Horticultural & Management

Improving the Systemic Uptake of Therapeutic Compounds by Trunk Injections

1. Please state project objectives and what work was done this quarter to address them:Objective 1: Using callose inhibitors to improve systemic uptake and reduce HLB symptoms.A study was implemented incorporating 12 replicates of all proposed treatments.  We continued our field experiment on sweet orange ~8 years old (Citrus x sinensis) trees: (1) injected control (water), (2) Oxytetracycline (2 g per tree), (3) DDG (0.1 mM), (4) DDG (0.1mM) + Oxytetracycline (2 g per tree), (5) DDG (1mM), (6) 3AB (0.1mM), (7) 3AB (0.1mM) + Oxytetracycline (2 g per tree), (8) 3AB (1mM). Then we designed the appropriate map for the experiment. We measured baseline stomatal conductance, trunk diameter, canopy volume and canopy density. Injection treatments were accompanied with measurements of canopy dimensions and density, and followed by measurements of stomatal conductance.  No treatment reduced stomatal conductance, and we conclude that the treatments do not negatively impact tree physiology in the short term. Canopy growth will be measured at 6 months post-treatment. Furthermore, six mature leaf samples per tree were collected to measure the CLas titer and quantify calloselevel of each tree. Leaf samples were collected to measure the CLas titre and quantify the callose level of trees 1 and 2 weeks after treatments. Lastly, we measured the Oxytetractcline on the trees. Suprisingly we saw that there was no difference between the different samples, and they were all the same. We went back and evaluated all our procedures. Unfortunatly, we found that we made a mistake in the Oxytetracycline measurements. and injected only a small amount, a small percentange of what we had planned. We decided to repeat the injections.Objective 2: Maintaining water-saturated injection site: Sealed trunk injection ports that stay functional by avoiding woundresponses.Experments planned.Objective 3: Targeted root delivery.No progress. 2. Please state what work is anticipated for next quarter:We will reinject trees and evaluate the trees for callose level and Clas titre monthly. We will also measure the canopy volume and density. We will begin experiments for objectives 2 and 3. 3. Please state budget status (underspend or overspend, and why):Underspend- since it took some time to initiate the work 4. Please show all potential commercialization products resulting from this research, and the status of each:We are still evaluating the effect of the callose inhibitor in the field trials  

Improving the Systemic Uptake of Therapeutic Compounds by Trunk Injections

1. Please state project objectives and what work was done this quarter to address them:Objective 1: Using callose inhibitors to improve systemic uptake and reduce HLB symptoms.A study was implemented incorporating 12 replicates of all proposed treatments.  We continued our field experiment on sweet orange ~8 years old (Citrus x sinensis) trees: (1) injected control (water), (2) Oxytetracycline (2 g per tree), (3) DDG (0.1 mM), (4) DDG (0.1mM) + Oxytetracycline (2 g per tree), (5) DDG (1mM), (6) 3AB (0.1mM), (7) 3AB (0.1mM) + Oxytetracycline (2 g per tree), (8) 3AB (1mM). Then we designed the appropriate map for the experiment. We measured baseline stomatal conductance, trunk diameter, canopy volume and canopy density. Injection treatments were accompanied with measurements of canopy dimensions and density, and followed by measurements of stomatal conductance.  No treatment reduced stomatal conductance, and we conclude that the treatments do not negatively impact tree physiology in the short term. Canopy growth will be measured at 6 months post-treatment. Furthermore, six mature leaf samples per tree were collected to measure the CLas titer and quantify calloselevel of each tree. Leaf samples were collected to measure the CLas titre and quantify the callose level of trees 1 and 2 weeks after treatments. Lastly, we measured the Oxytetractcline on the trees. Suprisingly we saw that there was no difference between the different samples, and they were all the same. We went back and evaluated all our procedures. Unfortunatly, we found that we made a mistake in the Oxytetracycline measurements. and injected only a small amount, a small percentange of what we had planned. We decided to repeat the injections.Objective 2: Maintaining water-saturated injection site: Sealed trunk injection ports that stay functional by avoiding woundresponses.Experments planned.Objective 3: Targeted root delivery.No progress. 2. Please state what work is anticipated for next quarter:We will reinject trees and evaluate the trees for callose level and Clas titre monthly. We will also measure the canopy volume and density. We will begin experiments for objectives 2 and 3. 3. Please state budget status (underspend or overspend, and why):Underspend- since it took some time to initiate the work 4. Please show all potential commercialization products resulting from this research, and the status of each:We are still evaluating the effect of the callose inhibitor in the field trials  

