1. Please state project objectives and what work was done this quarter to address them: The overall goal of the project is to develop fertilization strategies to best match nutrient supply and demand, and develop recommendations for optimal nutrient application timing as compared to a simple constant supply, which will improve fruit yield, quality, and reduce fruit drop. Objective 1) Test if a reduced N-P-K nutrient supply in the fall is safe for sustaining HLB-affected citrus, and whether it can improve fruit quality to facilitate earlier maturity / harvesting and reduce fruit drop: We completed the second split fertilizer application for designated treatments in early April, allowing a comparison of leaf nutrients sampled on May 2 at the 25% and 50% annual fertilizer allocations. For the Hamlin experiment, leaf N concentrations were significantly higher in the 50% complete treatment (2.53% N) than the 25% complete treatment (2.38% N). Leaf K concentrations were also significantly higher (1.41% K) in the 50% complete treatment than the 25% complete treatment (1.23% K). For the Valencia experiment, only leaf N was significantly higher for the 50% treatment (2.55% N) than the 25% treatment (2.33%). There were no other significant differences in foliar nutrients between treatments at that time. There were however deficiencies of Mn, and low levels of Ca, Mg, Zn, Fe and B in the two experiments according to the leaf analysis of May 2. Leaf samples collected on May 29 were analyzed and indicated improved nutrient status, with only Ca and Zn deficiencies in the experiments. Leaf N concentrations for Hamlin and Valencia experiments remained significantly different for the 50% and 25% completed fertilizer treatments (Hamlin: 2.69%, 2.81% N for 25%, 50% complete; Valencia: 2.49%, 2.66% N for 25%, 50% complete). The third split fertilizer application was in early June but the leaf samples were not analyzed yet. Dry and hot spring weather extending well into late June seemed detrimental to the trees despite daily irrigation. Fruit diameter was measured at every two weeks starting from phase 2 of fruit development (end of May), at 8 fruits per plot. Although fertilizer was applied 3 times, there was not any significant increase in fruit growth between treatments, but there was significant different in fruit growth between Hamlin and Valencia. The second Aerobotics drone survey flew at the end of May to collect data on tree size and health. There were no significant differences among treatments yet.Objective 2) Develop an optimized, practical fertilizer timing management profile to boost fruit quality and reduce fruit drop for HLB-affected citrus based in part on the sigmoidal nutrient demand curve defined by four physiological growth phases (0=bloom/fruit set; 1=cell division; 2=cell enlargement; 3=maturation):Our investigations to use the intensity of leaf symptom expression to help determine foliar nutrition in the field with smartphone apps is focusing on Mn first. We showed that we could visually classify 10 classes of Mn deficiency severity (all in the deficient range of <18 ppm). The corresponding leaf Mn concentrations correlated linearly with the 10 classes. The challenge will be to detect not yet easily visible Mn deficiency symptoms so that early diagnoses can be made. We plan to repeat the process with N, Mg, Zn, and Fe deficiency symptoms.B) New developments: sub-objectives concerning the Sugarbelle trial focusing on solving the current fruit quality issues are progressing well. We applied the first replicated foliar spray treatments to Sugarbelle trees at the city block consisting of KNO3 and KH2PO4. Two more applications will go out this summer. The purpose of the sprays is to increase peel thickness and strength to avoid soft fruit, as well as to improve fruit size. C) Issues: We are still concerned about the low fruit set in the city block compared to previous years. The early bloom in January followed by a dry hot spring has stressed the trees considerably. 2. Please state what work is anticipated for next quarter:The third and fourth fertilizer applications will be made to designated treatment plots in July and September. Soil, lysimeter sampling, leaf sampling, processing and analysis will be ongoing, as will tree size and fruit measurement. The third Aerobotics drone survey will fly in late September or early October, to evaluate tree health and size indicators. 3. Please state budget status (underspend or overspend, and why):Spending rate is approximately on track, slightly less than expected due to startup lag in Q1.
