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Loren E. Bode Loren E. Bode
Department of Agricultural
and Biological Engineering
(217) 333-8355
Scott Bretthauer Scott Bretthauer
Extension Specialist -
Application Technology
Department of Agricultural
and Biological Engineering
(217) 333-9418

How to Apply Soybean Rust Fungicides

Are you ready to effectively apply fungicides to control soybean rust if it infects your soybeans this year or next? Most Illinois farmers are very competent in applying herbicides and fertilizers but have only limited experience with the type of application needed for controlling small rust spores deep within a closed soybean canopy. The requirements for treating rust near the bottom of a soybean plant are much different than applying foliar herbicides or even insecticides. There are several myths that must be overcome in order to obtain satisfactory control. You need to study more about droplet sizes, nozzles, and gallonages required to obtain adequate coverage. Following are some practical recommendations for setting up your system to apply soybean rust protective or curative fungicides.

Myth: You need to apply very small droplets at very high pressures in order to "drive" the spray into the soybean canopy.
Truth: Fine droplets do not have sufficient mass to be driven into dense canopies and they do not deposit efficiently on soybean leaves.
Recommendation: Medium size drops (200 to 350 microns) are the most effective for rust control. There are many combinations of nozzle types, sizes, pressures and flow rates that create medium size droplets. You will need to have a copy of your nozzle manufacturers catalog available to make the proper selection. For ground applications we recommend an application rate of 15 GPA or higher (5 GPA for aerial). Using the travel speed of your sprayer and the selected GPA, you can select the proper nozzle size and pressure that produces droplets in the medium size spectrum.

Myth: Cone type nozzles are necessary to obtain coverage when applying fungicides.
Truth: Hollow cone nozzles create a large number of very small droplets that will not penetrate a dense soybean canopy. There are several types of nozzle tips that can be used for soybean rust. Many are more effective than traditional cone nozzles.
Recommendation: Extended-range flat-fan nozzles create a proper droplet spectrum as long as you do not exceed the upper pressure limit, which generates many fine droplets. Turbo flat-fan nozzles have a wide range of operating pressures for creating the desired droplet spectrum for controlling rust. While air induction nozzles are often considered only as drift control nozzles, there are several designs that produce medium droplet spectrums. They are designed to operate at higher pressures than other flat-fan designs and should be operated according to the manufacturer's recommendations. Twin spray nozzles allow for spraying at two angles, one directed forward and the other backward, and are a good choice for rust control. Using wide fan angles, such as 110 degrees, is recommended over narrower fan angles.

Myth: Air-assisted sprayers are not effective for controlling soybean rust.
Truth: Even with well equipped boom sprayers it is difficult to obtain good coverage near the bottom of a dense soybean canopy. If rust becomes a major limiting factor in producing soybeans in Illinois, farmers may need to invest in air-assisted sprayers. These systems utilize "air energy" to carry the spray particles into the bottom of the soybean plant. They are more expensive than traditional boom sprayers but may provide the answer to controlling this disease.
Recommendation: We are currently evaluating the effectiveness of air-assisted spray booms. They have proven effective in small grain production in Europe and preliminary results from Brazil indicate increased control of rust when using air energy to carry the chemical into the lower section of the canopy. We will continue to evaluate improved techniques for controlling Asian Soybean Rust.

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Department of Crop Sciences
College of Agriculture, Consumer and Environmental Sciences
University of Illinois Extension
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