Argentina Gives More Accurate Model for U.S. Soybean Rust Movement

Southern soybean growing areas could benefit from switching to shorter season varieties to save on fungicide costs. Jacqui Fatka 

Published on: Jun 12, 2006

Thankfully for U.S. soybean growers, the spread of Asian soybean rust has essentially remained contained to Southern states. And after the settle of the hype of Brazil's rapid spread of the devastating disease, researchers are beginning to understand more how rust travels in the United States.

Rust spores spread north of the equator from Brazil and sent producers into panic mode. Anxiety increased when producers heard that in Brazil rust spores could travel as fast as 300 miles per day.

Unlike Brazil's tropical, humid conditions, Argentina is approximately at the same latitude as the southern United States and offers a more realistic look at rust characteristics in the United States. It just completed its growing season and saw adequate containment of the disease, although it did spread predominantly in 15 days total.

Guillermo Bernado, a technology area specialist for Argentina's extension service, explains that soybean rust travels much differently in Argentina than in Brazil. "The disease goes very slower here and we have to have so many days of rain," he says. Then Argentina gets infection and the infection spreads slow, Bernado adds.

However, Argentina has fewer soybean pests compared to southern U.S. producers. Mississippi State University soybean Extension specialist Alan Blaine, saw many growers get consumed with rust and overlook other diseases. The best rust defense approach is fungicides between the R3 to R5 window, Blaine explains.

"Year in and year out fungicides in the south will pay," Blaine says.

In the Midwest it's another story, explains Dave Ruen, product technology specialist for Dow AgroSciences. USDA's rust tracking Web site ( identifies confirmed findings in southern states and pairs it with weather patterns and extension specialists recommendations. Similar to Argentina, there is humidity but also long period of dry spells, Ruen says. "We have a lot more time on our hands so we don't have to make hasty decisions."

Shorter season varieties offer another tool against spread

Bernado and Blaine say several effective fungicides provide the needed arsenal for soybean producers. In the United States another tool may be shorter season varieties of beans, explains Ruen. Shorter season beans greatly decrease the potential for rust occurring during the critical stages in relation to the amount of time you need to have suitable rainfall for probably infection conditions.

"Southern and central Midwest producers may consider reshaping planting and management plans to move towards more acreage with shorter varieties," Ruen says. This could mitigate the potential of spreading and in turn spending less on fungicides.