Grant Information
| Knowledge Area | Subject of Investigation | Field of Science | Percent |
|---|---|---|---|
| 102 - Soil, Plant, Water, Nutrient Relationships | 910 - Grapefruit | 1010 - Nutrition and metabolism | 25% |
| 111 - Conservation and Efficient Use of Water | 910 - Grapefruit | 2070 - Meteorology and climatology | 25% |
| 202 - Plant Genetic Resources | 910 - Grapefruit | 1020 - Physiology | 25% |
| 205 - Plant Management Systems | 910 - Grapefruit | 1060 - Biology (whole systems) | 25% |
Citrus (Citrus spp.) is Florida's most important agricultural commodity. The state produces citrus for different markets: round oranges (Citrus × sinensis) for juice; navels, mandarins (Citrus reticulata), grapefruit (Citrus × paradisi) and lemons (Citrus × limon) for the fresh fruit industry; and lemons for extracting peel oil for processing. The Indian River Citrus District, a narrow strip of land on the eastern coast of Florida, stretching nearly 200 miles from Daytona Beach to West Palm Beach, is considered the premier grapefruit production area in Florida.The Indian River Citrus District maintains approximately 13.5% of Florida's total citrus acreage inventory since 2000/01 (excluding the crop years 2004/06 due to hurricane damage) with drastic reduction in recent years. The number of grapefruit trees planted in Florida has increased since 2000/01; conversely, total bearing acreage and total bearing trees in the state have both declined by approximately 38% in the last decade. The total number of boxes of grapefruit produced in Florida has decreased from 40.9 million in 2003/04 to 10.8 million in 2015/16. Excluding season 2004/05, Florida's average grapefruit yield is quickly decreasing over time - from 497 boxes per acre in 2000/01 to only 288 boxes per acre in 2016/17. The reduction in grapefruit acreage, number of trees and yield was caused by huanglongbing (HLB) or citrus greening, one of the most destructive of all citrus diseases.HLB disease is associated with the bacterium Candidatus Liberibacter asiaticus (CLas), and is vectored by the Asian citrus psyllid (ACP, Diaphorina citri). HLB was confirmed in São Paulo, Brazil in 2004 and in Florida, United States in 2005. Since then, Florida's citrus commercial acreage has decreased from 748,555 to 480,121 acres, and the total citrus production reduced from 291,800,000 to 94,205,000 boxes in 2015/2016 season. The 36% reduction of citrus planted area and 68% drop in yield is severely impacting the state's citrus industry. HLB affects 90% of Florida's total citrus acreage, and on average 80% trees in an individual citrus operation are infected, resulting in 41% yield loss.Trees affected by HLB suffer from general canopy and root decline, yield reduction, and often lopsided fruit that is not suitable for sale on the fresh market. One characteristic of the disease is that yield losses precede visible foliar symptoms, indicating that fruit production is negatively affected before the disease is visually detected. Citrus trees affected by HLB show asymmetric, chlorotic, blotched or mottled leaves, sparse growth, twig dieback and malformed, off-colored fruits with reduced marketable yield. Most of the commercially available citrus varieties are susceptible to HLB. This is particularly devastating for Florida's fresh citrus growers, as fruit must maintain cosmetic appearances from harvest through the final purchase. The HLB epidemic has negatively affected the United States grapefruit market, where availability of Florida-based fresh fruit can no longer meet consumer demands.Strategies to mitigate the spread and damage caused by HLB rely heavily upon controlling the insect vector using insecticides. mitigation in Brazil is built upon maintaining HLB-free nursery stock, removing infected, symptomatic trees in the field and minimizing ACP activity. In Brazil, area-wide insecticide treatment programs combined with removing infected trees in large regions/areas were shown to be more effective in controlling HLB than programs focused only on small-scale farms. Area-wide insecticide applications and tree removal may not be an appropriate strategy for some fresh fruit citrus growers in