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55. Calibrate Your Sprayer


University studies have shown that about one out of every four sprayers is miscalibrated by more than 10 percent, which can mean overapplication, greater risk to water, and wasted money. With application costs at $25 per acre, overapplying chemicals by 10 percent would mean a loss of $2. 50 per acre-or $2,500 for a 1,000-acre farm.

Check the calibration of your spray equipment every few days during the season or whenever you change the pesticides being applied. New nozzles do not lessen the need to calibrate because some nozzles "wear in," which means they will increase their flow rate most rapidly during the first few hours of use.

calibrating your sprayer If you do the calibration yourself, the first step is to determine your sprayer's ground speed in miles per hour, according to existing field conditions. Then determine the effective sprayed width in inches for each nozzle—a measurement that will differ for different spray methods.
calculate your nozzle's flow rate in gallons per minute Next, calculate your nozzle's flow rate in gallons per minute using the equation shown here. GPA is the application rate in gallons per acre, MPH is the ground speed in miles per hour, and W is the effective spray width. Multiply them together and then divide by 5,940. The answer is the GPM, or gallons per minute that your nozzles should deliver.
sprayer After determining the required flow rate, check whether your nozzles are delivering the correct gallons per minute. The common way to do this is to use a stopwatch and a special container marked in ounces; with these materials, you can determine the number of ounces per minute that the nozzle delivers.
nozzle flow rate tester An easier, more efficient way to check nozzle flow rates is to purchase a nozzle flow rate tester—an inexpensive item that can be purchased from some spray equipment suppliers. It will tell you how many gallons per minute the nozzle is delivering.
different nozzles It's okay if the flow rate varies from the required flow rate, as long as you know that and adjust for it. However, the flow rate for different nozzles should not vary from each other by more than 5 to 10 percent. Be sure you operate spray nozzles within the recommended pressure range. This is important because as spray pressures increase or decrease, flow rates change.
electronic spray control system Once you have calibrated your sprayer, operate it in the field at the application rate and ground speed that you selected, and at the pressure you determined. Then check the liquid level in the tank to make sure your application rate is correct. An electronic spray control system provides you added confidence that your sprayer is properly calibrated. However, you still need to put the correct parameters into the electronic spray control systems, and that means calibrating your sprayer.

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