Raymond Schneider, Guidry, Kurt M., Padgett, Guy B., Lanclos, David Y., Benedict, Linda F. | 7/13/2005 8:54:36 PM
The trouble with Asian soybean rust, the disease most feared by soybean farmers, is that the spores that cause it can blow into a field from anywhere, anytime. And Hurricane Dennis could bring in a new wave from South America.
"It appears to be following the same path as Ivan," said Dr. Ray Schneider, LSU AgCenter plant pathologist, speaking of Hurricane Dennis. Schneider discovered Asian soybean rust for the first time in North America in the fall of 2004. And scientists have agreed that Hurricane Ivan carried the dangerous spores to this continent when it struck earlier that year.
The best way to prevent the disease, which spreads like wildfire once it takes hold, is to check fields thoroughly and often, warned a scientist from Brazil, who spoke to a group of about 100 Louisiana farmers at the LSU AgCenter’s Dean Lee Research Station in Alexandria on July 7.
Dr. Tadashi Yorinori came here at the invitation of LSU AgCenter scientists who had made a trip to Brazil in February to learn from that country’s experience with the disease. Yorinori is considered one of the world’s leading authorities on Asian soybean rust, Schneider said, and served as host to the delegation, which also included some Louisiana soybean farmers, during their 10-day stay in the country.
"Go to the doctor and get your eyes checked," Yorinori jokingly told the group as he demonstrated how to check soybean plant leaves for tiny spore-filled blisters on the underside of leaves.
Out in a soybean field at the research station, Yorinori used a bamboo stick the length of a yardstick to hold plants back so he could pick off leaves at the bottom. Rust starts on the bottom leaves making the disease difficult to check from a distance.
Unfortunately, most diseases that affect soybean plants start out as spots – again, making the disease difficult to detect.
"There is no yellow halo around rust spots," Yorinori told the group as he held up the leaves to the light. He advised to collect suspicious leaves, place them in a plastic bag, blow air in the bag like a balloon and close with a rubber band. The bags should not be exposed to direct sunlight. It is best to keep the bags in an air conditioned room.
"Check the leaves in the next day or two. If there are spores, you have rust," he said.
But growers are advised to have the leaves checked by a competent diagnostician, Schneider said, because a microscopic examination is required to determine whether or not they are rust spores or some other fungus.
"We encourage growers to contact their county agents if they suspect rust," said Dr. David Lanclos, LSU AgCenter soybean specialist at the station.
Then, the farmer has to decide if it’s wise from an economic standpoint to spray the field with fungicide, which is relatively expensive, to control the disease. If the disease strikes after the beans are mature, then the disease will not have a major impact on the yield.
But, the disease could spread to other fields where the beans are still vulnerable, Yorinori said.
In Brazil, some farmers plant two crops of soybeans so the crop is present year-round. Some farmers spray their fields up to six times with fungicide to control the disease and prevent yield loss.
"In 2003, 90 percent of the soybean fields had the disease," Yorinori said of the extent of Asian soybean rust in that country. In 2004, there was a drought in Brazil so that helped prevent the disease, since it tends to favor warm and humid conditions.
Yorinori will travel to other parts of the United States to give presentations on Asian soybean rust before heading back to Brazil. Brazilian-born, he received his master’s degree from Cornell University in New York and Ph.D. from the University of Illinois.
"We have a short history of Asian soybean rust, only five years," he said of the disease in his country. The disease was first discovered in the Western Hemisphere, probably moving from Africa, in 2001 – first in Paraguay, a country bordering Brazil to the southwest, and then Brazil.
Lanclos said most Louisiana soybeans are now in what is called the R4 and R5 stages of development, which means they are still vulnerable to the disease. At R8, the beans are ready for harvest.
"In another month, we should be out of danger," Lanclos said. Most of the Louisiana beans will be mature enough then so the disease, if it comes here, won’t affect yields.
Much of the soybean-producing area of Louisiana is experiencing drought-like conditions, so that has probably helped prevent the disease here, Lanclos said. Also, some farmers have sprayed soybean fields with fungicides already to prevent the spread of other diseases.
"There is no Asian soybean rust in Louisiana," Dr. Boyd Padgett, LSU AgCenter plant pathologist at the Northeast Research Station in St. Joseph, told the group. He’s the scientist who found rust-like spores in a spore trap on the station last month. His discovery served as a warning for farmers to boost their scouting of fields.
"We have found no rust in the fields that surround the trap," Padgett said.
The disease, however, has been confirmed in a couple of sentinel plots in Alabama and Florida – one in each state. Sentinel plots are plots planted early throughout the soybean-producing areas of the country to also serve as early warnings for the disease.
Lanclos said Louisiana has 900,000 acres planted in soybeans, according to U.S. Department of Agriculture estimates, which is slightly down from 2004, when there were 1 million acres planted in soybeans.
According to LSU AgCenter estimates, the 2004 soybean crop brought $241 million to the Louisiana economy, said Dr. Kurt Guidry, LSU AgCenter agricultural economist.
The latest information about Asian soybean rust is on the LSU AgCenter’s Web site (www.lsuagcenter.com).
Kurt Guidry, at (225) 578-4567 or firstname.lastname@example.org
David Lanclos, at (318) 473-6530 or email@example.com
Boyd Padgett, at (318) 435-2157 or firstname.lastname@example.org
Ray Schneider, at (225) 578-4880 or email@example.com
Linda Foster Benedict, at (225) 578-2937 or firstname.lastname@example.org