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Corn+Soybean Digest

Asian Soybean Rust Discovered

At press time, the impact of discovering Asian soybean rust in Louisiana and Mississippi continues to unfold. Here's an update on the situation so far. We'll bring you continual alerts in upcoming issues.


Asian soybean rust has now been found in Louisiana, Mississippi and Florida. It was originally discovered on two plots associated with a Louisiana State University (LSU) research farm near Baton Rouge.

Asian soybean rust is a fungal disease that interferes with photosynthesis. The plant can't grow, so yields can be severely restricted. The disease has been known to destroy entire fields of soybeans.

Ken Whitam, a plant pathologist with the LSU AgCenter, says studies have shown soybean rust could cost U.S. soybean producers anywhere from $240 million to $2 billion a year in crop losses and the added expense of fungicides.

There are two fungal species responsible for soybean rust. One type is Phakopsora pachyrhizi, commonly referred to as the Asian species. The other form, Phakopsora meibomiae, is known as the New World species. Asian soybean rust (ASR), the source of Louisiana's outbreak, is the most aggressive species.

Experts say the location of the samples is consistent with recent hurricane patterns — especially Ivan.


“While soybean rust is new to the U.S., it's not new throughout the world,” says United Soybean Board Chairman Criss Davis, a soybean farmer from Shullsburg, WI. “Like farmers in other rust-infected countries, U.S. soybean farmers will adjust and take the necessary steps to manage the disease.”

David Wright, director of production technologies for the Iowa Soybean Association says, “Producers should not panic. We have the tools available to manage this disease.”

Those tools include early disease detection and aggressive fungicide control programs, which producers should become familiar with this winter. Rust-resistant soybean varieties are not yet available.

As rust becomes more widespread here, however, producers will need to take immediate action against the fast-moving disease. “You have hours rather than days to apply fungicides,” in the words of one crop consultant.

“We should be ready to react quickly, but we need to be careful not to overreact,” says Greg Tylka, Iowa State University plant pathologist. “If we identify soybean rust in Iowa, there still may be times during next year's growing season when it wouldn't make economic sense to spray.”


South Dakota State University plant pathologist Marty Draper says soybean rust can't survive freezing temperatures, but says if the spores spread to host plants like kudzu that stay green through the winter, the fungus could likely overwinter in parts of Florida or Texas.

Fungicides can limit yield loss if the disease is discovered in its early stages. So far, two active compounds are registered for soybean rust in the U.S. — azoxystrobin (Quadris) and chlorothalonil (Bravo WeatherStik and Echo 720) — found in products made by Syngenta and Sipcam Agro.

Three additional active ingredients for control against rust have received labeling approval under Section 18 permits from the EPA. They include myclobutanil (marketed as Laredo EC and Laredo EW), tebuconazole (Folicur), and propiconazole (Tilt, Bumper and PropiMax EC), and others are being considered. However, Draper says each state will have to approve the use of these fungicides.

He estimates fungicide treatments will cost $10-20/acre in the U.S., but adds, “costs will vary by location.” And if rust infects the soybeans at the early reproductive stage, two or three applications could be necessary, causing those costs to climb.

Rust Resources

Also check out pages 16-17 in the “Pocket Scout for Soybeans” guide inserted in our November issue.

And see “Vigilance A Must For Rust,” pages 22-23, in the August 2004 issue of The Corn And Soybean Digest.

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