After first season of use, electrostatic spray system earns a
‘thumbs up’ from Texas operator Speck Thornton
Speck Thornton, who runs a three-plane operation called Independent Dusting Service at El
Campo, Texas, had a mission in mind when he flew into Reno for the NAAA convention last
December. He planned to look up a company called Spectrum Electrostatic Sprayers, Inc. at
the
NAAA trade show, and find out more about an innovative new aerial spray system he’d
heard about.
"After I read that this new electrostatic system operated at just one or two gallons
to the acre, I
started thinking about how many more acres I could spray compared to our normal five or
ten
gallon work," Thornton recalls. "When I looked at spraying the same acreage with
one load that
had been taking us three trips, it wasn’t hard to decide the system could pay for
itself in a hurry."
Early last season, Thornton became the first U.S. operator to put the electrostatic system
to work,
installing it on an AT 502. He then set out to convince his rice and cotton farmers to let
him try the
system on their fields.
"Most of my rice farmers are pretty conservative when it comes to trying something
new, so I
made a deal with them," he continues. "After I explained how the system worked,
I said, ‘Let me
put rice herbicides on 20 acres of your crop with the new system at reduced gallonages,
and I’ll
treat the rest of your field at standard rates with my regular spray setup. If I
don’t get the grass in
your rice, I’ll refly the field and furnish the chemical at my expense."
Not only did Thornton’s customers agree to let him try the new system on their
fields, but not
once was he asked to come back in to respray. By season’s end, Thornton had sprayed
40,000
acres of rice and cotton with the electrostatic system, applying chemicals ranging from
rice
herbicides and fungicides to cotton insecticides and defoliants. In every case, he
reports, control
of weeds, diseases and insect pests was as good as or better than that he got with a
conventional
spray system.
"By reducing our gallonage from five or ten gallons to just one or two gallons per
acre, we
significantly improved our efficiency and reduced our cost of operation," Thornton
continues.
"The electrostatic system let me spray two to three times more acreage with a single
load. And
that meant that instead of having a two-man loader crew, loader truck and water tank out
at a
remote strip, it was faster and less expensive to just fly to my home strip to
reload."
Electrostatic charge draws droplets to crop foliage.
One thing that sold Thornton on the electrostatic system was the research that had gone
into its
design. Developed by USDA-ARS engineers at College Station, Texas, the electrostatic
system
features specially-designed, non-electrically conductive nozzle tips that produce a hollow
cone
plume of spray. A small wire supplies an electrical charge from the aircraft battery to an
electrode surrounding each nozzle tip. The nozzles are designed to produce a low flow rate
of
about 500 milliliters per minute.
Unlike conventional nozzles, the electrostatic system is designed to produce an average
droplet
size of 150 microns at operating pressures of about 70 to 90 psi. While that’s
considerably
smaller than the 300 to 400 micron droplets Thornton produces through his straight stream
nozzles, it may actually produce less drift than a conventional system.
That’s because each spray droplet receives either a negative or a positive electrical
charge as it
leaves the nozzle, causing most droplets to be quickly drawn down into the target foliage.
In
fact, researchers suspect that many of the fine droplets that initially remain suspended
in the air
are attracted to their electrically-charged opposites until they, too, drop out of the air
and into the
crop canopy.
The number of nozzles required for a given spray job will vary according to application
rate,
type of material applied, and airspeed. Thornton equipped his AT 502 with 60 pairs of the
electrostatic nozzles in order to make one to two-gallon spray applications at an average
airspeed
of 130 mph.
"The people at Spectrum 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 my swath width," Thornton explains. "When I put out rice
herbicides
at a two-gallon rate, I flew a 45-foot swath. When we put out one-gallon rates, I flew 70-
to 75-foot swaths."