Florida. High-valued fresh fruit exports must meet stringent chemical residue testing, and area-wide insecticide treatment programs may conflict with the pre-harvest interval mandates. In addition, area-wide applications of synthetic insecticides will likely impede further development of organically grown fresh citrus. Insecticide-resistant populations of the ACP were already detected in citrus-producing regions of Florida.In response to the need of the industry to produce high quality, HLB-free grapefruit, a collaborative IRREC and CREC research team is investigating the feasibility of using totally enclosed anti-psyllid screen structures to cultivate fresh citrus fruit. Additionally, the Citrus Horticulture program is proposing developing management (irrigation and fertilization) and cultural (scion and rootstocks) practices to produce better quality trees in the nurseries and extend grove productivity where HLB is endemic.Overhead systems used by the citrus nursery industry are typically not uniform in distribution, often leading to excessive or deficient irrigation, reduced irrigation efficiency, and increased production costs. Improved irrigation techniques such as subirrigation can enhance plant growth, control plant vigor, shorten crop cycle, increase plant uniformity, improve water and nutrient use efficiency, reduce irrigation time and frequency, and reduce citrus nurseries' discharge of nutrients into the environment. Subirrigation uses capillary action to move water and nutrients vertically in the substrate. Water is pumped from a reservoir to a bench and applied directly to the bottom of the containers. After irrigation, the pump is turned off, and the unused fertilizer solution returns to the reservoir by gravity for recirculation. Sensors can be used to monitor substrate moisture and control subirrigation based on plant water demand instead of using timers according to a pre-determined schedule.Microirrigation (drip or microsprinklers) is the most used irrigation method on citrus groves due to higher irrigation efficiency. However, the minimum proportion of the root zone that needs to be irrigated for optimal efficiency is unknown. Microrrigation methods allow water and nutrients through fertigation to be applied at very frequent intervals. Nutrient management is also an important aspect of disease control as nutrients influence plant resistance and pathogen growth. HLB inhibits root growth and reduces water and nutrient uptake, causing leaf and fruit drop, deformed fruit with unpleasant flavor, and whole tree decline that is often lethal. Once citrus is affected, it becomes increasingly less productive. HLB induced reduction in root density reduces water and nutrient uptake, translocation, and utilization. The decline in fibrous root density contributes to weak tree canopies, poor fruit quality, and yield losses.HLB affects all citrus varieties, and since the disease discovery, the research continues seeking for a tolerant or possibly resistant selection. 'Ray Ruby' is the #1 grapefruit selection produced in the Indian River District. 'Ray Ruby' fruit are valued for their red flesh, low seed count, pink blush, and sweeter juice than other comparable varieties. Grapefruit is one of the most susceptible species to HLB, in particular when budded on 'Sour orange' (Citrus aurantium).The general goal of this project to is to develop durable, enhanced production technologies for grapefruit production in the Indian River District. To develop strategies for profitable production, we will improve strategies to cultivate fresh fruit in the Indian River District using Citrus Under Protective Screen systems, develop advanced horticultural practices for grapefruit production, and identify HLB- and canker-tolerant grapefruit scions and rootstocks for citrus production in the Indian River District. Novel citrus cropping systems that utilize inputs more efficiently and rapidly and can produce profitable yields under high disease pressure from HLB and canker will be tested. Integrated disease and pest management practices, grove design and planting density, and control of vegetative and root growth to increase fruit yield are also planned.
