As more Illinois farmers turn to cover crops to boost soil health, reduce erosion, and improve water quality, a key question remains: how do cover crops impact one of soybean’s most persistent threats—soybean cyst nematode (SCN)?

With SCN present in more than 80% of Illinois fields, understanding how management practices affect populations is critical. That’s exactly what a team led by Dr. Jason Bond and Dr. Ahmad Fakhoury of Southern Illinois University, along with agronomist John Pike of Pike Ag, set out to study in an Illinois Soybean checkoff-funded project. 

To mimic real-world farming conditions, the team collected nearly 3,000 soil samples from multiple on-farm cover crop trials across Illinois. These trials included a wide range of cover crop species—from cereal rye and annual ryegrass to clover, hairy vetch, and rapeseed—grown in diverse soils and climates. 

Samples were taken at four key times: 

• At cover crop planting in the fall 

• Before soybean planting in the spring 

• Mid-soybean season in August 

• After harvest (ongoing in 2024) 

This gave researchers a detailed picture of how SCN populations shift through the season and across cover crop treatments. 

So far, researchers observed the following: 

• No consistent SCN suppression was found in cereal rye plots compared to fallow ground. 

• In highly infested locations, some non-cover crop plots showed more SCN reduction, possibly due to drier soil in the cover crop treatments. 

• At the Henry White Farm site, most cover crop species (cereal rye, hairy vetch, rape, and clover) had similar SCN counts as no-cover treatments. 

• Annual ryegrass showed the most promise, with a notable reduction in SCN populations compared to untreated plots. 

The team is also investigating whether cover crop planting and termination dates influence SCN dynamics, something farmers may be able to adjust in their management plans. 

This research is still in progress, but the early takeaway is clear: not all cover crops affect SCN the same way, and context matters. Soil moisture, nematode pressure, species selection, and timing all play a role in outcomes. 

As data continues to roll in, Illinois soybean farmers will gain a better understanding of which cover crops might help suppress SCN—or at the very least, avoid making it worse. For now, annual ryegrass appears to be a cover crop worth watching, especially in fields with known SCN pressure. 

With resistance to PI88788—the most common source of SCN resistance in soybeans—on the rise, finding additional tools like cover crops could help farmers manage SCN long-term. 

The study will be finished during the 2025 growing season and project updates and findings will be shared via the Field Advisor Research Hub.  

Cover crop field. Photo by Illinois Soybean Association