Masoud Salyani

Investigation of Laser and Ultrasonic Ranging Sensors for Measurements of Citrus Canopy Volume

This study compared ultrasonic and laser measurements of citrus canopy volume with manual measurement methods. Fifteen trees with different canopy heights and volumes were used. Manual and ultrasonic measurements provided dimensions for computing the canopy volume whereas laser measurements gave information that could be used to compute a ‘laser canopy volume index.’ Ultrasonic and laser methods agreed with manual methods (R 2 > 0.85, RMSE < 2.15 m 3 ). Laser showed better prediction of canopy volume than the ultrasonic system because of the higher resolution. Ultrasonic or laser sensors can be used for automatic mapping and quantification of the canopy volumes of citrus trees.

Antifeedant and sublethal effects of imidacloprid on Asian citrus psyllid, Diaphorina citri

BACKGROUND Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, transmits the causal bacteria of the devastating citrus disease huanglongbing (HLB). Because of the variation in spatial and temporal uptake and systemic distribution of imidacloprid applied to citrus trees and its degradation over time in citrus trees, ACP adults and nymphs are exposed to concentrations that may not cause immediate mortality but rather sublethal effects. The objective of this laboratory study was to determine the effects of sublethal concentrations of imidacloprid on ACP life stages. RESULTS Feeding by ACP adults and nymphs on plants treated daily with a sublethal concentration (0.1 microg mL(-1)) of imidacloprid significantly decreased adult longevity (8 days), fecundity (33%) and fertility (6%), as well as nymph survival (12%) and developmental rate compared with untreated controls. The magnitude of these negative effects was directly related to exposure duration and concentration. Furthermore, ACP adults that fed on citrus leaves treated systemically with lethal and sublethal concentrations of imidacloprid excreted significantly less honeydew (7-94%) compared with controls in a concentration-dependent manner suggesting antifeedant activity of imidacloprid. CONCLUSIONS Sublethal concentrations of imidacloprid negatively affect development, reproduction, survival and longevity of ACP, which likely contributes to population reductions over time. Also, reduced feeding by ACP adults on plants treated with sublethal concentrations of imidacloprid may potentially decrease the capacity of ACP to successfully acquire and transmit the HLB causal pathogen.

Spray Drift From Ground and Aerial Applications

A field test was conducted to quantify spray drift from typical spray applications of citrus in Florida. Spray equipment included both fixed-wing and rotary-wing aircraft and high- and low-volume airblast ground sprayers. Spray solutions containing a fluorescent tracer dye were applied to the four tree rows, closest to the downwind edge of an orange grove, under commonly practiced operational conditions. Mylar targets as well as air samplers were used to sample spray fallout and airborne drift at several locations downwind of spray applications. All applications resulted in measurable drift up to 195 m downwind and more than 70% of drift deposits (including swath displacement) originated from sprays applied to the last two rows of the trees closest to the drift line. Averaged over all distances and replications, the highest and lowest drift fallout were from the fixed-wing and low-volume ground sprayer (2.4:1), but, the highest and lowest airborne drift were from low-volume and high-volume ground sprayers (2.6:1), respectively.

EFFECTS OF FOLIAGE DENSITY AND GROUND SPEED ON ULTRASONIC MEASUREMENT OF CITRUS TREE VOLUME

Ultrasonic sensors can be used to quantify and map tree canopy volume, which is useful for planning site-specific management practices within a grove and estimating crop yield. An experiment was conducted to examine the effects of the canopy foliage density and ground speed on the performance of the Durand-Wayland ultrasonic system in tree volume measurement. Fifteen densely foliated (dense) and 15 partially defoliated (light) citrus trees were scanned from both sides at three ground speeds in three replications. The measurements were compared to those calculated from manual measurements of the tree dimensions. The difference between ultrasonic and manual volumes was used to evaluate the performance of the ultrasonic system. The difference between ultrasonic and manual volumes ranged from –17.3% to 28.71% at the 95% confidence level. Ninety five percent of the ultrasonic measurements were repeatable within –12.7% to 30.9% of the manual volume. Canopy foliage density had significant effect on ultrasonic measurements of canopy volume. The volume difference was higher in light than dense trees. There was no significant effect of ground speed (1.6 to 4.7 km/h) on ultrasonic volume measurements. Variability of the measurements in partially defoliated canopies increased as ground speed increased. There was a significant difference between the volumes of two sides of the trees.

PRECISION FARMING APPLICATIONS IN FLORIDA CITRUS

A cooperative effort between researchers, manufacturers, and growers has been investigating precision farming applications in Florida citrus. Citrus yields, based on the location of volume-based containers, were mapped using a conventional fruit-loading truck, manual harvesters (> 99% of Florida citrus is manually harvested), and GIS/GPS components. These maps were overlaid on geo-referenced aerial photographs of the tree canopies. Two fruit weighing systems were mounted on a fruit-loading truck and integrated with the GIS/GPS components to investigate mapping weight-based yields. Results to date indicate the truck-mounted weighing systems were within 1 to 6% of certified scale weights on 20 t loads of fruit. Electronically recording harvester identity is being integrated with yield mapping to make the entire system more reliable and attractive to harvesters and growers.