1. Please state project objectives and what work was done this quarter to address them: Objective. To determine the influence of compost during the first three years of tree establishment on growth, productivity, and root and soil health of citrus trees on rootstocks with different vigor-inducing capacity. Another round of compost was applied at the usual rate. Flush ratings and soil moisture measurements continued. The soil moisture in the compost treated plots continues to be significantly higher than in the control plots and we are seeing significantly more (two to three-fold more) weed pressure in the compost treated plots. Soil and leaf samples were collected for macro- and micronutrient analysis. Many of the soil nutrients continue to be present in higher concentrations in the compost treated plots than in the control plots except for copper which was reduced by the compost. However, higher nutrient concentrations in the soil did not always translate to higher concentrations in the leaves. The cation exchange capacity and the soil pH were also significantly higher in compost plots than control plots.The fibrous root respiration was measured and roots from the compost plots have a higher respiration rate than roots from the control plots. Significant differences were also found among rootstocks with the citrandarins having higher rates than US-802. This was also reflected in the specific root length which was lowest for US-802 and highest for US-897. The specific root length appears to be moderately correlated with pounds soluble solids. A manuscript for publication was submitted and is under review. A Citrus Industry magazine article on this study was published in the June 2022 issue. 2. Please state what work is anticipated for next quarter:Flush ratings and soil moisture measurements will continue. Root respiration and specific root length will be measured. We will conduct tree ratings and tree size measurements. Leaves will be collected for CLas determination. The weed biomass will be determined.Data analyses will continue. 3. Please state budget status (underspend or overspend, and why): Most of the funds have been spent.
1. Please state project objectives and what work was done this quarter to address them: Objective. To determine the influence of compost during the first three years of tree establishment on growth, productivity, and root and soil health of citrus trees on rootstocks with different vigor-inducing capacity. Another round of compost was applied at the usual rate. Flush ratings and soil moisture measurements continued. The soil moisture in the compost treated plots continues to be significantly higher than in the control plots and we are seeing significantly more (two to three-fold more) weed pressure in the compost treated plots. Soil and leaf samples were collected for macro- and micronutrient analysis. Many of the soil nutrients continue to be present in higher concentrations in the compost treated plots than in the control plots except for copper which was reduced by the compost. However, higher nutrient concentrations in the soil did not always translate to higher concentrations in the leaves. The cation exchange capacity and the soil pH were also significantly higher in compost plots than control plots.The fibrous root respiration was measured and roots from the compost plots have a higher respiration rate than roots from the control plots. Significant differences were also found among rootstocks with the citrandarins having higher rates than US-802. This was also reflected in the specific root length which was lowest for US-802 and highest for US-897. The specific root length appears to be moderately correlated with pounds soluble solids. A manuscript for publication was submitted and is under review. A Citrus Industry magazine article on this study was published in the June 2022 issue. 2. Please state what work is anticipated for next quarter:Flush ratings and soil moisture measurements will continue. Root respiration and specific root length will be measured. We will conduct tree ratings and tree size measurements. Leaves will be collected for CLas determination. The weed biomass will be determined.Data analyses will continue. 3. Please state budget status (underspend or overspend, and why): Most of the funds have been spent.
The first oxamyl nematicide treatment occurred in the IPC trial on 25 April 2022 and the second on 24 May. The effects of these treatments on sting nematode populations were measured on 11 July, 48 days after the final treatment. Two soil cores (30 cm deep x 2.5 cm dia) per tree were composited in each 4-tree plot. Samples were weighed and nematodes were separated from subsamples (250 cm3) by sucrose centrifugation. Fibrous roots in the entire sample were collected, air dried and are currently being separated from weed roots for measurement. The sting nematode populations were low, averaging just 5 nematodes per 250 cm3 soil. Nevertheless, oxamyl was shown to reduce the (log-transformed ) sting nematodes (P=0.015) by 53% and there was a suggestion of an interaction (P=0.07) with the IPC treatment in which nematodes were reduced by 19% compared to 88% in the non-covered trees. The first rootstock lines were planted in the four large Rubbermaid tanks on 17 June (UFR-1, UFR-4, UFR-5, UFR-6, UFR-15, UFR-17, MG-11, FG#2, Orange 14, Orange 16, A+VolkxOrange19-11-8, LB8-9xS10-15-18, LB8-9xS13-15-16, S10xx639-12-32, S11xSO+50-7-16-12, LB8-9×50-7-16-4, Blue 1). Two tanks are infested with sting nematode and two are non-infested controls. Each tank contains 4 plants of each rootstock. The greenhouse renovation improved the ambient conditions, especially the temperature control. The plants will be evaluated for root and shoot mass and nematode induced stubby root and tip gall symptoms.
