Sprayer Calibration Tips
To get the right amount of spray materials in the right place, carefully calibrate your sprayer(s) at least once a year. For the most efficient spraying, calibrate your sprayer to match key canopy growth stages — dormant, full bloom, spring, preharvest, etc. If you calibrate your sprayer only once a year, do it just before your preharvest spray, when the canopies are the densest and uniform spray coverage and effective pest control is most challenging. The following is a review of the basic steps to calibrating an air-blast sprayer using hydraulic nozzles, such as Rears, Durand-Wayland Nelson-Hardie, Air-O-Fan, etc.
Accurate pesticide delivery per acre requires accurate delivery of spray volume per acre. However, sprayers must be calibrated to deliver the correct gallons per acre and that volume must be uniformly delivered throughout trees for effective pest control.
Seeing Is Believing
Proper sprayer air volume delivery is key to spray coverage quality. With the tank half-filled with clean water plus kaolin clay product (Surround, etc.), run the sprayer down a typical row in the orchard at the tractor gearing and RPMs you commonly use for preharvest spray. Shut off or deflect any air not directed into the tree. Check coverage in the hardest part of the tree for spray to reach — the top center.
No coverage or patchy coverage in the tree tops? Increase fan air volume delivery into each tree by slowing down ground speed, or changing fan gearing or blade angle — which works on sprayers with those options. Uniform but thin coverage in tree tops? Increase spray volume and check again. Once you find the settings that give good spray coverage, measure ground speed. Count trees per minute or drive the sprayer over a set distance. Using the ground speed in feet per minute and the distance across a tree row, calculate acre per minute (APM) sprayed.
Nozzles determine spray volume delivery. Select the spray volume — gallons per acre (GPA) — you want to spray. Calculate the gallons per minute (GPM) the sprayer needs to deliver. GPM = APM X GPA. Use the nozzle manufacturer’s catalog to select the proper size and number of nozzles to deliver the needed GPM.
In the field, set nozzles on the sprayer to match canopy thickness. Place larger nozzles adjacent to thicker canopy. Close nozzle ports that spray outside the canopy.
For a ground check, completely fill the sprayer with clean water. Park the sprayer and tractor in a flat, open location. Run the sprayer for one to three minutes at the pressure and RPM setting you will use in the orchard. Shut off the sprayer and measure back the amount of water it takes to completely refill the sprayer. A marked bucket works fine. GPM = gallons required to refill per time run (minutes). Checking volume output per time for each nozzle (nozzle GPM) and summing all to determine sprayer GPM is preferred (see photo). This approach identifies worn or damaged nozzles.
Calculate GPA sprayed as if you were running at the ground speed you determined earlier. GPA = GPM/APM. Is the sprayer delivering the GPA you want? If not, adjust nozzles (preferred) or pressure (if a small change is needed) to get the volume output you need. Repeat until you get the GPA you want. Note: Changes in pressure will change spray droplet size and possibly coverage, so recheck spray coverage if you change pressure to adjust spray volume (GPA) delivery.
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