Perspectives Online

N.C. growers brace for new soybean disease

With the help of the College, North Carolina growers prepare for Asiatic soybean rust.
Communication Services archive

As North Carolina soybean growers prepare to plant their fields this year, they are looking warily to the south, perhaps hoping for the best but expecting the worst from a plant disease the crept into the United States late last year.

Asiatic soybean rust, a plant disease that has heavily damaged soybean crops in other parts of the world, was found in the United States for the first time last November in Louisiana, said Dr. Steve Koenning, research assistant professor of plant pathology in the College of Agriculture and Life Sciences.

The disease was subsequently found in a number of other locations in the Southeast but not in North Carolina, which grows about 1.5 million acres of soybeans worth more than $200 million annually. This year, the disease was found in late February in Florida near Tampa.

Asiatic soybean rust is a fungus that produces spores that are carried by the wind. The presence of the disease in the Southeast United States means it is likely it will appear in North Carolina at some point. The College of Agriculture and Life Sciences is playing a central role in determining when that point will be and preparing growers for the disease.

College scientists developed - and the College is hosting - a Web site ( at which disease outbreaks will be noted and movement of the disease forecast.

Forecasting the movement of the disease is important. Koenning explained that fungicides that will protect soybeans from the disease are available; however, it will likely cost growers from $30 to $60 per acre to apply fungicide. It already costs from $175 to $200 per acre to grow soybeans in North Carolina, said Dr. Jim Dunphy, professor of crop science, so growers don't want to incur any additional expense unless it's absolutely necessary.

The forecasting system was developed by Dr. Charles Main, emeritus professor of plant pathology and an expert on the movement of fungal diseases spread by wind-blown spores. The forecasts will aid growers in deciding if and when to spray fungicides. If soybean growers can delay making an early application of fungicide, they may reduce the number of sprays needed to manage the disease, Koenning said.

At the same time, Koenning plans to plant sentinel crops of soybeans across the state. These will be planted at agricultural research stations and, working with North Carolina Cooperative Extension agents, in selected counties. These crops will be monitored for the disease, serving as a warning that it has reached the state. Soybeans are typically planted in North Carolina beginning in mid-May.

Soybean rust is native to Asia but has been found in 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.

Dunphy said the disease can destroy as much as half of an untreated soybean crop, so if the disease does make its way to North Carolina, growers will find themselves in a no-win situation. It will be expensive to treat their crops, but if they don't spray their crops with fungicide, they may lose a significant amount of the crop.

Koenning said predictive models suggest that conditions in Georgia, South Carolina, Virginia and North Carolina are favorable for development of an epidemic of soybean rust, but it's still anyone's guess how much damage the disease will do. The soybean rust pathogen is primarily tropical in distribution and will not survive the winter in North Carolina; however, models indicate the fungus can survive over winter in southern Florida and Texas.

The impact of the disease in North Carolina may be determined 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, but arrival of rust spores in June could reduce yields considerably.

Koenning and others have been working with the North Carolina Soybean Producers Association to prepare for the arrival of soybean rust. He and Dr. Andrea Cardinal, assistant professor of crop science, attended a world soybean research congress in Brazil in 2004 and visited Brazilian agricultural research stations.

The Soybean Producers are funding efforts by Cardinal, a plant breeder, to develop new soybean varieties that are resistant to soybean rust. None of the soybean varieties now grown in the U.S. are resistant. Koenning and Dunphy led educational efforts in 2004-05 to inform and train producers, Cooperative Extension agents, North Carolina Department of Agriculture and Consumer Services regional agronomists, crop consultants and others how best to deal with the disease.

Koenning also sought and received emergency approval from the North Carolina Pesticide Board for the use of fungicides not previously approved to manage soybean rust.

- Dave Caldwell