1.1Improve strategies to cultivate fresh fruit in the Indian River District using CUPS systemsObjective 1Measurements include monthly psyllid counting using insect sticky trap cards, yearly HLB infection rate diagnosis, plant growth (height, canopy width), fruit yield (total, fruit grading), fruit quality (external color, peel puncture resistance, soluble solids content, acidity, ratio, juice content), and leaf and soil nutrition data. Leaf samples will be analyzed for N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, and Zn to assess the effectiveness of fertilization rates and application methods. Soil samples will be collected once a year to determine soil nutrient concentrations.Objective 2The existing four irrigation zones (screen houses, open-air plots, in-ground and potted) will be expanded to 16 zones (2 coverings × 2 planting systems × 4 replications). The rootstocks will be eliminated as a factor for irrigation due to the lack of treatment difference from previous results (data not shown), and a new planting (described in Objective 4) is planned after the last data collection.Objective 3Each plot will receive one sensor to monitor soil moisture as volumetric water content (VWC), temperature and electrical conductivity (EC). Sensors will be connected to a data logger and multiplexer. Individual 1" solenoid valves will be connected to two relay drivers to supply water and nutrient to each plot based on the soil moisture readings. When the VWC drops below a set threshold, the solenoid will open and the plants will be irrigated for a certain time.The data collected will be transmitted to a computer using radio frequency modules. Radios will send the collected information to a database using omnidirectional and Yagi antennas. The system is designed to be energy-efficient, using a 10-W solar panel connected to a 12VDC solar charge controller, and a rechargeable 12VDC 7.2 Ah battery.Objective 4The existing IRREC CUPS project has primarily focused on 'Ray Ruby' grapefruit establishment and maintenance. It is now important to begin a more thorough evaluation of high-value varieties to gauge the longer-term efficacy of such a production system. The project currently has 32 plants/plot and two rootstocks ('Sour orange' and 'US-897'). The idea is to remove the rootstock as a factor, reducing the number of trees per treatment (8 plants/plot) and substituting the trees by different varieties (eight total, maintaining two of the existing combinations of 'Ray Ruby'/'Sour orange' and 'Ray Ruby'/'US-897'), adding six new mandarin varieties on several rootstock combinations.1.2Develop advanced horticultural practices for grapefruit production1.2.1Advance citrus nursery irrigation methodsThe study will be conducted for two consecutive production stages [liner (in cone-shaped containers) and budded tree (in citrus pots)] using the same irrigation equipment in at least two growing cycles. We are testing five individualized irrigation methods [three ebb-and-flow subirrigation benches with three different VWC to trigger subirrigation [0.24, 0.36 and 0.48 m3m-3], capillary mat and nursery manual overhead irrigation using breaker nozzles] and six citrus liners (rootstocks) and budded trees (scions on rootstocks) (to be determined based on market availability). Plots will be arranged in a 5×6 factorial split-plot design (irrigation method as main plot), with four replications. Automation will be performed using the same equipment as described in Objective 2.1.2.2Improve water and nutrient use efficiency by using precision irrigation and fertigation methods in field plantingsObjective 1The automated control system consists of a data logger connected to a multiplexer and two relay drivers. An identical setup will be assembled using the low-cost open-source microcontrollers (Arduino, Ivrea, Italy). Sensors needed for this study are already available on the Citrus Horticulture lab.Water and fertilizer solution will be applied by two different drip irrigation lines, consisting of ¾-inch polyethylene tubing with self-compensated emitters. Measurements will be taken every 15 min and averaged hourly. When the VWC drops below the set threshold (0.3 m3m-3), the systems will compare the EC reading to the thresholds (from 0.5-2.5 dS m-1). If the measured EC is higher than the threshold EC, a 1-inch 6-18VDC latching solenoid valve will open and the plants will be irrigated for 30 s; if the measured EC is lower than the threshold EC, another valve is going to open and the plants will be fertigated for 30 s.Objective 2The study will be repeated in several seasons to evaluate the results in different climatic conditions and crop cycles. The goal is to expose sensors to different temperatures, salinity, potting mixes, soils, environment, and weather conditions to test factors that could affect sensor reading and control accuracyObjective 3The data collected will be transmitted to a computer using radio frequency modules. Radios will send the collected information to a database using omnidirectional and Yagi antennas. All programming will be accomplished using the software LoggerNet v.4.3 and Arduino IDE v. 1.8 (Arduino, Ivrea, Italy).Objective 4The technology may provide proven water savings and reductions in production costs (due to reduced fertilizer losses and fuel costs associated with irrigation use) and possible yield improvements.1.2.3Enhance cropping systems and grove managementtools for grapefruit productionObjective 1An algorithm will be created to simulate the potential effect of different tree plant density on plant growth and physiological parameters. The model will take an increasing number of trees per acre, environmental parameters, varieties, and location into consideration. An independent data set will be tested using random field measurements in plantings with different densities across the State to test accuracy and build a database to take the HLB confounding effect into consideration.Objective 2Soil health improvement will be tested in collaboration with other UF/IFAS investigators to focus in the Indian River District by applying soil amendments and green manures (grass and cover crops) to evaluate pest and disease tolerance, yield and leaf nutrient content.Objective 3Canopy management of citrus trees is applied to training young and bearing trees and is critical to managing high-density plantings. Young tree training establishes the geometrically well-balanced form (3 to 6 or more well-spaced and oriented branches left to form the main limbs of mature trees) and mechanically strong load-bearing framework for precocious heavy bearing of high-quality fruit, by removal of rootstock and low trunk suckers; and dead, broken, diseased, poorly oriented, crossing over, or rubbing branches as soon as these become apparent and before the young tree allocates energy and reserves to unwanted branches.Objective 4Foliar and ground nutritional programs will be tested focusing on different forms and rates of macro and micronutrients to maintain tree root and shoot health. Nutritional programs may be combined to plant hormones and growth regulators to maximize plant production and extend grove life under HLB.1.3 Identify HLB- and canker-tolerant grapefruit scions and rootstocks for citrus production in the Indian River DistrictThe research will determine horticultural traits such as easiness of propagation, incompatibility, tree size (height, width), root volume, yield/tree and yield/acre, tolerance to high pH, clay and wet soil, drought and freezes. Additionally, we will evaluate tolerance to diseases and pests, physiological parameters. Leaf nutrient content and HLB diagnostics including assessment of titer are planned to gather specific information from each selection.?
