Electrostatic Aerial Spray System
Means More Acres Per Load

By Jimmy Reed

Managing Editor

If Speck Thornton's airplane hopper holds 400 gallons of liquid and he reduces the per-acre rate from 10 gallons to one, then obviously he covers 10 times as many acres before landing to refill his tank.

During the 2000 growing season, Thornton, owner and operator of Independent Dusting Service, Inc., El Campo, Texas, used the new Spectrum Electrostatic Aerial Spray system to treat 40,000 acres of cotton and rice with insecticides, fungicides, herbicides and defoliants. Compared to the usual spray volumes of five to 10 gallons per acre, he was able to give his customers the same desired results with just one, or at the most, two gallons per acre.

"The electrostatic spray boom worked so well for me last year that I've already used it on about 10,000 acres this spring, applying 2,4D and pre-plant herbicides," he says.

Pilot Saves, Producers Save
Not only can the electrostatic spray system deliver effective treatment rates at considerably less volume per acre, but it also makes the application process more efficient, allowing users like Thornton to pass on savings to cotton farming customers.

"I earn money only when airborne," Thornton explains. "If I do one-gallon instead of 10-gallon work, I eliminate water trailers, reduce labor and operate only from my home airstrip. That converts to considerable savings when you consider that, before using this system, I had to land and take off on rough strips and perhaps go 15 miles out in the country to draw water from canals. I save fuel for both the airplane and for ground vehicles, I reduce man hours, and I don't beat the plane to pieces operating from rough, unpaved surfaces."

Flying an airplane equipped with the electrostatic system, Thornton sprayed about 30,000 cotton acres last year, starting with insecticides and Pix early season and finishing with defoliants. He received no complaints from producers and was not required to re-treat any of these acres due to problems with the original application. Producers observed that the efficacy of chemicals applied with the electrostatic system was at least on a par with chemicals sprayed from a conventional system.

Thornton realized this spray system would pay for itself in a hurry if he could treat the same acreage with one load that previously required three, but he knew his customers were reluctant to try new ways, especially with chemical prices being what they are. So, he made several of them a proposition.

"I offered to apply rice herbicides on 20 acres of their crop with this system at reduced gallons per acre while treating the balance of their acreage with a conventional system," he says. "In every case, weed, disease, and insect control were as good as or better than the conventional method, and no one requested a re-spray of the 20-acre portion."

Opposites Attract
A chief determinant of chemical coverage and liquid volume in any spray regimen is droplet size. The average size of droplets ejected by the electrostatic system is approximately 150 microns. To appreciate how tiny this is, one must consider that a micron is equal to one millionth of a meter, and a meter is a shade less than 40 inches. This means the boom converts a gallon of spray solution to about 2.14 billion droplets. In conventional systems, that same gallon converts to about 267,750,000 droplets.

Basic laws of physics dictate that oppositely charged particles attract each other and similarly charged particles repel each other. To create the proper balance of oppositely charged droplets, the electrostatic system features non-electrically conducive nozzle tips that emit a hollow cone spray plume at about 500 milliliters of fluid per minute, generated by 70-90 pound spray pressures per square inch (psi). To ensure each droplet is not neutral but is either positively or negatively charged, an electrode surrounding each nozzle tip receives constant electrical charge from a wire connecting it to the aircraft's electrical system.

"In my first experimentation with this system, I equipped an Air Tractor 502 with 60 pairs of the electrostatic nozzles to make one to two-gallon spray applications at an average airspeed of 130 miles per hour," Thornton says. "The system's manufacturers told me that as long as I used a 50 percent water solution and kept my spray pressure at 70 psi to get proper atomization, I could switch between one- and two-gallon work by simply changing swath width. At a two-gallon rate, my swaths were 45 feet wide; at one gallon, they were 70 to 75 feet wide."

The Proof's In The Coverage
Farmers in Thornton's area use a variety of insecticides to control such pests as budworms, bollworms, stinkbugs, weevils, flea hoppers, aphids and thrips, any one of which can seriously endanger crop performance if not held in check in a timely and effective manner. Producers whose crops were treated by Thornton at the reduced gallons-per-acre rates while maintaining the same active ingredient rates detected no differences in control than previously received at much higher volumes.

Research has shown that as charged spray droplets approach the target crop, they induce an opposite charge on leaf and stem surfaces, thus activating electrostatic forces, which pull the droplets to the foliage. Unlike neutral droplets with no electrostatic charge that may settle on upper surfaces, the positively and negatively charged droplets are attracted to all plant surfaces, meaning they also land on leaf undersurfaces, where damaging insects often hide.

Banded Application From The Air
An experience Thornton had while defoliating cotton last year proves that the electrostatic spray system gives more complete coverage.

"One 300-acre field I spray has a large cross-country power line running through it, with a smaller line right beside it," he explains. "Since the poles for the different lines don't line up, I have to skid the airplane around them, leaving a diamond-shaped area about 200 feet long and 50 feet wide undefoliated. I used the electrostatic system to defoliate the field, and when I flew over it a few days later, the whole field appeared equally defoliated, even areas around the poles.

"When I asked the farmer if he finished up with a ground rig, he said, 'no, I thought you did it.'

That was probably the most visible evidence I saw that charged spray droplets really do improve spray deposition and penetration into the plant canopy."

But the real clincher that totally convinced Thornton and several of his cotton-producing customers that electrostatic spraying lives up to its manufacturer's claims happened shortly before the 2000 planting season and later on, when the cotton was about ten inches high. Curly dock is a real menace in Thornton's area. Once it reaches six to eight inches in height, it's almost impossible to kill with 2,4D, or with anything else but a good, sharp hoe.

"Last year, using the electrostatic boom I sprayed 2,4D on curly dock that was a foot to a foot and a half tall," Thornton recalls. "Because the weeds were larger and had more surface area to attract the electrostatic droplets, it was like dowsing them with a hand pump. The chemical coated the plants and killed them."

After his producers planted, they banded insecticides on cotton because they could get effective control without using broadcast rates. Rain interrupted ground-rig applications, and they had to call on Thornton to finish the job with his airplane.

"I talked a few of my farmers into letting me spray the same rate of chemical that they had been banding, instead of doubling it to a broadcast rate as I would normally have done," Thornton says. "Most of the cotton was anywhere from 10 inches to a foot tall and had plenty of foliage to attract the electrostatic droplets before they were attracted to the ground. We got the same rate of control from this spraying as they had previously gotten from the banded spray. Obviously, in terms of insecticide and application costs, this was a tremendous savings for them."