FLORIDA CITRUS PRODUCTION RESEARCH ADVISORY COUNCIL Administered by the Florida D...

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1 FLORIDA CITRUS PRODUCTION RESEARCH ADVISORY COUNCIL Administered by the Florida D... FLORIDA CITRUS PRODUCTION RESEARCH ADVISORY COUNCIL Administered by the Florida Department of Agriculture and Consumer Services Bob Crawford, Commissioner Page 1 of 43 NINTH ANNUAL REPORT July June 2001 Introduction Chairman's Message FCPRAC Funding by years Florida Citrus Production Overview Research Reports: Management/Physiology Pathology Entomology Plant Improvement/Other Dr. Larry K. Jackson, Scientific Coordinator 700 Experiment Station Road Lake Alfred, FL (863) , Fax (863) Pleas Strickland, Secretary to Council 425 Mayo Building Tallahassee, FL (850) , Fax (850) MEMBER Bill Barber (2002) Vice-Chairman 7 Lykes Road Lake Placid, FL (863) , Fax (863) Jim Simpson, Jr. (2002) 445 Limit Avenue Mount Dora, FL Deceased - June 29, 2001 John Strang (2002) Post Office Box 1364 Auburndale, FL (863) , Fax (863) Mark Sanchez (2004) 7735 County Road 512 Fellsmere, FL (561) , Fax (561) J. Peter McClure (2002) Bluefield Road Okeechobee, FL (863) , Fax (863) George Walker (2004) Bowline Street Bokeelia, FL (941) , Fax (941) Wayne Jackson (2002) Post Office Box 610 LaBelle, FL (863) , Fax (863) ALTERNATE Andrew Pike (2004) Chairman Post Office Box 985 Lake Placid, FL (863) , Fax (863) Larry Davis, Jr. (2004) Post Office Box 668 Wauchula, FL (863) Charles Counter (2004) Post Office Box 337 Haines City, FL (863) , Fax (863) Peter Spyke (2004) Okeechobee Road Ft. Pierce, FL (561) , Fax (561) Gary Simmons (2002) 2179 SW Oakwater Point Palm City, FL (561) , Fax (561) Ed English (2004) 9500 County Road 858 Immokalee, FL (941) , Fax (941) Jerry Newlin (2002) NE Highway 70 Arcadia, FL (863) , Fax (863)

2 FLORIDA CITRUS PRODUCTION RESEARCH ADVISORY COUNCIL Administered by the Florida D... Table of Contents Page 2 of 43 Management/Physiology Continuing Projects M - Rootstock Interactions with Disturbed Soil Profiles in Flatwoods Citrus M - Enhancing Citrus Cropping Through Controlling Flowering and Improving Fruit Size Through Thinning M - Ecolyst Application Timing, Juice Brix, and Profitability of Oranges M - Implementation of the Decision Information System for Florida Citrus M - Tree Pruning Studies to Improve the Production and Harvesting of Florida Oranges M - Development of a Precision Agriculture System to Manage Florida Citrus M - Phosphorus/Potassium Soil Test Calibration and Effects on Fresh Citrus Fruit Quality Completed Projects M - Sprayer Air Energy Demand for Satisfactory Spray Coverage M - A Computer Decision-Aid To Evaluate Tree Replacement Strategies M - Detecting and Managing Water Stress in Flatwoods Citrus Plant Pathology Continuing Projects P - Diaprepes Damage and Interactions with Phytophthora P - Investigations into an Unknown Flaky Bark Disease on Grapefruit P - Studies to Determine the Cause and Develop Strategies to Control Citrus Blight P - Evaluation of Exotic Pathogen Threats to Florida P - Development of Methods to Manage Citrus Tristeza Virus P - Development of Detection Methods for Citrus Psorosis Virus and Use of the Virus as a Vector to Express Foreign Genes in Citrus P - Optimization of PCR Viroid Detection in Budwood Source Trees Completed Projects P - Research in Support of Eradication and Control of Citrus Canker P - Improving Performance of Fungicides for Control of Postbloom Fruit Drop, Greasy Spot and Alternaria Brown Spot P - Reducing Postbloom Fruit Drop Through Use of Plant Growth Regulators to Concentrate Bloom Entomology Continuing Projects E - Residual Efficacy of Micromite on Diaprepes abbreviatus and Impact on Egg Parasitoids E - A Hydrophilic Particle Film for Control of Diaprepes abbreviatus and Other Citrus Pests E - Integrated Mite and Greasy Spot Control on Florida Citrus E - Biological and Chemical Controls for Citrus Root Weevil Larvae and Adults: Long-Term Control in Large Field Plots E - Mortality and Suppression of Egg Laying of Diaprepes abbreviatus E - Classical Biological Control of Citrus Psylla and Pink Mealybug E - Classical Biological Control of the Brown Citrus Aphid Completed Projects E - Evaluating Biological Control Potential of Native Florida Nematodes Against Citrus Root Weevil (Diaprepes) E - Classical Biological Control of Diaprepes abbreviatus E - Field Tests of Alternative Candidates for Malathion and Efficacy Test for Diazinon in Mediterranean Fruit Fly Eradication and Caribbean Fruit Fly Protocol Programs Plant Improvement/Other Continuing Projects I - A Scion and Rootstock Database for Information Management and Developing Recommendations for Growers I - Establishment of a Core Citrus Transformation Lab to Support the Genetic Improvement of Citrus I - Transfer and Testing of Potential Canker Resistance Genes to Florida Citrus I - Development and Evaluation of Improved Citrus Rootstocks