Target Audience
The target audience for this work are local farmers, the scientific community, and other players in the citrus industry, such as processors and crop advisors.
Changes / Problems
Nothing Reported
Training & Professional Development
The Citrus Horticulture Laboratory team organized two field days inside the CUPS and the large-scale field variety trial, hosted several tours for growers and visitors. The masters student attended a special course in root biology sponsored by the project.
Dissemination Streams
The Ferrarezi Lab organized the 2020 Florida Citrus Show to bring new information to more than 800 local growers. We prepared publications for refereed journals, citrus trade journals (Citrus Industry Magazine) and the UF/IFAS Citrus Production Guide. Abstracts were also presented in scientific conferences.
Next Reporting Steps
Improve strategies to cultivate fresh fruit in the Indian River District using Citrus Under Protective Screen systems Continue CUPS irrigation and fertigation management study; CUPS variety performance trial. Develop advanced horticultural practices for grapefruit production Advance citrus nursery irrigation methods Finalize one referred article. Improve water and nutrient use efficiency by using precision irrigation and fertigation methods in field plantings Finalize water management study using different water management strategies and irrigation systems (SW Block experimental area). Enhance cropping systems and grove management tools for grapefruit production Determine soil and foliar nutrient recommendations for grapefruit trees in the field (NE Block experimental area). Identify HLB- and canker-tolerant grapefruit scions and rootstocks for citrus production in the Indian River District Continue large-scale variety trials to test scions and rootstocks for citrus production in the Indian River District (Millennium Block and MAC experimental areas).
Target Audience
The target audience for this work are local farmers, the scientific community, and other players in the citrus industry, such as processors and crop advisors.
Changes / Problems
Objective 1 The CUPS screenhouses provide for disease exclusion, but environmental challenges such as hurricanes in Florida require a more comprehensive evaluation of structural modifications to deal with extreme weather. A tropical storm in April 2019 damaged the screenhouse roofs. IRREC CUPS screenhouses are 5 years old, and the screen is experiencing degradation from solar radiation, rainfall, and constant strong winds, resulting in screen rupture at several points in the roof. That task has been requiring a tremendous labor effort to patch the holes and repair those openings. Due to this degradation, the screen is currently under replacement. Leaf samples were collected and tested for HLB once per year. Diagnostics were performed by Southern Gardens in 2019. Inside screenhouse trees tested negative, while outside trees tested positive for HLB. We are expanding the varieties tested under the IRREC CUPS. However, no trees were available for 2018 or 2019 due to the shortage in the nurseries and the complexity of propagating so many varieties and rootstocks in small batches. An order was placed with Brite Leaf Nursery (Lake Panasofkee, FL) and trees will be delivered Spring 2020. Objective 2 Subobjective 2 N/A Subobjective 3 (Determination of adequate tree plant density) An algorithm was going to be created to simulate the potential effect of different tree plant density on plant growth and physiological parameters. The model was willing to anticipate increasing number of trees per acre, environmental parameters, varieties and location into consideration. An independent data set was going to be tested using random field measurements in plantings with different densities across the State to test accuracy and build a database to take the HLB confounding effect into consideration. Several of those activities were implemented but the undergraduate student dedicated to the task did not complete the activities. We stopped at the algorithm development phase. Objective 3 N/A
Training & Professional Development
The Citrus Horticulture Laboratory team visited the CREC CUPS once in 2019, hosted several tours for growers and visitors. The masters student attended a special course in root biology sponsored by the project.
