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College of Food, Agricultural, and Environmental Sciences


Calibration Important for Effective Soybean Rust Control

March 11, 2005

COLUMBUS, Ohio — Effectively managing soybean rust depends largely on proper chemical applications. And to ensure such success, sprayer calibration is a must.

Erdal Ozkan, an Ohio State University Extension agricultural engineer, said that calibration is the best way to find out if the sprayer is set up to deliver the desired application rate.

"There are no soybean varieties currently available that have high levels of resistance to soybean rust. This leaves us with only one option: be prepared to do as good a job as possible spraying fungicides registered to control this disease," said Ozkan, a professor with the Department of Food, Agricultural, and Biological Engineering. "March and April are the best times to thoroughly check the sprayer and calibrate it properly."

Ozkan said that the results of sprayer calibration clinics in Ohio show that only a third of applicators are accurately applying chemicals based on the U.S. Department of Agriculture and Environmental Protection Agency rate recommendation — which is within 5 percent of the intended rate for any given chemical.

"Of the two-thirds who are missing the mark, about half are under spraying and the other half are over spraying," said Ozkan. "Other states show similar accuracy levels."

Sprayer calibration takes anywhere from 30 minutes to 60 minutes and requires only three tools: a watch, a measuring tape and a jar graduated in ounces. Ozkan recommends the following calibration method:

• Fill a clean spray tank at least half-full with water.

• Measure the distance between nozzles in inches and then drive a designated distance depending on the nozzle spacing: for a nozzle spacing of 20 inches, drive 204 feet at normal spraying speed; drive 136 feet for 30-inch spacing; 113 feet for 36-inch spacing; and 102 feet for 40-inch spacing.

• Run the parked sprayer at the same pressure level, and collect the output of each nozzle for the same amount of time it took to drive the designated distance.

• Calculate the average nozzle output by dividing the total output from all nozzles by the number of nozzles tested. The average nozzle output in ounces equals the gallons per acre applied. For example, if you catch 15 ounces, the application rate is 15 gallons per acre.

• Then minimize the application error. If the difference between the intended application rate and the actual rate is greater than or less than 5 percent, adjustments are required. For example, if the intended application rate is 20 gallons per acre, the calibrated rate should be between 19 and 21. For small changes in the application rate try adjusting the pressure. For larger changes either adjust the travel speed or replace nozzles with the appropriate size.

This calibration method is explained in detail in Ohio State University Extension Fact Sheet AEX-520, "Boom Sprayer Calibration," available at any Ohio county Extension office, or by logging on to

"Sprayers should be calibrated several times a year. Changes in operating conditions and the type of chemical used may require a new calibration," said Ozkan. "And when it comes to soybean rust, calibrate early. The window of opportunity to spray for soybean rust is much narrower than for most pests. Growers will not want to take the time to calibrate after rust has arrived."

Ozkan also emphasized the importance of choosing the right nozzle and setting up the sprayer so that a uniform application is achieved across the sprayed area. "Just spraying the right amount of fungicide on each acre is not enough to achieve effective control of soybean rust," he said. "Uniform deposition and thorough coverage of the soybean plant from top to bottom is as important as the total amount deposited."

Candace Pollock
Erdal Ozkan