Soybean Cyst Nematode (Heterodera glycines) Distribution in North Carolina, U.S.A.

Soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is an obligate, sedentary, and devastating parasite that is the number one pathogen of soybean, causing more than twice as much yield loss than any other disease. Estimated annual yield losses in the United States and Canada from 2010 to 2014 were 123,481,000 bushels, worth approximately $1.2 billion at $9.70 per bushel (Allen et al. 2017). SCN was first discovered in the United States in New Hanover County, North Carolina, in 1954 (Winstead et al. 1955) and is believed to have been introduced from Asia (Riggs 2004). SCN is known to spread rapidly. By 2017, it was found in every soybean-producing state in the United States except for West Virginia (Tylka and Marett 2017). The North Carolina Department of Agriculture and Consumer Services’ (NCDA&CS) Agronomic Division has analyzed numerous nematode soil samples to monitor the spread and distribution of SCN. Plant-parasitic nematodes in 500 cm of soil were extracted by a combination of elutriation (Byrd et al. 1976) and sugar centrifugal flotation (Jenkins 1964) methods. The species identification is based on morphology of cysts and the second-stage juveniles and DNA sequencing on the near-full-length small subunit rDNA gene, internal transcribed spacer, and D2/D3 expansion segments of the large subunit rDNA gene when necessary. This report summarizes lab assay and survey results from July 1, 2014, to June 30, 2017. In this period, 100,118 soil samples were submitted voluntarily for routine nematode assay by growers of various crops in 97 North Carolina counties (Fig. 1). Only Alleghany, Clay, and McDowell counties were not represented in this sample population. SCN was detected in 21,922 of the soil samples (21.9%). The overall mean population density on the second-stage juveniles and females was 110 ± 266 (10 to 14,600) per 500 cm of soil. In 2016, a survey program was launched to collect soil samples from soybean fields located in counties where SCN had not been previously detected by