Xambr’ Paran’ Brazil Plots: The experiment is designed to quantify the effect of windbreaks, copper sprays, and insecticide sprays individual and combined effects on citrus canker management. In 2010 replicated field plots were established. I was soon evident that the screens used as windbreaks were not strong enough to provide the required effect. Thus in addition to the screens, we established natural windbreaks using Casuarina. Casuarina trees that are currently ~7 m high. There were a few new canker-affected plants in the experimental area that will be pruned every 3 weeks. Trees are well established now and have developed enough canopy to allow inoculation and to start the experiment in September/October 2013. During 2013 inspections, 25 plants were discovered with HLB symptoms. Florida Windbreak plots: The final data taken through September 2012 from the preliminary experiments last season confirmed that the number of wind gusts >11 mph increased with distance from the windbreak whether measured within the north-to-south rows or across the rows from east to west. Consequently, the highest fruit disease recorded in September in the cv. Valencia orange orchard (10 percent fruit cankered) was in the center of the 11-acre block and the lowest incidence (<2 percent fruit cankered) was in the east-west row location nearest the windbreak. The weather stations at the two locations (cv. Valencia orange, Estes Farm, Indian River Co. and cv. Rubyred grapefruit, Scott Farms, St. Lucie Co.) continue to be monitored this season with weather data being recorded and downloaded on a monthly basis. The disease data on leaves and the first sample on fruit have been taken and will be related to the wind and leaf wetness conditions from the weather data recorded in these orchards during the 2013 season. Programmable leaf wettnes controller: Further tests on the 'pin sensor' have proven problematic, as water retention control is difficult. First, to facilitate putting the silk onto the pins, the pins were lengthened off the board (approximately 1 cm). This allowed for 'cavities' between the pins, which allows too much water to be held, which lead to drying times being too long. We also determined that the board itself that the pins are mounted in will hold water, especially with the silk on top of it, which again led to longer water retention times. So, the next series of tests will include coating this board to prevent water uptake (we will attempt to use wax to coat the board to emulate the leaf surface a bit), followed by trying to keep the pins long enough to put through the silk, yet not be so long as to create cavities. Finally, a future test would be to NOT push the pins through the silk, but to keep the silk taunt across the tops of the pins, thus using the silk as not only a water absorption layer, but also a 'blocker' to prevent the water from sitting anywhere else within the sensor. Project publications: (In addition to the 7 previously reported publications relative to this project, the following was recently submitted as well) Bock, C. H., Gottwald, T. R. and Graham, J. H. 2013. A comparison of the bioassay test and culture to detect Xanthomonas citri subsp. citri . Plant Pathology 62: xx-xx.
1. Development and testing of efficient methods of statistical inference to estimate epidemiological parameters from maps of emerging epidemic.) Using citrus canker as a test system, we are developing and testing quantitative models to link weather variables to the rate of disease spread. We are also analysing models for anisotropic dispersal of the pathogen, in order to correlate the direction and extent of pathogen dispersal with wind direction/strength during extreme weather events (rainstorms). The outcome will be a set of epidemiological parameters that can be used as inputs for predictive modelling, with (at least) two different final goals: i. To produce risk maps for disease spread for large (state-wide) geographical areas and long time scales (several years), under different “what if” scenarios for favorable and unfavorable weather conditions; and ii. To produce a risk map on a smaller (county-wide) scale in response to a local storm. With knowledge of the distribution of disease prior to the storm, it should be possible to estimate the new distribution of disease using the strength and direction of wind, and other relevant weather parameters. This would help directing a post-storm sampling procedure (e.g. which areas surveyors should target for new symptoms). We have developed and tested a set of advanced spatial statistical methods for goodness of fit. The methods are based on the comparison of simulated and observed spatial patterns of infection. They have been successfully tested using model estimates for the Miami outbreak, and they were able to discriminate between good and less good dispersal models. Such methods are also a fundamental ingredient, hence a significant step forward, for the ABC (simulation-based) estimation algorithms that are currently being developed. The methodology being tested with citrus canker can be generalized to HLB. A paper on Markov chain Monte Carlo for estimation of epidemiological parameters in the Miami area has been submitted. 2. Develop a generic epidemiological model that can be used to compare control scenarios and to optimize the probability of controlling and managing high-risk pathogens of agricultural significance. We have built a model that represents the spread of HLB within an individual tree. Successful spread of the pathogen depends on transmission both within the vascular system of the tree and between leaves via psyllid vectors. The relative importance of these transmission routes is being explored, with the speed of spread of the pathogen dependent on whether transmission via psyllid vectors is frequency- or density- dependent: this depends on the population density of psyllids relative to the number of leaves. A novel feature of our modelling approach is that it explicitly incorporates the ability of Las bacteria to survive in the vascular system of the plant. Control: We are using this model for a variety of purposes. Firstly, we are investigating and comparing the efficacy of roguing, application of insecticide and the use of nutritional products and thermotherapy for disease control and mitigation. Secondly, we are using it to inform grove scale models for the spread of HLB. Grove scale models typically assume that each citrus plant is either entirely infected or not (instead of considering the proportion of the tree that is infected). This model is being used to inform the force of infection of each infected citrus tree in grove scale models. 3. Develop user friendly model ‘front ends’ that can be used by researchers and regulatory agencies. We are finalising the publication on Webidemics (http://www.webidemics.com/), the user-friendly front-end for control of citrus disease.
