New Season, Many Questions

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Asian Soybean Rust

As soybean planting begins, retailers and growers are wondering what Asian soybean rust will do this season. Will 2007 be the first year the U.S. experiences a major outbreak, or will it be another relatively mild year?

While no one can be sure what will happen this year, certainly the 2006 season provided new experiences and information for researchers, growers, and retailers.

Good Learning Experience

Asian soybean rust didn’t move out of the Southeast until late in the season, due in part to low inoculum and dry weather conditions, according to Scott Isard, Penn State University aerobiologist who studies the movement of organisms in the atmosphere. “It didn’t get a foothold until late in September and then only in Louisiana,” he says.

From there, soybean rust made a late run into the Ohio River Valley and up the East Coast. Too late to affect soybean yields, it did provide Extension personnel in those areas with a first-hand look and data for future movement models. 

Coming into the 2007 season, Asian soybean rust had been reported in Florida, Georgia, and Alabama early this winter, but then cold temperatures killed back kudzu deep into Florida, according to USDA’s Pest Information Platform for Extension and Education (PIPE) Web site (visit www.rustready.com or www.sbrusa.net).

As of March 15, the site noted that there have been no reports of soybean rust surviving the winter in Louisiana, Mississippi, or South Carolina.

That’s critical news. X.B. Yang, Iowa State University Extension plant pathologist, has been preach­ing the impact of soybean rust if it becomes established in Texas, Louisiana, and Mississippi. Accord­ing to Iowa State’s Web site, “if it overwinters in the Mississippi Delta or moves to this region from Florida or Georgia early in the year, rust could become a much bigger threat to Midwestern soybean growers.

“The movement of rust during October 2006 gives us a good example of how quickly rust can move into the Midwest if inoculum builds up in the wrong places,” the site adds.

Early-Season Hallmarks

Last month, CropLife® reported that the first soybean rust in a commercial non-Roundup Ready soybean field was confirmed in Texas on Feb. 16. Tom Isakeit, Texas A&M University Extension plant pathologist, says the rust-infected soybeans were destroyed on or around March 1 “when the field was cultivated and planted to corn. The grower also applied Roundup to the field.

Then on March 12, soybean rust was confirmed for the first time on plant tissue from Iowa. Iowa State says the soybean leaf was recovered from a bin of soybeans produced in the state during the 2006 season. That particular field in Mahaska County in southeast Iowa suffered low yields.

“The fungus and the spores that cause the disease cannot survive without green leaf tissue and will die during Iowa winters,” Iowa State’s news release notes. “The recently discovered rust fungus does not pose a risk of infection for the 2007 growing season in Iowa.”

“This discovery reminds us that it is possible for Iowa fields to become infected with this disease,” says David Wright, director of contract research at the Iowa Soybean Association. “Nonetheless, growers should not overreact to this development. Instead, growers must be ready to act appropriately and economically in 2007 should this disease again show up in Iowa and be a threat to soybean yields.”

Iowa officials are checking other farms to see if any additional rust activity may have existed last fall.

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