The objective of this research project is to investigate and develop a potential non-phytotoxic, environmentally-friendly film-forming ACP repellent solution for preventing HLB infection. In the last reporting period,OS-SG 6, 10, 11, 12 and 13 were studied for plant safety and rainfastness and these formulations were delivered to our collaborators for ACP infection trials. Preliminary results obtained from ACP infection trials on 02/14/2016 and 05/14/2016 revealed all of the formulations demonstrated lower infection rates compare to the control treatment. Among the formulations, OS-SG 10, 12 and 13 revealed minimal infection rate, while OS-SG 6 and 11 formulations displayed a moderate infection rate. In the last report period, OS-SG 15 formulation was proposed as improved version of OS-SG 12 and 13 formulations. In this report period, the formulation was optimized further to have high colloidal stability in aqueous solution, high surface coverage and moderate rain-fastness properties. The colloidal stability of the formulation was checked via measuring %Transmittance (%T) of the supernatant collected from the solution left undisturbed. The formulation revealed less than %50 transmittance up to 4 hours which was found to be comparable or better compare to commercial control -Surround WP- which is currently commercially available for growers. Safety analysis and plant leaf surface coverage of OS-SG 15 formulations were conducted using Cleopatra orange sp (common citrus variety) as a model plant. The formulations were sprayed at the application rate of 0.5 lbs/gallon (recommended rate for the commercial control) based on active content. The formulations revealed high plant leaf surface coverage at the application rate which was comparable to the commercial control. Phytotoxicity studies were conducted using a Panasonic Environmental Test Chamber (Model MLR- 352H) to control light intensity, humidity and temperature cycling to simulate summer conditions (85% RH, 32 Celsius). OS-SG 15 formulation did not cause any plant tissue damage at the applied rates, matching the commercial control. For next reporting period, the film adherence of the formulation will be tested using a rain-fastness experiment comparing the results to the commercial control and optimized version will be selected for future ACP trials.
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. 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 were shown to have toxicity to ACP in bioassays. Electron micrographs of ACP fed on the wild type ACP-active toxins confirmed damage to the midgut epithelium associated with ACP mortality. Modification of one of the selected ACP-active toxins with gut binding peptide 18 has been completed. Work is now underway to identify the optimal expression strategy for the modified toxin constructs.
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, Paran , 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 February 2016 (25 after ACC epidemics begun), 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: 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 (June 2016 28 months of epidemics) – Trees and leaves: incidence of trees with citrus canker have not changed significantly since last report. All treatments reached near 100% incidence, except the ones with Cu+Wb, which have currently 81 to 86% of the trees with symptoms of citrus canker. Incidence of leaves continued to increase and reached 41.1% for unmanaged trees and 2.0% for trees under complete management. – Fruits and yield: As of February 2016, the incidence of fruits with citrus canker on the trees was 50.1% for the unmanaged trees and 4.5% for trees under complete management. Fruit drop per tree due to canker has increased and reached 96.1 and 18.6 for unmanaged and managed trees, respectively. All other treatments are showing intermediate results. Overall, relative treatment performances in the second season is similar to the first season. The highest disease control and reduction of fruit loss is being achieved with Cu+Wb. The second harvest is planned for August 1st 2016.