3 FLORIDA CITRUS PRODUCTION RESEARCH ADVISORY COUNCIL Administered by the Florida D I - Utilization of Gene-Mapping and Marker-Assisted Selection for Citrus Variety Improvement I - Field Evaluation of Promising USDA Rootstock Selections I - New Scion Variety Development for Florida Citrus Growers Page 3 of 43 Completed Projects O - Development of a Central Internet Resource for Citrus Information Worldwide Top of Document FDACS Contents Page FCPRAC Projects Approved for FY INTRODUCTION Presented in this Ninth Annual Report is information about research conducted during Fiscal Year supported by the Florida Citrus Production Research Advisory Council operating under the Florida Citrus Production Research Funding Order. This research support program was established under the Florida Marketing Act which enables Florida citrus growers to tax themselves for the purpose of providing funding to support needed research. Growers approved this marketing order by referendum in 1991 and the Council began its work in Financial Summary for Fiscal Year Balance Forward $1,466, Collections thru ,918, Refunds 3, Total Cash $3,388, Disbursements Research Projects $1,172, Administrative Cost 44, Total Disbursements $1,216, Available for $2,172, CHAIRMAN S MESSAGE December 31, 2001

4 FLORIDA CITRUS PRODUCTION RESEARCH ADVISORY COUNCIL Administered by the Florida D... Dear Florida Citrus Grower: Page 4 of 43 Looking over the past year, there has been major turmoil in the world, in our country and in the Florida citrus industry. Our troubles seem small in comparison to the overall scheme of things and, tough as it may seem, if we remain clever and diligent, the industry will weather the storm. The Florida Citrus Production Research Advisory Council (FCPRAC) has completed its ninth year under the grower-approved Florida Citrus Production Research Funding Order. The assessment to raise funds for citrus production research remains at ¾ of a cent per box for FY The Council is striving towards coordinating research efforts statewide. Thus, eliminating duplication of work while encouraging cooperation. Some projects are long-term and broad in scope while many focus on short-term problems. More projects are forthcoming which will consolidate research agencies and pool research efforts. Administrative costs were 3.6% this year, due to the support of UF-IFAS CREC for office space and clerical support. Further savings are provided by UF-IFAS and USDA- ARS because they have waived normal overhead costs on all our projects. Collections for FY totaled $1,918,421. Funding for research projects was $1,172,437. Funding was provided for 38 projects selected from 44 proposals. 10 Plant Pathology 10 Entomology This includes: 10 Management/Physiology 8 Plant Improvement/Other Over the past nine years, FCPRAC has directed $10,753,000 in funding on 346 new and continued Florida citrus production research projects. Your funds have enhanced the citrus research effort, much of which would have been left undone without this program. A thank you goes to your Council members (listed previously) for their many volunteer hours away from work to make this program a success. I wish to express regret at the passing of Jim Simpson, who was past chairman of the council for four years. His quiet wisdom will be sorely missed! This is my final year as chairman of your Box Tax Committee. As we continue to strive to maintain world-class citrus research in Florida, communicate your needs to the Council members. Statewide coordination of research is vital to get the most out of our funding dollars. Great strides have been made in this area and hopefully these efforts continue into the future. Thank you for your support and God bless America. Andrew B. Pike FCPRAC Chairman FCPRAC Funding by Years for Each Category z Grant FY FY FY FY FY FY FY F Category Management/ Physiology (5) 183,627 (10) 280,262 (11) 379,888 (13) 415,392 (14) 372,064 (17) 462,291 (7) 163,965 (10)

5 FLORIDA CITRUS PRODUCTION RESEARCH ADVISORY COUNCIL Administered by the Florida D... Page 5 of 43 Plant Pathology (13) 322,015 (13) 293,443 (11) 266,011 (10) 337,804 (10) 363,354 (14) 453,379 (9) 300,513 (10) Entomology ( 4) 118,036 (15) 452,344 (11) 342,714 (12) 313,953 (13) 258,814 (16) 340,208 (13) 250,035 (10) Plant Improvement/ (3) 132,893 (3) 139,700 (2) 123,000 (2) 114,000 (3) 135,000 (4) 177,000 (9) 338,722 (8) Other Totals (25) 756,571 (41) l,l65,749 (35) 1,111,613 (37) 1,181,149 (40) 1,129,232 (51) 1,432,878 (38) 1,053,235 (38) Z Smaller numbers in parentheses are numbers of projects (new and continued), larger numbers are funding in dollars. FLORIDA CITRUS PRODUCTION OVERVIEW The Council views the monies invested through this program to be contributed by growers to enhance the existing research effort. In order to assure growers that their tax monies are in fact enhancing programs, the Council monitors overall citrus production research expenditures in relation to our funding. This section provides a summary of information received from IFAS and USDA-ARS regarding their research expenditures. The Council has not verified this information, and because we have not established firm definitions of each aspect of the research, we may see some adjustments in the future. Most of this information has not been presented in this form before. The Council can only provide this information because of the candid disclosures of the research institutions. We appreciate their openness and cooperation. 1. Council monies shown reflect actual expenditures by the institutions and do not reflect balance of grants held in reserve. 1. Council monies shown reflect actual expenditures by the institutions and do not reflect balance of grants held in reserve. Top of Document FDACS Contents Page RESEARCH REPORTS MANAGEMENT/PHYSIOLOGY Continuing Projects Rootstock Interactions with Disturbed Soil Profiles in Flatwoods Citrus Project No M Investigators: Bill Castle, IFAS-UF-CREC, Tom Obreza, IFAS-UF-SWFREC, Brian Boman,IFAS - UF - IRREC Progress Report for FY 00-01, Year 1 of 3. Rootstock selection in flatwoods Florida citrus groves is compromised to some extent by the natural variation among soil series, and the variation introduced by the bedding process required in these regions. The physical and chemical changes caused by bedding are largely unstudied.