Influence of Posttreatment Temperature on the Toxicity of Insecticides Against Diaphorina citri (Hemiptera: Psyllidae)

ABSTRACT The psyllid Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is one of the most important pests of citrus worldwide because it efficiently vectors three bacteria in the genus Candidatus Liberibacter that cause the devastating citrus greening disease (huanglongbing). Current management practices for this insect pest rely on multiple sprays of foliar insecticides and one or two applications of soil systemic insecticides per season. Effective psyllid and disease management in Florida requires insecticide applications throughout the entire season over wide ranging temperature and environmental conditions. Using a petri dish bioassay technique, the effect of posttreatment temperature (range, 17–37°C) on the toxicity of selected organophosphate (chlorpyrifos and dimethoate), carbamate (carbaryl), avermectin (abamectin), pyrethroid (bifenthrin, zeta-cypermethrin, fenpropathrin, and lambda-cyhalothrin), and neonicotinoid (acetamiprid, imidacloprid, and thiamethoxam) insecticides was evaluated against adult D. citri. The toxicity of both organophosphates showed a positive temperature correlation within the 17–37°C range. Similarly, carbaryl (carbamate) and abamectin (avermectin) exhibited increased toxicity with increasing temperature from 17 to 37°C, with abamectin showing higher overall temperature-dependent toxicity against D. citri adults than carbaryl. With the exception of bifenthrin, which showed a positive temperature-dependent toxicity correlation between 27 and 37°C, all other pyrethroids tested exhibited a negative correlation over the temperature range examined. The toxicity of fenpropathrin and lambda-cyhalothrin dramatically decreased with increasing temperature from 17 to 37°C. The neonicotinoids imidacloprid and thiamethoxam exhibited a mixed response to increasing temperature, whereas acetamiprid showed a positive temperature correlation. However, all three neonicotinoids showed positive temperature-dependent toxicity correlations against D. citri adults over the temperature range tested. These data will enable citrus growers to choose the most effective insecticides for D. citri control from the various classes currently available depending on the prevailing temperature conditions.

DEVELOPMENT OF A LASER SCANNER FOR MEASURING TREE CANOPY CHARACTERISTICS: PHASE 2. FOLIAGE DENSITY MEASUREMENT

This study used a laser scanning system to quantify foliage density of citrus trees. The density calculations were based on the laser sensor-canopy distance measurements and a canopy boundary-smoothing algorithm. Ten citrus trees with different foliage densities were scanned by the laser system, and the calculated results were compared with the corresponding visual assessments of tree densities. Overall, laser measurements and visual assessments had a good correlation (R2 = 0.96; RMSE = 6.1%). Laser density measurements also had a good repeatability, with an average coefficient of variation of less than 3%.

DEVELOPMENT OF A LASER SCANNER FOR MEASURING TREE CANOPY CHARACTERISTICS: PHASE 1. PROTOTYPE DEVELOPMENT

Automatically measuring canopy characteristics is an essential step for tree-specific management of a grove. Alaser scanning system and corresponding algorithms were developed for potential use in measurement of tree canopy height,width, and volume. Tests with fixed-length PVC pipes demonstrated that the system had accuracies of 97% for length measurementsin three perpendicular directions with coefficients of variation (CV) less than 4%. Volume measurement of a rectangularbox gave a CV of 5.4% and a relative error of 4.4%. Spatial resolution of the system was estimated to be smaller than6.0 cm (horizontal) × 1.9 cm (vertical) for potential field applications.

Spray Deposition and Mass Balance in Citrus Orchard Applications

A sampling system was used to quantify on-canopy spray deposition and off-target losses from five air-carrier sprayers commonly used in citrus spray applications. The samplers consisted of continuous loops of cotton ribbon that were stretched out above the tree canopies, on the tree sides, and above the orchard floor. The loops extended to the third rows on each side of the spray course. The sprayers had different design configurations, and their airflow rates, nozzle selections, droplet size spectra, and operating parameters varied markedly. Spray solutions containing a fluorescent tracer were applied between two tree rows, the targets were collected in small segments, and spray deposition on various sample sections was quantified by fluorometry. The study was conducted in five replications. Overall, there was no significant difference in canopy deposition of the sprayers, and spray deposition on tree rows adjacent to the sprayer accounted for 73.0 - 79.4% of the total sprayer output. Cumulative deposition of three rows on both sides of the sprayers ranged from 74.3 to 82.1%, and the off-target losses (ground deposit plus spray drift) amounted to 17.9 - 25.7%. Comparing ground deposits or drift estimates alone, there were significant differences among the five sprayers. Ground deposits ranged from 8.7 to 19.6%, and drift estimates were mostly in the 6.1 - 14.0% range.

MODELING OF SPRAY PENETRATION AND DEPOSITION ON CITRUS TREE CANOPIES

A simulation model has been developed to estimate spray deposition from air-carrier tower sprayers on orchard trees under different application conditions. The model includes spray transport from the sprayer to the canopy and spray displacement within the canopy. Spray velocity and mass flux at canopy boundaries were estimated. Spray velocity at the boundary was used to calculated spray velocity inside the canopy as a function of canopy depth and density. Spray velocity inside the canopy was coupled with mass flux to obtain deposition at canopy depths. Sensitivity of the model was evaluated for liquid flow rate, leaf area density, sprayer-tree distance, canopy diameter, tree height, airflow rate, and ground speed. Simulated air velocities and canopy depositions were in general agreement with the measured data. Deposition increased with liquid flow rate but decreased with increasing tree height and ground speed. Canopy diameter did not affect deposition. In the near side of the canopy, deposition increased with increasing maximum leaf area density and sprayer-tree distance but decreased with airflow rate.