A survey of soybean cyst nematode population densities and phenotypes in Illinois: 2018 and 2020

In Illinois, Soybean cyst nematode (SCN: Heterodera glycines), was estimated to cause over 15 million $U.S. in losses as recently as 2021. In addition, populations of SCN insensitive to PI88788 derived resistance, the most commonly used SCN resistance source in commercially available soybeans, continues to increase. Despite this, awareness of this pathogen and its current status in the state are relatively lacking. A survey was conducted in 2018 and 2020 to assess the presence, abundance, and virulence phenotypes of SCN in Illinois soybean fields. Soil samples were collected and processed for SCN eggs after harvest each year and samples exceeding threshold values of SCN eggs were virulence tested using the Hg type test. A total of 95 samples were collected, representing 46 counties. Eighty seven percent of fields sampled contained SCN eggs, with 38% containing population densities over 2,000 eggs /100 cm3. All samples included in the Hg type test had a female index >10 on indicator line PI88788, indicating insensitivity to this resistance source. Extrapolated across soybean production acres, these data indicate that approximately 4.4 million acres of soybeans contain levels of SCN requiring SCN management and over 54% of acres using cultivars derived from PI88788 are not fully protected from this pathogen.