Soil application of systemic neonicotinoid insecticides for control of psyllid vectors of Huanglongbing disease on young citrus trees also produces season-long SAR control of citrus canker caused by Xanthomonas citri subsp. citri. The neonicotinoids imidacloprid (IMID; Admire Pro, Bayer) and thiamethoxam (THIA;Platinum, Syngenta) were compared with soil or sprinkler applications of the commercial SAR inducer acibenzolar-S-methyl (ASM, Actigard, Syngenta) and foliar sprays of copper hydroxide (CH) and/or streptomycin (STREP) to evaluate their effects on the percentage of canker-infected leaves on 2-yr-old ‘Vernia’ orange and 3-yr-old ‘Ray Ruby’ grapefruit trees in Southeast Florida. All treatments significantly reduced incidence of foliar canker compared to the untreated check. Soil drenches of ASM and season long rotations with IMID and THIA were highly effective for suppressing foliar canker on young grapefruit and orange trees under weather conditions absent of high intensity rains or tropical storms. Sprinkler application of ASM was less effective than soil drench. The level of control for SAR treatments was comparable to eleven 21-day interval sprays of CH and/or STREP. SAR induced by soil-applied insecticides provides substantial benefits for canker disease management on young citrus trees that may be augmented with ASM. Currently, use of neo-nicotinoids insecticides for control of the psyllids and leafminer is limited to trees less than 2.75 m tall in part due to the potential risk for leaching of soil applied materials into the groundwater at the higher rates required for pest control on larger size trees. An alternative approach is spray application of the chemicals on the trunk. Four soil drench or trunk applications of IMID and THIA and ASM were compared to untreated controls and 9 or 10 standard 21-day interval copper sprays for protection of foliage and fruit on 5 to 6-yr old ‘Ray Ruby’ grapefruit trees. Soil drench and trunk applications similarly reduced the incidence of canker lesions on foliage and fruit but were less effective than copper sprays. SAR inducers appeared to protect fruit by reducing incidence of foliar disease, and thereby, when integrated with 21-day interval copper sprays may improve control canker on young, fruiting trees. Currently, we are collaborating with Syngenta in an EPA-approved Experimental Use Program (EUP) in two east coast grapefruit groves to support the labeling of Actigard (ASM) integrated with copper sprays for control of canker on bearing grapefruit.
Objective 1: Assays of non-bearing trees indicate that soil drench is an effective and consistent application method for increasing copper status of young leaves well above the baseline concentration. The preventative and curative activity of the copper bactericides are being followed in pre- and early stage HLB infected trees. In a trial located at Picos Farm in USDA-Ft. Pierce, Hamlin on Swingle citrumelo trees were root drenched with the copper bactericides: EXP, Cop-R-Quik, (CQ) Magna-Bon (MB), copper phosphite (CP) and zinc phosphite (ZP). In two other locations in ridge groves, healthy pre-bearing trees were drenched with copper chelates (CQ and MB). All three locations were assayed for HLB status this past winter. Thus far, insufficient HLB positive trees have been detected in the non-treated checks to measure treatment effects. A trial in a block of 4-yr old Valencia trees with symptomatic and pre-symptomatic HLB infection as determined by PCR status, no effect of MB or CQ on HLB decline rating was detected in December 2012. Samples for PCR status of the trees in all trials will be collected and analyzed this fall. In the meantime, grower trials of MB and CQ are underway based promising visual observations of improved tree health after 18 months of soil applications of rates varying from 1-2 gal product per application and 2-3 applications per season. One location will provide the opportunity to compare fruit drop in matched 3 acre sub-blocks with and without soil applications of CQ for the last seasons.