Improving the Systemic Uptake of Therapeutic Compounds by Trunk Injections

1. Please state project objectives and what work was done this quarter to address them:Objective 1: Using callose inhibitors to improve systemic uptake and reduce HLB symptoms.A study was implemented incorporating 12 replicates of all proposed treatments.  We continued our field experiment on sweet orange ~8 years old (Citrus x sinensis) trees: (1) injected control (water), (2) Oxytetracycline (2 g per tree), (3) DDG (0.1 mM), (4) DDG (0.1mM) + Oxytetracycline (2 g per tree), (5) DDG (1mM), (6) 3AB (0.1mM), (7) 3AB (0.1mM) + Oxytetracycline (2 g per tree), (8) 3AB (1mM). Then we designed the appropriate map for the experiment. We measured baseline stomatal conductance, trunk diameter, canopy volume and canopy density. Injection treatments were accompanied with measurements of canopy dimensions and density, and followed by measurements of stomatal conductance.  No treatment reduced stomatal conductance, and we conclude that the treatments do not negatively impact tree physiology in the short term. Canopy growth will be measured at 6 months post-treatment. Furthermore, six mature leaf samples per tree were collected to measure the CLas titer and quantify calloselevel of each tree. Leaf samples were collected to measure the CLas titre and quantify the callose level of trees 1 and 2 weeks after treatments. Lastly, we measured the Oxytetractcline on the trees. Suprisingly we saw that there was no difference between the different samples, and they were all the same. We went back and evaluated all our procedures. Unfortunatly, we found that we made a mistake in the Oxytetracycline measurements. and injected only a small amount, a small percentange of what we had planned. We decided to repeat the injections.Objective 2: Maintaining water-saturated injection site: Sealed trunk injection ports that stay functional by avoiding woundresponses.Experments planned.Objective 3: Targeted root delivery.No progress. 2. Please state what work is anticipated for next quarter:We will reinject trees and evaluate the trees for callose level and Clas titre monthly. We will also measure the canopy volume and density. We will begin experiments for objectives 2 and 3. 3. Please state budget status (underspend or overspend, and why):Underspend- since it took some time to initiate the work 4. Please show all potential commercialization products resulting from this research, and the status of each:We are still evaluating the effect of the callose inhibitor in the field trials  

OTC Directed Research Solicitation: Use of CRDF Rootstock Trial Locations for Testing Bactericides Inserted into Trees Through Systemic Delivery Devices

1. Please state project objectives and what work was done this quarter to address them: Main objective: To determine the large-scale efficacy of trunk injection of OTC on citrus tree health, fruit quality, and yield in existing rootstock trials in three different commercial growing environments. Sub-objectives: a) test the efficacy of OTC injection in the rootstock trunk compared to injection into the scion, and b) determine whether OTC injection increases/restores root densities and if there are interactions with the rootstock.  Leaves were collected for CLas analysis. Trunk injury/wound evaluations were conducted. PCR analyses were continued. Statistical data analyses continued. So far, data analysis showed the following: The uptake rate of the injected OTC solution (Rectify) did not differ whether injections were done into the rootstock or the scion trunk. However, there was a large variability during the day and among the trial sites – the uptake rate was anywhere from <30 minutes to >3 hours.Injections in the rootstock seemed to have caused slightly less visible injury than injections in the scion. Some rootstock differences were also noted.In one of the trials (Venus location), we measured lower CLas titer levels in injected trees.  2. Please state what work is anticipated for next quarter: Leaves will be collected for CLas and OTC analysis. Disease ratings will be conducted. We will prepare for the harvest. Harvest dates will depend on the grower collaborators. 3. Please state budget status (underspend or overspend, and why):The budget is as expected. 

