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Corn+Soybean Digest

Non-rust foliar diseases not best use of fungicide

In the interim leading up to soybean rust's potential arrival in Ohio and Indiana, growers may be compelled to use fungicides labeled for rust to control other soybean foliar diseases.

The investment may not be economically feasible, however, says Anne Dorrance, an Ohio State University plant pathologist.

"Some of the questions we've gotten from growers are, 'Can fungicides labeled for soybean rust be used to manage other foliar diseases?' and 'Is managing these other diseases warranted in Ohio with such fungicides?'" Dorrance says. "The answer is yes and no."

Fungicides identified for use by the United States Environmental Protection Agency in managing soybean rust have been labeled either Section 3 or Section 18.

Section 3 labeling is a full label, meaning that the fungicides can be used to control other soybean foliar diseases, such as Cercospora blight and brown spot. Section 3 fungicides include Headline and Quadris. Known as strobilurin compounds, both are identified as a preventive treatment against soybean rust.

"Both products are used in southern states to manage a number of foliar diseases," Dorrance says. "In Tennessee, for example, data shows good response in using the fungicides for control. However, when we look at the data from the northern states, we don't see a consistent response. The reason is that most of these diseases are not at yield limiting levels in these areas."

In other words, research results from the 2004 season gave no indication that Section 3 fungicides used to control other soybean foliar diseases will provide an economic return for Ohio and Indiana producers.

The remaining fungicides designed to control soybean rust are labeled Section 18 compounds. Section 18 labels are emergency use exemptions, as so identified by the EPA.

"Because of the exemption, these products can and should only be used for soybean rust as part of a grower's management plan," Dorrance says.

"Since there is no soybean rust predicted in Ohio as of now, they should just be left in their containers."

The fungicides labeled Section 18 are all triazoles -- curatives -- or a combination of triazole and strobilurin compounds. So far, eight Section 18 fungicides have been identified for use in Ohio. They are: Bumper, Domark, Folicur, Laredo EC, Propimax EC, Quilt, Stratego and Tilt. Those eight, plus Laredo EW and Orius, have been given Section 18 labels for emergency use in Indiana.

"The issue here is there is no efficacy data of these Section 18 compounds for other foliar diseases," Dorrance says. "We also don't want to jeopardize our emergency use labels with the EPA. And we want to make sure that if rust hits, we have enough material to use for that purpose."

Soybean foliar diseases, such as Cercospora blight, frogeye leaf spot and brown spot are common in the Midwest. Their disease symptoms are similar to soybean rust, and can be easily misdiagnosed without a trained eye. Section 3 and Section 18 fungicides are not effective against bacterial diseases, such as bacterial blight and bacterial pustule.

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