August 8, 2007
More soybean rust in Oklahoma, spores may be reaching Midwest
Asian soybean rust has appeared in north-central Oklahoma, representing the northernmost infection of the airborne fungus in US fields during 2007.
Reporting to the Agriculture Department's public rust website late Monday (August 6), Oklahoma State University extension plant pathologist John Damicone said the disease was found on a Stillwater-area soybean sentinel plot in Payne County, located only about 100 miles south of Wichita, Kan. Rust was also discovered in Atoka County, bringing Oklahoma's number of rust-positive counties to four.
"Full-season varieties are currently at risk for damage to soybean rust," Damicone said. "Fungicide sprays are recommended to protect soybeans from rust in affected counties and nearby counties to the north when soybeans are in the R1 to R5 (beginning bloom to beginning seed) growth stages."
The airborne fungus - which prematurely defoliates soybeans - can easily cause 50-80 percent yield losses, unless quickly countered with chemical fungicide.
The pathogen has now been spotted in 60 counties and parishes across Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, Oklahoma and Texas, this year. Although it eventually spread as far north as central Indiana last season, the Payne County outbreak is the farthest north that soybean rust has ever been found in the Great Plains. It first appeared on the continental US, in Louisiana, in November 2004.
An updated infection forecast published Monday by USDA warned that southerly winds could again transport rust spores - which effectively act as seeds for the disease - into soybean-intensive areas of the Midwest this week.
"While wind will be able to transport spores as far north as Iowa and Illinois, the likelihood for their survival is minimal, due to sunny and dry conditions," said the agency.
Asian soybean rust thrives in overcast conditions, at temperatures between 68-77 degrees Fahrenheit, when leaves remain damp for at least 10 consecutive hours.