The first oxamyl nematicide treatment occurred in the IPC trial on 25 April 2022 and the second on 24 May. The effects of these treatments on sting nematode populations were measured on 11 July, 48 days after the final treatment. Two soil cores (30 cm deep x 2.5 cm dia) per tree were composited in each 4-tree plot. Samples were weighed and nematodes were separated from subsamples (250 cm3) by sucrose centrifugation. Fibrous roots in the entire sample were collected, air dried and are currently being separated from weed roots for measurement. The sting nematode populations were low, averaging just 5 nematodes per 250 cm3 soil. Nevertheless, oxamyl was shown to reduce the (log-transformed ) sting nematodes (P=0.015) by 53% and there was a suggestion of an interaction (P=0.07) with the IPC treatment in which nematodes were reduced by 19% compared to 88% in the non-covered trees. The first rootstock lines were planted in the four large Rubbermaid tanks on 17 June (UFR-1, UFR-4, UFR-5, UFR-6, UFR-15, UFR-17, MG-11, FG#2, Orange 14, Orange 16, A+VolkxOrange19-11-8, LB8-9xS10-15-18, LB8-9xS13-15-16, S10xx639-12-32, S11xSO+50-7-16-12, LB8-9×50-7-16-4, Blue 1). Two tanks are infested with sting nematode and two are non-infested controls. Each tank contains 4 plants of each rootstock. The greenhouse renovation improved the ambient conditions, especially the temperature control. The plants will be evaluated for root and shoot mass and nematode induced stubby root and tip gall symptoms.
1. Please state project objectives and what work was done this quarter to address them: Objective 1: Determine effects of lowered soil pH on CLas populations and root physiology including internal root apoplast and vascular tissue pH. Due to a collapse in our inoculum trees, we are re-inoculating trees for these experiments and will start the greenhouse portion of the study at the end of July 2022 because some trees did not turn out positive for CLas in April 2022. All protocols are developed and pretesting for the study is finalized. Objective 2: Field test multiple acidification materials including organic acids for tree response CLas suppression, nutrient uptake, and root and vascular pH changes. In this quarter, we collected soil and leaf tissue samples which show sufficiency in all treatments. We are now evaluating root density, and PCR of selected trees. We also applied all acids and elemental S in the appropriate treatments and are monitoring canopy changes and soil trends as described in the project deliverables, Fruit harvest and fruit quality evaluations were completed in April 2022. 2. Please state what work is anticipated for next quarter: We will apply acids and elemental S in the next quarter. The greenhouse study on effects of pH on root physiology and CLas populations will also be conducted and completed in the next quarter. 3. Please state budget status (underspend or overspend, and why): The budget is on track and meeting the project milestones.
1. Please state project objectives and what work was done this quarter to address them: Objective 1: Determine effects of lowered soil pH on CLas populations and root physiology including internal root apoplast and vascular tissue pH. Due to a collapse in our inoculum trees, we are re-inoculating trees for these experiments and will start the greenhouse portion of the study at the end of July 2022 because some trees did not turn out positive for CLas in April 2022. All protocols are developed and pretesting for the study is finalized. Objective 2: Field test multiple acidification materials including organic acids for tree response CLas suppression, nutrient uptake, and root and vascular pH changes. In this quarter, we collected soil and leaf tissue samples which show sufficiency in all treatments. We are now evaluating root density, and PCR of selected trees. We also applied all acids and elemental S in the appropriate treatments and are monitoring canopy changes and soil trends as described in the project deliverables, Fruit harvest and fruit quality evaluations were completed in April 2022. 2. Please state what work is anticipated for next quarter: We will apply acids and elemental S in the next quarter. The greenhouse study on effects of pH on root physiology and CLas populations will also be conducted and completed in the next quarter. 3. Please state budget status (underspend or overspend, and why): The budget is on track and meeting the project milestones.