OTC Directed Research Solicitation: Use of CRDF Rootstock Trial Locations for Testing Bactericides Inserted into Trees Through Systemic Delivery Devices

1. Please state project objectives and what work was done this quarter to address them: Main objective: To determine the large-scale efficacy of trunk injection of OTC on citrus tree health, fruit quality, and yield in existing rootstock trials in three different commercial growing environments. Sub-objectives: a) test the efficacy of OTC injection in the rootstock trunk compared to injection into the scion, and b) determine whether OTC injection increases/restores root densities and if there are interactions with the rootstock.  Leaves were collected for CLas analysis. Trunk injury/wound evaluations were conducted. PCR analyses were continued. Statistical data analyses continued. So far, data analysis showed the following: The uptake rate of the injected OTC solution (Rectify) did not differ whether injections were done into the rootstock or the scion trunk. However, there was a large variability during the day and among the trial sites – the uptake rate was anywhere from <30 minutes to >3 hours.Injections in the rootstock seemed to have caused slightly less visible injury than injections in the scion. Some rootstock differences were also noted.In one of the trials (Venus location), we measured lower CLas titer levels in injected trees.  2. Please state what work is anticipated for next quarter: Leaves will be collected for CLas and OTC analysis. Disease ratings will be conducted. We will prepare for the harvest. Harvest dates will depend on the grower collaborators. 3. Please state budget status (underspend or overspend, and why):The budget is as expected. 

OTC Directed Research Solicitation: Use of CRDF Rootstock Trial Locations for Testing Bactericides Inserted into Trees Through Systemic Delivery Devices

1. Please state project objectives and what work was done this quarter to address them: Main objective: To determine the large-scale efficacy of trunk injection of OTC on citrus tree health, fruit quality, and yield in existing rootstock trials in three different commercial growing environments. Sub-objectives: a) test the efficacy of OTC injection in the rootstock trunk compared to injection into the scion, and b) determine whether OTC injection increases/restores root densities and if there are interactions with the rootstock.  Leaves were collected for CLas analysis. Trunk injury/wound evaluations were conducted. PCR analyses were continued. Statistical data analyses continued. So far, data analysis showed the following: The uptake rate of the injected OTC solution (Rectify) did not differ whether injections were done into the rootstock or the scion trunk. However, there was a large variability during the day and among the trial sites – the uptake rate was anywhere from <30 minutes to >3 hours.Injections in the rootstock seemed to have caused slightly less visible injury than injections in the scion. Some rootstock differences were also noted.In one of the trials (Venus location), we measured lower CLas titer levels in injected trees.  2. Please state what work is anticipated for next quarter: Leaves will be collected for CLas and OTC analysis. Disease ratings will be conducted. We will prepare for the harvest. Harvest dates will depend on the grower collaborators. 3. Please state budget status (underspend or overspend, and why):The budget is as expected. 

OTC Directed Research Solicitation: Use of CRDF Rootstock Trial Locations for Testing Bactericides Inserted into Trees Through Systemic Delivery Devices

1. Please state project objectives and what work was done this quarter to address them: Main objective: To determine the large-scale efficacy of trunk injection of OTC on citrus tree health, fruit quality, and yield in existing rootstock trials in three different commercial growing environments. Sub-objectives: a) test the efficacy of OTC injection in the rootstock trunk compared to injection into the scion, and b) determine whether OTC injection increases/restores root densities and if there are interactions with the rootstock.  Leaves were collected for CLas analysis. Trunk injury/wound evaluations were conducted. PCR analyses were continued. Statistical data analyses continued. So far, data analysis showed the following: The uptake rate of the injected OTC solution (Rectify) did not differ whether injections were done into the rootstock or the scion trunk. However, there was a large variability during the day and among the trial sites – the uptake rate was anywhere from <30 minutes to >3 hours.Injections in the rootstock seemed to have caused slightly less visible injury than injections in the scion. Some rootstock differences were also noted.In one of the trials (Venus location), we measured lower CLas titer levels in injected trees.  2. Please state what work is anticipated for next quarter: Leaves will be collected for CLas and OTC analysis. Disease ratings will be conducted. We will prepare for the harvest. Harvest dates will depend on the grower collaborators. 3. Please state budget status (underspend or overspend, and why):The budget is as expected. 

Organic acids compared to conventional acidification for improved nutrient uptake and root physiology

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 planned to 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. However, we still had few trees turning out positive in July and had to reinoculate the trees with CLas. A good number of trees are now postive for CLas and will now be subjected to varying pH levels in rhizotrons. 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,

2. Please state what work is anticipated for next quarter:
Fruit harvests and juice quality evaluations wll be 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 planned to 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. However, we still had few trees turning out positive in July and had to reinoculate the trees with CLas. A good number of trees are now postive for CLas and will now be subjected to varying pH levels in rhizotrons. 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,

2. Please state what work is anticipated for next quarter:
Fruit harvests and juice quality evaluations wll be 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.

