BARD Project No. US-1282-87; Duration: 3 Years; Budget: $190,000

Aerodynamic Dispersion and Electric-Force Deposition of Pesticide Sprays in Greenhouses

Law S.E. Athens GA U Georgia
Manor G. Haifa  Technion
Oetting R.D. Griffin GA U Georgia
Gan-Mor S. Bet Dagan  ARO
Dubitzki E. Kiryat Gat  SHAHAM
 

ABSTRACT
Electrostatic-induction spray-charging nozzles were developed into both laboratory-scale and full-size greenhouse equipment for low-volume, air-assisted, electrostatic application of conductive pesticide sprays. Successful operational characteristics of the aerodynamic-electrostatic method typically encompassed: 5-8 mC/kg spray charge-tomass ratio at 1/2 - 1 kV electrode voltage as electronically derived from a 9V transistor-radio battery; 50-250 mL/min liquid throughput to provide ca. 50 L/ha finished spray application having conductivity in the 20-4 - 10 siemens/m range; 3-6 m/s canopy-penetration air velocity from the 207 - 276 kPa inherent pneumatic air-carrier jet; and liquid viscosity up to that of 25% wettable-powder loadings. Hand-directed sprayers of both backpack and pushcart designs were included, as well as  self-propelled vehiclemounted units developed to provide uniform application speed and automated guidance (e.g., ultrasonic and electromagnetic) in unmanned greenhouse operation.

Computer simulation of aerodynamically delivered charged spray and field evaluations of air-carrier sprayer equipment assisted in system development and pulsed charged-cloud improvements. Advanced methodology for quantitatively assessing spray deposits was established via mathematical modelling of spray coverage on leaves and by the development of a fully operational, light-intensified, machine-vision, image-analysis system incorporating a computer-controlled x-y positioning stage.

Significant new documentation resulted regarding the micro-deposition characteristics and spatial distribution of deposits, especially onto leaf undersides and at deep-canopy penetration. Other theoretical and experimental studies confirmed the electrostatic deposition process to be appropriate for spraying plastic-potted plants having even greater than 109 ohms resistance to earth, and demonstrated beneficial modifications of dielectric boundaries (e.g. plastic greenhouse films) which enhance target deposition of charged sprays.

Laboratory and greenhouse spraying tests documented both the droplet deposition efficiency (via tracer fluorometry, GC foliar residue analysis and computer image analysis) and the insect-control efficacy achieved by three spray application methods:
 a) reduced-volume, air-assisted charges spray;
 b) reduced-volume, air-assisted uncharged spray; and
 c) conventional high-volume, hydraulically-automized spray.
The aerodynamic-electrostatic method (a) was confirmed to increase active-ingredient deposition between 2- to 4-fold as compared with the other two metods (b and c). Underleaf and deep-canopy deposition were especially enhanced by electrostatic forces. Underleaf and deep-canopy deposition were especially enhanced by electrostatic forces. Using the directed air-assistance to inject sprays into plant canopies, electrostatic charging did not significantly alter deposition onto the operator or greenhouse structural surfaces. Insect-control efficacy achieved with the reduced-volume aerodynamic-electrostatic method was at least equal to the other application methods tested when using label rates of pesticide, and it performed significantly better at lower rates of 1/4 and 1/2 label. Additionaly, application time was halved and potential for phototoxity reduced as compared with the conventional high-volume greenhouse spraying method.