Florida growers have reported that enhanced nutritional programs (ENPs) maintain productivity of HLB-infected trees. However, efficacy and sustainability of the nutritional approach for HLB disease management remains uncertain. Complementary studies of multiple ENPs and their individual components compared to the standard nutritional program (SNP) on nursery and field trees were initiated in 2010. Two independent nursery trials were initiated with final data collection finished and data analysis currently underway. From monitoring temporal bacterial movement and replication it was found that Candidatus Liberibacter asiaticus (Las) populations are similar for ENPs and the SNP. Minor differences in Las movement have been observed. Las invaded new flush tissue faster in ENP treated trees than SNP trees. Phosphite treatments have caused Las to favor early invasion of root tissue compared to other treatments. A reduction in visual symptom expression was observed with ENPs. However, there were no significant differences in the HLB-associated phloem plugging or reduction in leaf number, leaf size, and fibrous root mass. There was a consistent trend that the enhanced nutrition actually leads to a reduction in both root and canopy biomass. This suggests that while ENPs improve the appearance of trees by reducing the amount of blotchy mottle and nutrient deficiency associated yellowing, this change in visual appearance is masking the loss of biomass in these trees, which is more difficult to quantify with visual observations. Prior to the trial, field trees had been maintained with good horticultural practices using leaf testing to guide application of foliar nutrients to maintain optimal nutrition. In the field trial, ENPs did slow the development of HLB-induced nutrient deficiency in leaf tissue, but did not prevent the development of deficiency. However, this difference is not reflected in a difference in yield, disease incidence, or disease severity compared to trees in treatments lacking the micronutrient treatments. This supports the growing quantity of data suggesting that nutrient deficiencies are a secondary symptom of HLB and not responsible for HLB-induced yield loss. Combined with results from the greenhouse trial, this suggests that ENPs are masking visual symptoms rather than improving tree health.
Spring/summer 2013: we monitored 8 trials of leafminer attraction to pheromone blends, movement and suppression of trap catch where pheromones were deployed in collaboration with ISCA Technologies and grove managers. These trials address pheromone carrier, timing, deployment pattern and efficacy of mating disruption and leaf damage. Trial 1: Winter and spring application of pheromone (2013). Cooperator: Packers of Indian River. We continued a trial to test application of pheromone in winter and spring on suppression of CLM using a factorial design with split plots in four replicated blocks. Rubber dispensers loaded with triene (834 mg/ha) were treated in winter (Feb 6-8) and spring (Apr 24). Trap catch disruption in treated areas (winter + spring) has remained >95% at 20 wks after application. Flush shoots were evaluated a third time on 5 June. There were no differences in infestation between treated and untreated plots. Infestation severity was about 1-6 mines per flush shoot. Trials 2-3: Rubber dispensers (St. Lucie Co.). Cooperator: Golden River Fruit Co. We finished monitoring trap catch disruption in small plots (0.14 ha) treated with rubber dispensers (318 per ha) loaded with (1) a ‘natural’ 3:1 blend and (2) triene only. Trap catch disruption declined to about 32-41% at 49 wks after application. The equivalence of the two treatments suggests that both work by the same mechanism of non-competitive disruption. Near the same site, 56 ha were treated with a new rubber dispenser loaded with triene (2.5 mg) on 22-24 April, and these proved inferior for trap catch disruption compared to previous forms of the rubber dispenser. The site will be retreated in July 2013. Trial 4: Large plot rubber dispensers (St. Lucie Co.). Cooperator: Packers of Indian River. On 7 Sept an experiment was started to compare trap catch disruption in plots (0.87 ha) treated with rubber dispensers containing ‘natural’ 3:1 blend (330 dispensers/ha) versus untreated plots (0.87 ha). Plots were four times longer than they were wide. Trap catch disruption was 94% at 44 weeks (16 July). Evaluation of leafminers (11-12 June) showed no differences in incidence or severity of leafminers between treated and untreated plots. Trial 5: Large plot rubber dispensers (Charlotte Co.). Cooperator: TRB Groves. We monitoring a grower validation trial treated on 20-23 Aug (42 ha) with a deployment of rubber dispensers loaded with pheromone (natural blend). Modified rubber dispensers were deployed in April; however, this structure of rubber dispenser was found to be inferior for trap catch disruption. Therefore, another treatment of rubber dispensers is planned for July. Trial 6-7: Movement of citrus leafminer (St. Lucie