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New spray technology driven by drift

Drift, and drift control, have always been a concern. But now, due to a number of factors - including the new herbicide tolerant soybeans, increased use of postemergence products, focus on accuracy and environmental concern - drift control is driving research and product development at both university and company levels.

Don't think you have to accept spray drift anymore. Especially if you're planning on precise chemical application of new postemerge herbicides. "Drift has driven spraying technology more than anything else in the last few years," says University of Illinois ag engineer Bob Wolf.

Controlling droplet size is the major focus to improve spraying technology, he says. With smaller droplets, more "fines" will be present in the spray volume. Eliminating those smaller droplets means fewer fines and, potentially, less drift.

Advances in spraying technology range from relatively simple nozzle improvements and spray tank additives to electronically controlled sprayers and nozzles and high volume air-assisted sprayer systems aimed at putting the spray where it belongs. The bottom line is better control over your crop-protection products.

Even the best spraying technology, however, can be foiled by humans and nature. Current drift research focuses on reducing the number of droplets of 200 microns or less in size (a human hair is 100 microns). "The tendency for drift also depends on wind strength, along with temperature and humidity. Higher temperatures and lower humidity cause smaller droplets. And increased application pressure has the same shrinking effect," Wolf says.

At the same time, flow rates, pressure and ground speed can contribute to droplet size changes. The key to droplets is in the spray nozzle, Wolf believes. "The emphasis in nozzle design is creating a more uniform droplet spectrum with fewer fines and fewer bigger droplets, which means we're narrowing the spectrum closer to the desired droplet size," Wolf says.

For example, one comparison of two same-sized nozzles from Spraying Systems indicates a significant reduction in fines between older and new technology. Wolf reports that when a XR 110 flat-fan tip at 40 psi was compared with the new Turbo TeeJet 110 05 tip at 40 psi, "the new technology was responsible for a 12 to 15% reduction of droplets below 200 microns."

News is in the nozzles. Several new nozzles featuring precise control of droplet size through various forms of air-injection are hitting the market this season. Building on the strengths of its Turbo TeeJet nozzle, Spraying Systems introduces the AI - which stands for air-induction - TeeJet. Depending upon which chemical is sprayed, the nozzle produces large air-filled droplets through the use of a venturi air aspirator. The company says that larger droplets burst on the target area, or plant, forming smaller droplets for improved penetration and coverage. A stainless steel insert produces a tapered-edged flat spray pattern for uniform coverage in broadcast spraying. The nozzle works across a range of applications, the company says, from preemergence surface-applied herbicides with a minimum spray pressure of 40 psi or for postemergence contact herbicides at 80 psi and higher. Price of the AI TeeJet nozzle is $8 to $9. Circle 207.

Along the same lines, Delavan Spray Technologies developed The Ultra Low-Drift nozzle, introduced under John Deere's SprayMaster brand. It is a flat-fan nozzle with an air mixture chamber. According to Deere, the nozzle not only helps reduce fines but provides a uniformly sized, larger droplet for better coverage on target. Tests at the University of Tennessee produced a 600 micron droplet at 40 psi using a 2% Roundup and water formula. Only 4.4% of the droplets in that formulation are fines less than 191 microns at 40 psi.

Made of polypropylene with a stainless steel insert, the basic Ultra is an air-induction nozzle that fits most current equipment, including standard, combo or Hardi systems. The complete nozzle assembly lists for $8.24 and the tip alone lists for $6.09. Circle 208. Another approach to nozzle control comes from Spray Air USA. The nozzle is called Shear Guard Plus. It uses a control system in the tractor cab to adjust the force of the air and droplet size through atomization.

Called "Dial-a-Drop," technology, an orifice disc is used to control the amount of flow to each nozzle. The air passes over and around a liquid delivery tube in each nozzle, and the liquid is introduced in the center of the airflow. When the air and liquid meet, the liquid atomizes, resulting in better coverage with less carrier volume. Two cross-flow shaping jets in the nozzle form the spray pattern. The nozzle replicates the pattern of a hydraulic flat-fan nozzle, with the added advantage of variable droplet sizes and velocities. According to the company, the air physically moves the plant canopy and carries the spray droplets to their target.

