Corn+Soybean Digest

Rust Risk Remains

Even though the Corn Belt escaped feared soybean rust problems in 2005, in the coming year growers face at least as much risk as they did a year ago, says Dean Malvick, plant pathologist at the University of Minnesota. The level of risk, however, is uncertain, and based on many factors and questions that are still being researched.

“Soybean rust spores were detected in both Minnesota and South Dakota in July 2005,” even though growers didn't report disease problems this past summer, he says.

The spores were detected in rainwater that was collected in a special rainwater collection system.

Malvick says it's important to note that it's not known if the spores were living or dead. The test just detected DNA from the pathogen spores and cannot distinguish living from dead spores.

The origin of these spores remains a mystery, but Malvick says “one possible source is Mexico's Yucatan. Most of the focus has been on the southeast U.S., but the disease may also overwinter in other areas.”

It's possible for soybean rust spores to move from Mexico's Yucatan Peninsula across the Gulf of Mexico to Texas and then up to Minnesota and the Dakotas, Malvick explains. That said, soybean rust has not yet been confirmed in either Mexico or Central America.

The scientist adds that possible precedents for soybean rust moving north via these routes are cereal rusts, which move from Mexico and Texas all the way to North Dakota.

Given the right environmental conditions of optimal temperatures 66-84° and wetness for six hours — rain or dew — “long distance transport and spread of soybean rust is very possible,” Malvick says.

Because soybean rust needs the right environment to develop in soybean fields and move north, “there is no way yet to predict when soybean rust will do significant damage” in the Corn Belt, the scientist says.

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