2006 Update on
Spraying Technology for Asian Rust

While the threat of Asian rust still looms as an unknown in our minds after more than two years of limited experience in the U.S. in both 2005 and 2006 growing seasons, the technology for spraying the needed fungicides is a known quantity. Fungicide applications are not new, but just rare in most of Missouri. If Asian rust hits hard, we just need to be ready to spray for it using ordinary technology but with an eye for detail and precision. In fact this whole discussion can be reduced to just a few simple tips with a focus on fungicide application.

Identify the target
The target for a fungicide application to combat Asian Rust is the whole plant. We usually consider the target to be the top of the canopy when we spray herbicides, and specifically, the targets are the leaves of the weed plants. A fungicide application to combat Asian Rust should cover the entire crop plant to achieve maximum efficacy.

Select and stock the correct nozzle
To achieve good coverage, fungicides should be applied with a somewhat smaller droplet than we use for herbicides and those droplets must reach down inside the canopy to cover not only the leaves but also the lower stem where Asian Rust is most likely to first thrive. That means choosing a nozzle from a spray catalog that is rated excellent for fungicide applications and then adjusting the boom so that we get good canopy penetration.

A single turbo flat fan nozzle with the correct droplet spectra for fungicides appears to be as good as any of the new nozzles available for spraying fungicides deep into the canopy. A tip or combination of nozzles that provides dual spray fore and aft may better penetrate the canopy for more complete coverage. This configuration is available as a single unit or with the use of a Y adapter that supports two nozzles. However, the latest research provides little if any evidence that specially designed dual spray tips provide any significant advantage.

Use good calibration techniques
All sprayers need to be calibrated. All of the automatic controls in the world do not ensure that the sprayer is really calibrated. Efficacy depends on getting the right amount of spray in the right place at the right time. See MU publication G 1270 Calibrating Field Sprayers for details.

Lower the boom on Asian rust
Consider selecting a somewhat slower ground speed that you can live with because we want to get the boom somewhat closer to the top of the canopy for good penetration and also because we cannot do a good job with either bouncing or swinging booms. Consistency of the relationship of the tip to the canopy is a very significant factor.

Select a sufficient spray volume
Fungicide application techniques to combat Asian Rust can certainly be as simple as a few new tips and a couple of basic adjustments for as little as five to ten dollars per foot. Improve efficacy by mixing spray solutions with the maximum recommended carrier rates, which are reasonably about 20 gallons per acre. Although air-assist sprayers deserve recognition for excellent deposition of fungicides deep into the canopy, the additional cost of an air-assisted sprayer may run 30 to 50 times the cost of a few good tips.

Become a part of the discussion
Call or email for assistance in nozzle selection and for making adjustments specific to your sprayer and your particular situation. Then, look for more information and updates as they become available throughout the season right here at your Ag Ebb website, where our mission is to improve the lives and livelihoods of Missouri's agricultural producers.

Email your spraying questions to Cropping Systems Engineer Bill Casady or reach Dr. Casady by phone at 573 882-4370.

William W. Casady, Ph.D., PE,
Ext. Associate Professor and Professional Engineer
Commercial Agric Program Cropping Systems Engineer
University of Missouri Extension
casadyw@missouri.edu
www.fse.missouri.edu/home/casadyw/
PH(573)882-4370
FAX (573)884-5650