The orifice disc regulates flow from 5 to 60 psi and flow rates from 0.017 gpm to 0.37 gpm, or 11/2 gal./acre to 34 gal./acre at 8 mph. The Shear Guard Plus is used on Willmar Manufacturing's TriMizer boom and also is available as a replacement part on that boom for $7.65/nozzle. Circle 209. Spray-Air uses the nozzle on its own spraying equipment as well. Circle 210.

TurboDrop nozzles by Greenleaf Technologies generally deliver droplets that average 400+ microns within 30 to 90 psi. Adaptable to all types of sprayers, the TurboDrop's total pressure range is 30 to 150 psi. But between the drift-control range of 30 to 90 psi, they allow greater speed and application ranges, the company claims. The assembly's stabilization air/liquid mixing chamber results in a narrower droplet spectrum for precise control of droplet size. Price for a complete nozzle is $14 to $15. Circle 211. Electronically controlled hybrid. "A single, larger tip can be used to do the work of several tips," says Steve Willey of Tyler Enterprises. As long as you have control. The ability to control flow rates and pressure independently of each other is the key to Tyler's new electronically controlled, pulse-modulated system.

The system was developed through research at the University of California - Davis, and licensed to a company called Capstan Ag Systems (see Farm Industry News, page, 40, February 1996). It has the potential to be retrofitted to any sprayer, large or small. The pressure and droplet system's first commercial use will be in Tyler's Patriot-based AIM Command Spray System for commercial applicators. "If you can't control droplet size, or percentage of driftable fines in a particular spray pattern from a nozzle, you really do not have drift control," Willey claims.

For example, flow rates can vary over a 8 to 1 range in a fraction of a second without affecting the pressure, which means that droplet size doesn't change. Or, that independent control also means the operator could change droplet size on-the-go, to reduce drift, by changing the pressure without changing the flow rate.

Available from Tyler or Capstan dealers, the suggested list price on a system for a 50- to 90-ft. boom, depending upon number of nozzles, ranges from $10,000 to $14,500. Circle 212.

The air-assist approach. At the more sophisticated, higher end spectrum of drift control are spray technology systems using air-assist booms and air-assist nozzles. These air-assist systems operate with high-velocity fans that drive air through a tube located along the boom where the air is directed into or alongside the boom spray, primarily to force the spray downward. A summary:

Hardi was one of the first to introduce air-assist technology on its farmer-operated rigs in North America several years ago, based on technology used widely in Europe. Specifically designed for farmer-operators, the trailer-mounted Twin Systems air sprayers by Hardi feature booms ranging from 60 to 66 ft. that can be used as a conventional or air-assist spraying system. The fan can be set in variables from 0 to 70 mph to adjust for drift depending upon wind and crop conditions.

The nozzle assembly rotates, and the air slot can be adjusted 30 degrees forward or backward, allowing the spray to hit its target at a variety of angles. Cost for the complete sprayer system begins at $43,000. Circle 213.

Ag-Chem's commercial RoGator 854 postemergence liquid system applicator with an Airtec boom uses a high-capacity centrifugal fan to displace a high volume of air from 0 to 152 mph through an aluminum boom tube. The company says this air displacement at high velocities enables the spray solution to penetrate the crop canopy. The 80-ft. boom is fitted with cone venturi-type nozzles to optimize atomization of the solution. Circle 214.

Willmar Manufacturing offers its TriMizer boom on several of its self-propelled commercial sprayers. The boom offers three spray options fitted with conventional and Shear Guard nozzles: DynaJet, conventional hydraulic or air assist. DynaJet atomizes the spray mixture with air that, according to the company, can create 64 times more droplets than standard hydraulic systems. Powered by a centrifugal fan, the blast of air can be adjusted from 60 to 120 mph which allows control of droplet size to reduce drift. Where drift concerns are minimal, and DynaJet is not necessary, the sprayer can switch to its conventional hydraulic system or the air-assist system, which combines features from each of the other two systems. Circle 215.

Which pick for drift? Midwest farmers, however, deserve a word of caution on air-assist systems, according to Wolf. Those systems, traditionally, were developed to penetrate thick crop canopies and for windy conditions - not for drift control specifically. Although the air-assisted systems can cover their targets, the jury is still out as to their effectiveness in handling drift control, Wolf points out. "I'm a little hesitant to be a proponent of it for drift control unless you're using it with crops that have a dense canopy where that additional air is absorbed," he says.

