Electrostatics make plants eager to accept spray

Opposites attract | When positively charged droplets zero in on leaves, they become negative, allowing droplets to bond

The Spectrum system on Gary Johnson’s helicopter employs the same basic charged particle technology that the spray paint industry has used for decades.

The spray droplet is electrically charged, and the target has the opposite charge. The droplet can’t help but be drawn to the target.

It doesn’t matter if the target is a car or a corn plant, and the droplet can be anything from paint to poison. It always works.

Spectrum Electrostatic Sprayer Inc. of Houston, Texas, has been building this type of equipment for ground sprayers for 27 years, says founder, co-owner and technical director Blake Dobbins.

It began selling aerial systems for helicopters and fixed wing aircraft 13 years ago. Dobbins said commercial aerial applicators prove the electrostatic technology works better than conventional nozzles every time a plane flies in to do pattern tests.

Each aircraft sprays dye over strings and cards, and a computer measures the actual deposition of dye that sticks to the target cards.

“Conventional applicators generally get between 1.8 and two drops spraying at the recommended rate of three to five (U.S.) gallons liquid per acre,” said Dobbins.

“Applicators with electrostatic systems consistently get 2.8 to 3.6 drops spraying at just one U.S. gallon liquid per acre.”

Dobbins asked the U.S. Department of Agriculture to analyze droplets of both the conventional and electrostatic types of sprayers.

“The USDA determined that one gallon of water from a conventional sprayer has 267 million droplets of 350 microns. But they’re not charged. They find their target by chance. Randomly,” he said.

“One gallon of water from an electrostatic spray system has two billion, 200 million droplets of 150 microns. That’s eight times more droplets. So that’s significant in itself, but the USDA did not mention the fact that these smaller droplets are electrically charged so they’re attracted to the target.”

The droplets get their charge by travelling through an electrical field. The Spectrum equipment employs induction charging, which can either add electrons or extract electrons from the surface of a droplet.

When they add electrons, the droplet becomes negatively charged. When they extract electrons, the droplet becomes positively charged.

The charge is only on the surface of the droplet and does not change the chemical properties of the product inside the droplet.

Droplets for the left boom are always negative, and droplets for the right boom are always positive.

“If we used all positive or all negative, the aircraft builds up an electrical potential that could be discharged through the pilot when he touches the Earth.”

Although plants are neutral, they can be manipulated to serve as antennas.

“Plants don’t care if the plume of spray coming at them is negative or positive. The plant automatically mirrors the opposite charge of the droplets,” he said.

“If a positively charged droplet approaches the plant, the plant instantly becomes negative. If a negatively charged droplet approaches the plant, it instantly becomes positive.”

If a positively charged droplet approaches a neutral corn stalk, it repels some of the positive atoms resting on the stalk. The corn stalk becomes negative and the droplet instantly bonds to the stalk.

All this happens while the helicopter is travelling over the field at 85 m.p.h. at a height of 10 feet.

Spectrum is a high-pressure system, running 75 to 80 p.s.i.

Herbicides are made up of acids and salts and will take a charge with just six kilovolts. Fungicides need as much as an extra two kV or more to get a good charge.

“The system can only draw a maximum of five amps, but in typical spray conditions, we only draw two amps. The helicopter’s 12 or 28 volt electrical system easily handles that.”

Miniaturization of electronics and the ceramic spray tip has finally allowed electrostatic spraying to reach aerial sprayers.

“There were earlier systems, but they were heavy and took up so much room in the aircraft. They weren’t practical.”

Dobbins concedes some customers might use the system off label.

“The system is designed for one gallon per acre, and that’s off-label. We all know that.…But you don’t necessarily have to run off label. There are other financial benefits with the charged droplets if you run full rate.”

The Spectrum electrostatic spray system installed on a helicopter carries a list price of $38,000.

For more information, contact Dobbins at 210-822-8479 or visit www.spectrumsprayer.com.

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