Co.). Cooperator: Blue Goose. We continued a new experiment to test how far P. citrella flies to traps baited with pheromone and placed in a grassland pasture adjacent to a citrus grove. Traps were placed at 75, 150, 300, 600, and 1,200 meters along a transect west of a citrus grove that serves as a source for P. citrella. We captured moths at all these distances. We also set up potted citrus plants as sentinel plants along similar transects adjacent to the source and found that plants were infested at 1,200 m by 6 weeks after placement. Trial 8: Attraction of P. citrella and other Phyllocnistis species to ternary and binary pheromone blends (St. Lucie Co.). Several Phyllocnistis species are attracted to lures containing a binary pheromone blend optimized to catch P. citrella. We started an experiment on 19 April to determine if a ternary blend is as attractive to non-target Phyllocnistis species. Populations of non-target species are low; no differences in trap catch has been observed.
Using gas chromatograph-coupled electroantennography, we have discovered six compounds that elicit antennal responses from the Asian citrus psyllid. Two compounds elicited consistent results from both male and female antennae: neryl acetate and linalyl acetate. Less consistent results were obtained when beta-caryophyllene or geranyl acetate was puffed over the antenna of either males or females. We confirmed antennal responses to formic and acetic acids as degradation products from either citral (a racemic mixture of neral and geranial) or ‘-ocimene (a racemic mixture of cis and trans). Ocimene yielded relatively more acetic than formic acid; citral degradation resulted in more formic than acetic acid as determined by GC-MS. Female antennae responded more (n = 5) to acetic acid compared with males. No difference was detected in male and female responses to formic acid. Results suggest that formic is more stimulatory than acetic acid. These six compounds are now being tested in laboratory bioassays to determine their effect on Psyllid behavior.
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. Leaf samples were collected in August and December and the results of nutrient analysis of the leaf tissue are summarized below: *** August *** N is adequate P is OPTIMUM to high K is OPTIMUM Mg is OPTIMUM Ca is OPTIMUM for all treatments except low for the standard liq/dry treatment. S is OPTIMUM B is adequate but could probably use a boost for the spring bloom. Zn is OPTIMUM range on all treatments Mn is OPTIMUM for all treatments Fe is OPTIMUM for all treatments except low for the standard liq/dry treatment. Cu is above OPTIMUM to HIGH for all treatments *** December *** N is LOW to adequate P is OPTIMUM K is OPTIMUM Mg is OPTIMUM except LOW for the Ca foliar spray Ca is LOW for all treatments S is OPTIMUM B is LOW except for treatments receiving all liquid ground fertilizer Zn is just into the OPTIMUM range on all treatments Mn is OPTIMUM for all treatments Fe is LOW except OPTIMUM for treatments receiving all liquid ground fertilizer Cu is OPTIMUM to HIGH for all treatments
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. Following the March 2013 harvest and review of all the 2012/13 season data, the recommendations for the 2013/14 season should mainly involve any corrective action to avoid the possible detrimental effects of some foliar sprays on canopy growth, as evidenced by a suppression of canopy size and yield. Secondly, recent literature searches and discussions with other scientists have suggested that there may be some additional scope to mitigate HLB by adding plant growth regulators like 2,4-D to the foliar nutrient sprays. A very low but frequent dose of 2,4-D (a synthetic auxin hormone) mixed ONLY with the ‘prescription treatment’ is suggested. Using the CitrusFix formulation (40% w/v), a rate of 5 mL in 100 gal, producing 5.3 ppm a.i. is suggested for every spray that is applied from after 100% petal fall until winter. Leaf samples were collected in March 2013 and the results of nutrient analysis of the leaf tissue are summarized below: N is adequate P is OPTIMUM K is OPTIMUM except for one sample being lower Mg is OPTIMUM except for two samples slightly below optimum Ca is OPTIMUM for all treatments S is OPTIMUM B is adequate now and should be maintained Zn is OPTIMUM range on all treatments Mn is OPTIMUM for all treatments Fe is OPTIMUM for all treatments Cu is above OPTIMUM to HIGH for all treatments, particularly in the STD+Ca and the prescription foliar spray treatments It is evident after one year that the leaf tissue nutrient analyses are highly variable both spatially and temporally, and are also directly affected by growth rates of the trees. We are investigating the possible use of a real-time digital camera imaging system to periodically measure canopy color and other properties in the experiment plots. The unified expression of HLB and nutrient deficiency symptoms as chlorotic leaf colors may be useful for future interpretations and development of remedial actions.
