Each year, soybean farmers ask themselves if this will be the year Asian rust strikes.

"With the right conditions, rust could blow all the way up (from southern U.S.) to North Dakota," says Rick Ostlie, a Northwood, North Dakota, farmer.

Even if rust is not heading northward, it's a good idea to scout your soybeans from the R1 (beginning bloom) to R5 (beginning seed) stage. That pays dividends not only for Asian rust but also for late-season foliar diseases like anthracnose.

Asian rust is a low-lying disease that starts deep in the canopy and works its way up.

Suzanne Bissonnette, University of Illinois (U of I) Extension integrated pest management specialist, advises scouting 20 plants at five locations in a field. "This will require actual bending, pushing a plant aside, and looking on the underside," she says. "Look low as you go."

That doubles for rust fungicide applications. "If you just spray the top leaves, the fungicide wont go down where rust dwells," she says.

Scouting for rust also entails more than walking your soybean fields. "As soybeans approach flowering (R1), check with university Extension sources, Web sites, dealers, farm magazines and radio and television programs for information on soybean rust," says Carl Bradley, U of I Extension plant pathologist.

Growers can track rust progress since many states participate in the soybean rust sentinel plot program. A good Web site for tracking rust's progression throughout the country is USDA's site, www.sbrusa.net.

Rust spores travel primarily via wind, up to 400 miles a day, says Bissonnette. But just because spores travel that far and land in your area doesn't mean rust will surface in your field. Much hinges on local moisture conditions. Rust spores need adequate moisture to develop.

Ultraviolet light also has been shown to deter rust spores. That's something U.S. growers have more of than Brazilian farmers, who have fought infestations in recent years.

"Light intensity and duration increases as you move northward," says X. B. Yang, Iowa State University Extension plant pathologist. "We (in Iowa) have a lot more daylight in the summer compared to Brazil. So light might play a very crucial role in limiting this particular disease."