Thornton says that not once did he see an indication of burns or streaking, nor any sign
that the
spray hadn’t filled in between the swaths. "It appeared that the
electrically-charged droplets
were drawn almost straight down into the crop. In fact, when I’d get to the end of
the field and
pull up to go around, I didn’t even find myself flying back through my own spray
cloud."
Thornton experiments with reduced rates
One gallon of water contains 268 million individual droplets measuring exactly 300 microns
in
size. But if that same gallon was divided into 150 micron droplets, it would contain two
billion,
147 million droplets. Because the electrostatic system produces about eight times more
droplets
than a conventional spray system, with each droplet receiving an electrical charge to draw
it to
the crop foliage, more of the spray material reaches both the upper and lower leaf
surfaces.
That’s why Thornton decided to experiment with reducing the rate of active ingredient
in his spray tank.
"Grass control is the most important service we can provide to our rice farmers,
normally applied
at about a gallon of chemical in five to 10 gallons of solution per acre," he says.
"Many of the
rice farmers here would rather have us overapply their herbicide the first time around,
and take a
chance of burning the crop than risk missing some grass. But I talked them into letting me
experiment with cutting the herbicide a.i. rate by 25 percent. And in every case, the
grass and
weed control was just as good as it was at the full label rate."
Thornton also found that rice fungicides and cotton insecticides applied at one gallon per
acre
performed as well as they did at standard spray gallonages.
"Our cotton farmers use just about every insecticide you can think of to control
budworms and
bollworms, stinkbugs, weevils, flea hoppers, aphids and lygus bugs," he adds.
"We didn’t cut the
a.i. rates of the insecticides, but we did reduce the spray volume from two or three
gallons to just
one gallon per acre, and it appeared to have the same control as the higher gallonages
did. None
of our cotton farmers nor their consultants reported any differences in control."
Cotton defoliants deliver visual evidence of performance
The true test of the electrostatic system came in late July, when Thornton began applying
cotton
defoliants. "Most of our cotton is defoliated with a pound of Dropp per 10 acres, and
between 4
and 7 ounces of Def, at a rate of three or five gallons of solution per acre," he
says. "I was really
curious to see how the fields would look when we cut the solution to just one gallon. The
first
day we put out defoliants, I sprayed 40 acres with the electrostatic system, and then came
back to
finish the field with my standard boom at three gallons.
"A few days later, it actually looked like the defoliant put through the
electrostatic system started
working earlier than the rest of the application. It appeared that the crop sprayed with
the
electrostatic system was about 24 hours ahead of the three-gallon rate. And it stayed
ahead for
maybe three or four days, until the rest of the field caught up with it. I know we got
better
penetration of the plant canopy with the charged droplets compared to the three-gallon
work,
which let the defoliants start working a little sooner."
Thornton reports that he also saw evidence that the electrically-charged droplets may be
more
effective at filling in gaps between spray swaths than non-charged droplets.
"One of my customers has a 300-acre cotton field with a big cross-county power line
running
through it, and with a smaller line right beside it," he says. "The poles for
the two lines don’t
quite line up, and there isn’t enough room to get the airplane up under the lines to
clean up the
field when we defoliant. I have to skid the airplane around each side of the poles, which
leaves a
diamond-shaped area about 200 feet long and maybe 50 feet wide that doesn’t get
defoliated. It’s
always bothered me that the farmer had to get back in that field with a ground rig to
clean up
where I couldn’t defoliate with the airplane.
"This year, that was one of the fields we defoliated with the electrostatic system.
When I flew
back over the field a few days later, I saw that the cotton around the poles was
completely
defoliated. I assumed the farmer had cleaned it up with his ground rig, but when I asked
him
about it, he said, ‘No, I didn’t. I was wondering how you did it.
"That was probably the most visible evidence I saw that these charged spray droplets
really do
improve the deposition and penetration of the spray into the plant canopy. It appears that
the
electrostatic spray spread out just enough to fill in the gaps before it was pulled down
into the
crop."
