Dangerous Soybean Rust Found In Louisiana

Clayton Hollier, Merrill, Thomas A., Whitam, Kenneth, Schneider, Raymond W., Boethel, David J.  |  4/19/2005 10:29:24 PM

News Release Distributed 11/10/04

A costly and potentially devastating plant disease has been discovered in Louisiana – its first occurrence in the United States, officials confirmed Tuesday.

Known as Asian soybean rust, the fungal disease was confirmed to be in South Louisiana fields this week. Before that, it had been found in all major soybean growing areas of the world except the United States, and experts had predicted it would eventually make its way here.

The disease poses potentially devastating consequences in terms of soybean yields, but it poses no threat to the food supply.

Officials believe spores of the disease may have been carried into the area on winds associated with the active hurricane season of 2004. It has existed in South America since 2000, and speculation is that a storm picked up spores in Colombia and carried them here.

"We’re going to have some of our plant pathologists and extension agents examining other fields over the next few days to determine if they find more symptoms of the disease," said Dr. David Boethel, the LSU AgCenter’s vice chancellor for research.

Boethel said the LSU AgCenter will cooperate with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service, the Louisiana Department of Agriculture and Forestry and others in the ongoing investigation of this problem.

Symptoms of the disease – generally tan or brown lesions on the plant – were first spotted in a research field late last week by Dr. Ray Schneider, an LSU AgCenter soybean researcher. Samples were sent to the USDA’s laboratory in Beltsville, Md., and officials there confirmed it as Asian soybean rust Tuesday.

Since that time, work has begun to organize scouting teams from APHIS, the state Department of Agriculture and Forestry and the LSU AgCenter. The teams will search fields across South Louisiana for more symptoms of the disease.

"The discovery in our research field demonstrates how vigilant our faculty members have been in watching for any symptoms of this disease," said Dr. Bill Richardson, chancellor of the LSU AgCenter. "Those fields help us to see the first signs of any insects or diseases that may have invaded."

Louisiana Commissioner of Agriculture and Forestry Bob Odom said his department is going to work closely with the USDA's response team and LSU AgCenter personnel to determine if soybean rust has spread to other fields within the state.

"To best serve our soybean producers and help them in planning for next year's season, it is imperative that we know how extensive this outbreak of soybean rust is," Odom said. "My main concern right now is how this will affect the global markets and how they will react.

"Although other soybean-producing countries have this disease, just talking about it being in the United States could have an impact on the market," Odom said. "The financial ramifications of this disease have the potential to devastate our soybean industry. We have to be able to get our beans on the market. It is up to our trade officials to reassure those who import our beans that this fungus is not spread on the bean itself."

Asian soybean rust is an aggressive fungal disease that can reduce soybean yields by as much as 80 percent in an individual field if growing conditions are favorable for its spread. Fortunately, for this year’s Louisiana crop, more than 90 percent is harvested and therefore won’t face significant damage from the outbreak.

"Asian soybean rust is a potentially damaging disease, because its severity can double about every 10 days, depending on environmental conditions," LSU AgCenter plant pathologist Dr. Ken Whitam explained. "Although most people were not predicting it would enter the United States for another couple of years, there already have been some studies that indicate it could cost U.S. soybean producers anywhere from $240 million to $2 billion annually."

Those costs would come from yield losses and from the additional expenses of applying the fungicides necessary to try to protect soybean crops against the disease, explained Dr. Clayton Hollier, an LSU AgCenter plant pathologist and principal investigator for the Southern Pest Detection Network.

Asian soybean rust was first reported in Japan in 1902. It later moved through Asia, Australia and Africa before it was discovered in South America in 2000. The disease had been moving through South America since that time but had only been discovered as far north as 5 degrees North latitude in Colombia before the confirmation in Louisiana this week.

Experts predict the disease will be more devastating in the southern portion of the country, because of general weather conditions that would allow it to survive over winter here, the longer growing season and the variety of other plants that also can serve as hosts for the disease.

"All soybean-growing areas of the United States are at risk," Hollier said. "It’s just that the weather in the northern growing areas won’t be as favorable for the fungus to over-winter, so those areas may be reinfected by spores that travel from the South."

Hollier also said the most favorable weather conditions for problems with the disease during the growing season, based on 30-year averages, are in the Mississippi Delta region and the Midwest. The disease thrives in warm, moist climates.

"Although there are some people who predict even greater losses, most risk analyses seem to show that yield losses of 10 percent or so are possible in any U.S. soybean-growing region, and losses of up to 50 percent could be seen in the southeastern coastal states," Hollier said, adding, "Of course, this all depends on weather conditions during the growing season."

Another consideration is the approximately 20 species of plants that can "host" the disease. Those include such weeds and legumes as sweet peas, yellow sweet clover, vetch, medic, green beans, kidney beans, lima beans, butter beans and kudzu.

"It’s going to be vital for people to not only remove the soybean plants that might serve as a host to this disease over the winter but also to remove other host plants," Whitam said. "They also will want to keep those host plants away from soybean fields during the growing season."

Many of Louisiana’s other agricultural crops – such as sugarcane, cotton, rice, corn and other grain crops – are not hosts to Asian soybean rust.

Symptoms of the disease are tan, dark brown or reddish-brown lesions on a soybean plant. These lesions are most abundant on leaves, particularly on the underside of the leaves.

The disease destroys the photosynthetic tissue of the plants – causing premature defoliation, early maturation and lower yields.

Experts say the long-term hope for controlling the spread of the disease – and its devastating effects – will be the development of soybean varieties with resistance to it.

In the meantime, producers are urged to be on the lookout for symptoms of the disease and to clear their fields of any plant material, such as "green" soybeans that were abandoned, which could host the disease. Soybean growers also should begin investigating options for fungicides that may help them prevent the disease during the coming growing season.

"We will be ready with LSU AgCenter recommendations for next season for the grower meetings this coming January and February," Whitam said.

Additional general information on the disease can be obtained by visiting www.soybeanrust.info.


Clayton Hollier at (225) 578-1464 or chollier@agcenter.lsu.edu
Ken Whitam at (225) 578-2186 or kwhitam@agcenter.lsu.edu
David Boethel at (225) 578-4181 or dboethel@agcenter.lsu.edu
Ray Schneider at (225) 578-4880, or rschneider@agcenter.lsu.edu
Tom Merrill at (225) 578-2263 or tmerrill@agcenter.lsu.edu

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