Dissemination Streams
The Ferrarezi Lab organized the 2019 Florida Citrus Show to bring new information to more than 800 local growers. We prepared publications for citrus trade journals (Citrus Industry Magazine) and the UF/IFAS Citrus Production Guide. Abstracts were also presented in scientific conferences.
Next Reporting Steps
Improve strategies to cultivate fresh fruit in the Indian River District using Citrus Under Protective Screen systems Implement irrigation and fertigation management study. Develop advanced horticultural practices for grapefruit production Advance citrus nursery irrigation methods Finalize the two referred articles. Improve water and nutrient use efficiency by using precision irrigation and fertigation methods in field plantings Implement water management study using different water management strategies and irrigation systems. Enhance cropping systems and grove management tools for grapefruit production Determine soil and foliar nutrient recommendations for grapefruit trees in the field. Identify HLB- and canker-tolerant grapefruit scions and rootstocks for citrus production in the Indian River District Plant large-scale variety trials to test scions and rootstocks for citrus production in the Indian River District. <br><br>
<br>What was accomplished under these goals? Improve strategies to cultivate fresh fruit in the Indian River District using Citrus Under Protective Screen systems Citrus production under protected environments can reduce huanglongbing (HLB) disease incidence and damage by excluding the Asian Citrus Psyllid vector. Our objectives were assess the ability of covered structures to reduce HLB incidence and determine the yield of soil and container-grown 'Ray Ruby' grapefruit at super-high planting densities relative to in-ground open-air trees. We tested two production systems (screenhouse and open-air), two planting systems (in-ground and potted) and two rootstocks (Sour orange and US897). The experimental design was a RCBD split-split-plot with four replications. Trees were planted in Sept/2013 on a density of 1,957 trees/ha (total 896 trees/0.46 ha). Irrigation was performed on-demand using two 7.6-LPH drip emitters per tree, and fertigation was applied three times/week using 15N-2.6P-22.4K water soluble fertilizer at 180 kg N/ha. Psyllids were detected inside the screenhouses post Hurricane Irma, which damaged the screen structures in Sept/2017, leaving openings until repairs were completed in Apr/2018. HLB diagnosis indicated no disease in the screenhouses and fast disease progression in the open-air, with 100% infection in all outside treatments in Mar/2017. The 2017/18 season yield was greater inside the screenhouses due to the absence of HLB (0.33 boxes/tree; 263 boxes/acre) compared to the outside blocks (0.02 boxes/tree; 18 boxes/acre). Potted trees on sour orange and in-ground trees on US-897 resulted in higher yield compared to other treatments. Potted grapefruit trees cultivated inside CUPS had the highest soluble solids content. The screenhouses provide for disease exclusion, increased yield, and quality. The cost of the technology is still under evaluation along with structural modifications needed to deal with environmental challenges such as hurricanes in Florida. IRREC CUPS screenhouses are 5-years old, and the screen is experiencing degradation from UV, rainfall, and wind, resulting in screen rupture at several points in the roof, requiring replacement in the near future. Trees for the scion and rootstock selection for CUPS were ordered at Brite Leaf Nursery (Lake Panasofkee, FL) and trees will be delivered Spring 2020. Develop advanced horticultural practices for grapefruit production Advance citrus nursery irrigation methods The objectives of this study were: 1) automate ebb-and-flow subirrigation operation using soil moisture sensors, 2) evaluate the system performance on plant growth and water use, and 3) evaluate if subirrigation shorten crop cycle and accelerate citrus liners propagation time compared to overhead irrigation. The treatments tested were five irrigation methods [three ebb-and-flow subirrigation benches with different volumetric water content (VWC) to trigger subirrigation [? 0.24, 0.36 and 0.48 m3/m3], capillary mat and overhead irrigation] and six citrus rootstocks (Kuharske, UFR-2, UFR-16, US-802, US-812, and X-639), arranged in a 5×6 factorial split-plot design (irrigation method as main plot), with four replications. The system was automated by 20 capacitance sensors connected to a data logger, multiplexer and relay drivers, which controlled independent submersible pumps and solenoid valves. Subirrigation was turned on when VWC dropped below the set thresholds, while capillary mat and overhead ran on a rigid schedule. Sensors effectively monitored substrate VWC and controlled subirrigation. Treatments with highest VWC had higher substrate moisture and number of irrigations over time. Subirrigation at ? 