You heard it last year and you'll hear it again. Don't let your guard down when it comes to Asian soybean rust. That's the mantra from Monte Miles, USDA-Agriculture Research Service plant pathologist.
“I told producers last year that they needed a plan on how to handle rust. That won't change for next year, either. You have a 50-50 chance of having it,” Miles says.
The fact that rust wasn't a big problem in the U.S. this year is not a big surprise. “Not much inoculum was present,” says Miles. “If you look at the history where rust has occurred for the first time, the first year after infection the severity tended to be fairly low and not widespread.”
Experts say rust will act much like other rust pathogens — common rust of corn, Southern rust of corn and maybe even wheat rust — that come from the South each year. “Pathogens blow up from the Caribbean and Mexico almost every year,” Miles says. “They've got a long, established history there so we know there's inoculum being produced there.”
The big question for next year is where rust will overwinter and how much inoculum is being developed in those areas. The places to watch, Miles says, are the Yucatan peninsula in Mexico, islands in the Caribbean and the southern coastline of the U.S. Also, Cuba is an unknown.
“It will depend on where the frost line will be in the U.S. this year,” says Palle Pedersen, Extension soybean specialist at Iowa State University. “If the line is down at the Mexican Gulf like it was last year, I think we're going to be in good shape, especially here in Iowa. But there are still a lot of things we don't know. It can move fast as we've seen in Brazil.”
Pedersen doesn't see rust as a big threat, as long as growers are prepared for it. In Iowa, he thinks they are. Iowa started an Asian soybean rust taskforce 21/2 years ago.
“A majority of our farmers know what to do here and we're not scared about it. We've educated farmers and they've started to use the right spray nozzles and know how to apply fungicides,” Pedersen says.
Still, he says there are plenty of variables and unknowns. In fact, he plans to double his fungicide research trials next year.
“We'll get farmers up to speed on rust again this winter,” Pedersen says. “The pathogen is in the country and it can still come up here. And if it shows up in Iowa, especially during a wet period, we could get significant yield loss.
“With profit margins getting smaller, the best thing farmers can do is be 110% prepared for rust,” he says. “We still don't know how to predict what's going to happen with this pathogen.”
The big success story this past year, however, has been the sentinel plot system and the USDA Web site www.sbrusa.net, Miles says.
“The sentinel plots were the first place in the South that soybean rust was discovered,” he says. “It wasn't until later that we found it in producers' fields. Without this system, we'd have had to search producers' fields and had much less warning.”
Miles says some of the sentinel plots were hit so hard with rust, especially in Georgia and Florida, that they had to shut down research because plants were completely defoliated. Sentinel plots were infected at about the R1-R3 stage, ahead of soybean growth stages in farmers' fields.
“Rust is still a threat and still a problem,” Miles says. “We want producers to be prepared should this thing start to develop into an epidemic.”