CHARLES CITY - George Cummins, an Iowa State University Extension crop specialist, recently returned from an eight-day trip to Brazil with other Extension soybean experts. Their mission: Get a firsthand look at soybean rust to help Iowa farmers combat it.

The yield-robbing fungus arrived in the United States late last year after devastating crops in parts of the South American country, where yield losses have been reported as high as 80 percent.

Scouting is critical, Cummins said. If it is identified and treated in time, damage can be negated.

"In 2004, with rust, Brazil sold more soybeans and soy products in the first 10 months than the U.S. did all in all of 2004. They have obviously learned to live with rust," Cummins said.

Upon returning from Brazil, Cummins is not as worried as before. Southern Brazil, where the disease had little impact, resembles Iowa more than the hot, humid north, where rust thrives.

"It's hard to find in the south, but in the north it's endemic. I'm not saying farmers shouldn't be prepared, but I'm sleeping better," Cummins said.

Experts aren't certain when rust spores will arrive in Iowa from wintering grounds in southern U.S. states. Weather conditions and timing will determine the extent of any infestation.

Rust causes reddish-brown lesions, and makes plants drop leaves prematurely, slashing yields. If the disease doesn't arrive until after the beans are made, farmers have nothing to worry about. If it comes before pod fill, it could cause problems.

Farmers treating fields must be sure fungicide penetrates the soybean plant canopy and reaches even the underside of bottom leaves, where rust is most likely to grow first. Sprayer nozzles, spray volume, pressure and ground speed may all be different than normal herbicide application.

On Pioneer Hi-Bred International's Growing Point Web site, the company recommends spray volumes of between 10 to 20 gallons per acre. Spraying pressure for twin flat fan or flat fan nozzles should be set at 50 pounds per square inch. The boom height should be 12 inches above the top of leaves.