OSU Extension, Darke County
Now is the Time to Fine Tune Your Sprayer
By Sam Custer 

Higher pesticide costs and new chemicals designed to be used in lower doses make accurate application more important than ever. There is no better time than early spring to take a closer look at your sprayer. Erdal Ozkan, OSU Extension, points out the things he would check on a sprayer to achieve efficient and effective application of pesticides: 

 •Double-check your sprayer for mechanical problems before you start using it.  You won’t have time to do this when planting is in full swing. 

•Clean the sprayer tank thoroughly and make sure nozzle filters are clean. 

•Clean spray nozzles, check their flow rates, and replace the ones that are spraying more than 10 percent of the original output. 

•Check the agitator in the tank to make sure it’s working properly. 

•Run water through the spray system to make sure everything is working properly 

•Find out if the sprayer is delivering the proper application rate (gallons per acre).   

You can determine if the chemicals are applied at the proper rate only by carefully calibrating the sprayer. Calibration, perhaps more than anything else, will have a direct impact on achieving effective pest control and the cost of crop production. 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. Results of "Sprayer Calibration Clinics" in Ohio, and data from several other States show that only one out of three to four applicators are applying chemicals at a rate that is within 5 % (plus or minus) of their intended rate (an accuracy level recommended by USDA and EPA). Of those two-thirds of the applicators missing the mark, about half is under spraying while the other half is over spraying. In one particular case, the applicator would be over spraying by as much as 75% had he used the nozzles that he just purchased and installed on the boom.   

Sprayers should be calibrated several times a year. Changes in operating conditions and the type of chemical used require a new calibration. Frequent calibration is even more important with liquid application because nozzles wear out with use, increasing the flow rate. Over a decade ago, the University of Nebraska conducted an interesting survey. The survey results revealed that there is a direct positive correlation between application accuracy and the frequency of calibration. Approximately 67 percent of the operators who calibrated before every spray operation had application errors below 5 percent. Only 5 percent of the applicators who calibrated their equipment less than once a year (once every two, three, four years) achieved the same degree of application accuracy.             

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 watch showing seconds, a measuring tape, and a jar graduated in ounces. 

To calibrate a boom sprayer for broadcast applications this is perhaps the easiest method, follow these steps: 

Fill the sprayer tank (at least half full) with water.

Run the sprayer, inspect it for leaks, and make sure all vital parts function properly.

Measure the distance in inches between the nozzles. 

Measure an appropriate travel distance in the field based on this nozzle spacing. The appropriate distances for different nozzle spacing is as follows: 408 ft for a 10-inch spacing, 272 ft for a 15-inch spacing, 204 ft for 20-inch spacing, 136 feet for a 30-inch spacing, and 102 feet for a 40-inch spacing. (See extension publication AEX-520 for travel distances for other spacings, and for an explanation for selection of these specific travel distances for given nozzle spacing (http://ohioline.osu.edu/aex-fact/0520.html). 

Drive through the measured distance in the field at your normal spraying speed, and record the travel time in seconds. Repeat this procedure and average the two measurements. 

With the sprayer parked, run the sprayer at the same pressure level and catch the output from each nozzle in a measuring jar for the travel time required in step 5 above. 

Calculate the average nozzle output by adding the individual outputs and then dividing by the number of nozzles tested. The final average nozzle output in ounces you get is equal to the application rate in gallons per acre. For example, if you catch 15 ounces from a set of nozzles, the actual application rate of the sprayer is equal to 15 gallons per acre. 

Compare the actual application rate with the recommended or intended rate. If the actual rate is more than 5 percent higher or lower than the recommended or intended rate, you must make adjustments in either spray pressure or travel speed or in both. For example, to increase the flow rate you will need to either slow down, or increase the spray pressure. The opposite is true when you need to reduce application rate. As you make these changes stay within proper and safe operating condition of the sprayer. Remember increased pressure will result in increasing the number of small, drift-prone droplets. Using the trial-and error method to eventually reach the intended application rate takes some time. If you follow the equations given in Extension Publication AEX-520 on Calibration you can find optimum travel speed and pressure much faster. 

Recalibrate the sprayer (repeat steps 5-8 above) until the recommended application error of +5% is achieved. 

For more information, visit the Darke County OSU Extension web site at www.darke.osu.edu, the OSU Extension Darke County Facebook page or contact Sam Custer, at 937.548.5215.