Asian Soybean Rust - Frequently Asked Questions VI: Sprayer and Nozzle Technology

Author: Robert Grisso, Extension Engineer, Department of Biological Systems Engineering, Virginia Tech; David Holshouser, Extension Soybean Specialist, Tidewater Agricultural Research and Extension Center; Elizabeth Bush, Special Research Associate, Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech; Pat Phipps, Extension Plant Pathologist, Tidewater Agricultural Research and Extension Center; and Erik Stromberg, Extension Plant Pathologist, Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech

Publication Number: 450-306, posted March 2006

Do I need a new sprayer?

Which types of nozzles are recommended for canopy penetration and/or effective application?

It must be emphasized that many nozzles used for herbicide applications are not appropriate for rust control. For more details on nozzle selection, see the Virginia Soybean Update, Volume 8, No. 2, March 2005, http://www.vaes.vt.edu/tidewater/soybean/soybeanup/ 0503/0503.html, or the Asian Soybean Rust website at Virginia Tech.

Which is more important: spray volume, pressure, or droplet size?

Next in order of importance is the droplet size. A medium droplet size (200 to 300 microns) is required to penetrate the canopy and adequately cover the leaf surfaces. Fine to very fine droplets, like those produced from hollow cone nozzles, will not penetrate the canopy and are prone to drift. Large droplets will not give adequate coverage, may bounce off leaves, and because the total number of droplets is less, are more likely to miss the target and land on the ground.

The advantage of high pressure is mainly due to the smaller droplets that high pressure produces. If lowdrift, coarse-droplet nozzles (e.g. herbicide nozzles) are used; higher pressure might reduce droplet size into the medium size range. However, this is not guaranteed; please consult the nozzle manufacturer for droplet spectrum data. On the other hand, higher pressure could change medium-size droplets into fine or very fine droplets, resulting in less penetration of the canopy, more drift, and less control.

Obtaining 15 to 20 GPA of volume and medium sized droplets is a challenge. Certain combinations of sprayer speed, nozzle spacing, and/or nozzle flow rate will not allow 15 to 20 GPA. The easiest way to obtain this combination is to either reduce the sprayer speed or use double or twin nozzles. An Excel spreadsheet that can help determine the right combination of nozzles and speeds to give 15 to 20 gallons per acre and medium spray droplets can be found at the Asian Soybean Rust website, www.ppws.vt.edu/ipm/soybeanrust/index.htm, under Fungicide Equipment, Nozzle Selector Guide.

What are some general application recommendations to consider?

• Keep spray volume above 15 GPA for best results. With the soybean canopies taller than 24 inches 20 GPA is recommended.
• Choose the appropriate size and type of nozzles and operate them at a pressure that will allow them to produce medium-size droplets (200 to 300 microns).
• Nozzles that produce a flat-fan pattern seem to provide better coverage than nozzles that produce a cone pattern when there is a full canopy.
• Choose “low-drift” nozzles, which allow a grower to increase the pressure without increasing the number of small, drift-prone droplets (those at 100 microns or smaller). Operate these nozzles at slightly higher pressures (60 to 70 PSI) than usual. Higher spray pressures usually help the droplets penetrate the canopy better.
• Use directed spraying, if applicable, to improve coverage.
• Use twin-nozzle/pattern technology. Research has shown that two spray patterns, one angled forward and one angled backward, perform better than single nozzles spraying in one direction.
• If economically feasible, use air-assisted spraying. Research has shown that air-assisted spraying, which uses air to help droplets (100 microns or smaller) reach the interior of the plant canopy and the underside of leaves, consistently provides the best coverage and droplet penetration, especially when beans are at, or near, their full-growth stage. One should match air flow to canopy density when using air-assisted sprayers.

How should the boom be oriented to the crop canopy?

Is aerial application effective for ASR?

Will row spacing affect spray penetration?

Will the addition of spray additives (i.e., surfactants, crop oil concentrates, drift retardants, etc.) affect spray coverage and penetration?

Spray additives may affect penetration via changing the spray droplet size. However, because of specific properties of individual fungicides and individual additives, the effect on droplet size cannot be generalized. The crop protection industry and universities are conducting research to clarify these chemical interactions. Consult individual product labels for compatibility issues and other factors that might alter fungicide efficacy.

Why calibrate applicators?

Timely spraying is also a key to reducing potential ASR damage. Do maintenance checks on spray equipment so it will be ready when needed. 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. Be prepared to spray for ASR before it arrives and have your sprayer calibrated. Use the “Ounce” calibration methods as described in Fine Tuning a Sprayer with “Ounce” Calibration Method, Virginia Cooperative Extension publication 442-453, http://www.ext.vt.edu/ pubs/bse/442-453/442-453.html.

Other ASR Resources

USDA Soybean Rust Tracking site - http://www.sbrusa.net/

North American Plant Disease Forecast Center- http://www.ces.ncsu.edu/depts/pp/soybeanrust/

The Southern Plant Diagnostic Network - http://spdn.ifas.ufl.edu/soybean_rust.htm

Related Publications

Asian Soybean Rust - Frequently Asked Questions II: Identification, Biology, and Ecology, Virginia Cooperative Extension publication 450-302

Asian Soybean Rust - Frequently Asked Questions III: Control with Fungicides, Virginia Cooperative Extension publication 450-303

Asian Soybean Rust - Frequently Asked Questions IV: Cropping Systems and Cultural Practices, Virginia Cooperative Extension publication 450-304

Asian Soybean Rust - Frequently Asked Questions V: Monitoring, Tracking, and Scouting, Virginia Cooperative Extension publication 450-305

Acknowledgments

View this document in PDF format

Visit Virginia Cooperative Extension.