A Survey of Soybean Cyst Nematode Population Densities and Phenotypes in Illinois: 2018 and 2020

Abstract

In Illinois, soybean cyst nematode (SCN; Heterodera glycines) has been estimated to cause over $15 million in losses as recently as 2021. In addition, populations of SCN insensitive to PI 88788-derived resistance, the most commonly used SCN resistance source in commercially available soybeans, continues to increase in soybean production areas in the United States. Despite this, awareness of this pathogen and its current status in the state is relatively lacking. A survey was conducted in 2018 and 2020 to assess the presence, population level, and virulence phenotypes in Illinois soybean fields. Soil samples were collected and processed for SCN eggs after harvest each year, and samples with sufficient numbers 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 PI 88788, 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 PI 88788 are not fully protected from this pathogen.