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Corn+Soybean Digest

Wet-Weather Soybean Diseases Raise Concerns About Soybean Rust

Experts are advising producers not to confuse Asian soybean rust with common wet-weather soybean diseases. Soybean rust is not expected in the United States this year and has not been found north of the equator in South America.

Earlier this month the Iowa Soybean Rust Team invited crop professionals to a workshop to learn about soybean rust.

"It is important to emphasize that Asian soybean rust has not been found in the United States," says Alison Robertson, Iowa State assistant professor of plant pathology.

Two diseases often confused with soybean rust are brown spot and bacterial blight. The early stages of these diseases produce symptoms similar to soybean rust. Brown spot, which is a fungus, is spread from the soil to soybean plants by splashing rain and causes dark brown spots on both upper and lower leaf surfaces.

Bacterial blight causes small, angular, water-soaked, yellow-to-brown spots on leaves. The lesions enlarge in rainy weather and merge to produce large dead areas. The diseases don't cause significant yield losses in Iowa and are more frequent in areas that have had heavy rainfall.

"If brown spot is found, it is likely that bacterial blight also will be found because both are common in cool, rainy seasons," says X.B. Yang, Iowa State professor of plant pathology. "Diseases such as brown spot and bacterial blight can be mistaken for soybean rust."

Greg Tylka, Iowa State plant pathology professor says it's important to provide up-to-date information about soybean rust, which is the goal of the Iowa Soybean Rust Team formed last fall. The team includes representatives from Iowa State University, ISU Extension, Iowa Department of Agriculture and Land Stewardship, the Iowa Soybean Promotion Board/Iowa Soybean Association and the U.S. Department of Agriculture Animal and Plant Health Inspection Service.

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