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Deadly soybean disease surviving winter in Georgia

By Brad Haire
University of Georgia

University of Georgia scientists learned recently that Asiatic soybean rust, a deadly tropical soybean disease, can survive Georgia's winter weather. This raises concerns that it could spread earlier and stronger this year.

Other than soybeans, the disease thrives on Florida beggarweed and kudzu, an Asian vine that's notorious in the South.

It was found growing on live kudzu in Grady County Jan. 30 and Thomas County Feb. 10, said Bob Kemerait, a UGA Cooperative Extension plant pathologist. It has been confirmed on kudzu in two counties in south Alabama, too, and 11 counties in Florida so far this year, he said.

Kudzu, Florida beggarweed and any soybeans left from the previous year's harvest are usually killed by freezing temperatures each year in Georgia. But nothing is guaranteed.

"These sites answer the question, can Asiatic soybean rust overwinter in Georgia?" Kemerait said. "The answer is yes."

The infected kudzu in Grady County was found protected from the cold weather by a building in downtown Cairo, Ga. The infected kudzu in Thomas County was protected by a concrete culvert.

The living kudzu from the two sites was taken to the UGA Plant Disease Diagnostics Laboratory in Tifton, Ga., Feb. 17 to be studied. It will be destroyed, Kemerait said.

The disease is in Georgia now, he said. There are probably other south Georgia sites similar to those in Grady and Thomas counties where the disease and kudzu are protected from freezing weather.

Georgia farmers who choose to plant soybeans this year need to budget an extra $20 to $30 per acre to protect the crop with fungicides. Before the threat of the disease, Georgia farmers rarely needed to spray fungicides on soybeans.

Because of the threat the disease poses to Georgia and the rest of the country, Kemerait and UGA Extension agents in south Georgia monitored the state for it this winter. A U.S. Department of Agriculture grant has helped in the search.

Asiatic soybean rust first appeared in the United States in November 2004 on the Gulf Coast. Scientists believe it blew in on tropical storms that skirted South America, where the disease has already cost soybean farmers billions of dollars in damage.

Kemerait and other scientists with the UGA College of Agricultural and Environmental Sciences will conduct fungicide spray trials this year to determine the optimal time to spray for the disease and the best fungicides to use.

Georgia is not considered a major soybean-growing state. Georgia farmers grew about 170,000 acres in 2005. The crop is worth $30 million to $40 million annually.

Asiatic soybean rust is here to stay, Kemerait said.

When it first shows up and how fast it travels will determine how much of a threat it will be for the Midwest, where most U.S. soybeans are grown. The U.S. is the world's leading soybean producer. The crop is worth about $18 billion annually.

(Brad Haire is the former news editor with the University of Georgia College of Agricultural and Environmental Sciences.)

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