6 FLORIDA CITRUS PRODUCTION RESEARCH ADVISORY COUNCIL Administered by the Florida D... Page 6 of 43 Nevertheless, they are a key element in tree performance because the surface of the natural soil and the overburden added from bedding are where most tree roots are located. We propose to characterize the natural and disturbed profiles of several representative soils planted with citrus, and several sites in which bedding rendered the soil unsuitable for commercial rootstocks, or where the rootsystem was able to overcome adverse conditions by expanding into more favorable parts of the profile. 1. To understand how electrical conductivity data collected with a tractor-drawn sensor relates to soil physical and chemical data; 2. To survey citrus groves to locate and compare areas of poor and good tree performance that can be related to soil conditions and rootstock; 3. To characterize soils at sites that are apparently unsuitable for certain rootstocks; and, 4. To determine which soil properties are most responsible for poor rootstock performance. 5. Measure root distributions. A project manager was hired. The first phase of locating Indian River grove sites of poorly performing citrus trees on Swingle citrumelo, Carrizo citrange, Cleopatra mandarin, and Smooth Flat Seville rootstocks has been completed. These sites were matched with nearby locations, generally within the same block, of trees performing well. Samples have been taken from 20 such sites to confirm the Wabasso, Riviera, Winder, Chobee, and Pineda soils and characterize the specific locations. Tree sizes were measured, and tree condition described. Preliminary data to compare EM38 and Veris electrical conductivity measurements have been conducted; on Pineda soil, the correlation was excellent suggesting that both machines provide similar site information. Trees on 7 rootstocks planted in 5 soil types were measured for the second year, and two water table wells were installed in each site. FCPRAC Grants $ 30,000 Agency Contribution $ 35,000 Other Grants $ 48,000 Total $113,000 Enhancing Citrus Cropping Through Controlling Flowering and Improving Fruit Size Through Thinning Project No M Investigators: L. Gene Albrigo, IFAS - UF - CREC;Ed Stover,IFAS - UF - IRREC Progress Report for FY 00-01, Year 1 of 2. Excessive flowering compromises production of some Florida citrus varieties. GA applied during floral initiation reduces flowering, increases leafy bloom, alters bloom timing, and often increases total crop. Initial studies focused on Ambersweet and Navel, but other varieties may benefit from control of flowering. Time of GA application appears to influence tree response. We are studying the relationship between variety, environmental conditions before application, time of GA application, and tree response. GA was applied at mid Dec., early Jan., and late Jan. timings to Valencia, Ambersweet, and Late Navel and at the middle timing, three rates of GA were compared. Bloom was affected in all varieties, but only Ambersweet showed increased cropping. Cumulative effects of different thinning strategies were compared on Murcott, Sunburst and Flame. After one year, more large sized fruit were produced on NAA-thinned Sunburst and one of two Murcott blocks. Complete data on fruit number and yield per tree and fruit size distribution will be assessed again this year. 1. Compare varietal response to GA-treatments: flowering, fruit number, and fruit size. 2. Correlate weather conditions during floral induction through bloom on effectiveness of different GA timings. 3. Identify economically optimal GA rates. 4. Determine cumulative economics of regular chemical thinning. 5. Establish cropload thresholds for recommending chemical thinning.

7 FLORIDA CITRUS PRODUCTION RESEARCH ADVISORY COUNCIL Administered by the Florida D... Page 7 of 43 In the Ridge, GA applied to Ambersweet on Dec. 30, 1999 or Jan. 20, 2000 increased yields by 30% with no significant increase from the Jan. 11th timing. In the Indian River area, GA applications influenced timing of flowering in all varieties. Late Jan. or early Feb. 2000, GA reduced bloom duration in Ambersweet and Late Navel. Only Ambersweet displayed an overall reduction in flowering from GA applications in Only Ambersweet displayed a significant influence on cropping following GA treatment, with early Jan. treatments increasing cropping >50%. Initial results suggest that GA at 15 g/acre is as effective as 20 g/acre. Cumulative effects of different thinning strategies were compared on Murcott, Sunburst, and Flame. In the first year, more large sized fruit were produced on NAA-thinned Sunburst and one of two Murcott blocks. All experiments were established again this year. Flowering data were collected in the spring and complete data on fruit number and yield per tree and fruit size distribution will be assessed at harvest. FCPRAC Grants $ 34,000 Agency Contributions $ 75,000 Grower Contributions-Time $ 5,000 Other Grants $ 0 Total $114,000 Thirty percent of 1 faculty and 25 percent of 1 faculty were applied to this project. Other infrastructure support was supplied at two locations of the University of Florida. Ecolyst Application Timing, Juice Brix, and Profitability of Oranges Project No M Investigator: Fred Davies, UF - Gainesville Progress report for FY 00-01, Year 1 of 2. Ecolyst [diethyl -2-4-(4 methylbenzyloxy) ethyamine hydrochloride] is a recently developed plant growth regulator (PGR) that has been reported to increase juice Brix of Valencia oranges during preliminary experiments. Ecolyst has been applied during bloom; however, little is known about when and at what tree developmental stage Ecolyst should be applied for optimum results. Our objectives were to determine optimum application timing based on tree developmental stage, and to assess the overall effect of Ecolyst on yields, tree health, and grove profitability. Ecolyst was applied during Spring 2000 to 2 commercial blocks of Hamlin and Valencia oranges. Application times included: 1) prebloom; 2) 25-50% flowering; 3) full bloom; 4) petal fall; and 5) initial set. These times were chosen to determine if Ecolyst has effects on leaves alone, flowers and leaves, or leaves and fruitlets alone. Fruit were harvested in 2 locations at 4 dates and juice Brix, titratable acidity and ratio of Brix:acid determined. Early application of Ecolyst was most effective for increasing juice Brix by an average of Ecolyst increased Brix on 3 of the 8 harvest dates. Ecolyst did not affect any other fruit quality factor, tree vigor, health, or yields. 1. To determine effects of Ecolyst application time and repeated application on juice Brix levels. 2. To assess overall effect of Ecolyst on yield, tree health, and grove profitability. Ecolyst (6 g/acre) was applied to mature Hamlin and Valencia orange trees in Bartow and Lake Wales, Florida, in Spring of Applications were made at 5 different stages of flowering/fruit set from prebloom until initial fruit set. Ecolyst increased juice Brix on average by 0.28 and was effective on 3 of 8 harvest dates at the 2 locations. The reason for the variable response is unknown. The experiment was repeated in Spring 2001 using the same trees and application timings to determine if the product has cumulative effects. Ecolyst had no effect on juice acid, fruit size, yields, or tree vigor or appearance. Ecolyst has the potential to be of importance to the processing orange industry in Florida, but needs to be more consistent in its performance. FCPRAC Grants $24,000 Agency Contribution $30,000 Other Grants $20,000

