WEST LAFAYETTE, Ind. - Late soybean planting and active soybean rust in the southern U.S. has Indiana growers wondering if the disease could travel far enough north to affect the state's yields this year.
Soybean rust is a foliar disease caused by the fungus Phakospora pachyrhizi. The fungus forms tan lesions on soybean leaves, causing infected leaves to die and fall off, thereby limiting the plant's ability to produce seeds. Since its discovery in the U.S. in 2004, the disease has not traveled far enough north and early enough in the season to affect Indiana soybean yields.
This year could be the year that changes. But according to Purdue Extension plant pathologist Kiersten Wise, whether that happens will depend on many factors, including continued disease development in the South and favorable conditions for disease to develop if soybean rust makes it to Indiana.
"Soybean rust is active in the southern U.S. this year, and spores of the fungus that causes the disease are moving northward," she said. "Producers might be concerned that late-planted soybeans in Indiana are at greater risk for yield loss should this disease reach Indiana. However, Indiana is still in a 'wait and see' area for disease development based on the most recent risk prediction from the ipmPIPE Center."
The ipmPIPE Center, or Pest Information Platform for Extension and Education, is a collaboration between commodity groups, the U.S. Department of Agriculture, land-grant universities, plant diagnostic networks and other agricultural industry groups. The organization's website, http://www.ipmpipe.org/, includes maps showing areas where officials have scouted for soybean rust and where it has been found. While the site is not comprehensive, it is a resource to help growers track the disease.
Indiana doesn't have a formal soybean rust monitoring system, but Wise said she and other Purdue Extension specialists and educators will monitor selected fields as the growing season progresses. They will publish updated commentary throughout the season on disease progression in Purdue Extension's Pest and Crop Newsletter at http://extension.entm.purdue/edu/pestcrop.
She also said it's important to scout fields and to differentiate between soybean rust and other diseases with similar symptoms.
"Many foliar diseases can be confused with soybean rust, including brown spot, bacterial blight and bacterial pustule," Wise said. "Herbicide injury and insect feeding are two other issues that have been confused with soybean rust symptoms in the past."
Growers who suspect soybean rust should send samples to the Purdue Plant and Pest Diagnostic Laboratory for diagnosis. Information about submitting samples is at http://www.ppdl.purdue.edu/.