| [Image: boom-type sprayer] |
| [Image: catching sample from boom sprayer] |
| [Image: catching sample from gun sprayer] |
Calibration of vehicle-mounted boom-type sprayers (Figure 1) is simple and can be accurate; calibration of hand-carried sprayers is much more subjective, but it is simple to do.
Boom-Type Sprayers
Boom-type turf sprayers mounted on vehicles are calibrated in the same way as agricultural sprayers. The math involved is minimal. The following steps will lead you through a simple and effective procedure to find your rate of application:
1. Measure the spacing between adjacent nozzles.
2. Mark off a test run area (on turf) 200 feet long using flags, stakes, etc.
3. Drive the sprayer through the 200-foot test run at normal operating speed and time how long it takes to run between the marks. There is no need to spray while driving. Be sure to get up to speed before the first mark and not decelerate until after the second mark.
4. Put clean water in the spray tank and with the spreader stationary, start spraying at the pressure you intend to use in the field. Catch and measure the output from one nozzle for the same amount of time required to run 200 feet in the previous step (Figure 2).
5. Calculate the output:
Spray rate (in gallons/acre) =
nozzle output (in ounces) x 12 in/ft x 43,560 sq. ft./a
nozzle spacing (in inches) x 200 ft x 128 oz/gal
This can be reduced to:
Spray rate (in gallons/acre) =
20.4 x nozzle output (in ounces)
nozzle spacing (in inches)
You can’t get much simpler than this!
Note that using this method requires none of the calculations of sprayer ground speed in miles per hour or nozzle output in gallons per minute required by many other calibration methods. This method assumes all nozzles are equally spaced and of the same size. At least once a year, you should check the output from all nozzles; if all are not within 10 percent, replace the nozzles.
Single-Nozzle or Gun Sprayers
The typical gun-on-a-hose system used by many lawn care service applicators must be calibrated differently. The following procedure will help, but the results will still be subjective and depend on a consistent operator:
1. Mark off a rectangular area of 0.1 acre (100 feet by 43.6 feet).
2. With only water in the sprayer, treat this area in your usual manner (be sure to calibrate each person separately). Record the time to make this application.
3. With only clean water in the spray tank and the gun stationary, start spraying at the pressure you intend to use in the field. Catch and measure the output from the gun for the same amount of time required to treat 0.1 acre in the previous step (Figure 3).
4. Calculate the output as follows:
Spray rate (in gallons per acre) = 10 x gallons caught (or 0.078 x ounces caught)
The Final Steps
Once you have determined your spray rate, check the product label to see if you are within the recommended rate. If not, you will need to adjust travel speed, nozzle size or pressure and recalibrate until you are within the label recommendations. After you have a suitable overall rate, you will need to mix the chemical properly for that rate. Decide how much spray you need (gallons of spray = acres to be sprayed x gallons/acre). Multiply the label rate per acre x acres to get the amount of pesticide needed. Add this amount of pesticide to the correct amount of water. You may need more than one tankful to do the job.
Following the above procedures will help you obtain the correct rate of pesticide on your turfgrass. You should recalibrate a boom-type sprayer every time you spray.