Farmers across Illinois are being encouraged to take advantage of a free testing program for soybean cyst nematode (SCN) — the most damaging soybean pathogen in the United States. Despite its invisible symptoms above ground, SCN is silently cutting yields in fields across the state, where it has been detected in nearly every county.
Experts warn that SCN can go undetected for years because it attacks soybean roots without visible signs on the plant. Jason Bond, a plant pathologist at Southern Illinois University, says that SCN is present in roughly 80% of the fields surveyed in Illinois. “When farmers test for it, they’ll most likely find it,” he notes.
Since the Illinois Soybean Association (ISA) launched its checkoff-funded SCN testing program at the University of Illinois in 2023, more than 1,500 samples have been submitted from 72 counties. Results show average egg populations of about 1,500 eggs per 100 cubic centimeters of soil, with only a few counties reporting critical levels above 10,000.
Although an egg population of 400 to 500 per 100 cubic centimeters may seem low, experts stress that even these levels can reduce yields. Consistent management — including crop rotation, planting resistant varieties, and using different sources of SCN resistance — helps prevent populations from rising. “If egg counts stay around 500, it means your management is working,” Bond says.
However, once egg populations exceed 10,000, more aggressive strategies such as rotating to non-host crops are necessary. ISA agronomy director Abigail Peterson compares managing SCN to maintaining long-term health: “It’s like high blood pressure — you can’t eliminate it, but you can control it through several coordinated efforts.”
One of the major concerns among scientists is that SCN has adapted to overcome resistance genes used in most soybean varieties. Studies show that around 70% of nematode populations in Illinois can reproduce on PI 88788, a once-reliable resistance source. The pest also survives in soil for years and can reproduce on certain cover crops and weeds, making long-term control a continuous challenge.
