Are you part of the 66 to 77 percent of growers who spray more or less pesticide needed, leading to either money wasted down the nozzle or crop losses? If you don't know, there's one thing you can do about it, and now is the time to do it: Calibrate your sprayer.

Erdal Ozkan, an Ohio State University Extension agricultural engineer, says there's no better time than early spring for growers to take a look at their sprayers and find out if they are delivering the proper gallons-per-acre application rate.

"If you don't calibrate your sprayer frequently, it's as if you were driving your car with a speedometer that doesn't work," said Ozkan, who is also a professor in the Department of Food, Agricultural and Biological Engineering and a researcher with the Ohio Agricultural Research and Development Center. "You assume you know what speed you are traveling at from habit, but you are not really sure. The problem with a sprayer is that nozzles wear out with use, application rates change with different field conditions, and traveling speeds also change. Many growers don't take these factors into account."

Data from Ohio and other states indicates that only one out of every three to four applicators applies chemicals at rates that are within 5 percent (plus or minus) of the intended rates. Application rates within plus or minus 5 percent represent the accuracy level recommended by the U.S. Department of Agriculture and the U.S. Environmental Protection Agency.

Surveys also indicate that 67 percent of applicators who calibrated their equipment before every spray application had application errors below 5 percent, Ozkan said. Conversely, only 5 percent of applicators who calibrated their equipment less than once a year achieved the same degree of accuracy.

Ozkan said growers should calibrate their sprayers in early spring and every time operating conditions (different ground surfaces, for example) change or a different type of chemical is to be used.

"Frequent calibration is even more important with liquid applications because nozzles wear out with use, increasing the flow rate and leading to overuse of chemicals, which impacts growers' budgets and can lead to crop damage and contamination of groundwater and the environment," Ozkan explained.

How to Calibrate a Sprayer

Calibrating a boom sprayer, Ozkan said, is not as difficult as it sounds. 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 that measures ounces. The ultimate goal is to calculate the actual rate of application in gallons per acre to check for accuracy, or to make adjustments as needed.

Ozkan recommends a method based on spraying 1/128 of an acre per nozzle and collecting the amount of chemical that would be released during the time it takes to spray that area. This particular amount of land is chosen because there are 128 ounces of liquid in one gallon, making it easy to correlate the number of ounces sprayed on that small area to the number of gallons that would be sprayed on the whole 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.

For this method to be accurate, it is important to make sure that the time used to collect the spray from the nozzles is the same that it takes to cover 1/128 of an acre. A table available at http://ohioline.osu.edu/aex-fact/0520.html shows various nozzle and row spacings and the time you must travel to cover 1/128 of an acre for each spacing. For example, the travel distance for a 15-inch nozzle or row spacing is 272 feet; for a 20-inch nozzle or row spacing is 204 feet; and for a 30-inch nozzle or row spacing, the distance is 136 feet.

To calibrate a boom sprayer for broadcast applications using this method, follow these steps:

1. Fill the sprayer tank with water.

2. Run the sprayer, inspect it for leaks, and make sure all vital parts function properly.
 
3. Measure the distance in inches between the nozzles. Then measure an appropriate distance in the field based on this nozzle spacing, according to the table available at http://ohioline.osu.edu/aex-fact/0520.html.
 
4. Drive 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.
 
5. 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 4.
 
6. Calculate the average nozzle output by adding the individual outputs and then dividing by the number of nozzles tested. If an individual sample collected is more than 10 percent higher or lower than the average nozzle output rate, check for clogs and clean the tip, or replace the nozzle.
 
7. Repeat steps 5 and 6 until the variation in discharge rate for all nozzles is within 10 percent of the average.
 
8. The final average output in ounces you get is equal to the application rate in gallons per acre.
 
9. 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.
 
Learn how to make these adjustments and additional information about calibration at http://ohioline.osu.edu/aex-fact/0520.html.