Maintenance problems prove minor
Thornton admits he was a little worried at the start of the season that the electrostatic
system
would prove to be a high maintenance piece of equipment. But for the most part, he
concludes,
the system performed with very few problems.
"At the onset, I was worried that we’d have to hose the system off at the end of
every day, and
tighten things every time we came in for another load. And to be honest, we did have some
simple mechanical problems at the beginning. We had some dripping nozzles, and some small
leaks that we couldn’t see when the airplane was on the ground, but that showed up
when we
increased the pressure to 70 pounds."
"I finally figured out that I just hadn’t tightened things up enough. When you
run 20 or 25
pounds of pressure, it’s usually enough to barely put a wrench on the nozzle
fittings. But because
this system runs at 70 or 80 psi, we found we had to get the fittings cinched down. Once
we did,
our problems with leaks basically went away."
Thornton says he was also concerned that bird strikes would damage the electrodes, or snap
the
electrical wire. "But as it turned out, bird strikes really weren’t that big a
problem," he reports.
"Once in a while we’d hit a blackbird and the system would short out. So
we’d just find a place
to land and clean the guts and feathers out of the nozzle, and go back to work."
Apart from running at higher spray pressures, Thornton says he made very few changes to
his
flying techniques with the electrostatic system.
"We normally maintain air speeds of about 130 mph, and keep our wheels from two to
ten feet
above the top of the crop, depending on what we’re spraying, and whether we’re
working over
cotton or rice levies," he says. "I did notice that the electrostatic system
seemed to work best
with the wheels no more than four or five feet above the cotton. The closer we got to the
canopy,
the faster the spray droplets seemed to be pulled into the crop. Even when our wheels
skimmed
the tops of the plants, it appeared that the spray pattern came together in the middle of
the swath,
and penetrated the canopy evenly."
Flying the same acres with one less airplane.
Convinced that the electrostatic system will help him reduce operating costs and increase
his
profits, Thornton has already taken steps to change the way he’ll run his spray
operation next
season. He took the first step late last season, when he traded in one of his three AT
502s for a
new AT 402.
"The 502 is good for high volume work. And if we have to make multiple loads, or need
to ferry
for any distance, I figure the extra 100 gallons will pay for itself," he explains.
"But the 402 is
perfect for doing one and two gallon work with the electrostatic system. It’s a
little smaller and
more nimble than the 502, it fits under wires better, burns less fuel, and is less
expensive to
maintain."
Thornton also figures the electrostatic system will allow him to use just two aircraft
next season
to fly the same number of acres he flew with three aircraft last season.
"We’ll also be able to eliminate a ground crew for any liquid work we do with
the electrostatic
system," he adds. "Nearly all our work is within a 30-mile radius of our strip,
and this year we
found that the electrostatic system allowed us to fly half again as many acres in a
morning, and
still come home to reload."
Growers realize savings from new system
After confirming he could reduce rice herbicide rates by 25 percent through the
electrostatic
system and get comparable weed control, Thornton is convinced the system offers important
economic savings to growers as well as aerial applicators.
"Nearly all our farmers furnish their own chemical, and several of them have shown
considerable
interest in what one of them calls my ‘Buck Rogers boom’," says Thornton.
"Rice farmers here
spend about $40 per acre for a herbicide application, and if I can reduce the rate by 25
percent,
that’s a savings of $10 per acre that stays in their pocket.
"Our cotton growers are probably spending between $8 and $10 an acre every time they
put an
insecticide on their crop, and make 10 applications a season. If I can prove I can cut
their rates
by 25 percent and give them equivalent control, that could run up to real money."
Thornton believes Spectrum’s electrostatic spray system could prove to be a major
breakthrough
for aerial applicators struggling to reduce operating costs and increase their profits.
"Ultimately, I
think it could rank right up there with the introduction of turbine power and GPS
guidance," he
concludes. "I know it will definitely play a big role in our operation next
season."