CORN Newsletter: 2005-05, March 8, 2005

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C.O.R.N Newsletter 2005-05
March 8, 2005 - March 22, 2005

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The Fight Against Soybean Rust Starts with Calibrating Your Sprayer
by Erdal Ozkan


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The months of March and April are the best time to thoroughly check the sprayer and calibrate it properly. To do this now is more important than ever before because of the arrival of Asian Soybean Rust to the U.S. This disease has been detected in 9 southern states, as far north as Missouri. It may arrive in Ohio this year. 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.

Fungicides manufactured to control Soybean Rust work. However, success will largely depend on proper application. Proper application starts with selecting the right equipment, specifically nozzles, and spraying the right amount of fungicide uniformly across the field before the disease is detected.

Pesticide manufacturers have invested heavily to determine the most effective and economical application rate for the fungicides labeled for Soybean Rust. However, it is up to the applicator to make sure the recommended amount is applied.

Why calibrate?
Calibration is the best way to find out if the sprayer is ready to deliver the desired rate. And do it early. The window of opportunity to spray for soybean rust is much narrower than for most pests. You will not want to take time to calibrate after the rust has arrived.

Results of many "Sprayer Calibration Clinics" in Ohio show that only a third of applicators are applying chemicals at a rate within 5 percent (plus or minus) of the intended rate, which is the accuracy level recommended by USDA and EPA. Of the two-thirds who are missing the mark, about half are under spraying and the other half are over spraying. In one extreme case, the applicator would have been over spraying by 75% had he used the nozzles he just purchased and installed on the boom. Other states show similar accuracy levels.

Calibration takes about 30 to 60 minutes and requires only three "tools": a watch, a measuring tape, and a jar graduated in ounces. Several calibration methods are available but the one described below is simple, straightforward, and does not require the memorization of equations.

Calibration method
When the spray tank is clean, fill it at least half full with water since the amount of water in the tank may affect travel speed. 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. Then run the parked sprayer at the same pressure level for the same amount of time it took you to drive the designated distance, and collect the output of each nozzle. 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 rate is 15 gallons per acre.

The next step is to minimize the application error. If the difference between your intended application rate and the actual rate is greater than ± 5 percent of your intended rate you should make some adjustments. For example, if your intended application rate is 20 gpa, 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. You need to repeat the calibration process until your application error is no greater than ± 5 percent.

This calibration method is explained in detail in Ohio State University Extension (OSUE) Fact Sheet AEX-520, available from your County Extension Office, or from the Ohioline web site: http://ohioline.osu.edu/aex-fact/0520.html.

Just spraying the right amount of fungicide on each acre is not enough to achieve effective control of soybean rust. Uniform deposition on the spray target is as important as the total amount deposited. Each nozzle type produces a unique spray pattern. Some nozzles require precise overlapping of patterns from adjacent nozzles. Check the nozzle catalog to find out the appropriate boom height for your nozzle spacing that will produce uniform spraying across the boom.

Calibrate frequently
Sprayers should be calibrated several times a year. Changes in operating conditions and the type of chemical used may require a new calibration. A Nebraska survey showed that the more often a sprayer was calibrated, the more accurate the application rate. If you hear on the news this summer that Soybean Rust has reached States south and southwest of Ohio, be prepared to spray for soybean rust. Do this after recalibrating your sprayer.

Readers can subscribe electronically to this newsletter by signing up at http://agcrops.osu.edu/services/email.html. E-mail labarge.1@osu.edu if you have problems subscribing or no longer wish to receive this newsletter.

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868


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