Sprayer calibration is an important step when applying pesticides and should not be overlooked. A lot of different sprayers can be used in agriculture, including common types such as boom applicators, air blast applicators, and handgun applicators. The following information outlines the process for calibrating a boomless sprayer.

Determining Pesticides Per Acre

Boomless sprayers are used to make broadcast applications of pesticides to large areas, such as fields. Read the label for all pesticides before purchasing and applying them. The pesticide label is the law, and applicators should follow all label directions. Labels explain how much of the pesticide to apply per acre, as well as the gallons of water needed per acre, as recommended by the manufacturer. It is common for a pesticide label to recommend a range of 10 to 40 gallons of water per acre. For boomless sprayers, operating pressure, nozzle size, and operating speed determine the volume of water applied per acre. So, how much pesticide do you put in a tank? First, you need to determine how many gallons of water you are applying per acre. Then, you can calculate how much pesticide to add to the tank.

Calibration Steps

The following are the steps for a variation of the 1/128 calibration method, but other methods can be used. While calibration is done only using water in the tank, personal protective equipment should still be worn while calibrating.

The first step to calibrating any sprayer is to check and clean the sprayer’s tips, filter, hoses, and pump. Put only water in the tank and check the tips to make sure they are all functioning properly. Over time, tips, pumps, and other parts of a sprayer can wear out and may need to be replaced.

The next step is to determine the length of the calibration course. To do this, add water to the tank and engage the pump. The revolutions per minute (rpm) of the pump needs to be the same while calibrating as it will be when spraying the field. Measure the spray width in feet and divide it by a constant of 3,403. For example, if the spray width is 20 feet, the calibration course should be 170.2 feet long (3,403/20=170.15). The calibration course should be measured in the field where spraying will be done. Place a marker of some kind on each end of the calibration course. Then, determine the amount of time required to drive the equipment, such as a tractor, the length of the calibration course. You can drive the course several times in order to calculate an average speed. Keep note of the gear and rpm you are operating at while driving the calibration course. You should always use the same tractor with the same sprayer. If you change tractors or sprayers you will need to recalibrate.

The next step is to collect water from the sprayer nozzles for the same amount of time that was required to drive the calibration course. Collect this water while the sprayer is stationary and running at the same operating pressure that will be used for the application. The tractor should also be operating at the same rpm as it was while driving the calibration course. You can collect water by attaching a hose over the spray tips and allowing water to drain into a bucket. Another method is to attach a heavy-duty trash bag over the nozzles and cut a hole in the bottom of the trash bag, allowing the water to be collected in a large bucket. In this example, the trash bag would work as a homemade funnel.

Measure the volume of water caught in ounces. Divide the number of ounces caught by 10 to determine how many gallons of water is being applied per acre. You can change either the speed, nozzle size, or pressure to achieve the desired volume per acre. If you are applying 18 gallons per acre and would like to apply 20 gallons per acre, the simplest thing to change is usually the pressure. Once the pressure is adjusted, you can collect water again and check how many gallons are being applied per acre. With a little time, you can adjust the sprayer to apply 20 gallons of water per acre. If you have a 100-gallon tank and are applying 20 gallons of water per acre, then you can apply pesticides to 5 acres with every tank full. If the label recommends 1 pint of pesticide per acre, you will then add 5 pints of pesticide with every full tank.

More Information

Remember to always read the label before purchasing and applying pesticides, and always wear the recommended personal protective equipment. Contact your county Extension office if you have any questions.