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.