|By NANCY VORIS
WEST LAFAYETTE, Ind. — Asian soybean rust was found Oct. 18 on double-crop soybeans in southern Indiana counties. It was the first detection of soybean rust in the state.
“Perhaps the most important thing we have learned from the appearance of soybean rust in Kentucky, Illinois and Indiana is that southerly winds can carry spores long distances,” said Greg Shaner, Purdue University Extension plant pathologist.
“Winds carried these spores more than 500 miles before they landed, and these were still viable after the long journey.”
Plant pathologists from Purdue found one pustule on one leaf in Knox County and one leaf with several pustules in Posey County out of 100 leaves tested. Later, more rust was found in Vanderburgh and Warrick counties.
Because more than 90 percent of Indiana soybeans already have been harvested or have reached maturity, there isn’t much green, leafy plant tissue remaining for rust to infect, Shaner said.
The infection likely originated with the same introduction of spores that hit several counties in western Kentucky and southeastern Illinois.
Soybean rust is destroyed by freezing temperatures in the Midwest. In order for soybean rust to return to the Indiana, spores would have to build up again in regions where no killing frost existed and winds would have to carry the spores northward.
“The presence of rust in Indiana does not necessarily mean it will be a problem next year,” Shaner said.
What this means for Indiana soybean producers is that if soybean rust returns to the Midwest in future growing seasons, the process for identification will move much more quickly.
“One thing we have learned from this exercise is how difficult it is to detect rust at very low levels,” he said.
Diagnosticians looked over the surface of every leaf under a dissecting microscope, a three-hour process to examine 100 leaves. Leaves with pustules were flagged with a marker pen.
“When I looked at them with a pocket hand lens, the normal way of scouting for the disease in the field, it was difficult to see the pustule,” Shaner said. “Once a leaf is heavily rusted, it’s easy to diagnose the rust, but catching it very early, when a fungicide needs to be applied, will be tricky.”
Seed companies including Pioneer Hi-Bred International, Inc. continue research into building soybean rust-resistance in their products.
“The Pioneer soybean research team is working as efficiently and quickly as possible to develop defenses against rust if the issue becomes a problem for U.S. soybean growers, said Pioneer spokesman Jerry Harrington.
Researchers have been testing existing varieties to see the products that fare well against soybean rust, and are screening wild relatives of soybeans from India and the Philippines for rust resistance. Scientists are also searching gene banks to find plant sources that are resistant to rust so they can introduce those genes into Pioneer brand varieties.
“Researchers have run a line of soybean seeds through radiation (mutagenesis) to create mutations,” Harrington said. “They are currently testing those seeds to see if those modifications make them more resistant to rust.
“Of course, Pioneer researchers are moving ahead on a number of biotechnology approaches to insert a trait into soybeans that make them resistant to rust.”
For more information on soybean rust, visit the Purdue Plant and Pest Diagnostic Lab website at www.ppdl.purdue.edu/PPDL/soybean_rust.html or call the Purdue soybean rust hotline at 866-458-7878.
This Indiana farm news was published in the Oct. 25, 2006 issue of Farm World, serving Indiana, Ohio, Illinois, Kentucky, Michigan and Tennessee.