Soybean rust development stalled

WOOSTER, Ohio – Thanks to drought conditions in the southeastern U.S., soybean rust has stalled in its march northward to Ohio.
Earlier in the season when weather conditions were favorable for disease development, Ohio growers were bracing for the first soybean rust appearance in the state. Now, it appears soybean fields will escape the disease for a second year.
Just one. “There have been two positive finds of soybean rust in sentinel plots in the southeastern United States, and that was in Florida and second one on June 29 in Alabama,” said Anne Dorrance, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center, and the state’s leading soybean rust researcher.
The recent find in Alabama was in Baldwin County, near the coast. There, five soybean rust lesions were found on soybeans entering the R5-R6 growth stage.
“We are approaching the first flowering stage for soybeans in our sentinel plots in Ohio. It’s very unlikely with these low levels of inoculum that our growers are going to have to deal with this.”
According to the USDA’s Pest Information Platform for Extension and Education (http://sbrusa.net), soybean rust has been confirmed on kudzu patches in five counties in Alabama, 12 in Florida, four in Georgia, and one in Texas.
Monitoring. Despite the slow movement of the disease, Dorrance said plant pathologists and Ohio State University Extension Educators will monitor the 36 sentinel plots in Ohio throughout the remainder of the growing season.
“There is an outside chance of disease development on soybeans that have been planted late or had to be replanted, so the monitoring must continue,” said Dorrance, who also holds an Ohio State University Extension appointment.
“Overall, even though the disease may not appear, we still have to go through the process and collect the data because the negative data is often more important than the positive data.”
No epidemic. Even if a sudden inoculum buildup were to occur, an epidemic in Ohio is being discounted.
“At just a 3 percent infection level in soybean fields across the state, we would have to have 12 million spores hit every acre in the state all at the same time. With five million acres, that just doesn’t compute, and we’d know that soybean rust was present long before it ever reached that level because it would be everywhere,” Dorrance said.
Soybean rust can enter Ohio through a variety of routes: south through Kentucky, from North Carolina over the Appalachian mountains, or up the Mississippi River and along the Ohio River through southern Indiana and western Kentucky.
For information on soybean rust log on to http://agcrops.osu.edu.