We finished the experiment in the climatic chamber where we tested Asian citrus psyllid (ACP) flight capability depending of ambient temperature and relative humidity. We determined that temperature was the major driver of ACP dispersal, with a minimum temperature for flight comprised between 16 and 18 C, whereas relative humidity did not have a significant effect on ACP dispersion. We changed the fan of our new wind tunnel in order to increase the speed of the air flow. We are now studying potential thresholds for for flight initiation. Psyllids will be tested at increasing wind speed and we will determine the proportion of ACP attempting to fly. Our objectives are to determine the optimal wind speed at which ACP prefer flying and the maximum wind speed threshold beyond which psyllids avoid flying. We also developed a pressure chamber to measure psyllid dispersion depending of controlled pressure changes. We found that psyllids responded to barometric changes rather than to different stable pressures. Psyllids were not more active at 1009 mbar as compared with 1022 mbar. However, if the barometric pressure was decreased during the experiment, ACP did not attempt flying. We are currently conducting an experiment where we investigate ACP response to citrus odor in olfactometer depending on pressure changes. Due to the fact that ACP were less prone to fly when pressure was dropping, we hypothesized that psyllid may be less responsive to citrus odor during pressure changes. We found that similarly to flight behavior, psyllid response to citrus odor was similar when pressure was stable. However, when pressure changed (either increasing, or decreasing) psyllids were less responsive to citrus odor in the olfactometer. Finally, we are preparing a field experiment, where we will look at psyllid dispersion depending on abiotic factors under field conditions. We first checked in the lab that the immunomarking method with albumin was still working. We will soon spray a block of citrus trees with egg protein. Five concentric circles of yellow sticky trap will be deployed up to 250 m from the sprayed area. Psyllids will be collected on a daily basis and, at the end of the week an ELISA will be conducted to determine if captured ACP will be positive for albumin. If they are positive, it will indicate that ACP departed from the sprayed area and moved to the sticky trap. We will correlate number of psyllids captured on sticky traps with temperature, relative humidity, barometric pressure, wind speed and wind direction.
The first objective of this study was to develop a simple and fast tool to determine insecticide resistance in Asian citrus psyllid (ACP) and implement it for field monitoring of resistance in Florida citrus groves. For this experiment, we developed a timed bottle bioassay. LC50 and LC95 estimates were determined for eight commonly used insecticides against a laboratory susceptible ACP population 24 hours after treatment. Insecticide resistance diagnostic times were determined for dimethoate (45 minutes), fenpropathrin (45 minutes), imidacloprid (45 minutes), bifenthrin (45 minutes) and flupyradifurone (60 minutes). Also, using the diagnostic time, we surveyed two central Florida groves for five major insecticides. There was no resistance detected for any of the tested insecticides. The next objective of this study was to monitor ACP populations for insecticide susceptibility in Florida. We collected ACP adults from three field populations in Polk and Orange county. The susceptibility of ACP was evaluated using carbaryl, dimethoate, fenpropathrin, spinetoram, bifenthrin, imidacloprid, aldicarb and chlorpyriphos. These insecticides represent several modes of action and are among those that are currently used to manage ACP in commercial groves in Florida. The method used was a topical application technique previously developed in our lab. At least five adult insects were treated in five replicates at the LD50, LD75 and LD95 diagnostic doses. Mortality of LD50 ranged between 36% to 56%; mortality of LD75 ranged between the 40% to 83%; mortality of LD95 ranged between 80% to 100% for both field and laboratory populations. There was no significantly resistance levels in the three field populations tested. The final, objective of this study was to develop effective insecticide rotation schedules based on the understanding of fundamental resistance mechanisms in the field. We have investigated three different rotation modules using dimethoate, adamectin, fenpropathrin, diflubenzuron and imidacloprid which have five different modes of action. There were three rotation models, one positive control and one negative control. Each treatment had four replicates. Before application we used a leaf dip bioassay to determine susceptible levels of ACP populations. We monitored ACP adults, eggs and nymphs weekly and determined when insecticide applications should be made based on a threshold of adults = 2, eggs =5 and nymphs =5 per per average sampling per sample date. We have already sprayed two insecticide applications for this study. Results indicated susceptibility levels of the field population being tested were not significantly different from our laboratory suspectable population at the onset of this experiment. This experiment remains currently in progress.
