J. D. Whitney’s research while affiliated with University of Florida and other places

A key component in precision agriculture is exact delivery of liquid and solid materials to site-specific locations. Addressing this concern, Florida growers are in the initial phase of implementing best management practices for verious citrus growing areas. A 16.2-ha (40-acre) field trial was initiated with a grower in the Ridge growing section of the state. As part of that project, prescription maps were developed for multiple dry fertilizer applications throughout the season. A granular fertilizer unit with hydraulically powered dual split-chain outputs controlled from a MidTech Legacy 6000 controller was utilized. Data were collected on target and as-applied rates compensating for missing trees and resets. Additional mass balance data were obtained by weighing each load before and after spreader application. Application rates for each of 43 blocks (42 test, 1 conventional) were compared for eight tests conducted during the 2002-2003 and 2003-2004 fruit seasons. Prescription and as-applied rates exhibited a high correlation (r2 = 0.98) and linear relationship (slope = 0.98). Grand totals from vehicular weighing and controller discharge estimation produced an average absolute error of 7.7%.

Two air-carrier sprayers were used to investigate the feasibility of applying abscission materials from one side of the tree in a two-row bedded orange grove. One-sided (bed side) and two-sided (both bed and ditch side) applications at 2.4 and 4.8 km/h were compared using each sprayer. Tank mixture contained active ingredient (a.i.) 5-chloro-3-methyl-4-nitro-1-H-pyrazole (CMN-P) at about 350 mg/L a.i., a surfactant, a drift retardant, and a fluorescent tracer. Leaf samples were collected from different locations on the bed and ditch sides, and deposition was determined by fluorometry. The efficacy of abscission application was assessed in terms of fruit detachment force (FDF) and percent fruit removal (PFR) by trunk shakers. With both sprayers, one-sided applications resulted in comparable depositions to two-sided applications at the far side of the lower canopy level. This result implies that one-sided applications might provide acceptable spray coverage in lightly foliated canopies. Abscission sprays at one-half or full a.i. (526 or 1052 g/ha) rate reduced fruit detachment force significantly. The best results were obtained with two-sided applications at lower ground speed (highest volume/a.i. rate). The air-curtain sprayer at full a.i. rate and the air-blast sprayer at one-half or full a.i. rate resulted in a significant increase in percent fruit removal.

Description Fourteen peer-reviewed papers address the latest advances in pesticide formulations and delivery systems. Three sections cover: Formulations—addresses some of the new challenges in formulating pesticides, including the advent of GMOs (genetically modified organisms) and their effect on the chemical aspects of pest control; new uses of chemicals through formulation changes, liquid and solid formulations and applications, and fluorescent imaging to assess efficiency. Delivery Systems—discusses delivery and interactions of the pesticide with the target organism, including spray release height and drop size, aerial sprays, and abscission sprays. Adjuvants—covers the enhancement of pesticide formulation by the use of spray additives.

The accuracy and interaction among global positioning system (GPS) horizontal accuracy, differential GPS (DGPS) sampling frequencies and machine delay times of a hypothetical variable rate applicator for nitrogen (N) fertilizer application based on an application map in Florida citrus were studied. Parameters studied included: five GPS horizontal accuracy levels, two levels of DGPS horizontal accuracy, two DGPS sampling frequencies and two machine delay times. Two integrated models were developed which documented the effects of the parameters. Machine delay time was the most important factor and GPS horizontal accuracy was the second most important.