8 FLORIDA CITRUS PRODUCTION RESEARCH ADVISORY COUNCIL Administered by the Florida D... Total $74,000 Page 8 of 43 Implementation of the Decision Information Systems for Florida Citrus Project No M Investigators: L. Gene Albrigo; William S. Castle; Ronald P. Muraro; L. W. Timmer; T. Adair Wheaton, IFAS - UF - CREC Howard W. Beck ; James J. Ferguson; J. David Martsolf; Fedro S. Zazueta, UF - Gainesville Progress Report for FY 00-01, Year 1 of 2. Making decisions about the best production practices, their timing and integration of options, has become very complex. Growers can use helpguides to effectively consider all of the options. Expert systems tied together on the basis of vegetative and fruit development stage can help to clarify and suggest timely options, provide production practices record keeping and free up time for other management decisions. Several units for the eventual integrated decision support system for citrus were developed to the stage of functioning prototypes during the early years of work. During this year s support, the Copper Spray Schedule was tested for the third year by growers and the data collected for flowering intensity and bloom date was modeled and incorporated into a flowering expert system to be tested in Develop data and a model of flowering intensity and bloom date for the Production Practices Scheduling System so that practices can be based on accurate prediction of citrus growth events and management decisions can be made ahead of and applied at the proper time. 2. Test and further evaluate the Copper Spray Scheduling System. 3. Develop and demonstrate a Preplant (rootstock selection) Decision System. 4. Develop a tree size and yield system to be used as a baseline for comparing tree growth and yield. 5. Integrate these various applications within a user-friendly operating system that includes a flexible record keeping format. The Cu Spray Scheduling System for disease control was validated by grower tests and Cu residue analysis for a third year. Data was collected to add additional cultivar growth curves; some data was available to add temperature effects on rate of fruit growth. The Production Practices Scheduling System was improved and further developed through interaction with 3 grove production operations. Grower requirements for record keeping continue to be emphasized and will be tested in Most work has concerned climatic effects on flowering intensity and time of bloom. Flowering data has been modeled and a flowering expert system was developed to run in The production practices prototype will run and have grower testing in Several growers continue to cooperate in the integration of production practices, development of appropriate record keeping and improvement of the user interface. FCPRAC Grants $ 32,500 Agency Contributions $ 44,500 Grower Contributions-Time $ 20,000 Total $ 97,000 Other Grants $ 0 Ten percent of 2 faculty, plus 5 percent of 3 growers and 10 percent of 1 grower s time were used. Other infrastructure support was supplied at two locations of the University of Florida. Tree Pruning Studies to Improve the Production and Harvesting of Florida Oranges Project No M Investigators: J. D. Whitney; T. A. Wheaton; W. S. Castle; S. H. Futch; J. K Burns, IFAS - UF - CREC

