SPRAYER AIR technologies have been around for more than 20 years, but until recently, corn and soybean growers didn't use them much. That has changed, due in part to the threat of Asian soybean rust (ASR), which has farmers looking for greater efficacy and efficiency in spraying. Air technologies may offer both.

There are differences between air assist and air atomization. Air-assist sprayers do what their name implies; they “assist” spray droplets, using a curtain of air forced down in front of the nozzles to create a wind tunnel that drives the droplets deep into the crop canopy. The sprayer operator uses a controller in the cab to change air speed on the fly with fingertip controls. Three companies offering air-assist sprayers are Hardi (www.hardi-international.com), Jacto (www.jacto.com) and Gregson Technologies (www.radinter.com/gregson/eng/home.html).

Air-atomizing nozzles, on the other hand, primarily control droplet size. While most air-assist sprayers use standard nozzles, air-atomizing nozzles are designed to mix the liquid and air inside the nozzle, creating drops that are forced out of the nozzle with the airstream. Adjusting the airflow creates a highly adjustable droplet range. This allows an applicator, without changing the nozzle or the orifice size, to choose a range of droplets that may be most effective in treating a particular pest. One company offering air-atomizing technology is Spraying Systems Company (www.spray.com).

A third air technology is a hybrid of air assist and air atomization. This “air delivery” system drives spray droplets into the crop canopy like an air-assist sprayer, while using air-atomization nozzles. Spray-Air Technologies (www.sprayair.com) offers the Shear Guard Plus nozzles on its Trident series sprayers.

Comparative advantages

The droplet range achieved by air-atomizing sprayers would require three to four different nozzles on conventional sprayers, according to Erdal Ozkan, agricultural engineer at The Ohio State University (OSU). “If our focus is getting our droplets deep inside the canopy, as in the case of soybean rust, the air-assisted sprayers are likely to produce better results than air atomizers,” Ozkan says. “Depending on the type of air-atomizing setup you have, there is actually either very little air or not sufficient enough air coming out of the air-atomizing nozzles. And compared to air-assisted sprayers, the airflow just doesn't have enough air power [velocity and rate] to create any type of turbulence, which is what opens up the canopy for better penetration of droplets.”

“It takes a lot of air to get to the bottom of a 3-ft.-tall dense canopy of beans and push the droplets in to coat both sides of the leaves,” points out Lee Burgard, territory manager for Hardi.

In Ozkan's tests, which he and his colleagues designed to measure canopy penetration in a likely soybean rust scenario, the Jacto air-assisted sprayer performed best in every test. A sprayer equipped with Spraying Systems air-atomizing AirJet nozzles ranked second or third in every category, edging out all six of the conventional nozzle configurations. Ozkan did not test other air-assist sprayers, air-atomizing nozzles or Spray-Air's hybrid of the two technologies, the Shear Guard Plus nozzles mounted on the company's Trident series sprayers.

For Ozkan's complete results on canopy penetration simulating ASR spraying conditions, visit fabe.osu.edu/FACULTY/Report_Rust_study_2005.pdf.

As for air atomization, the biggest advantage is separating droplet size from travel speed.

“That's the holy grail of spraying,” says Rich Gould, product manager for Spraying Systems. “With a hydraulic [conventional] sprayer, if you change the flow rate or the pressure, you're changing droplet size, so it's a constant compromise between the variables. With an air-atomizing nozzle, those variables are separated, and you control the droplet size independently.”

That advantage is a boon for growers. The in-cab spray controller keeps the droplet size constant, even if the applicator reduces travel speed for field obstacles, point rows or turnarounds, Ozkan says.

With the hybrid of the two, the Shear Guard system, the air delivery nozzle allows the operator to “dial in” the ideal droplet size range and, when spraying for ASR, drives the spray deep into the canopy with a velocity of up to 100 mph, says Tim Criddle, corporate sales and marketing manager for Spray-Air.

“We have a unique technology; it's a patented hybrid of both air-assist and air-atomizing systems,” Criddle says. “This system combines the best of air-assist technology driving the spray droplets into the crop canopy, while creating optimum uniform droplet sizes regardless of travel speed or liquid pressure as an air atomizer.”