Two Zinkicide formulations (film forming plate structure or nanoparticle structure) provided better citrus canker control in a grapefruit field trial compared to industry standard copper-based products when applied at the same pounds metallic rate. The project was extended to cover a second year of field trials because the timing of funding did not align with the canker management season. The Zinkicide formulations remained effective against Xanthomonas at much lower rates than copper in culture media, so half and quarter rates were tested in the second year of the field trial. All rates of the plate forming Zinkicide and the half rate of the nanoparticle Zinkicide continued to be more effective than copper. However, the quarter rate nanoparticle Zinkicide formulation lost some efficacy and was equally effective as copper. This was surprising since the nanoparticle Zinkicide formulation was about 4 times more effective than the plate structure Zinkicide. It is hypothesized that this results form systemic movement. The entire applied rate of the plate structure Zinkicide would remain on or in the leaf keeping an effective concentration. If the nanoparticle Zinkicide moves systemically as supported by preliminary greenhouse soil drench experiments, the concentration of Zinkicide would be diluted by systemic movement. The loss of effective dose at the leaf surface suggests that the dose used in HLB trials was underestimated. In continuing projects funded by the USDA, we have adjusted our Zinkicide application rates to adjust for dilution from systemic movement in an attempt to get effective concentrations distributed throughout the plant vascular system. HLB field trials were applied at the half rate described above, which likely suffered from the same dilution problems. No significant changes in bacterial titer was observed with this low rate of Zinkicide. However, significant increases in fruit size were observed in Zinkicide treated trees, suggesting that some beneficial effects of Zinkicide on HLB were observed at these low rates. Ongoing trials funded by the USDA are using increased rates to attempt to match greenhouse efficacy observed with soil drenches on citrus canker and HLB. Without the relatively rapid canker field data, the application rate problem that limited control, but is suggestive of systemic movement, would have been overlooked. Commercialization and registration of Zinkicide is actively being pursued by Dr. Santra’s lab and an industry licensee.
Valencia harvests were completed and fruit/tree, fruit drop and leaf drop data collected. Juice analyses data is being analyzed. Fruit drop data was 22 % and 19 %, respectively, for Hamlin and Valencia trials at Babson Park. Drop % were 22 % and 20 % at Sebring and 18 % and 15 % at Ft. Meade, respectively, for Hamlins and Valencias. No differences were found between the low concentration PGR treatments and Controls at any of the sites for either healthier or more declined trees. The reduced fruit drop in treated trees after the first year did not occur in the second year. Leaf drop was heavier in September than later in the fall or winter for Hamlin trees and leaf loss was heavier for Valencias in December than later in the winter or spring. No differences were found between PGR-treated and Control trees in the amopunt of leaf drop. At each site there was no difference in the fruit per tree between the Control and PGR treatments in the second year after one year of treatments.
The low concentrations (1/4 rate) of Citrus Fix (2, 4-D) and MaxCel (Cytokinin) with or without ProGibb (GA) every 45 days to Valencia 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 400 leaves for the Control trees and the treated trees had 7 to 17 % more for the 3 treatents (MaxCel + 2, 4-D, GA treatments and combined). Most of the difference was in the accumulated summer leaf drop, August count. A similar result occured with the Hamlin trial. Percentage fruit drop was near 15 % for the Control and all the treatments.. The fruit per tree in the second year after one year of treatments was plus or minus 4 % of the Control for all the treatments and not significant. Fruit quality data was collected and will be presented in the next report..
The evaluation of the up-graded on-line ‘Citrus Flowering Monitor System’ continued with extensive grower and extension use and in making advisories to growers. No adverse comments were received and the system worked very well in collecting data for grower advisories. 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 and spray scheduling a large challenge for the Florida citrus industry. Although we only have one year of data, it looks like 5 to 10 % open flowers is reached about 21 to 27 days before full bloom. Therefore, open flowers for PFD invasion was about March 3 to 9 for the first wave. This was the same date for stopping psyllid sprays that were not bee friendly. From May 3 to 9 flowers with petals were available to sustain PFD innoculum. The first estimates of vegetative flush were 7 to 10 days earlier than the 5-10 % open flower date suggesting a one week window for flush spray coverage with more effective chemicals for psyllid control.