Directed research – Evaluation of different trunk injection devices and oxytetracycline formulations for efficacy against HLB, phytotoxicity, and feasibility

  1. Please state project objectives and what work was done this quarter to address them: Objectives: 1) Test the efficacy of different injection devices, 2) Determine the most effective formulation of OTC, 3) Determine the best month of injection and most appropriate OTC concentration based on tree size. Trial 1: Located in SW Florida (Duda) – 8-year-old Valencia/Carrizo trees.   – We conducted tree health ratings, fruit size assessments, monthly fruit drop measurements, and tree size measurements.  Trial 2: Located in SW Florida (Graves Bros) – 8-year-old Valencia/Kuharske trees.    – We conducted tree health ratings, fruit size assessments, monthly fruit drop measurements, and tree size measurements. Trial 3: Located on the east coast (Graves Bros) – 9 year-old Valencia/sour orange trees.   – We conducted tree health ratings, tree size measurements, monthly fruit drop measurements, and collected leaves for CLas detection.   Trial 4: Located on the east coast (Graves Bros) – 4-year-old Valencia/x639 trees.  – We conducted tree health ratings and monthly fruit drop measurements, and collected leaves for CLas detection.   Trial 5: Located on the central ridge (King Ranch) – 4-year-old OLL-8/x639 trees.   – We conducted tree health ratings and monthly fruit drop measurements, and collected leaves for CLas detection.    2. Please state what work is anticipated for next quarter:Fruit drop countings will continue. We will prepare for fruit quality and yield assessment (pending the desired harvest time of the grower collaborator).3. Please state budget status (underspend or overspend, and why): Budget status is as anticipated (the majority of the budget will be for fruit quality and residue analyses at the end of the first year).  

Determining new cost-benefit guided Phytophthora propagule treatment thresholds for HLB-affected citrus

1. Please state project objectives and what work was done this quarter to address them: 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. In this quarter, we collected root samples from the Felda area grove.  The root density was measured and the raw data appear to show that some treatments have greater density than the control for the Hamlin oranges.  There is much more variation in the Valencia plots and the trends are unclear.  Trends are also unclear from the populations of the two phytophthora species.  We have been working on the analysis of these plots and are reworking the analysis to use time as a factor.  We have harvested one of the hamlin sites and have the second site scheduled with the grower for the first week of January.  The fruit quality and size data have been gathered but not yet entered into the computer.  Objective 2) Determine benefit-cost thresholds for Phytophthora treatment on HLB-affected treesThe co-PI responsible for the economic analysis of this project, asked to have their funds returned.  I am not sure whether they will provide an analysis of this project. 2. Please state what work is anticipated for next quarter:  The second Hamlin harvest.  The Valencia harvests and spring applications of the treatments.  Data analysis will continue to confirm whether there any treatment differences in yeild, fruit quality, root density, or inoculum levels of phytophthora.   3. Please state budget status (underspend or overspend, and why): The budget is underspent because when I took over the project, there had not been staff appointed to the project for several months.  This caused funds not to be spent in a timely manner.  Also I had been planning to ask for the no cost extension so that we could harvest the Valencia plots so I needed to make sure there were funds available for that purpose.   

Determining new cost-benefit guided Phytophthora propagule treatment thresholds for HLB-affected citrus

1. Please state project objectives and what work was done this quarter to address them: 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. In this quarter, we collected root samples from the Felda area grove.  The root density was measured and the raw data appear to show that some treatments have greater density than the control for the Hamlin oranges.  There is much more variation in the Valencia plots and the trends are unclear.  Trends are also unclear from the populations of the two phytophthora species.  We have been working on the analysis of these plots and are reworking the analysis to use time as a factor.  We have harvested one of the hamlin sites and have the second site scheduled with the grower for the first week of January.  The fruit quality and size data have been gathered but not yet entered into the computer.  Objective 2) Determine benefit-cost thresholds for Phytophthora treatment on HLB-affected treesThe co-PI responsible for the economic analysis of this project, asked to have their funds returned.  I am not sure whether they will provide an analysis of this project. 2. Please state what work is anticipated for next quarter:  The second Hamlin harvest.  The Valencia harvests and spring applications of the treatments.  Data analysis will continue to confirm whether there any treatment differences in yeild, fruit quality, root density, or inoculum levels of phytophthora.   3. Please state budget status (underspend or overspend, and why): The budget is underspent because when I took over the project, there had not been staff appointed to the project for several months.  This caused funds not to be spent in a timely manner.  Also I had been planning to ask for the no cost extension so that we could harvest the Valencia plots so I needed to make sure there were funds available for that purpose.   

