by Ernesto Franzen
TAIM, BRAZIL--The first operator in Brazil to use the Spectrum Electrostatic Spray System extensively is very pleased with its results after over 110,000 acres flown, with more than 90,000 acres of herbicide applications. And what's more important - so are his customers. "In the beginning", says Taim Aeroagrícola pilot/owner Alan Poulsen, "they didn't want to hear about lower rates. They'd say, 'you can do it with the electrostatic, as long as it is 3 GPA'. I had to stick out my neck and assume the risk to do it at one GPA."
Of course, Alan wouldn't take this risk blindly; he hired agronomist Eduardo Araújo of Agrotec Tecnologia Agrícola e Industrial Ltda. to carefully check the electrostatic spray deposition in every situation before risking it on actual crops.
The result is that now customers demand electrostatic application. Granjas 4 Irmáos' agronomer, Guinter Frantz, is so pleased with it, that he'll even delay an application for two days, in order to wait for the electrostatic-equipped airplane to be available (Taim Aeroagrícola owns two Ipanemas). And they're also selecting chemicals on a "what electro-charges best" basis, usually a matter of oil content - chemicals resulting in a mix with over 2% of oil won't charge as good as water-based ones.
The Learning Curve
In the beginning, the system's novelty presented some problems. "Sometimes we would lose one hour looking at it, trying to solve an electrical short", says Alan. The high boom pressures (60 to 70 PSI) demanded by the system caused repetitive pump problems that were only solved by balancing the pump fan. Boom angle parallel to flight line was found to be important, as otherwise the spray plume would touch the electrodes - chemical or dirt deposited on them were found to make for likelier shorts.
Now, Alan's knowledge of the system allows him to ward off most problems easily, "But we're still learning something new every day". The first problem they had helped prove the electrostatic efficiency. During a RoundUp application, a nozzle isolator got burned and shorted out one of the booms; not knowing what to do about it (they could have replaced it in minutes), they switched back to conventional spraying. After five days, you could see the difference in the field, as weeds in the electrostatic-treated plot were dying faster.
The Acid Test
"RoundUp is the acid test", says Alan, "that's where you can see if an application system really works". And as usual, rice season starts with RoundUp applications. And, Alan's customers couldn't be happier. Besides increased application efficiency, there was no streaking at all; you couldn't tell which way the passes were flown over the field by looking at it.
Most other chemicals also proved to perform better with the electrostatic application. Alan sprayed almost every rice herbicide in the market; Facet, Stam, Nominee and others, and chemical representatives were all surprised at the high degree of weed control. Even contact pyretroid insecticides benefited from the electrostatic spray's even coverage, which also reached bugs hiding under crop leaves. "This we had already noticed in the Mato Grosso cotton tests," explains Alan.
Of course, there are some limitations. Clean water is a must and the mixed chemical must have 50% of it, although Alan sprayed once a 40% mix. Liquid formulations work best; wettable powders and granules have to be carefully and thoroughly pre-mixed, as any undissolved powder might clog the 50-mesh nozzle filters. Some chemicals like Touchdown IQ and RoundUp WG demand higher voltages to charge properly and this increases the possibility of shorts. But, the only chemical that they really couldn't use was Stam WG; it turned into a paste that clogged the system so bad they had to disassemble the boom and clean it nozzle by nozzle. Its high concentration requires a higher dilution than one GPA offers.
Increased Productivity
Besides the obvious productivity gains of flying at one GPA instead of the two, three or four = GPA used in Brazil for most applications, Alan found another benefit of the electrostatic sprayer; extended application windows.
Alan found through his testing that electrically charged spray "clings" much faster to the crops than regular spray, so droplets spend less time free-floating in the air and thus suffer less evaporation. This allows for an electrostatic application to be done in temperature and humidity conditions that would have already stopped conventional application. In fact, the drier the air, the best droplets hold their charge. And actually, you can't use the system above 90% humidity, as it may short. Alan has sprayed at 40% humidity without any problems.
So, an electrostatic-equipped airplane yields more both ways; by flying more acres per hour and by flying longer into the day before temperature and humidity conditions bring spraying to a stop. Another benefit of the system is freedom from wind direction; most fields Alan flew were much longer in the direction of the prevailing wind, and Alan found no streaking from flying that way.
Wind speed, however, still is a concern as a drift factor. As Eduardo Araújo says, "the number of droplets generated is enormous and most deposit very quickly onto the crops." But, those left floating are very small and with a high content of active ingredient. How far they go is still to be found. Alan and Araújo have noticed that the higher the crop or foliage, the quicker it "traps" spray, but further testing still has to be done. Another factor that helped reduce drift is the use of winglets on the airplane, although preliminary testing showed their benefits to be more pronounced on conventional spray deposition than on electrostatic spraying.
Getting a Taste of Its Use
Even though I had the chance to fly a Spectrum-equipped Ipanema in the factory tests last April in Botucatu, I couldn't let pass Alan's invitation to do it again. Matter of fact, I was supposed to watch an actual application and maybe fly a load, but weather precluded that. However, I was able to fly the airplane with a water load the day before it rained. White fungicide deposits on the plane's leading edges were proof that some spray still floats for a while, despite the charge. This system was exactly like the one described in the July 2001 issue of AAU, only its operation was different, as per Spectrum's recommendations.
Instead of increasing the voltage in one boom until the corona peaks, then increasing the other to zero the corona, you now increase one boom's amperage until around 500 miliamperes, then increase the other boom charge to zero the corona. From then on, as long as you don't switch chemicals and temperature, and humidity conditions don't change significantly, you don't need to touch the system's controls, only turn it on and off between loads. But you do have to watch the voltage/amperage combo gauges to detect any shorts and in this particular Ipanema installation, they were above the windshield; you don't just shift your gaze to watch them, you have actually to turn your head up.
Worse, you have to do the whole set up procedure while actually spraying the first pass; even though you may plot your A-B GPS line before, I think it's too distracting. In our flying environment, no pilot workload increase is welcome. I wished it had some automatic control, with a "short warning" light where your peripheral vision could see it during the pass. Alan thinks the opposite; he says all this becomes second nature after a while, and he thinks the system should be kept as simple as possible. Since he has "only" 200 times my experience with the system, he may have a point.
