Scientists worry soybean rust may be coming to U.S.

URBANA, Ill. -- Scientists have been watching the invader for more than 30 years, powerless to stop its movement around the globe.

Carried by the wind, it attaches itself to the leaves of soybean plants and reproduces rapidly, preventing proper plant development and dramatically reducing crop yields.

Soybean rust, or Phakospora pachyrhizi, has hasn't made it from its origins in Australia to North America yet, but researchers say its arrival is inevitable. It was spotted in Hawaii in 1995, and reports of crop damage in Brazil last year have U.S. researchers pushing ahead with efforts to develop fungus-resistant plants.

They're also asking farmers in major soybean-producing states to be vigilant.

"The worst-case scenario? We could end up with devastating losses," said Glenn L. Hartman, a scientist at the National Soybean Research Laboratory on the University of Illinois campus in Urbana. "That would mean that the fungus would have to spread throughout the whole soybean belt. In that case, we're probably looking at 30 to 50 percent losses."

Crop losses

The U.S. Department of Agriculture has found that crop losses in countries that already have been infected have ranged from 10 percent to 60 percent.

Rust first appears as small, irregularly shaped spots on the leaves of soybean plants. The spots gradually increase in size and turn brown or reddish as the disease progresses.

Soybean rust causes premature leaf loss, leading to a smaller number of bean pods, fewer seeds per pod, and early maturity, all of which adds up to lost crop yield, according to the U.S. Department of Agriculture.

Research on soybean rust in the United States began in 1971. It was one of the first diseases to be studied as part of a USDA mission to study foreign diseases that could threaten U.S. crops. It already had caused major yield losses in Australia.

The researchers also identified a weaker form of soybean rust. That pathogen, which does not devastate crop yield, was first discovered in the Western Hemisphere in Puerto Rico in 1976.

The USDA acknowledges it will be impossible to contain and eradicate soybean rust -- it moves too rapidly and it can live off other plants, such as the weed kudzu, which grow wild in many parts of the country. So several USDA agencies have developed a strategy that includes making efforts to prevent an accidental introduction, educating producers and handlers of soybeans about the disease and developing fungicides and rust-resistant plant varieties.

South most vulnerable

The South is likely to be hit hardest if soybean rust lands in the United States because of the warm, moist climate. The fungus has been most prevalent in tropical climates and does not survive cold winters because the cold also causes host plants to go dormant or die, Hartman said.

Rust struck soybean producers in Brazil and Paraguay last year, with reports of up to 60 percent crop losses, according to the USDA.

Brazilian producers are spraying their fields with fungicide twice a year, Hainline said. Chemicals would also be a first defense for U.S. producers, Hartman said.

"We feel that if it does get in, there are some fungicides we're able to use right away," he said.

"The first line of defense would be fungicides, because farmers could get out and start spraying right away."

However, the best way to control the spread of the fungus will be development of resistant plants, Hartman said. Experiments continue at a secure laboratory in Maryland, but rust-resistant seed won't be available for several years, he said.

"The resistance needs to be more durable or long-term, so if you find resistance that's good for a season, you have to make sure that resistance is good for a few years," Hartman said.

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On the Net:

USDA's Soybean Rust Strategic Plan: http://www.aphis.usda.gov/ppq/ep/soybean--rust/

National Soybean Research Laboratory: http://www.nrsl.uiuc.edu