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USDA Agricultural Research Service and
Associate Professor, Dept. of Crop Sciences
(217) 244-3258; firstname.lastname@example.org
USDA Agricultural Research Service
(217) 244-3257; email@example.com
Fungicides for Control of Soybean Rust - Are You Prepared?
Soybean rust has continued to spread in South America and is found through out the major soybean production areas of Brazil, Bolivia, Paraguay and northern Argentina. Fungicides will be the primary tools used to control soybean rust when it arrives onto the continental US. There are two fungicide compounds that are registered for use on soybean and labeled for soybean rust. These are chlorothalonil, sold as Bravo®, and Echo® and azoxystrobin sold as Quadris®. Additionally, there are seven compounds or mixtures of compounds that have been submitted to the EPA under a Section 18 Emergency Exemption request to help combat the disease. Included in this list are several triazoles and two additional strobalurins. All fungicides are not the same; they differ in site and mode of action, level of translocation as well as residual effect. Some fungicides are curative others are effective only when used preventatively. When used correctly fungicides have been effective in controlling soybean rust. However, in the past two years there have been significant yield losses in Brazil, even when fungicides were used. These losses can all be attributed to applying the wrong fungicides or applying the products too late for effective disease control.
The most current recommendations for fungicide use are from Southern Africa and South America. To control soybean rust fungicides need to be applied early in the epidemic, soon after flowering. Preventative fungicides need to be applied before the disease is present, the strobalurins should be used preventatively, once the disease severity reaches 3 to 5 % their effectiveness decreases. The curative compounds (triazoles) can be used after the rust is present. However, once the disease reaches as little as 10% severity the fungicides may not provide full yield protection. The most successful recommendations for control of soybean rust are to apply the first fungicide at of soon after flowering; a second application should be made 14 to 20 days later. A third application may be needed only in a severe epidemic. Fungicides will need to be used in rotation; strobalurins should be used only once each season, no more than one of two applications in mixes.
To be prepared for soybean rust producers will need to be familiar with the fungicides that will be available, when they are effective, how to apply them and the economics of their use.