Drift reduction

“The smaller the droplet, the more drift-prone it is,” Ozkan says. “And the more drift you have, the less chemical staying on your crop. If 10% of your spray drifts, you've reduced your rate, wasted chemicals and possibly caused problems with your neighbors.”

Having a controllable droplet size gives you a better buffer between your field and potential problem areas, such as a neighbor's home, a creek or a chemically sensitive crop, Spray-Air's Criddle says.

“Following the ASAE Droplet Classification Standard, you can dial in an extremely uniform droplet size range, depending on the application type, with only one nozzle,” he says. “High water volumes usually mean large droplets and wasteful applications. The Shear Guard sprays with the optimum droplet size for each application and wasting far less water.”

Because the air itself is forcing droplets down into the canopy, which then slows the droplets, manufacturers of the air-technology sprayers claim they “virtually eliminate” drift.

With some air-assist sprayers, like the Hardi Twin Force or Jacto Vortex, the air angle is adjustable within the cab, providing greater control to further reduce drift, Burgard says. “You may want to angle the air just enough to counteract the wind,” he says.

However, in preemergence or early post applications, air, if not turned off or adjusted properly, can be a bad thing, Ozkan says. “In these situations, you may actually get more drift than with a conventional sprayer, due to the kickback effect of the air bouncing off the ground,” he explains.

However, most manufacturers say that concern is easily addressed: With air-atomizing sprayers, the operator can completely turn off the air and use the unit as a conventional sprayer; and with an air-assist sprayer the operator can turn the air off or down to the point where kickback isn't an issue.

Reduced carrier and chemistry

The manufacturers of both air-atomizing nozzles and air-assist sprayers say that, because the sprayer uses air, less water is needed. Some even say you can get by with a lower amount of chemicals due to increased plant coverage.

“We recommend that you use half the normal carrier volume [water] while keeping the chemical rate,” says Lee Richey, vice president of Jacto. “An 800-gal. tank spraying half the water volume can stay out in the field as long as a conventional sprayer with a 1,600-gal. tank.”

He says this will not reduce efficacy, because the smaller, air-assist droplets are more efficient.

“You're not using an off-label rate as long as you're using the correct amount of chemical per acre, but not necessarily their carrier rate,” Richey says.

Better, more timely coverage

“Coverage has been an important issue as more spraying is being done postemergence,” says Alain Grégorie, sales manager, Gregson Technologies.

Because air-assist sprayers cover more leaf surface area — including the underside of the leaves — companies say they're seeing increased effectiveness.

Being able to spray in windy conditions is another benefit of air-assist sprayers because, when it's time to spray, every day you wait for wind speeds to decrease can cause yield reductions.

“We have documented research that shows these units can spray in wind speeds up to 22 mph,” says Jacto's Richey. “With the increased number of days you can spray with an air-assisted sprayer versus a conventional sprayer, you are saving money because you can spray when you need to.”

With the need to spray within three to five days after discovering ASR, having the largest available spray window has become ever more important, Richey adds.

Money

These sprayers, with their added benefits, also come with an added cost. The price tag for any of the units is $10,000 to $20,000 more than for a similar-sized conventional sprayer. However, the manufacturers claim the units' efficiencies justify their extra expense.

“Chemicals are expensive, so every percent of added efficiency translates into big savings,” Grégorie says. “If air assist gives farmers a bigger window to spray because of reduced drift, while still using nozzles that will give good coverage, this can be very critical for those who have many acres to cover and cannot wait for the perfect day to spray.”

Spray Air grower surveys indicate farmers are saving an average $8 to $10/acre on fuel, labor, time and water by spraying at the lowest herbicide rates, Criddle says.

“Combine that with increasing yields, and the return on investment gets even better. A 2,000-acre farmer is saving, on average, close to $20,000,” Criddle adds. “Many times, farmers are able to save $20,000 annually by spending an initial $15,000 premium on their sprayer. They're coming out ahead for many years to follow.”