Soybean crops in the Midwest have yet to suffer any economic damage from Asian soybean rust (ASR).

Still, the disease was present in commercial soybean fields late last fall as far north as northern Iowa, northern Illinois and even Ontario, Canada, in 2007, says Carl Bradley, University of Illinois Extension plant pathologist. Had the disease traveled to those areas earlier in the year, it would probably have caused some economic damage — and could do so next year, he adds.

“Soybean rust took a different route north this year,” says Bradley. “It went straight north from Texas, up through Oklahoma, Kansas and Nebraska and then spread east into Iowa and Illinois.”

Whether ASR will follow that same route again next year is anyone’s guess, says Bradley. He says ASR was first found in U.S. soybeans in Louisiana late in 2004. It stayed mostly around the Southeast in 2005, but in 2006 it followed the Mississippi River Valley and went as far north as central Indiana. Last year brought ASR into the heart of U.S. soybean production areas, although too late in the year to reduce yields.

“ASR has not yet caused any economic losses in states like Iowa, Indiana, Illinois or Missouri,” says Bradley. “However, that could certainly happen in the future if the weather south of us is conducive to producing the disease spores, and the right weather system moves them north when Midwestern soybeans are in a susceptible growth stage. However, weather conditions would need to stay wet long enough for the disease to take off here.”

Growers in some southeastern states had to spray soybeans for ASR in 2005, but in 2006 conditions were too dry for ASR to cause problems. This year, “some applications were warranted for ASR control in parts of Oklahoma, but in other areas there was some panic spraying that didn’t need to be done,” says Bradley.

Farmers who want to avoid unnecessary spray applications next year should stay in touch with ASR sentinel plot scouting reports, “which give an advanced warning if rust is in the area or heading our way,” advises Bradley. For more information on ASR sentinel plot reports, visit: www.sbrusa.net or www.plantmanagementnetwork.org/.