August 8, 2008

Don't worry about soybean rust, experts scouting near and far

WEST LAFAYETTE, Ind. - No soybean rust pustules have been found in the Midwest, including Ohio, Illinois, Indiana, Kentucky and Missouri, say Purdue and other university experts.

The recent tropical storms in southern parts of the United States have concerned many growers, but soybean rust experts Kiersten Wise, Purdue University Extension; Anne Dorrance, Ohio State University Extension; and Don Hershman, University of Kentucky Extension don't recommend applying fungicide for soybean rust at this time.

They have, however, intensified soybean rust field monitoring efforts by increasing the number of soybean leaves collected in sentinel plots. Wise said they also are increasing scouting in areas that have even the slightest chance of favorable conditions for soybean rust infections.

"Even if we were to find soybean rust this week, it would not be at the level that requires immediate treatment," Wise says. "In comparison to Brazil, our initial soybean rust spores are extremely low, which gives us extra time to apply fungicides, if they are needed at all."

Experts agree that Kentucky soybeans planted in May and Ohio and Indiana soybeans planted in April, which have reached full pod/beginning seed, are in the clear.  They continue to monitor fields for soybean rust because late-planted fields are still at risk.

The most recent soybean rust information and management updates are available at the U.S. Department of Agriculture's National Soybean Rust Web site, http://www.sbrusa.net.

If soybean rust infection is suspected in any field, samples should be forwarded immediately to a state Extension specialist for diagnosis. Official confirmation of soybean rust can only be made at the state level and crop insurance claims cannot be processed without an accurate diagnosis.

Soybean rust has never been confirmed in Ohio and must meet Animal Plant Health Inspection Service requirements for a new invasive pathogen. If soybean rust is confirmed in a location, extension educators and certified crop advisers will be notified and updates will be sent.

From previous research, experts have observed that the spores of soybean rust fungus are killed by sunlight and desiccation. This means that most of the spores that reach the traps are more than likely dead, but researchers have no way to measure the viability of spores. They can only measure if there is a spore.

To track soybean rust levels, soybean leaves are collected weekly from sentinel plots located around the state and sent to laboratories, where they are closely examined for soybean rust. In addition to the sentinel plots, spore traps are used to monitor spores of the soybean rust fungus, Phakopsora pachyrhizae, throughout the United States. Rain traps are also monitored, which is a joint collaboration of the United Soybean Board and the U.S. Department of Agriculture's Agriculture Research Service. This year traps throughout the Midwest tested positive during June, July and August for spores, which holds true to the pattern for the previous three years.

For more information, contact Wise at (765) 796-2170 or kawise@purdue.edu; Dorrance at (330) 202-3560 or dorrance.1@osu.edu; or Hershman at (270) 365-7541 Ext. 215 or dhershma@uky.edu.

Writer:  Julie Douglas, (765) 496-1050, douglajk@purdue.edu

Sources:  Kiersten Wise, (765) 496-2170, kawise@purdue.edu

Ag Communications: (765) 494-2722;
Beth Forbes, forbes@purdue.edu
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