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

Erdal Ozkan, an Ohio State University Extensionagricultural engineer, says there's no better time than early spring forgrowers to takea look at their sprayers and find out if they are deliveringthe 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 andBiological Engineering and a researcher with the Ohio AgriculturalResearch andDevelopment Center. "You assume you know what speed you are traveling at fromhabit, but you are not really sure.The problem with a sprayer is that nozzleswear out with use, application rates change with different field conditions,and travelingspeeds also change. Many growers don't take these factors intoaccount."

Data from Ohio and other states indicates that onlyone out of every three to four applicators applies chemicals at rates that arewithin 5percent (plus or minus) of the intended rates. Application rateswithin plus or minus 5 percent represent the accuracy levelrecommended by theU.S. Department of Agriculture and the U.S. Environmental Protection Agency.

Surveys also indicate that 67 percent of applicatorswho calibrated their equipment before every spray application had applicationerrorsbelow 5 percent, Ozkan said. Conversely, only 5 percent of applicatorswho calibrated their equipment less than once a year achievedthe same degreeof accuracy.

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

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

How to Calibrate aSprayer

Calibrating a boom sprayer, Ozkan said, is not asdifficult as it sounds. It usually doesn’t take more than 30 minutes, and onlythreethings are needed: a watch showing seconds, a measuring tape, and a jarthat measures ounces. The ultimate goal is to calculate theactual rate ofapplication in gallons per acre to check for accuracy, or to make adjustmentsas needed.

Ozkan recommends a method based on spraying 1/128 ofan acre per nozzle and collecting the amount of chemical that would bereleasedduring the time it takes to spray that area. This particular amount of land ischosen because there are 128 ounces of liquid inone gallon, making it easy tocorrelate the number of ounces sprayed on that small area to the number ofgallons that would be sprayedon the whole acre. For example, if you catch 15ounces from a set of nozzles, the actual application rate of the sprayer isequal to 15gallons per acre.

For this method to be accurate, it is important tomake sure that the time used to collect the spray from the nozzles is the same thatittakes to cover 1/128 of an acre. A table available at various nozzle and row spacingsand the time you must travel to cover1/128 of an acre for each spacing. For example, the travel distance for a 15-inchnozzle or rowspacing is 272 feet; for a 20-inch nozzle or row spacing is 204feet; and for a 30-inch nozzle or row spacing, the distance is 136 feet.

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

1. Fill the sprayer tank with water.

2. Run the sprayer, inspect it for leaks, andmake sure all vital parts function properly.

3. Measure the distance in inches between thenozzles. Then measure an appropriate distance in the field based on thisnozzle spacing, according to thetable available at

4. Drive the measured distance in the field atyour normal spraying speed, and record the travel time in seconds. Repeatthis procedure and average thetwo measurements.

5. With the sprayer parked, run the sprayer atthe same pressure level and catch the output from each nozzle in ameasuring jar for the travel timerequired in step 4.

6. Calculate the average nozzle output byadding the individual outputs and then dividing by the number of nozzlestested. If an individual samplecollected is more than 10 percent higheror lower than the average nozzle output rate, check for clogs and cleanthe tip, or replace the nozzle.

7. Repeat steps 5 and 6 until the variation indischarge rate for all nozzles is within 10 percent of the average.

8. The final average output in ounces you get isequal to the application rate in gallons per acre.

9. Compare the actual application rate with therecommended or intended rate. If the actual rate is more than 5 percenthigher or lower than therecommended or intended rate, you must makeadjustments.

Learn how to make these adjustments and additionalinformation about calibration at