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," says Dorrance. "None of the samples we collected contained rust pustules. If it was here, it was less than 1 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 USDA’s 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 says 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," says Dorrance, who also holds an Ohio State University Extension appointment. "We’ve already had our first frost that spread south to Tennessee."