This blog documents efforts to evaluate containment spraying in apple orchards in Massachusetts. The project was funded by a USDA Specialty Crops Block Grant from the Massachusetts Department of Agricultural Resources.
After the previous session with the tunnel srayer and the airblast sprayer, it was clear that we were getting better coverage with the airblast. This was puzzling, since our calculations suggested that they should have been applying the same amount of water, and there was considerably more drift with the airblast. On May 17, we measured actual flow from the nozzles. The airblast nozzles put out the correct volume of water, but the tunnel sprayer nozzles only put out 1/5 of the projected quantity. We used a nozzle chart from the company that had everything in English units. Apparently, there is an error in this chart. When we used their metric chart and converted to English units, we got the correct flow.
Unfortunately, we needed to increase pressure to 300 psi to obtain our desired flow, 100 gallons per acre (or about 7.8 gallons per minute). This high pressure resulted in small droplet size which drifted more than desired.
So, our next steps will be to change nozzles to ones that would give adequate flow at lower pressure. Also, we will test air-induction nozzles in the sprayer to determine the effect of larger droplet size.
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.