"You have the potential to put out a 100-mph airstream and, if you're looking at bare soil beneath the boom, that is a serious concern. If you're pulling it over a wheat crop like they do in Europe, Canada or the Dakotas, or a solid crop of soybeans or potatoes, or you're putting an insecticide or fungicide down into that canopy, there are some advantages. "My major point with corn and soybeans is that we want to think twice about it as a drift control device when we're still looking at some bare ground. A canopy absorbs extra air energy," Wolf says.

Drift-control additives. If you're not ready to climb onto the high-tech bandwagon, Wolf says you can use spray tank additives to initiate drift control economically with your existing system. University of Illinois data show that additives have reduced the amount of off-target movement by as much as 50 to 80% and they're cheap, at less than $1/acre. One of the concerns with the products is that they are not regulated by EPA. "I caution most people to purchase any product on a trial basis and test it on their systems before they go hog-wild on it," he adds.

"You really need to follow the directions carefully," Wolf says. "In some cases, with the higher active ingredients, say 30 or 40% active, they'll have a use-rate of maybe 2 to 8 oz./100 gal. of water. I caution them to work around the 1- to 2-oz. level. If you put too much into a tank mix, it could turn into a gelatin-type mixture that can plug up the system, making it impossible to spray uniformly."

Some additives are susceptible to pump shear when they're going through the recycle process in the tank during application. That means the pump grinds down the good, drift-reduction molecules and they become more like water molecules and eliminate the original protection.

One company, Rhone-Poulenc, has developed DR2000, a water-soluble powder additive that reduces susceptibility to pump shear. Precision Labs sells this additive, called Border EG250, as doesRosen's, which is called Array.

Start with the basics. If you're interested in taking the jump to drift control through new technology, Wolf advises you look first at nozzles, specifically turbo flood nozzles for soil applications and turbo flat-fan nozzles for postemergence applications. "If a grower wants to look further ahead, he might want to start investigating and locate some of the air-inject technology like turbo drop or other air-injection nozzles," he says. "Changing nozzles is easy, not expensive, and you'll be ahead of the drift control game.

"Then consider increasing volume, lowering pressure and driving slower." That's not because fast ground speeds, in and of themselves, cause drift, but speed relates to rates and pressures on the new electronic systems.

Also, speed affects boom height as you bounce across the field. The higher the boom is above the canopy, the more susceptible those droplets are to drift."

Even if you want to use flat-fan nozzles, you can lower the pressure and go to a larger-size nozzle and make some dramatic changes, Wolf adds.

The whole idea, says Wolf, is to make bigger droplets by lowering the pressure and then put out more volume per acre. To accomplish that, you need to use a bigger tip and lower the pressure.

Finally, whether you depend on a custom applicator or apply herbicides yourself, it's the producer's responsibility to make rational application decisions during that frantic narrow window of opportunity. "Farmers put pressure on the commercial outfits to get the job done, and the commercial people want to get the acres covered," Wolf says. That causes some high-stress situations and chemical application in less than ideal environments. No matter what, "if it's too windy, you've got to stop."

The four factors that determine spray application rates are sprayer pressure, the nozzle orifice, ground speed and the spacing of nozzles. As manufacturers and applicators tackle the drift issue with technological changes, they are particularly interested in fine-tuning pressure and flow rates and choosing the correct air-assisted nozzle as prescribed by each particular spraying situation.

Here's how these four factors interact. Pressure: Increasing pressure also increases the nozzle output proportional to the square root of the pressure increase. In other words, the pressure would have to be increased four times to double the output of the nozzle. Low pressures are recommended to reduce the drift potential of herbicides.

Nozzle orifice: The capacity of nozzles is rated in gal./min. at a certain pressure. Manufacturers' data outline proper nozzle selection for the desired rate of chemical at a selected speed and pressure.

Sprayer ground speed: Proper nozzles need be used to get the desired application rate at the speed best suited to the particular operation or field conditions.

Nozzle spacing: The amount of spray depends upon the number of nozzles on the boom. The application rate in a band-treated area decreases with a given nozzle as the band width increases.

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