0.48 m3/m3 increased plant growth in 29% and reduced water use in 98% compared to capillary mat and overhead irrigation. Subirrigation shortened crop cycle and accelerated citrus liners propagation time compared to overhead irrigation, anticipating the liners transplanting for grafting. The volume of water applied was higher on capillary mat and overhead irrigation. VWC ? 0.48 m3/m3 is indicated for liner production in cone-shaped containers. US-802, US-812, and X-639 rootstocks resulted in the tallest seedlings, while Kuharske showed the widest stem diameter. Improve water and nutrient use efficiency by using precision irrigation and fertigation methods in field plantings Precise irrigation and fertigation management provide a less-limiting environment to roots while minimizing over irrigation and leaching of nutrients. This concept can improve tree growth in the presence of HLB and help optimize water and nutrient use. Higher tree density can increase fruit yield per area under high HLB pressure. This study evaluated the efficiency of open hydroponics on 'Ray Ruby' grapefruit production under different irrigation systems and tree density. We tested a combination of rootstocks (Sour orange and US897), tree spacing [standard and high density staggered (HDS)], fertilization (dry granular and fertigation), and irrigation systems (drip and microjet), arranged on five treatments: RR/SO_STD_dry_MS) SO + standard spacing + dry granular fertilizer + micro jet, RR/SO_HDS_fert_DD) SO + HDS + fertigation + drip, RR/897_HDS_fert_MS) US897 + HDS + fertigation + microjet, RR/897_HDS_fert_DD) 'US897' + HDS + fertigation + drip, and RR/SO_HDS_fert_MS) SO + HDS + fertigation + microjet. Foliar nutrient, insecticide and fungicide were sprayed using standard practices. We scouted for psyllids, leaf minors and other citrus pests monthly. HLB incidence reached 100% after five years of planting. Trunk diameter and canopy volume increased over time, and were higher on RR/SO_STD_dry_MS compared to other treatments. Total number of fruit and fruit yield were 226% and 183% higher in 2016 compared to 2015. RR/SO_STD_dry_MS yielded 7,309 kg/ha in 2017 compared to an average of 22,153 kg/ha for other treatments. Soluble solid contents, acidity, and ratio were not significant (p>0.05). Total solids per hectare was always low in RR/SO_STD_dry_MS. High density staggered (HDS) planting resulted in higher fruit yield, irrespective of rootstock and irrigation system, representing an important advance to the grapefruit production system. However, labor cost and effect on plant growth over time still need to be determined for commercial recommendation. Enhance cropping systems and grove management tools for grapefruit production Identify HLB- and canker-tolerant grapefruit scions and rootstocks for citrus production in the Indian River District We proposed and obtained funding for four large-scale studies over 3 years that will evaluate numerous grapefruit scions and multiple rootstock trials on 'Ray Ruby' grapefruit. The CRDF proposal "Performance of newly released grapefruit cultivars and rootstocks in the Indian River Citrus District" objectives are (i) assess performance of new grapefruit scions and rootstocks under HLB endemic conditions in the IR and (ii) evaluate the influence of UFR rootstocks on grapefruit in the IR in comparison to legacy and new alternatives. We secured funding from the USDA-APHIS-MAC group "Evaluation of Potential HLB Tolerant Grapefruit Rootstock/Scion Combinations in the Indian River District of Florida" to plant large field trials of some of the most promising experimental grapefruit scion/rootstock combinations that may have more tolerance to HLB and monitor them over the next 8 to 10 years. For this proposed project, a total of seven scions and seven rootstocks will be evaluated on thirty representative ten-acre block trials located within the Indian River district and other growing regions. To accomplish this project, the partner institutions will be seeking multiple year funding opportunities as this project. <br><br><b>Publications</b><br>
Target Audience
The target audience for this work are local farmers, current and prospective CUPS growers, the scientific community, and other players in the citrus industry, such as processors and crop advisors.
