WOOSTER, Ohio -- As the 2007 soybean production season comes to a close, Ohio and Michigan remain the only major soybean-producing states east of the Mississippi River to be free from soybean rust.
Despite the latest news that soybean rust was found in Ontario, Canada, field scouting in both sentinel plots and commercial fields and testing leaf samples throughout Ohio have turned up negative for soybean rust. Anne Dorrance, an Ohio State University research plant pathologist and the state's soybean rust expert, said that even if rust had made it to Ohio, the soybean crop was already in the bin thanks to an early harvest, eliminating any disease threat.
"Leaf samples with soybean rust were found in Ontario the last week of October, and we scouted what soybeans we could find up until mid-October," said Dorrance, with the Ohio Agricultural Research and Development Center. "None of the samples we collected contained rust pustules. If it was here, it was less than one pustule per 100 leaves, which is about what the other states are reporting. The rate of infection on the samples collected in Ontario was very low."
According to the U.S. Department of Agriculture Pest Information Platform for Extension and Education (http://sbrusa.net), which monitors national rust development, soybean rust was detected in 19 states and 285 counties from January to November 2007. In the Midwest, Iowa, Illinois, Missouri, Indiana and Kentucky have positively identified the disease. Indiana's find was also only in one field, with very low levels, and specialists did not find more due to the early harvest.
Dorrance said that weather most likely contributed to the spread of soybean rust as far as Canada, but the disease won't have a lasting impact in the Great Lakes region.
"There is no threat to Ohio because soybean rust can't overwinter. It needs living green tissue to survive and multiply," said Dorrance, who also holds an Ohio State University Extension appointment. "We've already had our first frost that spread south to Tennessee."
Dorrance said that tracking national soybean rust news is important when it comes to Ohio's monitoring efforts, even when no rust is found in the state.
"It's helping us build our forecast models and our tracking systems, and gives us information as to how concentrated these rust spores are on leaf samples. Such information is going to help us predict future risk, when soybean rust may arrive and what the next recommendation to manage it will be," said Dorrance.
Dorrance and her colleagues have been monitoring soybean rust in Ohio for the past three years using sentinel plots -- fields with early-maturing soybean varieties designed to be the first line of defense in identifying the presence of the disease.
"The sentinel plot system serves multiple purposes. The first one is determining the presence of the disease and the level of risk during the crop season. The second is for future model predictions," said Dorrance. "We will continue the program again next year, which is good for our growers, because it's just as important to know that rust is not in Ohio, as it is to know that rust is present."
For more information on OSU Extension's soybean rust efforts, log on to http://agcrops.osu.edu/soybean.