Determining new cost-benefit guided Phytophthora propagule treatment thresholds for HLB-affected citrus

1. Please state project objectives and what work was done this quarter to address them: 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. In this quarter, we collected root samples from the Felda area grove.  The root density was measured and the raw data appear to show that some treatments have greater density than the control for the Hamlin oranges.  There is much more variation in the Valencia plots and the trends are unclear.  Trends are also unclear from the populations of the two phytophthora species.  We have been working on the analysis of these plots and are reworking the analysis to use time as a factor.  We have harvested one of the hamlin sites and have the second site scheduled with the grower for the first week of January.  The fruit quality and size data have been gathered but not yet entered into the computer.  Objective 2) Determine benefit-cost thresholds for Phytophthora treatment on HLB-affected treesThe co-PI responsible for the economic analysis of this project, asked to have their funds returned.  I am not sure whether they will provide an analysis of this project. 2. Please state what work is anticipated for next quarter:  The second Hamlin harvest.  The Valencia harvests and spring applications of the treatments.  Data analysis will continue to confirm whether there any treatment differences in yeild, fruit quality, root density, or inoculum levels of phytophthora.   3. Please state budget status (underspend or overspend, and why): The budget is underspent because when I took over the project, there had not been staff appointed to the project for several months.  This caused funds not to be spent in a timely manner.  Also I had been planning to ask for the no cost extension so that we could harvest the Valencia plots so I needed to make sure there were funds available for that purpose.   

Integrated management of sting nematode in newly planted citrus trees

  Trees in the field trial were measured on 22 November, eight months after planting and more than 6 months following the first nematicide application.  The heights of the IPC trees were 14% greater than those of uncovered trees (P=0.000) and trunk girth one inch above the bud union was 13% greater on covered than uncovered trees (NS).  Nematicide treatment had no effect on the tree size.  As noted previously, by summer the nematicides reduced the sting nematodes (P=0.02) by 87% on the uncovered trees and 13% on the covered trees.  The apparent interaction for the nematicide effect was marginally significant (P=0.08).  The final nematicide treatment of 2022 occurred in November and the effects on the winter population density will be measured in January. The first 16 rootstocks from the UF breeding program were evaluated for sting nematode tolerance during the first week of November, approximately 18 weeks after planting in nematode infested tanks.  Compared to unchallenged trees, the root damage was readily evident on the most susceptible lines and was documented photographically for each plant in the trial. The average fibrous root mass of the infested compared to the the uninfested lines was highly correlated (0.80) with the subjective visual damage rating assigned each seedling and was used to rank the genotypes.  The mean ratio of the average fibrous root mass infested/uninfested for the four most ‘tolerant’ lines was five-fold that of the four least tolerant lines. Three of the most tolerant lines were derived from crosses between the same tetrazygotic parents and the fourth had 3 of the 4 ancestral genotypes.  Two additional tanks were established in July and a 2nd trial was initiated using USDA rootstocks and a number of conventional rootstocks. The second trial will be completed in February 2023.     

Use of compost and interaction with low- and high-vigor rootstocks to accelerate young sweet orange tree establishment and enhance productivity

