Clayton Hollier | 3/18/2006 4:51:59 AM
LSU AgCenter experts are preparing to monitor for Asian soybean rust in Louisiana this year as the fungus threatens to enter the state from a new direction – the west.
Asian soybean rust has been verified in kudzu in the Beaumont, Texas, area and on soybeans in Weslaco, Texas, as well as in two Mexican states bordering the United States, according to Dr. Clayton Hollier, a plant pathologist with the LSU AgCenter.
The rust disease, which is spread by windborne spores, is feared because it’s hard to detect until it’s too late to do anything to stop it. The symptoms first appear on the bottom leaves – hidden from view. By the time it’s obvious, the disease, which has been known to destroy entire fields, generally has taken hold.
Hollier is concerned because prevailing winds from the southwest could bring spores from Mexico and Texas into Louisiana more easily than from the east, where most of the infestations in this country had been located in relation to Louisiana until recently.
Because the hosts of Asian soybean rust fungus are killed by freezing weather, new infections are caused by spores that are blown in on winds from warm areas, such as southern Texas and Florida. LSU AgCenter scientists have been monitoring known Asian soybean rust colonies in Louisiana and believe all the hosts were killed by frost during the past winter.
Asian soybean rust has been around since the early part of the 20th century. But it had been confined to Asia until recently – when it spread to Africa and then on to South America. It was first discovered in the Western Hemisphere in Paraguay in 2000.
The first discovery of the plant disease in the United States was made in Louisiana in November 2004. Officials believe it had been brought in from South America on the winds of one of that summer’s tropical storms.
Hollier said the soybean plant is the preferred host for the disease, and kudzu appears to be the second choice. But scientists have identified 95 plants on which Asian soybean rust can live.
Dry conditions in Louisiana in 2005 are believed to have suppressed the disease and kept it from spreading from the southeastern United States, where it apparently overwintered in central Florida. The potentially devastating disease spread north through Florida and into Georgia, Alabama and South Carolina during the 2005 growing season.
To provide early warning for Louisiana soybean growers, the LSU AgCenter has been planting sentinel plots, which are carefully monitored for signs of the disease.
"We’re putting the plots out early – not just where soybeans are grown but where there may be spore showers coming through," Hollier said.
Hollier said the LSU AgCenter will plant 15 sentinel plots around the state, as it had done last year. He said the AgCenter has moved two of the plots farther west to try to intercept and identify rust spores from Texas before they reach the soybean-growing areas of the state. Other plots are scattered throughout the state, including those in southeastern Louisiana near the Pearl River and in extreme South Louisiana to monitor potential infestations being blown in on storms from South America.
Dr. David Lanclos, the LSU AgCenter’s state soybean specialist, said he’s planting sentinel plots now.
"The LSU AgCenter is not crying wolf," Lanclos said. "But we have to be aware."
Lanclos said the disease won’t deter Louisiana growers from planting soybeans "because we have methods to control Asian soybean rust."
He said producers don’t have to do anything until they find rust. And if they find it, they can treat their fields with fungicides.
"Everyone in the soybean industry is going to know within hours if and when Asian soybean rust is found in Louisiana," he said.
Lanclos said he expects to see more Asian soybean rust in 2006 compared to last year – when only small infestations were found late in the season after the time when it could have had an economic effect on the crop. Like Hollier, Lanclos said he also is concerned because the fungus has been found in Mexico and Texas, where it can more easily blow into Louisiana on prevailing winds.
"The rust is subtle," Hollier said. "It first infects the underside of the lower leaves of the plants. When you see the symptoms from a distance, it’s too late."
Hollier said the first symptoms can only be seen by carefully looking at the lower leaves – by scouting often and thoroughly.
"First detectors are out there," he said, referring to LSU AgCenter agents, crop consultants and many growers, who "know where to go and what to look for.
"Once it’s in the area, since all varieties are susceptible to some degree, fungicide applications will be called for," Hollier said.
Despite the threat of the new disease, farmers will plant soybeans, Lanclos said.
"It goes to financial decisions," he said. "Beans are a good choice to plant despite the threat of rust."