Changes / Problems
Objective 1 The CUPS experimental area has some chronical issues related to the study design and implementation back in 2013. The most limiting factor is the small area dedicated to production, since the IRREC CUPS has four independent ¼-acre screenhouses. That creates a practical challenging related to machinery movement among screenhouses, since everything is exposed to the open-air while transiting from one house to another, increasing the potential for pest and disease dissemination. The four independent screenhouses also drastically reduces the number of trees that can be cultivated inside the enclosure since we need space for machinery turning and operation. All potted trees were planted in a sand-based potting mix: 50% washed sand, 15% Florida peat, 20% cypress dust, 7.5% perlite, and 7.5% coconut coir with 3 kg/m3 dolomite (mixed on site in cement mixer). That poor media reduced tree growth overtime, leading to small trees compared to the in-ground trees. The potted trees are certainly not reaching their maximum production potential. The study was also implemented with only one grapefruit variety on two rootstocks (Sour orange and US-897). There is need for several other varieties and a mix of advanced cultural practices to justify the use of an expensive enclosure. We are limited by the number of trees per screenhouse, and need to perform studies in commercial collaborators to overcome the reduced amount of trees available. There is one missing row of trees per rootstock in the open-air production system, resulting in six rows per plot instead of eight. On top of that, the screens have had multiple opens throughout the years; plants were not looking healthy when the current center horticulturalist assumed the position; and there was no walking-through station for disinfection of personnel and equipment in all houses. The CUPS screenhouses provide for disease exclusion, but environmental challenges such as hurricanes in Florida require a more comprehensive evaluation of structural modifications to deal with extreme weather. Hurricane Irma damaged the screen structures in September 2017, leaving openings until repairs were completed in April 2018. In March of 2018, monitoring of psyllids with sticky cards changed from once monthly to twice monthly in response to the detection of psyllids inside the screenhouses post Irma. On top of the psyllid detection, there was an inefficient psyllid control due to product coverage issues and difficulties in scheduling applications during the peak of Florida's rainy season (21 days of non-stop rain late May/early June, 2018). IRREC CUPS screenhouses are 5 years old, and the screen is experiencing degradation from solar radiation, rainfall, and constant strong winds, resulting in screen rupture at several points in the roof. That task has been requiring a tremendous labor effort to patch the holes and repair those openings. Due to this degradation, the screen will have to be replaced in the near future. Leaf samples were collected and tested for HLB once per year. Diagnostics were performed by Southern Gardens in 2018. Inside screenhouse trees tested negative, while outside trees tested positive for HLB. New testing is scheduled to March 2019. The research graduate (a PhD candidate) in charge of implementing several of the IRREC CUPS project objectives was replaced on 01/01/2019 due to low performance. Even though there were multiples attempts to solve the situation, the student failed in performing several activities: 1) designing the irrigation and fertigation management study using soil moisture sensors on CUPS, 2) implementing the new irrigation system on CUPS for the irrigation/fertigation management study, and 3) starting the study with different screen colors on CUPS. A new research graduate started right away and is working to catch up the delay caused by the lack of proactivity from the previous PhD candidate. We are expanding the varieties tested under the IRREC CUPS. However, no trees were available for 2018 or 2019 due to the shortage in the nurseries and the complexity of propagating so many varieties and rootstocks in small batches. An order was placed with Brite Leaf Nursery (Lake Panasofkee, FL) and trees will be delivered Spring 2020. Objective 2 Subobjective 2 The project PI inherited multiple legacy projects at the UF/IFAS IRREC Research Grove (established prior Dr. Ferrarezi's arrival) that were implemented prior to his hiring in November/2016. Those projects have been continued but present some chronical issues that will be reported here. Few problems have been fixed over the course of this new project. Grapefruit Open Hydroponics System: pesticide sprays were not on schedule; plants are small; "Blue" treatment has only 4 replications; there is no standard tree spacing treatment with 'US-897' rootstock; there was no control with drip irrigation; the soil moisture sensors collecting data for comparison of non-mulched versus mulched and plastic tray stopped