Our project is examining phloem gene expression changes in response to CLas infection in HLB-susceptible sweet orange and HLB-resistant Poncirus and Carrizo (a sweet orange – Poncirus cross). We are using a recently developed methodology for woody crops that allows gene expression profiling of phloem tissues. The method leverages a translating ribosome affinity purification strategy (called TRAP) to isolate and characterize translating mRNAs from phloem specific tissues. Our approach is unlike other gene expression profiling methods in that it only samples gene transcripts that are actively being transcribed into proteins and is thus a better representation of active cellular processes than total cellular mRNA. Sweet orange, and HLB-resistant Poncirus and Carrizo (sweet orange x Poncirus) will be transformed to express the tagged ribosomal proteins under the control of characterized phloem-specific promoters; tagged ribosomal proteins under control of the nearly ubiquitous CaMV 35S promoter will be used as a control. Transgenic plants will be exposed to CLas+ or CLas- ACP and leaves sampled 30, 60, 90, and 120 days later. Ribosome-associated mRNA will be sequenced and analyzed to identify differentially regulated genes at each time point and between each citrus cultivar. Comparisons of susceptible and resistant phloem cell responses to CLas will identify those genes that are differentially regulated during these host responses. Identified genes will represent unique phloem specific targets for CRISPR knockout or overexpression, permitting the generation of HLB-resistant variants of major citrus cultivars.During this most recent quarter, the 2nd quarter of our 1st 6 month no cost extension (the original end date was 11/30/2021; we were granted one 6 month no cost extension and one 3 month one; the current end date is 08/31/2022), the Stover lab sent the last of the transgenic lines needed for the project to the Rogers lab. Now at least 4 high expressing lines for each of the 9 promoter/genotype combinations are in the containment greenhouse facility at Ft. Detrick and are being prepared for no-choice psyllid inoculation experiments.The Rogers lab has continued no-choice psyllid inoculation experiments on the rooted cuttings available and ribosome pull-downs from the tissue collected. Work has progressed more quickly since the ARS 25% occupancy cap was lifted on Monday, March 28th. We have still not been able to identify a qualified and interested post-doc candidate and with less than 3 month left on the grant, now do not have time to hire someone. As many translatome RNA samples as possible will be sent for sequencing in July, leaving the month of August for data analysis.
This project is an continuation of an objective of existing CRDF funded project (# 00124558 ; ended in March 2019, final report submited to CRDF) with some added treatments to be evaluated in comparison to control (dry conventional fertilizer with foliar micronutrients). Altogether currently there are 25 treatments of citrus nutrition that are being compared to control. In this quarter the project has been completed. A comprehensive final report has been submitted. Overall, the 5 years yield and fruit quality results suggest that soil applied micronutrient in form of Tiger-Sul product are beneficial for the trees. Foliar micronutrient should not be used as sole source of any nutrient. The soil-applied program takes time to show its effect and therefore, fertilizer programs should be evaluated with patience over the years. It is to be noted that fertilizer program should be site specific as results of one site cannot be replicated at other site. Therefore, the fertilizer program should be tweaked to address the specific needs of each unique site. Altogether, the best treatments (trts # 4, 6,7,10 in Arcadia) and (trts # 9 in Fort Meade) yielded about a box per tree more fruit than the control – suggesting a substantial increase in profit/acre. In addition we saw improvement in total soluble solids with use of tiger micronutrients. These data support our data and conclusions from field experiments that micronutrients delivered to the roots can improve health and productivity of HLB-affected trees.
