ending 9/30/14 During the period of 7/1/14 to 9/30/14 we shifted focus from analyzing citrus nectar to analysis of citrus leaf tissue for the presence of neonicotinoid insecticides and thier associated metabolites. Shifting from nectar to leaf tissue requires changing columns and solvents used for the analysis. THus, a considerable amount of time was spent calibrating the equipment and then validating the new methods used for leaf tissue analysis. By late August / early september, we completed the validation process and thus are now able to accurately quantify imidacloprid, thiamethoxam, clothianidin and their associated metabolites in leaf tissue. Because (accurate) information is not available on the anticipated levels of these compounds in citrus leaf tissue following application to trees in the field, we began sampling trees from commercial groves to understand what our detection range should be. Once complete, the next steps will be to begin analysis of leaf samples from field and lab studies we have planned.
This research seeks to determine whether young trees infected with CLas and displaying typical HLB symptoms can be brought to maturity and produce an economically viable yield. This will be achieved by managing a 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 based on frequent leaf tissue analyses, visual symptoms, and the growth of the tree canopies and yield. There are six replications of treatments, with two being pure replications. The grove continues to grow well and also look normal, despite the nearly 100% HLB incidence. Foliation of canopies is dense, and leaf color in the summer and fall was a healthy green. Tree heights, canopy sizes and chlorophyll indices were measured in Fall, 2014, and analyzed. There were no significant treatment differences for measured variates, and selected data are summarized below: Table 1. Tree canopy height (feet) STD-Ca STD+Ca Prescrip SOIL FERT Liq/Dry 8.46 8.02 8.45 Liq 7.91 7.47 8.42 Liq/Dry-Ca 8.13 8.05 7.36 Table 2. Tree canopy volume (cu.ft/tree) STD-Ca STD+Ca Prescrip SOIL FERT Liq/Dry 521 388 495 Liq 413 367 485 Liq/Dry-Ca 454 419 348 Table 3. Tree canopy leaf chlorophyll index (SPAD index) STD-Ca STD+Ca Prescrip SOIL FERT Liq/Dry 72.60 72.20 75.45 Liq 73.50 75.20 74.95 Liq/Dry-Ca 77.05 75.35 74.30
This is the first year of a three-year project. This overall 3 year project will focused on determining the optimum combination of chemotherapy, thermo-therapy, and nutrient therapy that can be registered for use in field citrus and control HLB. In this quarter (Oct 2014 to Dec 2014), we evaluated the efficiency of chemical compounds (Amp and silver dyne) against Las bacterium to combat HLB disease by gravity bag infusion. In our previous study, Al(OH)3 was difficult to be absorbed in citrus trees due to its low solubility in water. Therefore, in this quarter, Al(OH)3 was replaced in the field trial by silver dyne (SD), which was effective in the graft-based test in the greenhouse. The preliminary results indicated that Amp could suppress HLB bacterial titer in several citrus rootstocks after about one year, and SD had no significant effect on reducing HLB bacterial titer, 2 months after initial treatment. Because HLB bacterial titers in various citrus rootstocks were different in response to chemical compound, we continue to evaluate effect of Amp and SD against HLB bacterial in the future. Meanwhile, agronomic performance of treated trees will be investigated, and the nutrition and heat treatment therapy with several additional molecules will be conducted in next quarter.
Three growers agreed to apply 1/4th the regular rate of Citrus Fix (2, 4-D) and MaxCel (cytokinin) every 45 days on approximately 1 acre each of Hamlin and Valencia orange trees. Grove locations are Sebring, Babson Park and Ft. Meade. One grower applied an application early spring of 2014 while the other two growers waited until the crop was harvested so that they would not be subjected to crop destruct rules for the 2013-14 year’s crop. The last application for the growing season occurred in October, 2014. Comparable control rows are being monitored two rows from the sprayed trees. Treated and Control trees were categorized as to tree health and are monitored for fruit drop, flushing, yield, etc. No apparent differences in flushing pattern were detected during the summer flush. Tree condition (decline status) was evaluated at the end of the fall period. Fruit drop was measured and yields obtained for the Hamlin blocks. Yields were not different for year one, but fruit drop was numerically less for the treated trees by 3 % compared to the Control plots at one site where the data is analyzed. All Hamlin blocks have now been harvested. Flowering is being checked for any difference in timing or intensity. Valencia yields and drop as well as flowering are being evaluated under a new project contract with CRDF. Applications of Citrus Fix, Maxcel and including ProGibb this growing season have started for the second year. Growers have been diligent in making timely applications. Details of flowering and harvest yields for Hamlin orange plots will be in the March report for year 2.
Four growers agreed to treat Valencia plots of one acre each with Citrus Fix (2, 4-D) and Retain (AVG) at five locations. Treatments were applied using 2.8 fl. oz. of 2, 4-D or 100 gm ai/acre of Retain. Two locations were harvested almost immediately after application so that no data was obtained for these locations. The three remaining tests were treated on 2/11 (Lake Placid), 2/13 (east Lake Wales) or 2/19/2014 (Sebring). There was no significant difference between the PGRs, 2, 4-D and Retain, and the Control in any of the 3 trials. Overall preharvest drop rates were 25 to 35, 40 to 45 and 50 to 55 % for the three groves. In two of the groves the treatments had almost 5 % more drop than the Control, while at the other location the Control had almost 5 % more drop than the treatments. In the grove with less fruit drop for the treated trees (East Lake Wales), there was 6 % less drop in mild HLB decline trees and 8 % less drop in nearly healthy trees compared to similar Control trees. There was no difference between Control and treated trees that were more severely declining. The Control trees had 48, 59 and 59 % drop for healthy, mild and severely declining trees, respectively. The other two grower tests (east of Lake Placid and north of Sebring) had 3 to 4 % more drop in treated trees, both Citrus Fix and Retain, than the Control trees. These differences were not significant. The Control trees averaged 29 and 41 % fruit drop, and again the healthiest trees had 6 and 21 % less drop than declining trees for these two grower tests. These tests did not support the idea that 2, 4-D could consistently reduce preharvest drop associated with HLB disease when applied in late January. They did support the idea that more declined HLB trees will usually drop more of their fruit than declining trees before harvest.
Two trials were established that included sprays of Citrus Fix (2..8 floz/ac), Retain (100 g ai/ac), S-ABA (100g,ai/ac), 1-MCP (company determined rate) and the Control. These locations were Auburndale and Lake Wales. A third location did not include 1-MCP. The treatments at the first two mentioned tests were applied from February 10 to 12, 2014, while the third location (Lake Alfred) was treated earlier and twice (September and October). The preharvest drop values at the Lake Alfred site were low on January 25th (5 % drop) but increased to 18-30 % depending on treatment by harvest on March 25th. The ProGibb and ProGibb + Citrus Fix had the lowest fruit drop, but the values were not significantly different than the control. The other 2 sites had ranges of 33 to 37 % drop and 47 to 58 % drop between all the treatments, not significantly different. Consistent with all of the other tests, healthier trees had lower drop rates than more severely declined trees (20 % versus 30 and 34 % for mild and severely declined trees, respectively, at Lake Alfred). In another grove the % drop values ranged from 30-50 % for healthier trees and 50 to 70 % for mild and severely declining trees. In all cases differences between treatments and the Control were not significant probably partly due to tree condition within the plots. After these trials, plot sizes were increased to 10 trees.
(863) 956-8817
(863) 956-5894
700 Experiment Station Road
Lake Alfred, FL 33850
Email Us
