Making the grade

03/01/2007 02:00:00 AM

Mobile testing program helps growers reduce drift by providing an orchard sprayer report card

By Vicky Boyd

Always on a quest to improve sprayer efficiency and reduce drift and environmental impact, Modesto, Calif.-area almond and walnut grower Paul Wenger switched to longer-wearing ceramic spray nozzles about 10 years ago.

He routinely measures nozzle orifice diameters to check for wear, and he keeps track of the amount of pesticides applied compared to the acreage.

“We know how long it takes to put out a tank—about 55 minutes,” he says. “If it’s taking less than that, we know something’s wrong, like a broken hose. We’ve got it dialed in pretty well.”

When Parry Klassen, executive director of the Dinuba, Calif.-based Coalition for Urban/Rural Environmental Stewardship, approached Wenger about being a test subject for the group’s new portable sprayer calibration instrument, he readily agreed.

The Austrian-built Pessl Instruments Sprayertest 1000, which measures individual sprayer nozzle output and overall spray distribution pattern, gave Wenger’s Nelson Hardie 500-gallon airblast sprayer passing marks.

“[The sprayer is] doing what it was set up to do, and if they’re getting the right output per acre, they’re doing fine,” says Robert McMurry, a CURES environmental technician from Davis, Calif.
But not all growers are as mindful of sprayer calibration as Wenger.

“We’ve found some growers who are on top of it, and [the calibration] is almost perfect,” McMurry says. “And other growers have sprayers that are really dirty, and you have to clean up just about every nozzle and you have to replace a lot of nozzles.”

The sprayer calibrations are part of a larger effort by CURES to educate growers about reducing pesticide runoff into California Central Valley waterways. The nonprofit group received a grant from California’s State Water Quality Control Board to purchase the $75,000 portable sprayer tester and conduct grower outreach programs.

The three-year project calls for CURES to test at least 100 sprayers. In its first year, the group has evaluated about 30, and the results are all over the board, Klassen says.

“We’ll use this as an educational tool, but it will also give us an idea of what’s going on in the sprayer fleet, Mobile testing program helps growers reduce drift by providing an orchard sprayer report card so to speak,” he says. “If it shows they are really a mess, then there will be more educational emphasis on tuning up sprayers.”

A two-fold approach
The testing unit actually measures two different sprayer components—individual nozzle output and sprayer pattern distribution.

During the first testing phase, the technician hooks each nozzle to a hose that flows to sensors. The grower starts the sprayer, and the spray tester measures individual nozzle output.

A computer records the results for printout, but they also are visible in tubes at the end of the tester. Each tube holds the flow from one nozzle.

For the second part of the test, the technician removes the hoses from one side of the sprayer. A panel full of acoustic sensors is moved close to the side of the sprayer without the hoses. Once the grower starts the sprayer, the sensors measure where the spray droplets hit.

The desired spray pattern depends on the crop, McMurry says. Wenger uses his sprayers for walnuts, so he wants more from the middle and upper nozzles to reach into the tall, overhanging tree canopy. He achieves this by using two different nozzle sizes or even turning off some of the bottom nozzles.

“You don’t want much on the bottom because there’s not much canopy there,” McMurry says.

Citrus growers, on the other hand, typically would want more spray coverage on the bottom and possibly none from the upper one or two nozzles, he says. Citrus trees tend to have lower-hanging foliage and are smaller and hedged.

If the top nozzles aren’t shut off, they may waste product by shooting it into the air where there is no canopy to intercept it.

One of many drift-control tools
Klassen and Ken Giles, a University of California, Davis agricultural engineering professor working with CURES, emphasize that the Pessl Instruments Sprayertest 1000 is just one of many tools to help growers control drift.

Because the equipment was designed for European orchards, the technician must interpret the results differently for U.S. use.

European growers, for example, use much lower dilutions than their U.S. counterparts, Giles says.

“They are spraying at 15, 20, 40 gallons per acre, and our growers are starting at 100 and going up from there,” Giles says.

European producers also rely mostly on power-take-off-driven sprayers, whereas U.S. growers typically use engine-type sprayers because of the higher volumes of air movement required.
Despite the differences, Giles says the Pessl provides a good overall picture of sprayer performance.

“It also gives us a chance to talk to growers and have them consider their nozzle wear—has there been some misuse of nozzles over time?” Giles says. “It makes them a little more aware of their sprayer and their accuracy.”

Richard Derksen, an agricultural engineer with the Agricultural Research Service in Wooster, Ohio, hasn’t used the Pessl test machine. But he says he thinks it could be useful.

“I’ve done this type of calibration testing by hand for growers in Ohio and New York, and we checked about 50 different sprayers,” Derksen says. “I found they did need calibration, but it wasn’t just checking nozzle output. It was also important to check sprayer speed and the condition of pressure gauges.”


Coalition for Urban/Rural Environmental Stewardship

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