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. In March 2013, the first fruit harvest of plots was conducted since the experiment was started in the previous spring of 2012. It was quite difficult to locate and photograph trees not showing any HLB symptoms, so it is safe to assume that infection levels are close to 100%. Despite the widespread HLB infection in the block, it was striking that most HLB-affected trees had over-wintered very well and had already produced a vigorous flush of new leaves. The bloom period was greatly prolonged due to the incessant flowering of HLB-symptomatic trees that have lost their normal synchronization of flowering with chill units, warming temperatures and increasing daylength. We were surprised that it was not possible to detect any differences between the appearance of trees during March 2013 in the different fertilization treatments, and that could be said for the entire growing season. There was evidence of mild to moderate preharvest fruit drop in the experiment, and that too could not be attributed to a treatment. In general, the trees in the experimental block looked good considering the HLB infection level. Average yield measured in all plots was 68 boxes/acre, which is well below average for fourth-year yield of ‘Valencia’. A possible remedy for boosting block yields when 100% HLB infection is expected as early as 2-3 years is to increase the planting density, (for example 151 to 242 trees/acre). The fruit yield was significantly higher for the foliar treatment excluding calcium (1). The cause of this yield difference was traced to the trees on that treatment having larger canopies than the trees receiving the Ca foliar sprays (2 + 3). Fruit size was unaffected, but fruit counts per tree were different, and furthermore, the fruit count per unit of canopy was the same, thus proving that the actual tree sizes were responsible for the differences in fruit yield per acre. A follow up investigation should examine the foliar sprays applied last year (2012) to see if there is a traceable component that could have caused foliage burn or similar damage to the +Ca treated trees. It seems unlikely that the Ca itself was responsible and likewise it seems unlikely that the ‘Ca treatment would have boosted growth more than the other treatments. It was noted that foliage copper levels were excessive, and higher in the +Ca foliar spray treatments (March leaf sampling). There were also a few significant differences in some of the juice quality parameters, and in general the values were fairly typical of young trees picked early in the season.
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 look good and actually improve, despite the nearly 100% HLB incidence. Foliation of canopies is dense, and leaf color through summer and into September was a healthy green, with vigorous new leaf flushes emerging frequently. Leaf samples were collected on September 10, 2013 and the results of nutrient analysis of the leaf tissue are summarized below: N is adequate P is OPTIMUM K is OPTIMUM Mg is OPTIMUM Ca is marginally low on the no-Ca soil treatment S is OPTIMUM B is OPTIMUM in most, but marginally low in the ‘Ca foliar treatment Zn is OPTIMUM on most, but marginally low for some foliar sprays with Ca Mn is OPTIMUM for all treatments but the same trend as for Zn was noticed: lower levels in the sprays with Ca Fe is low (<60) in some treatments Cu is OPTIMUM All the different fertilizer strategies chosen for testing in this block appear to be working equally well. There appear to be some adverse interactions of foliar calcium sprays with the other spray ingredients and / or the trees, as reflected in an altered nutrient concentration in the leaves. The block will produce a viable harvest although the fruit set should be better. Fruit sizing is normal as in healthy Valencia trees. Tree canopy sizes will be measured in November, to be reported in the next quarterly report.
