ISWS Researchers Monitor Soybean Rust Spores in the Atmosphere, Illinois State Water Survey

ISWS Press Release

For Immediate Release July 6, 2008
ISWS Researchers Monitor Soybean Rust Spores in the Atmosphere
David Gay - (217) 244-0462,
Lisa Sheppard - (217) 244-7270,

Spores of soybean rust disease can travel great distances, buffeted by wind and rain, from field to field, crossing county, state, and even country lines. Using a network of precipitation-monitoring sites, researchers at the Illinois State Water Survey (ISWS), a division of the Institute of Natural Resource Sustainability at the University of Illinois, along with the U.S. Department of Agriculture and the University of Minnesota, are discovering where spores appear and studying how they might predict future soybean rust infestation in local areas.

Soybean rust is a significant disease in which tan spots appear first on the underside of soybean leaves, causing yield losses greater than 50 percent under certain conditions. Blisters that form in the spots break open and release spores.

From May to October, nearly 80 ISWS National Atmospheric Deposition Program (NADP) stations in the Midwest and South are used for analyzing weekly rainfall samples for the presence of soybean rust spores. The spores are large enough to be washed out of the lower atmosphere when it rains, and are detected, according to David Gay, coordinator of the NADP at the Illinois State Water Survey.

"Since the NADP is used to monitor precipitation chemistry nationwide, it was an ideal platform to study deposition of soybean rust spores," he said. "If there is a presence of spores in the sample, we can find it."

The NADP began monitoring for spores in 2005, soon after soybean rust was first confirmed in the United States.

Precipitation filtrate samples are sent to the U.S. Department of Agriculture where gene tests are performed to determine the presence and number of spores in a sample. In the future, researchers will be able to determine where the spores originated by studying weather patterns from the recent past.

Ideal conditions for spores to travel long distances are strong winds with storm systems that lift spores high into the atmosphere, Gay said. Rain redistributes spores locally and in part provides the damp conditions that spores need to thrive.

Spores overwinter in southern U.S. and in Central and South America where they infect other plant species, including kudzu, year-round.

"The spores are distributed in waves into the U.S. year after year," Gay said. "Theoretically, one plant in South America could produce the soybean rust spores that infect a field in Illinois."

Once soybean rust infects a field, costly fungicide treatments may be needed. If left untreated, the disease can potentially cause yield losses due to premature defoliation, fewer seeds per pod, and decreased numbers of filled pods per plant.

Working with researchers at the University of Minnesota, Gay and ISWS colleagues developed a warning system to predict the risk of the disease. An atmospheric model was developed and tested in Minnesota with daily predictions up to seven days in advance using forecast data from the U.S. National Weather Service. The model showed 65 percent accuracy.

Warnings about soybean rust spore locations and ideal weather conditions could assist producers with disease management decisions, Gay said.

Daily risk predictions are available through the University of Minnesota Extension at:

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