April 2016 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. There was greater G. citricarpa DNA in the control whereas for G. mangiferae there was more DNA in the soilset treatment. The soilset treatment had the lowest disease incidence in 2015 (1st year trt) and 2016 (2nd year). The third year treatment was applied and will be assessed next spring. 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 is being 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 general, conidia are always present but ascospores are related to the level of leaf decay. Because there is an increase in pathogen presence in 2015, we have decided to continue sampling since levels were very low in 2014 In Australia, confirmation of the ascospore and conidia production results continues. They continue to sample leaf litter in two groves in Queensland mandarin growing region. Inoculations of fruit are underway in the field but no symptoms from this year. Confirmatory inoculations of promising germplasm accessions are incubating and will be ready soon. They are repeating the fungicide work to confirm previous results. As in 2015, mulch was the best treatment to reduce the amount of leaf litter under trees. The high volume fungicide applications did slightly reduce decomposition of the leaf litter but may not be significant. Our manuscript for the mating type work has been fully accepted and is currently available as a first look at http://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-12-15-0338-R
April 2105 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 spore germination experiments for Cannonball and Vanguard are near completion and the data will be analyzed soon. The assays for the SDHI fungicides have been completed and the data are being analyzed and manuscript prepared. Molecular characterization of the SDHB, C, D is underway. Objective 2: CBS was assessed by two methods. On 21 Dec 2015, 21 Jan 2016, and 18 Feb 2016, fruit on trees were assessed by holding a m^2 frame to both sides of three center trees in plots and counting the total number of fruit within. The number of symptomatic fruit with CBS lesions was counted within the same the same square meter. Percentage of fruit with CBS was calculated from the number of symptomatic fruit divided by the total number of fruit. The number of fruit on ground was assessed on 29 Jan 2016. Dropped fruit was counted under the canopy on the ground of the middle three trees within plot and scored for presence or absence of CBS lesions. The number of fruit with CBS lesions were added to the number of fruit without CBS lesions to get a total fruit drop and then the percent fruit with CBS was calculated. Objective 3: No update for this objective was given by Co-PI in charge despite requests. Objective 4: The volatiles from ClO2 in liquid or crystal form were tested to see if they inhibited mycelial growth of G. citricarpa. Both liquid ClO2 and powder ClO2 volatiles at 100 L/L inhibited mycelial growth of G. citricarpa. Liquid ClO2 inhibited mycelial growth by 73%, and powder ClO2 inhibited mycelial growth by 79%. Liquid ClO2 or powder ClO2 volatiles at 50 L/L did not inhibit mycelial growth of G. citricarpa. Another essential oil containing product, Genysis (0.4%v/v) was added to media and the effect on mycelial growth was observed. The product Genysis inhibited mycelial growth of G. citricarpa by 81% after 14 d incubation. We are making preparations for the final report.
April 2016 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. After the inconclusive results of the second experiment, we started a third experiment. We used fresh cultures to ensure better pycnidia performance. It is currently incubating 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 have rebuilt a spore tower and have been testing with Diaporthe citri to ensure everything is working. Twigs from a P. citricarpa infested grove were collected and will be tested soon. Studies were conducted to examine P. citricarpa conidiospore survival under conditions existing in the grove and associated equipment. We found that when spores are maintined on inert surface with free moisture incubation periods of up to 3h do not affect the survival of the pycnidiospores at temperatures of 15-30. Spore survival under these moisture and temperature conditions persisted for at least 48 hours. Above 30 C, we saw a rapid decrease in spore survival. At 40 C spore survival of 1 to 2% was observed at 12 and 24 hours and no spores were able to survive for 48 hours. Similarly, for 50 C spore survival dropped to 1 to 2% by 3h and no spores survived for 12 hours. Spores deposited in free moisture but allowed to dry exhibited very poor survival regardless of temperature treatment. Upon rehydration, no spores survived beyond 3 hours.
April 2016 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. There was greater G. citricarpa DNA in the control whereas for G. mangiferae there was more DNA in the soilset treatment. The soilset treatment had the lowest disease incidence in 2015 (1st year trt) and 2016 (2nd year). The third year treatment was applied and will be assessed next spring. 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 is being 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 general, conidia are always present but ascospores are related to the level of leaf decay. Because there is an increase in pathogen presence in 2015, we have decided to continue sampling since levels were very low in 2014 In Australia, confirmation of the ascospore and conidia production results continues. They continue to sample leaf litter in two groves in Queensland mandarin growing region. Inoculations of fruit are underway in the field but no symptoms from this year. Confirmatory inoculations of promising germplasm accessions are incubating and will be ready soon. They are repeating the fungicide work to confirm previous results. As in 2015, mulch was the best treatment to reduce the amount of leaf litter under trees. The high volume fungicide applications did slightly reduce decomposition of the leaf litter but may not be significant.
