Efforts to identify and treat rust — should it show it's ugly head — are under way across the country. USDA's Animal and Plant Health Inspection Service (APHIS), other state and federal agencies as well as universities and companies marketing rust fungicides are intently focused on how to prepare for the fungus.

At press time, no Asian soybean rust has been identified on continental U.S. shores. In fact, there have been no confirmed reports north of the equator.

“Once soybean leaves start to go into senescence, you're probably safe from any kind of economic effect from rust. Your crop is made,” says Monte Miles, plant pathologist with USDA's Agricultural Research Service at the University of Illinois. “Prior to that, everything is a combination of how much of the pathogen is in the field and what the environmental conditions are to drive the development of the epidemic and the host.”

Miles reports that late-season epidemics in southern Africa have caused 20-30% yield losses in research plots. “That's a rust epidemic that starts at R5,” he says. “We just don't know what it's going to do here in the U.S.”

In northern states, like Minnesota, soybean plants need all the energy they can get in late August for oil and protein production, says Seth Naeve, University of Minnesota soybean specialist.

“If anything interferes with the leaves then, it will impact yield and quality,” he says.

X.B. Yang, Iowa State University plant pathologist, and other experts have developed models that predict how the pathogen might travel.

“A model is built by inputting environmental information,” Yang says. “This helps us predict what will happen with diseases, just like forecasting weather.”

Based on the models, Yang is convinced the fungal disease will eventually arrive, but it's unlikely to be carried to North America by winds this year. And if it is carried by winds to the southern U.S., it won't appear in states like Iowa until later in the growing season.

“If the disease shows up with only a few weeks of the growing season left, it's not going to cause any significant damage like it would if it were present throughout the season,” Yang says.

Fortunately, the battle against rust is being fought worldwide. “I'm confident that information on rust is being shared around the world, especially the last couple of years. We're learning from our predecessors,” says David Wright, plant health coordinator for the North Central Soybean Research Program.