HLB is known to make citrus roots more susceptible to Phytophthora root rot. It also reduces the efficacy of chemical management of Phytophthora root rot, creating a difficult management scenario. Current Phytophthora management recommendations are based on pre-HLB work done in the 1980s. These three conditions raise the question of whether yield improvement from Phytophthora management is enough to pay for the management costs themselves. The goal of this project is to develop new soil propagule density managment thresholds and recommendations for chemical management of Phytophthora root rot based on ecomonic analysis of yield responses in different soil conditions. Objective 1) Determine if labelled Phytophthora management maintains efficacy in the field on HLB-affected trees for reducing fibrous root loss and improving yield.No further phytophthora counts have been taken from the southwest Florida site this quarter. However, yield data from Valencia was taken in February. In the preliminary data, there were no significant differences among the treatments but there was also a tremendous amount of variation within the treatments. The phosphite alternated with Presidio treatment had less than half the variation among plots that the other treatments. Differential variation among the treatments was also observed for Acid and brix but not as strongly for the ratio. This means that further analysis will be needed to reduce the amount of variation among the treatments. From this preliminary analysis of the sugars, there was no significant difference among treatment quality measures for the Valencia.We initiated a second location for two new trials, early oranges and Valencia in the Wachula area. The sites have a history of phytophthora. The preliminary counts from the blocks varied between 40 and 128. We have taken the per plot data after laying out the trials but counts are not complete. It is expected that treatments will start in the first week of June. We plan to have all the treatments of the first set of trials with the additon of Orondis Ultra. Objective 2) Determine benefit-cost thresholds for Phytophthora treatment on HLB-affected treesI have spoken to Ariel Singerman and determined what data he needs to proceed and I preparing it to send to him for the 2021 season.
The first nematicide treatment occurred in the IPC trial in late April 2022 and the second will occur in late May. The effects of these treatments will be determined in early July when soil samples will be taken to obtain the first nematode and root mass density measurements. The site is on a hilltop and is extremely windy. We spent several days following planting installing grade stakes inside the IPCs to better support the PVC frames. To date they are secure.As noted previously, maintenance and new construction on our greenhouse that started at the beginning of January was still ongoing in April, precluding further research on the rootstock tolerance trials until completed. Plants and cultures had to be moved to a laboratory facility to protect the citrus from psyllid infestations and to protect all of the cultures from excessively high temperatures when the evaporative cooling systems were being replaced. Plants were reinstalled in the greenhouse during the second week of April and pruned to reinitiate growth in preparation for innoculations to occur in June. Cultures were sampled and found to contain fewer nematodes than previously, but were still in good condition and will recover. The sting nematode populations in the large tanks that remained in the greenhouse were in good condition. Presumably, the depth of soil allowed the nematodes to persist despite the high ambient temperatures they experienced for a week. The first rootstock lines are ready and will be installed in the tanks during the first week of June.
1. Please state project objectives and what work was done this quarter to address them: Specific objectives are:1) To determine the right timing for Zn and K treatments to minimize fruit drop. 2) To determine effects of GA3 and 2,4D applications on fruit retention when applied at different times during fruit development. 3) To develop a strong and proactive outreach program. During this initial quarter, for objectives 1 and 2 we have identified the trees from Hamlin and Valencia in Central and Southwest Florida that we will be using in our studies, flagged them and organized them in a completely randomized block design. We have also taken baseline initial data on HLB severity ratings, tree height, canopy volume, leaf area index, and scion and rootstock diameters. Also, leaf samples for nutrient analysis and determination of initial Ct values for HLB have been taken.For objective 2, GA3 and 2,4D treatments have already started. For objective 1, we are starting first set of treatments by the end of May.Objective 3: Outreach-F. Alferez, Foliar applications of Zinc and Potassium to increase yield by reducing fruit drop in Hamlin oranges. 2022 Florida Citrus Growers’ Institute, Avom Park April 5, 2022.-T. Vashisth, Update on Gibberellic acid studies.2022 Florida Citrus Growers’ Institute, Avom Park April 5, 2022.-T, Vashisth and F. Alferez., wokshop by zoom on “gibberellic acid research update and other PGRs for Florida citrus”. 217 registered participants. 2. Please state what work is anticipated for next quarter: In the second quarter, we will perform first set of treatments for objective 1 in both Valencia and Hamlin trees and continue with data collection. Treatments for objective 2 will continue as planned (applications every 45 days). Importantly, a new PhD student, Dyvia Aryal, Ms graduated from University of Hannover, Germany, will join the project in June-July, to conduct studies on this project under Dr Alferez supervision 3. Please state budget status (underspend or overspend, and why): There has been underspending on student salary and tuition, because student could not join in January as expected, due to a delay in proposal approval. As stated above, Dyvia will join in Summer, as soon as she gets her visa approved (in process).
