This is the time to check the accuracy of your sprayer. While applying too little pesticide may result in ineffective pest control, too much pesticide wastes money, may damage the crop and increases the potential risk of contaminating ground water and environment. The primary goal with calibration is to determine the actual rate of application in gallons per acre, then to make adjustments if the difference between the actual rate and the intended rate is greater or less than 5% of the intended rate. This is a recommended guideline by USEPA and USDA.
I get this question all the time: “Why should I calibrate my sprayer? I have a rate controller on the sprayer. I just enter the application rate I want, the controller does the rest”. This statement is correct, only if you are sure about the accuracy of the rate controller which is highly affected by the accuracy of the sprayer travel speed data that goes in the rate controller. If the speed is determined by a sensor that measures the revolution of the tractor rear wheels, the travel speed calculated may not be accurate for several reasons: such as the tire pressure being low (causing a smaller tire rolling radius), or the ground conditions that may cause tire slippage (such as wet ground, or soft, sandy soil). So, it is always a good idea to do a manual calibration of the sprayer and compare the actual application rate with what is displayed on the rate controller. In addition, a rate controller may not pinpoint a plugged, or worn out nozzle on the boom. Overall, you may get the desired gal/acre application rate, but you may not have the uniform application across the boom unless you check all the nozzles individually. That is also a part of the calibration, as well as finding out the application rate. Clean all the plugged nozzles. Check the output of all the nozzles for a given length of time at a given spray pressure. Compare the measured output from each nozzle with the expected output of a brand new nozzle shown in the nozzle catalog for the same spray pressure. Replace the nozzles showing an output error of more than 10% of the output of the new nozzle. Once you do all this, now you are ready to calibrate your sprayer.
There are several ways to calibrate a sprayer. Regardless of which method you choose, it usually doesn’t take more than 30 minutes, and only three things are needed: a timer (or watch or smart phones) showing seconds, a measuring tape, and a jar graduated in ounces. Here, I will describe perhaps the easiest of all the methods to determine the actual application rate of a sprayer for broadcast applications:
Don’t forget one very important thing while calibrating, and especially operating a sprayer: safety. Although clean water is used during calibration, you should still protect yourself from getting in contact with pesticides inside or outside sprayer equipment. Wear personal protective equipment, at least gloves and goggles. Happy spraying!
Source: Erdal Ozkan, Ohio State University
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