AMES, Iowa - An Iowa State University researcher is using computer models to figure out how brown stem rot causes damage in soybean fields, and how to better manage the disease, which can cause yield losses of up to 28 percent.

Bill Batchelor, associate professor of agricultural and biosystems engineering, has been developing a computer model to study brown stem rot (BSR), a late-season, cool-temperature disease caused by a fungus. BSR is present in up to 90 percent of soybean fields in the north-central US.

His research is part of the "Yields Project," a multi-state effort to understand factors limiting soybean yields. The project, which Batchelor coordinates, also involves the University of Illinois, the University of Wisconsin and Southern Illinois University.

"When you understand something well enough to model it, then you really understand it," Batchelor explained. "A computer model also can point to gaps in our knowledge and allow us to customize information. It allows for 'what-ifs'."

Batchelor can use the model to turn on and off stresses, like BSR and soybean cyst nematode. That ability can help determine the relative impact of each on soybean growth and yield. Statistical data can tell researchers whether changes are significant, but say nothing about the relative effect of multiple stresses, Batchelor said. Computer models can help researchers determine how different stresses interact, and the relative impact of each stress on growth and yield, he said.

"We've studied how BSR defoliates the canopy, which is the first step to understanding the damage," he said. "Now we're figuring out how to apply that knowledge to on-farm use."

Soybean growers don't have a good way to assess defoliation, Batchelor said, but they know all about the "browning" of their plants. Researchers are now using the length of stem browning at the end of the season to determine the extent of damage and when it starts to occur.

"If we know the date when BSR symptoms begin, we may be able to predict the onset of the disease," Batchelor said.

He is working on ways to make computer tools accessible to farmers. On the farm, a computer program could be used to assess the risk of the decisions farmers make. Batchelor said the model could help soybean growers select which soybean varieties, tillage methods and herbicides to use when BSR is present.

In future research, Batchelor plans to study the cumulative effect of multiple stresses on yields. He also will be studying the environmental risks of corn and soybean systems such as nitrate leaching and phosphorus movement.

The Yields Project is a multi-state research program funded by Iowa and Illinois checkoff dollars through the Soybean Research and Development Council (SRDC). The Yields Project is one of the largest soybean research projects ever undertaken to understand factors that limit soybean yields.