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October 31, 2005

Soybean disease found in North Carolina

A plant disease that has heavily damaged soybean crops in other parts of the world has made its way for the first time to North Carolina, although it is too late in the growing season for the disease to damage soybeans this year, said an expert at North Carolina State University.

As a result of monitoring activities conducted by N.C. State University, Asiatic soybean rust was identified on soybean leaf samples collected from Brunswick, Columbus and Robeson counties on Oct. 25 and on soybean leaf samples collected in Beaufort and Craven counties on Oct. 26.

Dr. Steve Koenning, research assistant professor of plant pathology and North Carolina Cooperative Extension specialist at N.C. State, made a tentative diagnosis of Asiatic soybean rust. Subsequently, the U.S. Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) confirmed the presence of soybean rust.

Soybean rust is native to Asia but has spread to other parts of the world in recent years. Koenning said the disease was found in Africa in 2000 and in South America in 2001 and 2002. The disease, which is spread by wind-blown spores, has caused considerable damage to Brazilian soybean crops.

Koenning said the disease was found in Louisiana, Mississippi, Florida, Alabama, Arkansas, Missouri, Tennessee, Georgia and South Carolina in 2004. This is the first report of the disease in North Carolina, although already in 2005 it has been found in Alabama, Florida, Georgia, Mississippi and South Carolina.

Soybean rust will not impact North Carolina soybean production in the 2005 growing season because more than 80 percent of the crop is mature, Koenning said. The impact on the state's remaining soybeans will be minimal because of the late entry of the disease pathogen into the state. Koenning said soybean rust does not infect seed and will not contribute to seed rots.

The soybean rust pathogen is primarily tropical in distribution and will not survive the winter in North Carolina; however, models indicate the fungus would be able to survive over the winter in Southern Florida and Texas. Because wind-blown spores must move to North Carolina from southern regions of the U.S., Caribbean or Central America each year, the impact of the disease in North Carolina will be determined each year by how early in the growing season the disease arrives and environmental conditions at that time. If rust spores do not arrive until September, any yield impact would be minimal, whereas the arrival of rust spores in June could reduce yields considerably.

The disease can be managed with fungicides, but applying fungicides is costly. Koenning said the two to three fungicide applications that would probably be necessary to manage the disease would add $30 to $60 per acre to a farmer's production costs.

Working with the North Carolina Soybean Producers Association, the U.S. Department of Agriculture and the N.C. Department of Agriculture and Consumer Services, Koenning and other N.C. State faculty members have launched a wide-ranging effort to help the state's farmers fight the disease.

That effort includes a network of monitoring plots for early detection of the disease. It was this effort that detected the disease. And at least 5,000 farmers and others involved in agriculture have attended training sessions designed to teach them to identify and manage soybean rust. A communications network was established to keep N.C. Cooperative Extension agents, NCDA&CS agronomists and agricultural consultants informed about the progress of soybean rust and other soybean diseases in North Carolina and the U.S. in 2005.

N.C. State scientists are also working to breed new soybean varieties that are resistant to the disease and to model spore movement. In addition, Koenning was instrumental in obtaining permission from the N.C. Pesticide Board for farmers to use additional fungicides to manage the disease.

--Dave Caldwell

Posted by Natalie at October 31, 2005 02:03 PM