July 2013 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. We are in the process of hiring some personnel for the project. Others have been hired and will be starting shortly. Small plots were set up an Immokalee area grove with 5% urea, CaCO3, Soil set, Compost Aid, Soil Set and Compost aid, and an untreated control. Leaves were collected and treated. The samples were collected and are being processed. To look at the effect of bagasse, the Senior Biological Scientist and the post doctoral associate worked on assembling the necessary supplies and components to carry out the controlled experiment portion of this project. This involves an in vitro study of the decomposition of citrus leaves and inactivation of G. citricarpa by various amendments including bagasse. A microbial consortium of fungal and bacterial strains to aid in the decomposition of bagasse and of citrus leaves was identified. Cultures of these microbes were obtained and are stored in our laboratory. Delivery of the bagasse for the controlled experiment was arranged and scheduled. Future availability of bagasse for the controlled experiment as well as for the field experiment was confirmed. Sources for field soil and both healthy and infected citrus leaves were found. Available lab facilities to house the controlled experiment were confirmed. A laboratory on the UF campus was identified that could perform the leaf tissue, fiber, nitrogen and carbon analysis. This analysis will be used to monitor leaf litter and bagasse decomposition. Construction of the plastic boxes with spore traps is currently in the planning stage. State regulations for working with Guignardia citricarpa were discussed with Tim Schubert at the Division of Plant Industry. There are reports of significant resistance to black spot in sour orange types, most notably ‘Chinotto’. The USHRL scion breeding program has a large population of seedlings from crosses between ‘Chinotto’ and the USDA mandarin hybrid selection 1-37-12, which are now fruiting, and have been evaluated for a number of fruit characteristics. Some of these approach commercial fruit quality and it is reasonable to expect that this population may be segregating for resistance to black spot. Ten seedlings of each of 20 selected Chinotto x 1-37-12 hybrids, the two parent genotypes, and the susceptible standard ‘Valencia’ have been developed at the USHRL and are ready for trial exposed to black spot inoculum. The subcontracting process with the University of Queensland is still underway.
July 2013 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: Isolates were single spored in preparation for the in vitro experiments. Preliminary data on tetraconazole and propiconazole, two unregister demethylation inhibition fungicides was collected to determine the optimal dosages to use. So far 36 isolates have been used for the effective concentration calculations. The preliminary experiments for difenoconazole and fenbuconazole have been initiated. Objective 2: The field trial was established in a commercial grove that was identified with ‘Valencia’ fruit with black spot. In spring 2013, the site was was scouted and rows of ‘Valencia’ were identified that had fairly even distribution of fruit with symptoms of black spot. Plots contained three trees with at least two trees serving as buffers between each plot. There were four replications per treatment arranged in a randomized complete block design. Sprays were initiated in May after fruit harvest. Applications were applied with an Air blast sprayer calibrated to deliver 126 gal per A operating at 200 psi and 3 mph with a 25 gallon mix. Objective 3: We are currently looking for suitable sites to conduct the spatial studies. This study will begin in earnest close to fruit maturity when symptoms become apparent. Objective 4: An experiment to determine if thiabendazole, imazalil, SOPP (2%), graduate A+, salicylic acid and chitosan produced either an inhibition zone of conidia germination or reduced mycelia growth measurements was initiated but is currently on-going. An experiment to look at the heat tolerance of conidia, plates were held at 50, 35 or 20C for 5 days. After 5 additional days, at 20C growth was observed on the 20C treatment plates but not 35 or 50C. After 10 days there was sporadic growth at 35C but still nothing at 50C.
June 30, 2013 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. Sample collection of psyllids, phenology and plants has continued through the spring and summer. More Psyllids have been collected from 2 sites but remain elusive at the 3rd site. At the most severely affected site, the trees have begun to decline considerably and are not flushing frequently. Plant and psyllid samples have begun to be extracted again. PCR has begun to calculate the pool size for the remaining samples. This will help to clear the back log of samples and get the project back on track.
June 30, 2013 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 has begun. The quality of the sequence is better and we are considering resequencing G. citricarpa. The full mating type gene has been located and the information will be used to better characterize the mating gene from G. citricarpa which appears to be missing a section. Since the GFP labeled strain, does not reliably retain the gpf gene, we have started greenhouse experiments using sectioning to locate and follow G. citricarpa in the leaf. We continue to work with the gfp labelled strains but will not rely on the labeling for the experiments.
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