9 FLORIDA CITRUS PRODUCTION RESEARCH ADVISORY COUNCIL Administered by the Florida D... R. E. Rouse,IFAS - UF - SWFREC Page 9 of 43 Progress Report for FY 00-01, Year 1 of 3-5 years. Controlling tree size and maintaining good fruit production have been a problem in some orange plantings, particularly in cases where vigorous scion/rootstock combinations have been planted at close tree spacings. Fruit production is usually high early in the life of these plantings, and then becomes marginal after the trees have reached containment size. Low fruit production not only reduces gross returns but further reduces net returns because the per box harvesting costs can be higher. Hedging, topping, nutritional, irrigation and tree thinning treatments have been under investigation to improve production and improve manual harvesting. The effects of many of these treatments on fruit yields and quality in Florida are not known. 1. Determine the effects of hedging, topping, nutritional, and irrigation treatments on the subsequent fruit yields, fruit characteristics, and conventional harvesting rates of mature hedgerow orange trees with declining production levels due to close spacing and excessive vigor. 2. Determine the effects of tree thinning on subsequent fruit yields and quality. This was the final year that data (5 years total) were collected in Experiments 1 and 2 in FCPRAC and are included in this report. In the hedging/topping/skirting experiment (Experiment 1) in 15 ft tall Valencia Rohde Red/Carrizo trees, fall topping had higher box and lb solids/acre yields than did spring topping for the third consecutive year. After October hedging and topping, some young flush was killed by 3 January freezes (grower recorded lows in the mid 20s). Angle topping had higher box and lb solids/acre yields than did flat topping. In the adjacent nutrition (nitrogen)/irrigation experiment (Experiment 2) in the same Valencia grove, irrigation (no irrigation 7/00-2/01 vs. grower irrigation year round) and nitrogen (130 to 220 lb/acre) effects were not significant. The droughty conditions in fall 2000 and the lack of differences in these data and similar data from previous years all provide evidence that these trees (particularly those with no irrigation at 130 lb N/acre) on 2-row beds may have been receiving a substantial portion of their nutrients and water from the water table below the root system. Manual harvesting rates were positively correlated with box/acre yields at an average fruit size of 154 fruit/box. In the 11-year-old 24 x 8 ft Hamlin/Carrizo tree thinning experiment (Experiment 5), the 12/98 clipping of every second and every third trees reduced lb solids and box/acre yields for the second subsequent season compared to solid hedgerow. A similar thinning experiment was initiated (trees clipped 5/00) in 11-year-old 24 x 8 ft Valencia/Swingle trees. Unexpectedly, as with the thinned Hamlin trees last season, per tree yields of the thinned Valencia trees for the first season after thinning were less than the hedgerow trees. FCPRAC Grants $21,865 IFAS Contribution $25,000 Orange Service Co. Pruning in-kind donation $ 7,000 Total $53,865 Development of a Precision Agriculture System to Manage Florida Citrus Project No M Investigators: J. D. Whitney; T. A. Wheaton; W. M. Miller, IFAS - UF - CREC J. K. Schueller,IFAS - UF - Gainesville Progress Report for FY 00-01, Year 2 of 3. Although citrus growers usually manage their groves on a whole grove or block basis with uniform production inputs, considerable variability in

10 various grove characteristics may exist. Some of the characteristics critical to management decisions are fruit yield and quality, tree size and health, soil type and fertility, leaf analysis, pest populations, water requirements, etc. Precision agriculture techniques can provide the tools that will allow grove owners to determine these characteristics in site-specific areas within the grove. Using these characteristics, the grower can then make decisions on adjustments to cultural practice inputs that will increase profits and apply the inputs in site-specific areas with precision agriculture equipment. Accurate yield maps are essential for determining profits/losses in site-specific areas and for determining whether changes in cultural practice inputs improve profits. 1. Develop a system to accurately map citrus yields using conventional harvesting methods. 2. Develop a sensor system to measure tree canopy characteristics. 3. Integrate yield maps with aerial photography, topography, soil factors, etc., to determine causes of yield variation. We integrated components of a GeoFocus, Inc. yield monitor unit with an automatic triggering system that actuated the yield monitor to record a DGPS location each time a fruit tub was loaded on a goat truck. The system replaced the need for the goat truck operator to push a button which is often forgotten and a source of error in citrus yield mapping. In field tests with a commercial harvester, the triggering system functioned satisfactorily but the GeoFocus unit would record no information if the DGPS signal was not available. We designed, fabricated, and field tested our own system by integrating an automatic triggering system, a microprocessor, and a DGPS unit. Missed tub locations were 2% or less in commercial harvesting operations. Progress was made on a method of dynamically weighing fruit as it was loaded in the grove. Ultrasonic and laser sensors were tested and found to give reasonably good measures of tree canopy sizes. The laser sensor also has good potential for measuring foliage density that could provide an index of tree health. We have continued to work with interested growers to identify reasons for spatial variability in yield and tree size/health, and to determine the reasons and possible remedial actions. In most cases, the variability has been related to soil characteristics and/or water drainage. An analysis was made of errors resulting from implementation of variable rate fertilizer applications. The CREC hosted a precision agriculture workshop October 10, FCPRAC Grants $ 35,000 IFAS Contribution $ 65,000 FDACS Grant $ 5,000 Total $105,000 Page 10 of 43 Phosphorus/Potassium Soil Test Calibration and Effects on Fresh Citrus Fruit Quality Project No M Investigators: Thomas Obreza; Robert Rouse, IFAS - UF - SWFREC Progress Report for FY 00-01, Year 3 of 5. Phosphorus movement to surface water and nutritional effects on fruit quality emphasize judicious use of P fertilizer. Citrus response to P is rare because it usually accumulates in soil. A calibration experiment using modern soil extractants was started in 1998 in a newly-planted citrus grove that was very low in soil-test P and K. A range of P and K fertilizer rates were applied to generate a wide range of soil-test P and K. Tree growth and fruit yield were measured and related to soil tests. This research will enable the Florida citrus industry to more appropriately allocate P and K fertilizer costs, minimize impact on surface water quality, and produce higher quality fruit by understanding the main effects and interactions of P and K. 1. Calibrate a P (and possibly K) soil test for Florida citrus production, considering both yield and fruit quality as response variables in the calibration process. 2. Determine the main effects and interactions of P and K fertilization on yield and fresh fruit quality of Flame grapefruit and Hamlin orange. 3. Develop fertilization recommendations that will produce qualities most desired by fresh fruit consumers.

