Triazoles Great Fit for First Application Against Asian Soybean Rust

Indianapolis, IN - March 01, 2005

Producers are sorting through volumes of information about Asian soybean rust as they consider management decisions for what soybean rust fungicide to apply - and when, if needed.

While the amount of information available is substantial, the list of fungicide classes comes as a simple trio: triazoles, strobilurins and nitriles. The strobilurins and nitriles provide preventive control only, while the triazoles offer both preventive and curative activity.

"Products should be applied with activity in mind," says Bob Gordon, fungicide marketing specialist for Dow AgroSciences. "Unless growers are at a point where they need a fungicide with curative activity, the list of fungicides available for preventive applications are broad."

Gordon, who has 30 years of experience working with fungicides, says a preventive product should be applied before a soybean rust infection occurs. Meanwhile, a product with curative activity should be applied when infection is suspected - even if there are no disease symptoms present.

"You may not see disease symptoms for up to seven to 10 days," Gordon said. "If a field is even suspected of being infected by soybean rust, applying a fungicide that contains curative activity will be beneficial. At any rate, there should be few or no disease symptoms present when you make your first application."

Gordon says triazole fungicides are ideal for first applications because they contain both preventive and curative activity, and offer protection whether or not soybeans are infected. For example, Laredo^® fungicide, which contains the active ingredient myclobutanil, is highly systemic, meaning that the fungicide moves throughout the leaf tissue and plant to give protection. Triazoles also offer protection to new growth.

To protect yield potential, triazoles should be applied before 5 percent disease incidence occurs in the lower canopy. With applications made beyond that point, growers can expect some yield loss.

Strobilurins and nitriles are labeled for preventive applications only. These fungicides work by coating the surface of the plant, which protects by blocking the rust fungus from entering the plant. Without thorough coverage, however, a plant's defenses can be compromised.

In a rust management program, Gordon recommends a triazole for the first application, followed by a strobilurin or nitrile as a resistance management tool. The interval between sprays is determined by the extent of existing inoculum and the level to which conditions favor disease development. Triazoles provide up to 21 days of residual activity.

"It's important for soybean producers to know that they have many fungicides to choose from for preventive applications," Gordon adds. "Some people have stated incorrectly that triazoles have curative activity only. That's wrong and has caused confusion.

The triazoles have preventive activity that's every bit as good as the strobilurin fungicides. It's when you get to the point that curative activity is necessary that your fungicide choices narrow to the triazole class."

For more information about management of Asian soybean rust, visit www.DefeatSoybeanRust.com.

Always read and follow label directions.

For Editorial Information:

Amanda Powell
Bader Rutter & Associates
(770) 356-1480
apowell@bader-rutter.com