Field experiments were conducted to investigate the effect of sprayer type, airflow rate, and nozzle output on deposition of active ingredient and mechanical harvesting of 'Valencia' orange (Citrus sinensis). Fruit detachment force (FDF) and percentage of fruit removal (PFK) by trunk shaker were used as mechanical harvesting parameters. A PowerBlast sprayer discharging radially and a Titan sprayer discharging over the entire canopy were used. The spray mixture contained an abscission chemical (CMN-pyrazole), a surfactant (Kinetic) and a fluorescent tracer (Pyranine-10G). Deposition was determined at three different heights outside and inside of the canopy. With the PowerBlast, higher airflow and lower nozzle output reduced deposition of the active ingredient. The mean FDF of sprayed treatments was less than that of the non-sprayed control but the difference among the four spray treatments was not significant. The lower airflow rate with lower nozzle output had higher PFR than that of the control. With the Titan sprayer, the mean deposition at lower airflow was similar to or higher than the higher airflow. At higher airflow, the lower nozzle output gave higher mean deposition. The Titan sprayer treatments resulted in less FDF than the control. At both airflow rates, the FDF was less at lower nozzle output than at higher nozzle output. The PFR of these treatments were not different from that of control.

Description This unique, new volume provides sixteen peer-reviewed papers, which address global topics related to the delivery of crop protection agents to their intended target sites. These papers demonstrate how the industry is working together in a rational and integrated manner with a view to continuing the production of CPA’s that are safe to the user, the consumer and the environment. Subjects covered, include: From Clinton to Bush: Continuity and Change in Federal Pesticide Policy--addresses topics relating to the legal issues facing the industry and matters concerning inert ingredients Formulation Ingredients and Design--covers a range of topics including novel polymeric dispersants, clays as microbial carriers, and Alkyl Citrate Ester surfactants. The sessions on formulation ingredients and design were created to appeal to formulation chemists and suppliers of formulation ingredients, as well as to biologists and engineers. Delivery Strategies--examines non-traditional topics, including bees as delivery agents. More conventional topics include the multiple roles of surfactants in foliar application of systemic compounds; drift reduction using air inclusion nozzle technology; pulse width modulated sprays used for flow rate and droplet size control; application of abscission sprays to orange trees; use of adjuvants to influence Diuron and Norflurazon activity; and the use of humectants to with sulfosulfuron and glyphosate. Audience: This volume is a valuable source of information for formulation chemists, regulators, and those in industries related to application, e.g., sprayer and nozzle manufacturers.

A five-year experiment was conducted on 10-feet-tall Valencia trees on Swingle rootstock to determine the effects of skirting (lower limb removal) at 20 and 36 inches above ground level on yields and fruit quality. Average yields were not significantly affected by skirting at 20 and 36 inches. Fruit from the bottom of the unskirted trees showed significantly increased rind blemishes, were generally smaller in size, but had juice qualities at least equivalent to other fruit on the tree.

A 5-year hedging, topping, and skirting experiment was conducted in 9-year-old Rohde Red Valencia (Citrus sin-ensis L. Osbeck.) orange on Carrizo citrange (C. sinensis × P. trifoliate) rootstock to investigate their effect on yield and fruit quality. Spring hedging resulted in higher juice brix than did fall hedging, but there were no consistent differences in yield. Compared to flat topping at 15 ft, flat topping at 12 ft reduced juice brix and pound solids/box, but yield was not consistently reduced. Angle topping resulted in consistently higher yield than did flat topping. Compared to no skirting, skirting at 20 and 36 inches high had no consistent effects on yield and fruit quality.

Site-specific monitoring of citrus yield is important in understanding yield variability and its causes. A microcontroller-based system was designed to automatically monitor citrus yield harvested into individual tubs. The microcontroller was interfaced with a differential global positioning system (DGPS), a flash memory key, two limit switches, a buzzer, and a counter, which provided position information, storage, triggering, acknowledgement, and counting, respectively. The microcontroller system was mounted on a special truck (goat) that handles fruit and fruit tubs in the groves. The system was designed such that whenever the fruit was dumped into the truck bed, DGPS information was acquired and the counter and buzzer were triggered. The position information was then stored into a flash key and later downloaded to a personal computer for data analysis and mapping. This article details the design and evaluation of the citrus yield monitoring system. The evaluation phase showed that the system was able to detect the dumping events and store the DGPS locations, 100 and 98% of the time, respectively.