Objective 1. To illustrate whether application of bactericides via trunk injection could efficiently manage citrus HLB and how bactericides via trunk injection affects Las and HLB diseased trees. 1.1. Determination of the in planta minimum bactericidal concentrations (MBCs) of bactericides against LasWe developed a new method for evaluating the effects of oxytetracycline (OTC) treatment on CLas titers in infected plants and determined the relationship between OTC residue levels and control levels achieved for CLas using mathematical modeling in greenhouse and field experiments. In both greenhouse and field, OTC spray did not reduce the titers of CLas, and it produced undetectable or mild levels of OTC residue in leaves within 7 days post-application (DPA). In greenhouse, OTC injection at 0.05 g per tree decreased CLas titers to an undetectable level (cycle threshold value = 36.0) from 7 to 30 DPA and produced a residue level of OTC at 0.68 to 0.73 µg/g of fresh tissue over this period. In the field, OTC injection at 0.50 g per tree resulted in the decline of CLas titers by 1.52 log reduction from 14 to 60 DPA, with residue levels of OTC at 0.27 to 0.33 µg/g of fresh tissue. In both trials, a first-order compart model of OTC residue dynamics in leaves of trunk-injected trees was specified for estimating the retention of effective concentrations. Furthermore, nonlinear modeling revealed significant positive correlations between OTC residue levels in leaves and the control levels for CLas achieved. The results suggested that the minimum concentrations of OTC required to suppress CLas populations in planta to below the detection limit are 0.68 and 0.86 µg/g and that the minimum concentrations of OTC required for initial inhibition of CLas growth in planta are ~0.17 and ~0.215 µg/g in leaf tissues under greenhouse and field conditions, respectively. This finding highlights that a minimum concentration of OTC should be guaranteed to be delivered to target CLas in infected plants for effective control of citrus HLB.We investigated the in planta minimum bactericidal concentrations of streptomycin (STR) and its effect on CLas titers in planta applied by foliar spray and trunk injection of 3-year-old citrus trees that were naturally infected by CLas in the field. After foliar spray, STR levels in leaves peaked at 2 to 7 days postapplication (dpa) and gradually declined thereafter. The STR spray did not significantly affect CLas titers in leaves of treated plants as determined by quantitative PCR. After trunk injection, peak levels of STR were observed 7 to 14 dpa in the leaf and root tissues, and near-peak levels were sustained for another 14 days before significantly declining. At 12 months after injection, moderate to low or undetectable levels of STR were observed in the leaf, root, and fruit, depending on the doses of STR injected, with a residue level of 0.28 µg/g in harvested fruit at the highest injection concentration of 2.0 µg/tree. CLas titers in leaves were significantly reduced by trunk injection of STR at 1.0 or 2.0 g/tree, starting from 7 dpa and throughout the experimental period. The reduction of CLas titers was positively correlated with STR residue levels in leaves. The in planta minimum effective concentration of STR needed to suppress the CLas titer to an undetectable level (cycle threshold =36.0) was 1.92 µg/g fresh weight. Determination of the in planta minimum effective concentration of STR against CLas and its spatiotemporal residue levels in planta provides the guidance to use STR for HLB management. 