Growers Others Urged To Step Up Watch For Rust In Soybeans

Raymond Schneider, Padgett, Guy B., Coreil, Paul D., Hollier, Clayton A., Boethel, David J., Benedict, Linda F.  |  6/23/2005 2:46:58 AM

News Release Distributed 06/22/05

Spores like those associated with Asian soybean rust have been found in a trap set up by the LSU AgCenter in a field near the Northeast Louisiana town of St. Joseph.

"This is not a cause for alarm," said Dr. David J. Boethel, vice chancellor for research at the LSU AgCenter. "Because of the small number of spores found, confirmation is not possible at this time. But they appear similar to those that cause Asian soybean rust, and scouting efforts should be increased."

Word about the spores’ resemblance to the kind that cause Asian soybean rust – the disease most dreaded by soybean growers because of its potential to quickly destroy entire fields of the crop – came late Tuesday (June 21) from a laboratory at the University of Arkansas.

Dr. Ray Schneider, an LSU AgCenter plant pathologist who discovered Asian soybean rust for the first time in North America in a soybean field near Baton Rouge, said the Arkansas lab was recently established to run tests of spores from spore traps sent in from soybean-producing states. Funding for the trapping system comes from Syngenta, an agribusiness company, Schneider said.

The traps, mounted on stakes in selected soybean fields across the state, include a slide (for a microscope) covered with a sticky substance, Schneider said. These slides are sent to the Arkansas lab once or twice a week.

Only three suspicious spores were on the slide, which was sent to the lab by Dr. Boyd Padgett, a plant pathologist at the LSU AgCenter’s Northeast Research Station. The trap was in a soybean field at the station, which is located near the Mississippi River in northeast Louisiana. An adjacent soybean field is not exhibiting symptoms of Asian soybean rust, Padgett said.

"About 100 spores are required to do the DNA tests for confirmation of Asian soybean rust," Schneider said.

The next step is to watch for symptoms of the disease on soybean plants. Finding the spores doesn’t mean soybean plants will necessarily get infected.

"That all depends on conditions," Schneider said. "Moisture is required for an infection to start. If we get regular rain and heavy dews, the occurrence of the disease is more likely."

If the spores are the ones that cause the dangerous disease and if conditions are right, it will be about two weeks following the "spore shower" before symptoms of the disease show up. Symptoms include rusty-colored pustules on leaves. The leaves then dry, turn yellow and fall off the plant.

"Our county agents have been trained to detect rust and provide farmers with the appropriate actions to take," said Dr. Paul Coreil, vice chancellor for extension at the LSU AgCenter.

Because of last year’s late-season discovery of Asian soybean rust in the country, soybean growers, industry people and university experts had some early warning and have been able to prepare to manage the disease – should it develop in this year’s crop.

The disease, first discovered in Asia in the early 1900s, has steadily been spreading. It also is in Africa and South America, where it has caused devastating yield losses because it spreads quickly if it goes undetected.

"The disease is difficult to detect because it starts on the lower leaves of the plant. Management requires intense scouting," said Dr. Clayton Hollier, an LSU AgCenter plant pathologist.

To help with early warning of the disease, the LSU AgCenter monitors sentinel plots, which were planted earlier this year, and selected soybean production fields.

Even though the spore discovery does not mean farmers will see the disease this year, it does require a stepped-up scouting effort, experts say.

"We are alerting growers to continue and increase their scouting efforts," Hollier said. "Growers certainly need to be prepared to spray for the disease.

"If a grower is applying fungicides for the Cercospora diseases, a tank mix or pre-mix to take care of Cercospora and rust may be prudent," Hollier said. "We encourage growers to contact their local county agents for advice."

Louisiana farmers commonly spray soybean fields to control Cercospora diseases, which are diseases somewhat similar to Asian soybean rust in that they cause defoliation and yield losses.

The traps being used in fields provide an even earlier warning system than the sentinel plots, said John Rupe, plant pathologist at the University of Arkansas, who is in charge of the testing lab there.

"We are just getting started with this," Rupe said. "So far, six states are participating and more will be joining the effort."

Besides Louisiana and Arkansas, the other states are Illinois, Kentucky, Mississippi and Tennessee.

"This is a very important find," said Glen Hartman, research plant pathologist with the U.S. Department of Agriculture’s Agricultural Research Service and an associate professor at the University of Illinois at Urbana-Champaign. He’s one of the nation’s leading experts on Asian soybean rust, Schneider said.

"What it means is that we’re forewarned that the disease may be getting a start this growing season," Hartman said. "Scouting must be intensified.

"If we can get to the R6 growth stage without finding the disease, we are out of the danger period," Hartman said.

Asian soybean rust can destroy soybeans through the R6 growth stage, which is when the pods are forming. The disease can’t hurt yields in the last two stages (R7 and R8) when the beans yellow and the plant is harvested.

The latest information about Asian soybean rust is on the LSU AgCenter’s Web site at 


David J. Boethel at (225) 578-4181 or
Paul Coreil at (225) 578-6083 or
Glen Hartman at (217) 244-3258 or
Clayton Hollier at (225) 578-2186 or
Boyd Padgett at (318) 435-2157 or
John Rupe at (479) 575-2778
Ray Schneider at (225) 578-4880 or

Linda Foster Benedict at (225) 578-2937 or

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