Two citrus groves, one – 20 year-old Hamlin sweet orange trees predominately on Swingle rootstock and a second consisting of three year old Hamlin sweet orange trees on Swingle rootstock have received acid injection to selected blocks with and without sulfur applications for twenty-four months. Irrigation water was acidified at one of four target water pH (7.5, 6.0, 5.0, and 4.0). A controlled released form of elemental sulfur (Tiger 90) was allied at a rate of 500 pounds per treated acre to plots receiving either acidified irrigation water or control plots receiving irrigation water that was not acidified in December. Significant increases in nutrient concentrations of leaves collected in March 2016 were found in plots at both sites with reduced water and/or soil pH. Average mature leaf calcium concentrations have increased by 13.6% from an average of 2.32% when the study began in 2013 to 3.37% in the spring 2016 samples. Similar increases in leaf Mg (5.7%), Zn (16.9%), Fe (11.1%), Mn (8.6%), and B (7.8%) were found compared with no substantial increase in leaf nutrient concentrations for the control trees with no irrigation water or soil pH moderation. These results may indicate increased nutrient uptake from soils with soil solutions below 6.5 and is presumed to be because of lower soil pH levels (4.0 to 6.0). Average water uptake by trees affected with HLB continued to be 20%-25% lower than healthy trees in the greenhouse lysimeters. Water uptake for trees receiving water supplemented with calcium bicarbonate was significantly reduced (10-15%) compared with health trees but not to the extent found in the HLB affected trees. For the first time, tree root densities were significantly different for healthy trees irrigated with water supplemented with calcium carbonate (1.2 cm/cm3) when compared with healthy trees irrigated without supplemental calcium carbonate(2.1 cm/cm3). Tree size were similar for HLB affected and healthy trees irrigated with calcium carbonate but significantly smaller than healthy trees not receiving modified irrigation water.
The objective of this research project is to develop and study a potential non-phytotoxic, environmentally-friendly film-forming ACP repellent material for preventing HLB infection. In the last reporting period, OS-SG 11, 12 and 13 were studied for plant safety and rainfastness and these formulations were delivered to our collaborators for ACP infection trials. In this reporting period, a new series of formulations OS-SG 15 were developed using an EPA approved polymer, dispersant (EPA approved “for food use” only) and clay source (EPK clay, local supplier). This version of material is intentionally developed to have a fair comparison with an existing commercial product (Surround WP; as proposed to be used as control). Optimization process involved adjusting ratios of different components (dispersant, polymer and silica-alumina) to have best combination of formulations to achieve high colloidal stability in aqueous solution and high leaf surface coverage for foliar application. The material characterization was done using Fourier Transform Infra-Red (FT-IR) spectroscopy. FT-IR spectra suggested interaction between the EPK particulate with other ingredients (polymer and dispersant materials). The colloidal dispersity in aqueous solution of formulations was measured using UV-VIS transmittance technique and the measurements were done at different time intervals. High colloidal dispersity was achieved up to 4 hours which was comparable/improved compared to Surround WP control. Safety analysis and plant leaf surface coverage of OS-SG 15 formulations were conducted using Cleopatra orange (common citrus variety) as a model plant. The formulations were sprayed at the application rate of 0.5 lbs/gallon (recommended rate for the commercial control). Phytotoxicity studies were conducted using a Panasonic Environmental Test Chamber (Model MLR- 352H) to control light intensity, humidity and temperature cycling to simulate summer conditions (85% RH, 34 degree C). The formulations revealed high plant leaf surface coverage at the application rate which was comparable to the commercial control. OS-SG 15 series did not cause any plant tissue damage at the applied rates, neither the commercial control. Temperature testing was conducted to determine if the presence of polymer posed a risk of increasing the heat buildup on the plant surface. The OS-SG 15 series did not exhibit any significant increase in temperature over the commercial control. Film adherence (rainfastness) will be studied using AAS and atomic force microscopy (AFM). From the OS-SG 15 series, one or two best performing formulations will be delivered for the ACP trial.
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