1.2. Effect of bactericides via trunk injection on citrus HLB disease progression, tree health, yield and fruit quality in different aged trees with a different disease severityThe field experiments were performed at four different groves on different aged trees with a different disease severity. They are one located in Avon Park, FL, 3-year old Valencia trees; one in Bartow, FL, 2-year old W. Murrcot trees; and one in Auburndale, FL, 7-year old Hamlin trees (planted in 02/2012). The last one is in CREC-, Lake Alfred, FL, 20-year old Hamlin trees. The HLB disease severity and tree size (canopy volume and trunk diameter) in the four groves were estimated immediately prior to treatment application. For the field tests, the experiment design is a randomized complete block design (RCBD) for 9 treatments, including 6 injection treatments (3 different doses for OTC or STR), 2 spray treatments (OTC or STR spraying), and one No treatment as a negative control. Each injection treatment consisted of 9 or 15 trees divided into 3 blocks of 3 or 5 trees each. Each spray treatment consisted of 30 trees divided into 3 blocks of 10 trees each. For all the four field trials, the injection treatment applications were completed by the end of April 2019. The 1st application of spray treatments were completed during spring flushing in February or March 2019, the 2nd applications were conducted in late June to early July 2019, and the 3rd applications were conducted in early to middle October 2019. Leaf samples have been collected from the treated trees at the following time points: 0 (pre- injection), 7, 14, 28 days, 2, 4, 6, 8, 10 and 12 months after treatment (MPT). Our data demonstrate that for 6-year-old trees, 2.0 g OTC/tree, but not 1.0 g OTC /tree via trunk injection significantly reduced CLas titers. However, neither concentrations reduced CLas titers for 22-year-old trees. Spray had no effect on CLas titers. STC at 1 g or 2 g/tree via trunk injection had no effect on CLas titers. OTC (2.0 g/tree) and STR (2.0 g/tree) but not at lower concentrations significantly increased fruit yield, but had no effect on quality. Objective 2. To examine the dynamics and residues of bactericide injected into citrus and systemic movement within the vascular system of trees and characterize the degradation metabolites of bactericides in citrus. Residues of OTC or STR in fruit harvested from 22-year old Hamlin sweet orange trees injected with OTC or STR at different doses were determined. Injections were conducted in February-March 2021 and fruit was harvested in January 2022. Neither OTC or STR was detected at 1 g or 2 g/tree via trunk injection.Residue of OTC or STR in fruit harvested from 6-year old Hamlin sweet orange trees injected with OTC or STR at different doses were determined. Injections were conducted in March 2021 and fruit was harvested in January 2022. The following residues were observed: OTC (1.0 g/tree): 0.08 ppm ± 0.03; OTC (2.0 g/tree): 0.19 ppm ± 0.07, STR (1.0 g/tree): 0.09 ppm ± 0.03; STR (2.0 g/tree): 0.17 ppm ± 0.08. Objective 3. To determine whether trunk injection of bactericides could decrease Las acquisition by Asian citrus psyllids (ACP)Twenty 1.5-year old citrus (Valencia sweet orange) plants were graft-inoculated by Las carrying buds in February 2020. These plants are being tested for Las infection and 4 plants were confirmed with Las infection (Ct values are between 34.0 and 35.0) at 4 months after grafting. They will be subjected to OTC or STR treatment by trunk injection and ACP acquisition access for 7 to 14 days. We have determined the time points to test OTC and STR treatment on ACP acquisition of Las. We have conducted the test regarding how trunk injection of OTC affect ACP acquisition of Las. OTC significantly reduced ACP acquisition of Las. Objective 4. To monitor resistance development in Las against bactericides and evaluate potential side effects of trunk injection of bactericides Monitoring resistance development in Las against bactericides. Leaf samples for this test have been collected from 5 trees injected with OTC and 5 trees injected with STR at the highest doses in each of the three groves at 6 and 9 months after the injection, respectively. PCR-sequencing analysis on Las 16SrRNA gene showed there was no mutation compared with the reported sequence. However, accurate evaluation needs to be conducted once CLas is cultured. No obvious side effects were observed at low OTC or STR concentrations. However, at some high concentrations, phytotoxicity was observed on leaves.