11 Page 11 of 43 In autumn 1997, Flame grapefruit and Hamlin orange trees were planted at the SWFREC-Immokalee. Three-tree plots have been fertilized with four rates each of P2O5 and K2O to establish a range of soil test values. To assess fertilizer effects in , soil and leaves were sampled in July, canopy volume was measured in September, and the first grapefruit yield was measured in February. Mehlich I soil test P increased from Very Low to Very High as P fertilizer increased from 0 to 200 lb P 2O5/acre. Since P had accumulated in the soil, P fertilization was discontinued for the season. Soil test K only slightly increased (from Very Low to Low) as K fertilizer increased from 0 to 400 lb K2O/acre. Increasing the P or K fertilizer rate resulted in progressively higher leaf tissue P and K concentrations. This effect was much stronger for K than for P. Grapefruit tree canopy volume increased from 230 to 319 cu. ft. as K fertilizer increased from 0 to 200 lb K2O/acre, while yield increased from 3 to 15 lb/tree as K fertilizer increased from 0 to 400 lb K2O/acre. Fertilization with P did not positively affect tree canopy volume or grapefruit yield. The continued failure of K to accumulate in the soil will support the current practice of annually applying K fertilizer at similar rates as N. The lack of tree response to P fertilizer is surprising considering the very low soil test P in the control plots. FCPRAC Grants $ 6,000 Agency Contribution (IFAS citrus grove and grove care, salaries) $12,000 Other Grants (Foundation for Agronomic Research) $ 2,000 Total $20,000 Sprayer Air Energy Demand for Satisfactory Spray Coverage Project No M Investigator: Masoud Salyani, IFAS - UF - CREC Project Report for FY 00-01, Year 1 of 1. MANAGEMENT/PHYSIOLOGY Completed Projects Sprayer air volume/energy, air distribution in open area and within canopy, and spray deposition were measured, using a Curtec, PowerBlast (4 fan sizes), and Titan tower (2 fan speeds). Ground speed and volume rate ranges were 0-4 mph and gpa for air velocity and deposition measurements, respectively. Weather data were recorded during all experiments. Air velocities decreased as ground speed increased. Mean deposition of Curtec was affected by spray volume and deposition increased at higher rates. With PowerBlast, spray volume did not have a significant effect on mean deposition but the fan size did. With Titan, deposition was affected by spray volume but not by the fan speed. The interaction between air volume and spray volume was significant in PB applications. The results suggest that high air volume rates may not give significant increase in spray deposition. The air and spray penetration largely depended on the tree canopy structure and prevailing wind direction. 1. Determine the effects of the sprayer air energy and volume on canopy air displacement, droplet transport, and spray coverage. 2. Determine the interaction of the ground speed and air energy in canopy penetration. 3. Determine the interaction of the spray volume and air volume in spray coverage. 1. Air volume/energy of Curtec, PowerBlast, and Titan sprayers were estimated by air velocity measurements at fan outlets. Ranges of air

12 velocity and volume were mph and cfm. A 46% increase in cfm increased PowerBlast fan input energy by 310%. 2. Curtec and 8 PB sprayer configurations were operated in open area and air velocities were measured at 24 spatial locations, at 0, 1.5, and 3 mph. At each height air velocity decreased rapidly with distance. Curtec gave more uniform distribution than PB sprayers. Spatial air velocities were proportional to outlet air and decreased for moving sprayer. 3. Curtec and 9 PB configurations were operated at 0, 1, 2, 3, and 4 mph. Air velocities were measured outside and inside the canopy at 2 heights. Air velocities decreased as ground speed increased, particularly at inner and higher locations. On average, air velocity dropped fpm per ft of canopy depth. 4. Deposition test treatments included 3 Curtec (26, 104, 208 gpa), 12 PowerBlast (4 fans at 26, 104, 384 gpa), and 4 Titan (2 fan speeds at 78 and 200 gpa). Spray deposition was sampled at 2 canopy heights and 7 depths. Curtec deposition was affected by spray volume and increased at higher rates. Spray volume did not have a significant effect on mean deposition of PowerBlast but the fan size did. With Titan, mean deposition was affected by spray volume but not by the fan speed. The interaction between air volume and spray volume was significant in PowerBlast applications. FCPRAC Grants OPS Technician $13,500 Operating Expenses $ 6,500 $20,000 IFAS/CREC Eng. Technician 50% P. Investigator 25% Other $ 0 Total $20,000 Page 12 of 43 A Computer Decision-Aid To Evaluate Tree Replacement Strategies Project No M Investigators: Fritz Roka, UF - IFAS- SWFREC Ronald Muraro, UF - IFAS - CREC Progress Report for FY 00-01, Year 1 of 1. Citrus growers face a variety of tree replacement strategies ranging from annual resetting individual trees to pushing and replanting entire blocks. A generic recommendation, which would define the most profitable course of action, is difficult, if not impossible given the number of horticultural and economic variables that need to be considered. This project develops a decision-aid tool, which incorporates a grower s individual economic and production situation, and analyzes alternative tree replacement strategies. 1. Identify the biological and economic variables that are important to the tree replacement decision. 2. Collect cost and production data related to various tree replacement decisions. 3. Reset versus solid set planting - planting and young tree care costs. 4. Reset versus solid set planting - tree yields over time. 5. Disease progression curve for CTV. 6. Construct an economic simulation model that incorporates the relevant biological and economic variables and one which can be customized to a specific grove. A preliminary citrus reset analysis program has been developed and is being circulated for review. Additional material is available outlining data requirements and output results. The current model is the third revision and has evolved from interviews with selected growers. Default values for input costs and tree yields are imbedded in the model. Annual budget data provide a guide for input costs and an ongoing yield study in southwest Florida provides a basis for yield estimates by tree age. Multiple reset strategies can be specified. Tree replacement scenarios are compared by estimating a 15-year cumulative cash flow. The program