working and were removed; all trees received the same fertilizer amount. Valencia Sweet Orange Plant Density and Irrigation Methods: pesticide sprays were not on schedule; plants are small; there were too many, unnecessary reps; experimental design is missing one factor (north and south blocks are treated as 8 reps but are 2 factors); all trees received the same fertilizer amount Grapefruit Plant Density: pesticide sprays were not on schedule; plants are small; no supplemental foliar sprays; there were too many, unnecessary reps; experimental design is missing one factor (red and yellow rectangles are treated as 8 reps but are 2 factors); all trees received the same fertilizer amount Subobjective 3 (Determination of adequate tree plant density) An algorithm was going to be created to simulate the potential effect of different tree plant density on plant growth and physiological parameters. The model was willing to anticipate increasing number of trees per acre, environmental parameters, varieties and location into consideration. An independent data set was going to be tested using random field measurements in plantings with different densities across the State to test accuracy and build a database to take the HLB confounding effect into consideration. Several of those activities were implemented but the undergraduate student dedicated to the task did not complete the activities. We stopped at the algorithm development phase. Objective 3 Citrus variety trials at the UF/IFAS Indian River Research and Education Center (IRREC) began in 1950 when several scions and rootstocks were tested for soil adaptation, blight, exocortis, and tristeza. Researchers maintained a diverse germplasm to release adapted varieties to grapefruit growers, including the 'Ruby Red' grapefruit mother nucellar tree that was used by the Department of Plant Industry (DPI) to propagate millions of trees in Florida. The original Millennium Block trials started at UF/IFAS IRREC in early 2000s but eradicated in 2004 together with all citrus field trials due to canker, and no variety trials have been conducted since then. The previous IRREC director Dr. Peter Stoffella identified the need to replant citrus trees on the Center's farm and invested approximately $100K during two years (2014-2016) preparing the area for his successor and the Center's citrus horticulturist. Dr. Ronald Cave continued the Center's new grove development by securing $80K seed funding from the UF/IFAS Dean of Research in August 2016 to purchase citrus trees and cover the mixed variety trial planting costs. A proposal named "Assessing performance of new grapefruit scions and rootstocks in the Indian River District" was submitted to the Florida Citrus Research and Development Foundation (CRDF) but not funded in the fiscal year 2018. The PI is going to resubmit in 2019.
Training & Professional Development
The Citrus Horticulture Laboratory team visited the CREC CUPS twice in 2018, and hosted multiple tours for growers and visitors at the IRREC CUPS. The previous PhD candidate sponsored by the grant attended a training about using the LI-6400XT photosynthesis gas analyzer at Licor (Lincoln, NE), and was leading an independent trial to use sap flow sensors in citrus trees that was going to be useful for measuring water uptake on CUPS trees.
Dissemination Streams
One field day was performed in one commercial CUPS location at Jerry Mixon's operation in Bartow, FL on Nov 15, 2018 with approximately 45 participants. The canopy management study was prepared for demonstration, but due to the tight schedule and lack of yield and cost results to accompany the study explanation the presentation was skipped. We also prepared publications for citrus trade journals (Citrus Industry Magazine) and the UF/IFAS Citrus Production Guide. Results were presented in scientific conferences.
Next Reporting Steps
1. Improve strategies to cultivate fresh fruit in the Indian River District using Citrus Under Protective Screen systems 2. Develop advanced horticultural practices for grapefruit production 1. Advance citrus nursery irrigation methods 2. Improve water and nutrient use efficiency by using precision irrigation and fertigation methods in field plantings 3. Enhance cropping systems and grove management tools for grapefruit production 3. Identify HLB- and canker-tolerant grapefruit scions and rootstocks for citrus production in the Indian River District <br><br>
<br>What was accomplished under these goals? Improve strategies to cultivate fresh fruit in the Indian River District using Citrus Under Protective Screen systems The 2017/18 season was the third year that yield was determined. 'Ray Ruby' grapefruit yield was greater inside the screenhouses due to the absence of HLB (≈0.33 boxes/tree; 263 boxes/acre) compared to the outside blocks (≈0.02 boxes/tree; 18 boxes/acre). In 2017/18, potted trees on sour orange and in-ground trees on US-897 resulted in higher yield compared to other treatments (P<br><b>Publications</b><br>