New products continually offer greater flexibility and effectiveness to growers in controlling diseases and pests in their crops. In the crunch of getting crops into the field, coping with weather and labor issues, and keeping up with regulations, sprayer calibration is a task that is often given low priority. However, since it will affect your crops, and thus bottom line profitability, the task should be considered a high priority.

Calibrating your sprayer can help you avoid thecosts of overapplication and underapplication.

Calibrating your sprayer can help you avoid the costs of overapplication and underapplication.
Photo by Valio/

Minimizing drift, nozzle selection and maintenance all complement the calibration process and are extremely important elements in effective spraying. Calibration basics and emerging technology combine to increase effectiveness of spraying and help growers control one more rising cost.

Dr. Andrew Landers, Cornell University senior extension associate, is an expert in pesticide application. Landers recommends a preseason tune-up that includes cleaning and calibrating everything. The preseason calibration should be followed by a midseason calibration of nozzles. The costs of overapplication or underapplication are a primary issue spurring the need to assure correct calibration of sprayers, according to Landers. He also noted the importance of staying within maximum rates as labeled, which are set by law.

Costs of overapplying

  • Spending more money than necessary on spraying
  • Polluting watersheds
  • Unintentional killing of crops
  • Spray drifting onto neighboring properties, leading to angry neighbors and lawsuits
  • Rendering soil sterile through spills

Costs of underapplying

  • Loss of effectiveness, resulting in reduced killing or no killing of pests
  • Weeds, diseases and pests developing resistance to chemicals

There are a number of factors that can lead to overapplication or underapplication. The forward speed of sprayers can be too fast or too slow, which can occur if sprayer weight and ground slope or conditions are not considered. A very small increase in engine speed can result in a large increase in pressure, Landers noted. Low pressure in the sprayer unit produces droplets that are too large and tend to bounce, while high pressure produces droplets that are too small and don’t stick to the target, often resulting in drift.

Andrew Landers conducts a workshop on sprayer calibration.

Andrew Landers conducts a workshop on sprayer calibration.
Photos courtesy of Andrew Landers, Cornell University, Unless otherwise noted.

Avoiding drift

Avoiding drift is an essential element in effective spraying, and there are several factors that contribute to drift. If the pressure is too high in the sprayer unit, it could create droplets that are too fine and lack enough mass to go down onto the target, causing the spray to drift off instead. Pressure should be kept as low as possible. Spraying in wind should be avoided. Even a slight breeze with wind speeds more than 4 mph presents conditions that are too windy for spraying.

Several causes of drift can easily be prevented. Proper nozzle size for the target must be used. Nozzles that are too small or worn are more likely to cause drift. Some additional steps that can help prevent drift include using shielded booms, getting the boom closer to the target, using nozzles with angles of either 80 or 100 degrees, staying alert to changes in wind speed and direction, and establishing buffer strips or barrier crops.

Landers offered suggestions for increasing the likelihood that a spray application will reach its target. One suggestion is avoiding the use of fans on sprayers during pre-bloom spraying in fruit crops, since high airflow is not necessary without dense canopy. If fans are used, higher forward speeds deflect air rearward at an angle into the target. During mid to late season, driving more slowly allows time for the spray to penetrate the canopy. He also cited the importance of spraying every row, rather than alternate rows. “Trials show better deposition occurs when every row is sprayed,” Landers said.

Output is collected in a numbered container to check each nozzle.

Output is collected in a numbered container to check each nozzle.

Nozzle selection and maintenance

Proper nozzle selection is an essential first step in calibrating sprayers for effective spray applications. The function of nozzles is to create the right droplet for the target, and to propel the droplet to the target, providing even coverage. Nozzles are primarily used to produce fine, medium or coarse droplet sizes.

Landers said, “One day, all new labels on pesticide containers will state which nozzle spray classification should be used.” He noted that sprayer handbooks and nozzle catalogs should be checked for pressure and nozzle size selection.

Fine droplets are essential for contact spraying, where the spray actually needs to hit the target insect or disease. Medium droplet sizes are the proper choice for systemic spraying, where the spray is expected to be absorbed through the plant leaf. Coarse droplets are used for sprays that will be incorporated into the soil, such as preemergent herbicides used before planting.

Calibration procedure

It’s essential to properly clean the nozzles. A soft brush, such as an old toothbrush, or an air line can be used to clean the nozzle if it is blocked. Landers emphasized that wire should never be used to clear the nozzle. Spare nozzles should always be kept on hand.

“Check that all nozzles on the boom are the same and all are in good condition, with no streaks or irregularities in the spray pattern,” Landers said. All nozzles must be clean and deliver to within plus or minus 5 percent of the manufacturer’s chart value. Landers noted, “Some suggest 10 percent, but I prefer 5 percent, as pesticides cost so much money.”

Proper calibration can be accomplished by marking off a course 100, 200 or 300 feet long and filling the tank half full of water. Using a stopwatch, run the course twice, timing each way and recording the time it takes. Divide by 2 to average the time.

Record operating speed, corresponding gear selection and operating pressure, along with the nozzle type. Note the recommended application volume from the manufacturer’s label, and calculate the required nozzle output in gallons per minute, where GPM = (GPA x S x W)/5,940. GPA is the sprayer application in gallons per acre, S is the speed in mph, W is the nozzle spacing in inches, and 5,940 is a constant for conversion of units. If your GPA is 20, S is 6 mph, and W is 15 inches, you would multiply 20 by 6 by 15 and divide that number by 5,940 to arrive at a GPM of .303.

Andrew Landers discussessprayer calibration techniques.

Andrew Landers discusses sprayer calibration techniques.

The following procedure can be used to determine whether or not nozzles are dispensing the required output:

  1. Park the sprayer and operate it at the same pressure and engine speed.
  2. Set the correct pressure using the pressure regulating valve.
  3. Collect and measure the output of each nozzle for exactly one minute, using a stopwatch to assure accuracy.
  4. Replace any nozzle tips that are inaccurate by more than 5 or 10 percent.

Technology assures greater accuracy

Technology is increasingly employed in all phases of agriculture, and spray calibration is more easily accomplished with the use of technology. Hand-held, hiking-type GPS models help in calculating speed and distance covered.

Dr. Andrew Landers, Cornell University senior extension associate, noted the availability of online courses to help you understand the different ways to increase spray effectiveness. For example, Cornell Extension offers two classes at no cost through an IPM grant.

  • Effective spraying with backpack sprayers for organic growers
  • Effective spraying with boom sprayers for organic growers

You can find out more about these classes at: Also, check with your local university extension for similar courses.

As an online resource, Landers created eight videos on calibrating airblast sprayers for orchards and/or vineyards. They can be found on YouTube.

If you prefer information in print, check out “Effective Vineyard Spraying,” authored by Landers, which includes a chapter on boom spraying. The cost is $55, with discounts for multiple copies, and it can be found at

Landers said, “Within the last two years, devices have become available that are very fast and simplify the calibration process.” The devices are easy to use and include large, digital displays. Landers recommended the Spot On, available from Gempler’s ( Another option is the AppliMax unit available from Agritronics ( Landers noted that calibration devices will help to increase accuracy and save time.

Nancy Riggs is a freelance writer from Mount Zion, Ill.