April, 2000
Revolutionary new electrostatic spray system for agricultural aviation
now in first commercial use
Houston, TX -- An innovative new aircraft spray system which uses an electrical charge to enhance the electrical attraction of spray droplets to the target vegetation has been shown to improve spray deposition, reduce drift, and reduce total pesticide use compared to conventional spray systems.
The electrostatic spray system, developed by retired USDA-ARS agricultural engineer Dr. James B. Carlton at College Station and patented by the USDA-ARS, has been commercialized by Spectrum Electrostatic Sprayers, Inc. of Houston, Texas. This season, the first commercial versions of the system were installed on a Turbo Thrush agricultural aircraft operated by Dole in Costa Rica, and on an Air Tractor 502 operated in south-central Texas.
Like iron filings drawn to a magnet
Electrostatic spray technology applies a charge of static electricity to liquid solutions of crop protection chemicals and fertilizers, increasing the number of negative electric particles within the droplet atoms. The spray droplets are attracted by the electric force to the positive particles within target vegetation, must like iron filings are attracted to a magnet.
At the heart of this system are electrostatic spray nozzles equipped with non-electrically conductive nozzle tips to produce a hollow cone plume of spray. A stainless steel cylindrical electrode encircles the end of the nozzle tip to create a high voltage induced electric field on the spray shearing region. A brass body mounts the nozzle to the spray boom.
The spray system includes two electric systems coupled to the 28-volt aircraft battery to provide both positive and negative electrical charges. Dual voltmeters mounted inside the cockpit permit the pilot to monitor the electrical current, while dual rheostat controls allow the pilot to adjust positive and negative polarity. The direct charging current, typically 8 to 10 kilovolts, is supplied to the electrode surrounding each nozzle tips by means of a small wire. The electrical ground connection to each nozzle is made through the aircraft frame.
The electrostatic nozzles are designed to produce an extremely low flow rate on the order of 500 microliters per minute. The number and configuration of the nozzles mounted on the spray boom vary depending on application rate, type of material applied, and aircraft speed. According to Dr. Carlton, 50 or more pairs of nozzles can produce an outflow of 8 liters (.88 gallons) per acre, while as few as five or six nozzles on either side of the boom may be sufficient to make an ultra low volume application of 12 to 16 ounces per acre,
The spray system can be operated in one of two different modes. In the bipolar charging mode, which is generally applicable to aircraft flying low over crop fields. nozzles mounted on one side of the spray boom will produce negatively-charged spray droplets, while the nozzles mounted on the opposing side will produce positively-charged spray droplets.
The system can also be switched to the coalescence mode, suitable for aircraft operating at higher altitudes or applying materials that may be more sensitive to environmental conditions., In this mode, the spray nozzles are mounted in pairs, with one nozzle in each pair set for negative polarity, the other for positive polarity.
Improved pest control with less pesticide used
Field tests have yielded impressive evidence that electrostatic spray technology can reduce the total volume of material applied by air by as much as 90 percent, and significantly improve insect control compared to conventional spray methods.
In 1995, Dr. Carlton and fellow USDA-ARS scientists I.W. Kirk and M.A.. Latheef conducted studies to compare the performance of aerial electrostatic charged sprays with conventional aerial sprays for season-long control of sweetpotato whitefly (SWF) on cotton. The study used a Cessna AgHusky alternatively equipped with the electrostatic spray system, and with a spray boom fitted with conventional spray nozzles.
The spray mixture was applied through the electrostatic spray system at a rate of 4.68 liter per hectare, and through the conventional spray system at a rate of 46.8 liters per hectare. Results of the study showed that an electrostatic charged spray of endosulfan + amitraz and fenpropathrin + acephate significantly reduced SWF adults in cotton to a level comparable to that of conventional sprays. Electrostatic sprays with esfenvalerate + profenofos significantly reduced populations of SWF adults compared to conventional sprays.
Dr. Carlton reports that the electrostatic spray system can be used to apply nearly any liquid material which uses a water carrier. "The system should adapt to any insecticide, fungicide, herbicide or liquid fertilizer with a water-based carrier that can accept an electrical charge," he explains. "The only materials that would not adapt would be those with a crop-oil carrier."
Benefits of electrostatic spray technology proven over two decades
Blake Dobbins, president of Spectrum Electrostatic Sprayers, Inc., says that while electrostatic spray technology is new to agricultural aviation, it is widely used in low volume ground sprayers for orchards, specialty crops and mosquito control.
"Low volume electrostatic sprayers use from 50 to 80 percent less water than high-pressure sprayers, allowing operators to cover more acres per hour," he says. "The spray efficacy is improved because the negatively-charged atoms within the spray droplets are attracted to the target vegetation, with less spray solution reaching the soil and groundwater."
That can add up to impressive savings, says Dobbins. University and private studies show that electrostatic sprayers consume up to 70 percent less fuel than high-volume sprayers to treat the same acreage. And because more of the spray solution reaches the target vegetation with less run-off, electrostatic sprayers can reduce total pesticide use by as much as 25 percent over conventional spray systems. Less total pesticide sprayed means less risk to workers, and reduced impact on the environment.