 This three-year project was designed to study the effects of regular applications of compost on Valencia orange tree growth and productivity during the first three years of establishment. Trees were planted on 22 acres of land in a commercial citrus grove in southwest Florida near Felda. The trial was established in 2019 on eight raised beds at a planting density of 15 x 22 feet. The experimental design was a split-plot design with eight replications and a total of 3200 trees (145/acre). The main plot was treatment at two levels: compost or no-compost. For the compost treatment compost was applied at a rate of 5 tons per acre twice annually (May and November). To study the interaction with rootstock, four different rootstocks were included as the sub-plot: US-802, US-897, US-812, and X-639. Trees were arranged in two rows per bed, each row containing 100 trees with each rootstock sub-plot containing 50 trees. As root health is a major concern in the HLB era, this project complemented standard horticultural evaluations with evaluations of root health indicators, including anatomical and metabolic root health traits as well as the rhizosphere microbial community composition. We tested the hypothesis that increased nutrient retention through application of compost during the early phase of tree growth will result in better tree establishment and health and therefore higher productivity once trees become mature. We found that the biannual applications of compost increased several soil physicochemical properties such as CEC, pH, organic matter, and water content. Despite some variations across sampling times, soil potassium, magnesium, calcium, and boron content were generally increased after compost applications, while soil copper content was decreased. Increases in soil nutrient content translated into increases in leaf nutrient content in some instances such as for potassium. In addition to changes in soil properties and leaf nutrient status, compost amendments resulted in an increase in the fibrous root respiration rate, indicating a higher metabolic activity, but fibrous root length was not affected. Despite improvements in soil physicochemical properties and nutrient status, we did not measure any increases in growth or productivity after three years of field study. However, the total soluble solids content of fruits was decreased by the compost amendments. There were also differences associated with the rootstock, with US-897 producing the most and best-quality fruits. US-897 also had the longest and finest roots, which may be one reason for the higher fruit quality commonly associated with this rootstock. Changes in the rhizosphere microbiome were also measured in response to the compost amendments, but the impact was only correlated with specific changes in root nutrients for US-812 and US-897. One concern regarding the compost amendments was that they provided a favorable environment for weed growth, evidenced by a higher weed biomass measured in compost-treated vs. non-treated plots in some instances. The competition with weeds may have contributed to the lower amount of soluble solids measured in trees from compost-amended plots. Taken together, biannual compost applications at the rate and with the methodology used in our study did not result in any measurable effect on tree growth and productivity during the first three years after tree establishment despite some measurable improvements in soil and root health parameters.    

Determine optimal timing for application of fertilizer to improve fruit quality and reduce preharvest drop

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: In order to compare the effects of early versus late / sustained fertilization on health and fruit production of Hamlin and Valencia trees, the following completed treatments were evaluated in the third quarter of 2022:Treatments: Early fertilization as % completed of the recommended fertilization (RF; 160 lb N/acre) before June T1: 25% of RF   (T25%)T2: 50% of RF    (T50%)T3: 75% of RF    (T75%)T4: 100% of RF   (T100%)The remaining mid- to late-season fertilizer treatments were applied during the third quarter and the results will be reported in the following quarter. Leaf samples were collected on monthly intervals and analyzed to determine the leaf nutrient concentrations. The preliminary results showed that if 50% of total nutrient requirement was applied before May, there was improvement in tree health (NDVE) and vigor (NDVI) indices, and canopy volume. The same treatment resulted in higher leaf nutrient concentrations but only nitrogen was statistically significant. The fruit growth (diameter) was not significantly difference between early fertilization treatment even applying 75% or 100% of total fertilizer. Early fertilization with higher rates increased fruit size but growth increments diminished over time in all treatments, as expected when fruit development enters growth stage 2 in summer.Preliminary results showed that there was a positive trend of crop health, fruit growth and leaf nutrient concentration with early higher fertilization but didn’t observe statistically significant differences.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):The growth and yield data associated with all different timed fertilizer events in year 1 is not complete yet and therefore we don’t have new results to report for this objective. Our investigations to use the intensity of  leaf symptom expression throughout the season to help determine foliar nutrition in the field with smartphone apps is continuing.B) New developments: The Sugarbelle trials focusing on solving the soft fruit quality issues are progressing well. We have now applied three replicated foliar spray treatments to Sugarbelle trees at the city block and on healthy trees in the CUPS, consisting of KNO3 and KH2PO4. 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: The fruit drop and tree lodging/ branch breaking damage caused by hurricane Ian to the outdoor Hamlin, Valencia and Sugarbelle experiments is considerable. The Sugarbelle experiment in the CUPS sustained no damage. We expect that the reduced yield data will not be useful for calibrating the fertilizer timing models, but we will collect and use fruit quality data where possible.  2. Please state what work is anticipated for next quarter:The final late fertilizer applications will be made to designated treatment plots in November. Soil, lysimeter sampling, leaf sampling, processing and analysis will be ongoing, as will tree size and fruit measurement. We plan to assess fruit yield and quality for the Hamlin and Sugarbelle experiments in December / January. The third Aerobotics drone survey will now fly in late November due to delays from Hurricanes Ian and Nicole.   3. Please state budget status (underspend or overspend, and why):Spending rate is approximately on track.