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Soybean rust reaches U.S., infects South

Missouri farmers, almost done with this year’s crop, look to ‘05.
Monday, November 22, 2004 | 12:00 a.m. CST; updated 1:45 p.m. CDT, Monday, June 30, 2008

Mid-Missouri farmers are thankful for bumper soybean yields this year, but a new fungal disease in the United States leaves uncertainties for future growing seasons.

The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service confirmed the first case of soybean rust in the continental United States on Nov. 10. The disease traveled to the United States from South America during the extended hurricane season.

There are 10 confirmed cases of soybean rust spanning across Louisiana, Florida, Mississippi, Alabama and Georgia.

“I knew we were going to get it sooner or later, whether it was this year or next year,” said Gary Riedel, a farmer in Boone and Audrain counties. “It was just a matter of time.”

Soybean rust is a fungal disease that spreads primarily by wind-borne spores. Once it reaches the plant, it attacks the leaves and causes them to drop early, limiting pod setting and reducing yields. Soybean rust has accounted for yield losses from 10 to 80 percent.

There are two fungal species of soybean rust: the Asian species and the New World species. The cases found in the South were the more aggressive Asian species.

The first report of Asian soybean rust was in Japan in 1903. It now can be found in Asia, Australia, Africa and South America and in the Hawaiian and the Caribbean islands, according to a USDA report.

Identifying soybean rust is difficult because it starts in the plant’s lower canopy leaving initial symptoms hard to detect, said Laura Sweets, an MU Extension plant pathologist. Soybean producers will have to walk their fields frequently and look at the plant’s bottom leaves.

Soybean rust tends to infect plants when they are moving from the vegetative stages to the reproductive stages of growth, but it also has infected plants two or three weeks old, Sweets said.

With 80 percent of Missouri’s soybean crop harvested for 2004 according to a Nov. 15 report from the Missouri Agricultural Statistics Service, Sweet said there is no need for concern this year. However, she said farmers should be aware of the problem in preparing for the next growing season.

On Nov. 1, the USDA projected Missouri’s soybean production to top out at a record 227 million bushels, 22 percent above the previous record production of 2001. A record yield of 46 bushels per acre was also expected.

Soybean rust characteristics are similar to other diseases such as brown spot, bacterial blight, bacterial pustule and downy mildew. The disease is microscopic — magnifying glass is necessary to spot blisters while scouting a field.

The disease deposits small blisters on the bottom of leaves and infects the leaf tissues, Sweets said. On the upper leaf there are visible yellow or brownish spots. Within the blister, spores are produced. Once the blister bursts, spores release. There can be several blisters on each leaf.

The success of soybean rust in a region depends primarily on the weather. The disease flourishes in moderate temperatures with wet conditions so it can stick to the leaves. It dies in cold weather making it almost impossible to survive a Missouri winter.

For farmers who find soybean rust, the only method available to minimize the risks of yield loss is to spray with a fungicide. There are currently two approved by the Environmental Protection Agency. Others are pending approval, but are on a list which grants emergency use during an infestation.

It could cost a producer $15 to $25 per spraying trip, said Melvin Brees, MU Extension agricultural economist at the Food and Agriculture Policy Research Institute.

Switching soybean acres to corn is an option for farmers, but operating costs for corn is predicted at $250 per acre. Soybean is predicted at about $134 per acre, Brees said.

Researchers are developing rust resistant varieties of soybean, but according to the American Soybean Association the new varieties are 5 to 10 years away. Research is ongoing and Sweets said MU is working on varieties in Vietnam.

The economic impact of the disease could be costly for the United States because countries have reported losses up to 80 percent as a result of soybean rust, Brees said.

An April 2004 report from the USDA’s Economic Research Service said losses to U.S. producers and consumers could range from $640 million to $1.3 billion in the infestation’s first year.

“I’m trying to be as optimistic about this as I can,” said Kelly Forck, Cole County farmer. “It is an issue that I think we can work through as a whole and I think a lot of it is a matter of understanding the disease and learning how to manage it and learning the tools we have available to handle it.”


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