13 allows a grower to input specific cost and production values that match their specific situations. The program also allows a grower to input their best guess as to future market conditions. The model has already been used to demonstrate that, under conditions of individual tree decline (i.e., CTV, blight, etc.), an annual reset strategy returns the highest cumulative net cash flow. This result assumes that the only decision is when to replace a tree and not whether to change scion variety or grove infrastructure (i.e., irrigation, tree density, drainage flows, etc.). The model s value as a decision making tool increases under conditions of general grove decline, or when changes to grove infrastructure, variety and/or rootstock selections are being considered. A final round of field testing is underway and computer programmers are being consulted to improve usability and model performance. FCPRAC Grants $14,445 Agency contribution (IFAS) $12,000 Other Grants $ 0 Total $26,445 Page 13 of 43 Detecting and Managing Water Stress in Flatwoods Citrus Project No M Investigator: Brian J. Boman,UF - IFAS - IRREC Progress Report for FY 00-01, Year 2 of 2. This project investigates the effects of irrigation management and soil water status on tree response for both young and mature flatwoods citrus. Tensiometers and EnviroSCAN capacitance sensors are used to monitor to soil moisture status. Moisture stress in the trees is determined with measurements of stomatal conductance. Measurements have been taken on stressed and unstressed trees under various evaporative demand, soil moisture, and water table conditions. Soil moisture and stomatal conductance will be correlated to develop stress indices for various water table depths, soil moisture content, time of day, and climatic conditions. One experiment is being conducted on young Valencia on smooth flat Seville trees that were planted in Trees are watered with 4 regimes: daily, 3 times/day, every 3 days, and at a soil moisture of 15 cbar. Treatment effects are evaluated with tree growth and flush status measurements. Another experiment is in a Valencia on rough lemon rootstock block that is 12 years old. Irrigation treatments are either on a daily or twice per week basis. Measurements of stomatal resistance under various soil moisture and environmental conditions have been taken. Fruit yield and juice quality parameters will be measured at harvest. 1. Determine soil water extraction rates and patterns of citrus trees during periods with various evaporative demand rates (i.e., hot-humid versus warm-dry, etc.). 2. Correlate stomatal resistance with soil moisture levels as measured with EnviroSCAN capacitance probes. 3. Develop irrigation and drainage guidelines that will minimize stress levels to trees. Both the young tree and mature tree experiments were started in the summer of 1999 when the Enviroscan system, tensiometers, and irrigation systems were installed for both experiments. Rainfall, since the study began, has been significantly lower than the long-term normal, requiring frequent irrigations. Growth measurements taken at two-month intervals on the young trees have shown that increases in trunk diameter were similar for all treatments throughout the first year of the study. Multiple irrigation per day has resulted in essentially the same trunk growth as the once-a-day treatment. By May of 2001, the treatments watered once or more daily had 10% more trunk diameter increase than the tensiometer and 3-day irrigation interval treatments. Canopy growth was similar for all treatments for most of 1999 and By March of 2001, the daily irrigation regime had resulted in resulted in the greatest canopy development. Canopy diameter for the daily irrigation was about 6% more than the 3-day or 3-times per day treatments and about 10% more than the trees with tensiometer-controlled irrigations.

14 In the mature Valencia experiment, soil moisture, weather parameter, and stomatal resistance measurements have been taken under a variety of conditions to characterize stress levels. Yields in April of 2001 showed the higher irrigation rate to have about 13% higher yields than the low irrigation level. Yields and juice quality measurements will be taken at the normal harvest time in the spring of 2002 to conclude the experiment. FCPRAC Grant $18,000 (FY 2000) $16,000 (FY 2001) IFAS Contribution $18,000 Other grants $12,000 Total $64,000 Top of Document FDACS Contents Page Page 14 of 43 PLANT PATHOLOGY Continuing Projects Diaprepes Damage and Interactions with Phytophthora Project No P Investigators: J. H. Graham,IFAS - UF - CREC K. D. Bowman,USDA-ARS, Ft. Pierce Progress Report for FY 00-01, Year 1 of 3. Interactions of several stress agents in Florida citrus groves exacerbate Phytophthora diseases, even on a normally resistant rootstock like Swingle citrumelo. A more aggressive species of Phytophthora, P. palmivora, attacks Swingle, as well as Carrizo citrange and other rootstocks infested with Diaprepes abbreviatus on heavier, calcareous soils in other areas of the industry, even in absence of Diaprepes. Specific methods for identification and evaluation of Phytophthora resistance and tolerance to Diaprepes and marginal soils are proposed. The goal of this project is to continue research directed toward providing rootstock options for management of root weevils and other prevalent soil stress agents in Florida groves. This will be accomplished through greater resistance of rootstocks to Phytophthora spp. to increase tolerance of soil and pest interactions. 1. To survey for P. palmivora in groves on Swingle with decline symptoms in comparison to other rootstocks. 2. To identify sexual and somatic hybrids with greater resistance than Swingle to Phytophthora palmivora and P. nicotianae using in vitro and greenhouse assays. 3. To screen hybrids with Phytophthora resistance in greenhouse and field assays to confirm that resistance is maintained when challenged with Diaprepes larval feeding. A Diaprepes-infested grove planted on poorly-drained soils types with damaging populations of Phytophthora palmivora and P. nicotianae was selected for intensive sampling of Diaprepes and Phytophthora populations in relation to maintenance of tree health with Ridomil Gold. Nova tangelo trees on Cleopatra mandarin did not decline between Oct 1999 and May 2000, while trees in alternating beds of Sunburst tangerine on Swingle citrumelo declined significantly. Relative abundance of Diaprepes adults from 99 locations did not differ between trees on the two rootstocks indicating that larval feeding pressure was similar. Populations of P. nicotianae from the same 99 sites were also similar on the two rootstocks, while populations of P. palmivora were significantly higher for trees on Swingle than Cleopatra. Higher populations of P. nicotianae from Swingle were correlated with greater recovery of Diaprepes adults from these tree locations. Decline in tree condition on Swingle citrumelo was correlated with P. palmivora populations but not with P. nicotianae. For Swingle, the interaction with P. palmivora results in tree death while

