QUINCY, Ill. — With excellent growing conditions and planted acreage likely leading to a record soybean harvest this year, a soil-based disease could take a bite out of yields in Illinois, particularly in the west-central part of the state.

Signs of sudden death syndrome (SDS) caused by the fusarium organism began to surface in parts of Illinois fields about three weeks ago, and its presence is continuing to spread, according to University of Illinois Extension trackers. How much it will impact yield is the million-dollar question, and there’s no scientific way to determine the answer at this point.

“Some years you see initial infection, then it stalls out and doesn’t progress any further along the plant,” said Extension educator Mike Roegge. “When that happens, you don’t see a lot of yield loss. Other years it continues to progress, kills the plant prematurely and expands in the field to take a larger portion.”

First discovered in Arkansas in the early 1970s, the disease since has spread to all areas of the Midwest, but its impact varies from year to year.

What scientists know about the infection is that it becomes more prevalent when beans are planted in cooler-than-normal temperatures and in generally wetter conditions than average, Roegge said. It worsens if fields are hit with heavier-than-normal amounts of rain during mid-summer

Early spring in central and northern Illinois this year was noticeably cooler and wetter than normal, said Roberta Simpson Dolbeare, a Pike County farmer and board member for the Illinois Soybean Assoc.

“The crops aren’t going to be what we thought they might be,” Dolbeare said. “We’re going to see some reduction in yield, but how much, I’m not real sure.”

Managing fields with SDS is not easy, and growers have few options to limiting its impact. Some soybean varieties believed to be the most resistant to SDS is one option, but scientists emphasized the importance of documenting the areas impacted each year and look to rotate crops on different schedules.

“The primary method of managing SDS is to choose the most resistant soybean varieties available,” said University of Illinois plant pathologist Carl Bradley. “Some evidence has shown that high soybean cyst nematode (SCN) egg populations may also increase the likelihood of severe SDS; therefore, managing SCN populations through resistant varieties and crop rotation may also reduce the risk of SDS.”

Based on its most recent crop estimates released Sept. 12, the nation as a whole is expected to harvest a record 3.91 billion bushels of beans, up 19 percent over last year’s total. Yields are expected to average about 47 bushels per acre. In Illinois, though, bean yields are anticipated in the 56-bushel-per-acre range with a harvest of about 562.8 million.