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 United States.