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College of Food, Agricultural, and Environmental Sciences


Soybean Rust Infections Remain Low

July 13, 2005

Editor's note: This is part of a periodic series on information regarding soybean rust. The goal is to provide media with the latest updates on the disease and Ohio State's role in research and education. These updates are expected to continue throughout 2005.

WOOSTER, Ohio — Depending on what the remnants of Tropical Depression Dennis has in store for Ohio, incidences of soybean rust may remain very low for the next month.

Anne Dorrance, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center and the state's leading soybean rust researcher, said that inoculum levels are so low in areas that have reported soybean rust that an epidemic is highly unlikely. Additionally, if soybean rust were to make an appearance in Ohio its arrival may be at a point in the crop's development where yields would not be affected.

"We are dealing with much lower levels of inoculum than what we expected. Winter was really harsh and the freeze line went all the way down to the coast (Gulf of Mexico). It's just taken what seems like forever for this thing to get rolling," said Dorrance. "We are going to intensify our scouting (in sentinel plots) to two times a week the last week of July and beginning of August to see if anything came in with Dennis. If we are negative at that point then we can potentially say that we are out of the woods."

Latest finds of spores in spore traps in soybean fields in Louisiana, Alabama, Tennessee and Kentucky may have given some growers cause for concern, but Dorrance said that there is no need to spray their fields unnecessarily.

"I think growers are worried because something was potentially found, but the spore count was so low that it hasn't even been determined if the spores found are soybean rust," said Dorrance. "And 10 spores in a spore trap are not the same as sporulating lesions on a plant. Just because you have spores, doesn't mean you have conditions right for infection."

Soybeans are flowering in Ohio, the critical stage of development where pods are formed and yields are determined. If spores were to be blown up from Hurricane Dennis, odds are that there would be little, if any, impact, said Dorrance.

"If people can remember, this situation is somewhat like (Hurricane) Ivan. It took almost six weeks for spores to be detected and those fields didn't need spraying. There was no yield loss due to soybean rust," said Dorrance.

The storm system from Tropical Depression Dennis has been sitting over the Ohio Valley since early this week, dumping rain showers in such areas as Illinois, Indiana and Kentucky.

Candace Pollock
Anne Dorrance