Pre-Season Airblast Sprayer Calibration

Prep your sprayer for bloom (blight) sprays.  If you use stainless steel nozzles, toss out last year’s and buy new ones. If you are using ceramic nozzles, check them for wear. Ceramic nozzles do wear out, eventually. Once you are happy with your nozzles, check pump and system strainers as well as those at the nozzle. Replace any that need it (screen holes, clogging, poor/damaged end seals, etc.). Pull off all nozzles/strainers and run clean water through the system to blow out any solids that could collect at the nozzle screens and slow/clog flow. Check the pressure gauge, too. Does the pressure it reads match up with the flow rate from the sprayer based on the manufacturer specs? If you are using Spray Systems nozzles, the TeeJet catalog 51A is available as a free download or as a hardcopy from your local dealer. Look for leaks and fix where found. Now calibrate the sprayer to deliver the GPA you want.

  • Set a ground speed that allows sprayer air [and the pesticide carried by it] to reach just above the tops of the trees. Use flagging in the tree tops to see if sprayer air is moving through the canopy. The speed you decide on should be faster than that used for summer sprays (mites, worms, etc.) so the application is more cost-effective and still effective – assuming you are happy with the results of your summer sprays. Measure speed in ft/minute in the field over a distance of at least 100’. [Don’t trust the MPH on the tractor tach] For use later in the process, calculate acres per minute (APM) sprayed by multiplying ground speed in feet/minute by the row spacing. [For example, if the sprayer travels 176 ft in a minute down a tree row that is 28 feet wide, it will spray an area of 4,928 sq ft/min. Divide that number by 43560 sq ft/acre to get 0.11 acres/minute.]
  • Gallons per acre = gallons/minute divided by acres/minute. With a certain gallons per acre (GPA) in mind and working from the nozzle manufacturer’s catalog, select the number and sizes of nozzles to deliver the needed gallons per minute. Set up the nozzles on the sprayer so that most of the spray (~70-80% of flow) targets the upper tree canopy. Rain will recycle the upper deposits, washing the blight materials downwards onto green tissue below. [The more material high in the tree, the longer the protection will last in the upper tree, plus there is a bigger reservoir to wash down and protect the lower tissues as the lower residues are removed by rainwater.]
  • Check actual sprayer GPA by filling the sprayer to overflowing, running it at field settings (rpms, system pressure, etc.) for 2-3 minutes, making sure to note exactly how long the nozzles were open. Refill the tank just to overflowing with a flow meter on a hose or calibrated buckets. Divide the total gallons replaced into the sprayer by minutes of run time and you have the actual gallons per minute (GPM) put out by the sprayer. Divide gal/minute by acres/minute to get actual GPA sprayed. Repeat at least once more to make sure you have it right. Now you can add pesticides to the tank with confidence that the intended rate per acre is being delivered.
  • Double check calibration throughout the spray job by checking trees/minute at different times and knowing the number of rows or trees per tank at the particular GPA.

Recalibrate the sprayer for summer work once the early leaves are fully expanded (May?). The target will be larger (more GPA) and the canopy more dense (slower ground speed needed) at that time and a good bloom calibration will not deliver the needed coverage.


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