Sudden death syndrome (SDS) and soybean cyst nematode (SCN) are two significant diseases that greatly affect soybean yields. Between 1996 and 2023, estimated total yield losses in North Dakota due to both SCN and SDS reached $0.9 billion (Crop Protection Network 2024). Both pathogens can infect soybean roots early in the growing season, highlighting the need for effective early-season management strategies. SDS initially manifests as interveinal chlorosis and necrosis of the leaves in the upper canopy, potentially leading to defoliation over time. In contrast, SCN damage is typically observed in stunted and yellowed plants within fields. However, the symptoms of SCN damage may not always be obvious, and yield losses can reach as high as 30%. Furthermore, the presence of SCN can exacerbate the foliar symptoms associated with SDS. In 2024, SDS was confirmed in several North Dakota counties, including Cass, Richland, and Dickey, where high populations of SCN are also reported. Given the economic importance of soybeans in the state and the growing prevalence of both SCN and SDS, it is critical to develop strategies that address the dual threat posed by these pathogens. This study aims to explore the interactions between SCN and SDS, providing insights to inform the development of more effective management strategies for soybean farmers.

Objective 1: To assess how varying soil moisture levels affect SCN populations and SDS (F. virguliforme) severity in soybeans.

Objective 2: Examine how resistance to SCN affects the severity of SDS.

• A protocol will be developed to screen soybean varieties for susceptibility to SCN and SDS, using isolates from North Dakota.
• We will create a comprehensive overview of the interactions between SCN and SDS, highlighting knowledge gaps and areas for further investigation in two peer-reviewed manuscripts.
• Extension materials will be prepared for soybean farmers, emphasizing the relationship between SCN and SDS based on our research findings.

Soybeans are an important crop for farmers in North Dakota. However, SCN and SDS threaten soybean yields, and in counties where both SCN and SDS are prevalent, yield losses can be severe, making it essential to develop effective management strategies for these pathogens. This research focuses on understanding the interactions between SCN and SDS, providing valuable insights into how these pathogens jointly affect soybean health. With this knowledge, more targeted and effective management strategies can be developed to address both pathogens simultaneously. The goal of this research is to help farmers implement precise control measures that will reduce crop damage, minimize yield losses, and improve profitability. Additionally, the research could contribute to the broader understanding of pathogen interactions in agricultural systems, benefiting soybean growers beyond North Dakota.