All Charged Up
Aerial
electrostatic spraying could improve pest control while reducing chemicals
applied.
By Vicky Boyd
Editor
Speck Thornton is standing on the edge of the next revolution in aerial
application, and rice growers could benefit.
First came the turbine engine, then global positioning systems (GPS) and now
aerial electrostatic spray systems, which can potentially reduce drift,
reduce the amount of pesticide applied and in many cases, improve pest
control.
The only challenge to the technology taking off is the Environmental
Protection Agency, as well as many state agricultural departments, currently
don’t allow using less water because it goes against product labels.
“This has the potential to be right behind GPS guidance, but it has to be
legalized,” says Thornton, a second-generation aerial applicator in El
Campo, Texas.
But things are looking up. Dow AgroScience is currently working on 24C
labels for propanil and Propamax fungicide for Texas this season. The
special local needs labels would allow Thornton as well as another operator
in Bay City to use less water.
BASF is working on either 24C or 2EE labels for their products for this
season. Either one would allow aerial applicators with electrostatic units
to use less water.
Four years ago, Thornton became the first person in the United States to
purchase a Spectrum electrostatic spray system for his airplane.
He had read about the physics behind the technology and thought it made
sense.
“We always want to use as fine a spray droplet as we can, but we can’t
because they are uncontrollable,” he says. That is, until now.
Less water, better coverage
The electrostatic system is designed to produce an average droplet size of
150 microns at operating pressures of about 70 to 90 psi. That’s
considerably smaller than the 300 to 400 micron droplets Thornton produces
through his straight-stream nozzles, although it may actually produce less
drift than a conventional system.
The reason is an electrode surrounding each nozzle and connected to the
airplane’s electrical system charges each particle either negatively or
positively, depending on which boom the nozzles are on.
Two 24-volt batteries produce about 7,000 to 8,000 volts of electricity. But
each electrode only emits 200 to 400 microamps, which is similar to the
charge on an electric fence.
Based on the laws of physics, particles with the same charges repel, and
particles with opposite charges attract.
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 that pull the droplets to the foliage.
Unlike neutral droplets with no electrostatic charge that may settle where
they may, the charged droplets are attracted to both the upper and under
leaf surfaces.
With many crop-protection materials, the label calls for mixing it with 5 to
10 gallons of water per acre.
But Thornton says he can get away with using 1 to 2 gallons of water per
acre because more of the droplets land on the target.
All charged up
The nozzle and electrostatically-charged chemical spraying system were
developed by ARS agricultural engineer James B. Carlton, now retired.
Carlton designed the aerial application system while working at the agency’s
Areawide Pest Management Research Unit in College Station, Texas.
The system may reduce the amount of chemical that must be sprayed and helps
get the chemical onto the crop with less drift.
Spectrum Electrostatic Sprayers of Houston is marketing the nozzles and
spraying system for airplanes. The system is most effective for low volume (LV)
and ultra-low volume (ULV) pesticide applications.
Thornton’s systems are two of only a few in the United States, although
Spectrum has sold others to aerial applicators in Brazil, Australia and
South Africa.
Blake Dobbins, president of Spectrum, says he had one pilot in southern
Brazil who treated a large number of rice acres buy a second system after
just one season.
“Before the second season, his farmers said, ‘we don’t want your other plane
back, and we only want your electrostatic system,’” Dobbins says the pilot
told him.
So the pilot purchased another system, despite interest rates of more than
20 percent.
Putting the sprayer to the test
A demonstration conducted in June 2002 by Spectrum and Thornton using
florescent dye reinforced Thornton’s contentions.
A pilot flew over target crop plots using conventional nozzles and 5- and
10-gallon rates of water treated with a florescent dye. In the next plot, he
used the electrostatic system and a 1-gallon rate.
That night, participants went into the field with a black light that would
make the droplets glow to assess the coverage.
Dr. Joe Krausz, a Texas A&M Extension plant pathologist, was one of the
observers.
“I was pretty impressed by the electrostatic application,” Krausz says. “I
thought it gave better coverage in the canopy and on both sides of the
leaf.”
Fighting tough weeds
Thornton also believes the electrostatic units provide better weed control.
“On rice fields—especially your first herbicide shot—if you miss weeds,
you’ll have problems all year long,” he says.
Later in the season, Thornton also has seen benefits in treating mats or
large stands of barnyardgrass with low-use-rate products, such as Regiment.
A conventional application using 10 gallons of water will only burn the top
of the matted vegetation, leaving the lower part to regenerate tillers.
But the electrically charged finer droplets penetrate the dense vegetation,
providing improved control.
Unit boosts cotton defoliation
But no where may the benefits be most noticeable than during cotton
defoliation. Thornton says area growers typically go with a two-shot system.
The first treatment knocks the leaves off the upper canopy. About five to
seven days later, the aerial applicator returns and applies a second
treatment. Without the leaves in the upper canopy, the second application
can reach the lower leaves.
Thornton can make one pass and totally defoliate the plant because the
electrically charged particles reach deep into the canopy.
A test involving about 250 acres of cotton drove the point home to a grower.
“I did the first three fields with 1 gallon per acre, and I knocked every
leaf off of every plant from the top to the bottom,” Thornton says of the
electrostatic system.
Improved applicator efficiency
For the aerial operator, being able to get away with less water means
improved efficiency. The Air Tractor 402 that Thornton currently flies has
about a 400-gallon tank. With conventional nozzles, Thornton may use a
10-gallon rate, so he could treat only 40 acres without returning to reload.
The electrostatic system, on the other hand, allows him to treat at least
200 acres without returning. The savings can be passed along to the grower.
But the electrostatic system is not cheap. Thornton says a system using 120
nozzles costs about 10 times more than a conventional system using 55
straight-stream nozzles.
A single operator could recoup the investment in less than a year because of
the additional acres he could treat.
“I am more efficient, and my work is better,” Thornton says.