15 health of trees on Cleopatra is maintained with applications of Ridomil Gold. These relationships indicate that the interaction of P. nicotianae is with fibrous roots during the initial stages of root attack by larvae and that the interaction of P. palmovora is with advanced stages of structural root attack. The differential susceptibility of Cleopatra vs. Swingle to the Phytophthora palmivora/diaprepes complex is further justification for seeking sources of resistance to P. palmivora in citrus species such as mandarins and pummelos. FCPRAC Grants $ 44,900 Agency Contribution $120,000 Other grants $ 20,000 Total $184,900 Page 15 of 43 Investigations into an Unknown Flaky Bark Disease on Grapefruit Project No P Investigators: P. D. Roberts,IFAS - UF - SWFREC T. R. Gottwald,USDA-ARS, Ft. Pierce P. J. Sieburth,FDACS - DPI S. M. Garnsey,IFAS - UF - CREC (USDA-ARS-Retired) Progress Report for FY 00-01, Year 2 of 3. A disease problem of unknown etiology that causes severe bark flaking in grapefruit was found in several commercial groves in SW and central Florida in 1998 and in additional groves in subsequent years. Trees exhibiting symptoms are typically 4-7 years. Affected grapefruit varieties are White Marsh, Rio Red, and Flame. Trees are on Carrizo, Swingle, and Rough Lemon. An associated decline is reported and trees with flaky bark were removed on 400 acres. Initial investigations into the cause of the flaky bark symptoms were negative for any insect or pathogen, environmental stresses, nutritional or ph related damage. Observed trees showed a slow increase in disease incidence and severity during from indicating spread and persistence of the disease. Identification of the cause of the flaky bark disease and its impact on trees will lead to understanding and control of the problem. 1. Identify the cause of the flaky bark disease. 2. Measure the increase and spread of flaky bark symptoms. 3. Determine the impact of flaky bark on tree health related to decline and yield. 4. Determine the extent of the problem on citrus in different production regions beyond Central and Southwest Florida. 5. Formulate control methods. Plots were established at three groves containing symptomatic trees. Each tree in a 20 x 20 tree plot was visually assessed for presence of flaky bark and rated for severity. Trees were re-examined after 6 months and will be monitored at yearly intervals. Trees exhibited an increase of flaky bark incidence and severity confirming preliminary data of persistence and spread of the disease. The data collected during 3 years will be analyzed by temporal and spatial modeling programs to characterize whether spread is consistent with movement via a vector, mechanical transmission, or occurs randomly. To determine whether an insect pest or fungal or bacterial pathogen is involved, trees at 2 test sites in 4 replicate plots of 5 to 10 trees were sprayed on the lesions with at a solution of copper and Ridomil or an insecticide. Control trees were untreated. Trees are being monitored for any change in symptoms using the methodology described above. Both control and inoculated trees in the transmission studies established in 1998 showed symptoms in Additional inoculations were made or will be made to other varieties in the field and greenhouse trials. Development of symptoms will indicate a transmissible agent.

16 Non-pathogenic factors and association continue to be examined. Fungi and bacteria were isolated from diseased samples. Only one fungus was consistently recovered but it is also a common saprophyte; its pathogenic role is under investigation. Additional sites were identified but none are beyond central and southwest Florida. FCPRAC Grant $21,500 UF, SWFREC $ 0 Other Grants $ 0 Total $21,500 Page 16 of 43 Studies to Determine the Cause and Develop Strategies to Control Citrus Blight Project No P Investigator: Kenneth Derrick, IFAS - UF - CREC Progress Report for FY 00-01, Year 2 of 3. The Florida citrus industry loses more than 600,000 bearing trees per year to citrus blight. There are no reliable methods for controlling blight and the cause of the disease is unknown. The symptoms associated with citrus blight can be reproduced by root graft inoculations, which indicates the disease is caused by a pathogen. A major research objective is to induce symptoms of blight in producing trees in a grove or in plants in the greenhouse by inoculations using either cultures of microorganisms or extracts from roots of trees with blight. Blight associated protein p12 is always present in trees with blight and appears to be involved in cell growth. Research is in progress to determine if p12 produced by the tree in an effort to resist the disease and with transgenic expression of the p12 gene in scions and rootstocks provide resistance to blight. In addition, using cdna subtraction methods, we have found several additional genes that are either up or down regulated in blight affected trees. 1. To determine the cause of citrus blight. 2. To determine the function of the blight protein p To develop strategies to control citrus blight. We have developed an efficient Agrobacterium-mediated transformation system for citrus. The p12 gene has been used to produce transgenic rootstocks (rough lemon, Carrizo citrange) expressing both sense (p12 producing) and antisense (blocking p12 production) directions. Some of the transgenic plants have multiple copies as shown by Southern blots. Further evaluations of these plants are in progress. Selected plants will be increased to produce trees for field trails for resistance to blight. This past year we have made a search for additional genes that are either up or down regulated in response to blight using cdna subtraction methods. Numerous genes that are affected by trees with blight have been identified, some of which are expected for diseased plants and some of which are of unknown function. Numerous trees have been inoculated with either cultures or extracts from roots of trees with blight. These trees are being monitored by p12 assays and observed for symptoms of blight. Attempts to associate pathogen DNA with blight are being made using DNA subtraction methods. FCPRAC Grant $56,822 OE from IFAS $ 1,500 Total $58,322 Evaluation of Exotic Pathogen Threats to Florida