Adjustments to the Tunnel Sprayer and Comparison with Airblast

On May 2, we took the tunnel sprayer out again. This time, we adjusted flow rate out of the nozzles to match the dilute gallonage of the trees being sprayed, about 100 gallons per acre (13' row spacing and 3 mph = 7.8 gallons per minute spread across 16 nozzles -- the top two on each side were shut off). We also narrowed the tunnel to reduce the impact of wind blowing through it.

As with last week, there was a reasonably stiff breeze from the south, parallel to the row, so the wind blew into the back of the sprayer in one direction and into the front in the other direction. With the reduced flow, we saw less drift out of the tunnel than last week, but some drift still occurred. We also fired up an airblast and calibrated it also to spray 100 gallons per acre (7.8 gallons per minute). As you will see from the following video, drift was much greater with the airblast. Coverage, however, appeared better with the airblast than the tunnel. I know that this observation doesn't make sense. Next week, we will measure actual nozzle output (with some of Jon Clements' sprayer calibration equipment) and not rely on the charts and on our calculations.