HLB is known to make citrus roots more susceptible to Phytophthora root rot. It also reduces the efficacy of chemical management of Phytophthora root rot, creating a difficult management scenario. Current Phytophthora management recommendations are based on pre-HLB work done in the 1980s. These three conditions raise the question of whether yield improvement from Phytophthora management is enough to pay for the management costs themselves. The goal of this project is to develop new soil propagule density managment thresholds and recommendations for chemical management of Phytophthora root rot based on ecomonic analysis of yield responses in different soil conditions. Objective 1) Determine if labelled Phytophthora management maintains efficacy in the field on HLB-affected trees for reducing fibrous root loss and improving yield.During this quarter, soil samples for root density and phythophthora counts were collected from both sites. The Hamlin block was harvested. The quality and sizing data were generated in the packinghouse facility.In preliminarily reviewing the data, there were significant differences among the root densities for Hamlin but not the Valencia. The range for Hamlin was 0.096 to 0.314 roots/ml of soil and for Valencia it was 0.032 to 0.076 roots/ml soil. The treatment with the greatest number of roots was the Ridomil, Presidio, Phosphite, and Orondis regimen and it had significantly more than the UTC. There were no significant differences among the total phytophthora propagule count for the Valencia which ranged from 2.8 to 9.6 propagules/cm3 of soil. When separated for the species there was also no difference. In the Hamlin trees, there was a significant difference among treatments. The Ridomil, Presidio, Phosphite, and Orondis treatment still had no propagules and a statitically equivalent number were observed in the Phosphite alternated with Orondis tretatment. The treatment with the most propagules was Phosphite alternated with Ridomil treatment which had 56.0 propagules/cm3 of soil, significantly higher than other treatments. In the fall propagules counts at both sites, the block effect was much weaker but additional statistical analysis will still be needed to take this factor into account in a better manner. When looking at the Hamlin fruit weights, there was no treatment effect but there was a significant block effect. In looking at the pounds solid per box from each plot, there was a weakly significant effect (P < 0.1) for treatments which ranged from 5.40 to 5.02 lb solids/box. The best treatment was the Phosphite treatment and block was highly significant. The brix and acid had no signficant differences but the brix acid ratio with the highest ratio is for the UTC (16.36) and lowest was Phosphites rotated with Presidio (15.24). Objective 2) Determine benefit-cost thresholds for Phytophthora treatment on HLB-affected treesAs planned in the proposal, this objective awaits this years yield results to begin calculating benefit-cost based on a combination of change in yield from the previous year and comparison among treatments within blocks.
HLB is known to make citrus roots more susceptible to Phytophthora root rot. It also reduces the efficacy of chemical management of Phytophthora root rot, creating a difficult management scenario. Current Phytophthora management recommendations are based on pre-HLB work done in the 1980s. These three conditions raise the question of whether yield improvement from Phytophthora management is enough to pay for the management costs themselves. The goal of this project is to develop new soil propagule density managment thresholds and recommendations for chemical management of Phytophthora root rot based on ecomonic analysis of yield responses in different soil conditions. Objective 1) Determine if labelled Phytophthora management maintains efficacy in the field on HLB-affected trees for reducing fibrous root loss and improving yield.During this quarter, Prophyte treatments were applied to the Hamlin and Valencia sites in July and October. The root density and phytophthora counts for all treatments were done in August. Soil applied treatments were undertaken in late September and early October.In preliminarily reviewing the data, there were no significant differences among the root densities for Hamlin and Valencia. The range for Hamlin was 0.046 to 0.092 roots/ml of soil and for Valencia it was 0.02 to 0.072 roots/ml soil. There were no significant differences among the total phytophthora propagule count for the Valencia which ranged from 12.8 to 23.2 propagules/cm3 of soil. When separated for the species there was alss no difference. In the Hamlin trees, there was a significant difference among treatments. The Ridomil, Presidio, Phosphite, and Orondis treatment had no propagules and this was signficantly fewer than the Phosphite alternated with Ridomil treatment which had 19.2 propagules/cm3 of soil. In both sites, there was a significant block effect and a new statistical analysis will be needed to take this factor into account. No brown rot measurements were taken this year.Objective 2) Determine benefit-cost thresholds for Phytophthora treatment on HLB-affected treesAs planned in the proposal, this objective awaits this years yield results to begin calculating benefit-cost based on a combination of change in yield from the previous year and comparison among treatments within blocks.
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