Air-assist systems reduce spray drift

WOODSTOCK, Ont. — A lot is asked of farm sprayers and nozzles.

Big, air-filled droplet packages are required that will resist drift under windy and thermal inversion conditions and are able to keep even the most aggressive herbicides from going off target.

However, fine particles are also needed and must be applied like paint to each of a target plant’s surfaces so that contact fungicides create a barrier to disease.

Tailoring applications on the farm isn’t always easy.

Jason Deveau of Ontario Agriculture filled the bleachers with farmers looking for guidance on this topic and a few new ideas during last week’s Canada’s Outdoor Farm Show in Woodstock.

“It doesn’t matter where you are in the world … the issues that farmers face (when it comes to pesticide application) are the same,” he said.

Getting as much pest control from the least investment with as few effects on the environment as possible is the goal for most producers.

Efficiency is the name of the game when spraying. Growers want the products they use to make it to their targets and stay there.

“But really what they want is to stop a pest from taking all the profits out of the crop,” said Deveau, a researcher and extension agronomist.

However, producers also want systems to be as simple as possible.

Deveau and Tom Wolf, a researcher from Saskatoon, operate a website called sprayers101.com.

A producer recently wrote to Deveau on the site that he wanted a twin fan that would give him good vertical coverage on corn but also mite control in strawberries.

“One nozzle will not solve all the problems. I have seen excellent nozzles used wrong and nozzles that shouldn’t be used, used pretty darned well,” he said.

“Mite control and head blight in wheat … that nozzle doesn’t exist.”

For example, twin fan nozzles can be effective as long as they are close to the wheat heads.

“But if your nozzles are too high, wind and gravity will (impair) the application.… That spray will mostly fall straight down. You might as well just have used a flat fan,” he said. “You have to get those booms down to the crop.”

The ideal spray is a fine droplet that coats the plants. Large droplets, even air infused, have a hard time coming into contact with all plant surfaces. As well, controlling those light packages of liquid can be a challenge in all but the best conditions.

However, a mechanical system has potential when it comes to putting finer droplets into the right place and keeping them there.

Deveau demonstrated a twin air-assisted system from spraying equipment manufacturer Hardi.

The machine uses a pair of large fans to feed canvas-type manifolds an operator-variable airflow that augments spray droplets and keeps them where they should be rather than allowing them to drift.

“If you get the right air for the canopy, you can get a fine droplet where you want it to be and it will do the rest,” he said.

The system takes advantage of small droplets’ ability to float about and blows them into the right place to do that: under leaves and in the middle and bottom of the canopy.

The system pushes enough wind that it can open dense crop canopies and allow the spray to enter. Too much air can cause problems, so properly setting the system for the canopy, wind speed and product is important.

“When it is set right, you can use it to spray bare ground and you won’t see any drift,” said Deveau.

Gary McCutcheon of Hardi said operators can also independently adjust the booms 30 degrees forward and 40 degrees back.

This can compensate for speed of travel or attack angles for various products.

Deveau said producers who move to air-assist type machines often don’t switch back.

“Some find they can reduce water and chemical volumes and get the same coverage or better,” he said.

“That helps justify the (added) cost, but better efficacy is likely, I think, why they like the machines.”

McCutcheon said growers also like the system’s drift control ability in windy conditions.

“If you can add an hour or two per day, especially on the Prairies, that can mean a lot of acres and im-proved timing. People get hooked on it I think,” he said.

Demonstration tests done at the farm show in Woodstock showed how the airflow controls drift in fine droplet sprays in a challenging wind.

However, colour-change blotter paper placed in the crop’s canopy showed only a slight advantage for under-leaf coverage in a dense soybean stand.

Deveau said that was probably because the sprayer was set up more for a farm show demonstration than for specific crop conditions.

The air-assist boom concept has been around for decades.

New Holland’s Miller Air Blast relies on air nozzles every 10 inches across the boom.

Small companies, such as Big John from Nebraska, also offer the units.

Europe’s Agrifac has been offering downdraft systems for many years and has two dealers in North America.

In Europe, wide boom sizes allow producers to operate at lower speeds, and that region offers a greater variety of airflow systems. Farmers there rely on thorough applications of fungicides too be-cause of the high moisture environment and generally moderate to mild climate.

Agrifac’s Airflow Plus places a fan every nine feet along the boom to drive down the spray. Kyndestoft Air and Danfoil offer a down draft machine design. Hardi has kept its self propelled Alpha Evo with Twin booms on the east side of the Atlantic but has plans to bring it to North America. For now, its air assist units in North America are pull-type.

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