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ASR found in Iowa residue

Asian soybean rust spores were found in mid-March on soybeans grown in Iowa. While a first for Iowa, the ASR discovery had no market consequences and generated little alarm.

Like other ASR finds, the Iowa incident was an accident. “It was an absolute fluke, actually,” says David Wright, Iowa Soybean Association director of contract research. “A gentleman was removing soybeans from a grain bin in southeast Iowa and noticed some plant residue that didn’t look quite right. He gathered it and sent it in to the diagnostic lab at Iowa State University (ISU). Shortly thereafter, it was diagnosed as ASR.”

Following protocol, the ISU lab then sent samples to the USDA laboratory in Beltsville, Md., for final confirmation. Further tests there — including molecular analysis — proved positive for the disease.

ASR, which can devastate soybean yields through premature defoliation, has been a problem in soybean-growing areas of South America for years. It first showed up in the United States in the fall of 2004 when it was found outside Baton Rouge, La.

The disease is combated with the use of fungicides and a large monitoring effort. While it has steadily spread through the South, ASR has yet to hammer U.S. yields.

“The big news in this is that ASR made it to Iowa,” says Wright. “Beyond that, really, this discovery isn’t that big of a deal. It certainly has no bearing on what will happen in the coming months. By itself, this is no concern for the 2007 crop.

“I’m quite surprised at the amount of attention this particular ASR find is getting. We’ve always believed ASR could reach Iowa and this proves that and lets us know it could show up again. It likely will.”

To survive, ASR must be on green tissue. “That’s an absolute. That means any spores on the crop residue, intermingled with the seed, are undoubtedly dead. Previous research shows that the viability of such spores decreases rapidly. Eight weeks following the tissue’s death, there will be no spores left alive.”

The infected Iowa soybeans were harvested last Oct. 10. “Here we are in March, so those spores are dead.”

“In the past, we’ve had 20 sentinel plots. That’s the same number as in many other states. We’ll have the sentinel plots again this year. We’ll also proceed with the same education and message to producers that we’ve been giving right along. That is: you should be vigilant in scouting fields and keep your ears open to Extension reports. When the risk for ASR increases (the Iowa ASR monitoring team) will immediately tell producers.”

The find is “very interesting and should be a wake-up call for soybean producers (outside the South),” says Wright. “Some producers have become a bit complacent here in the Midwest believing ASR hasn’t shown up in two years and so it won’t ever. This shows that isn’t the case.”


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