Distribution and Economic Impact of SCN

Soybean cyst nematode (SCN), also known as Heterodera glycines, was first found in the U.S. in North Carolina in 1954. Prior to that time SCN was known only from China, Japan, and Korea. The nematode now occurs in many production areas worldwide including Canada and South American countries such as Brazil and Colombia. There are unconfirmed reports of SCN in other South American countries.

 The nematode may have been introduced into the U.S. several times during the late 1800's in soil imported from the Orient for the purpose of obtaining bacteria to modulate soybean roots.

Distribution of SCN in 1992 is indicated by red dots (distribution of areas where soybean production exceeds 5,000 acres per county is shown in green).

During the ensuing years, bacterium infested soil was used as inoculant which was spread locally by growers and was sent to various state experiment stations for research purposes.

 The early use of soybean in the U.S. was primarily as a forage or green manure crop. In 1919, 99,000 acres of soybean were planted for production of seed. During the WWII era, soybean acreage for production of seed increased from 4.2 million acres in 1939 to about 9 million acres in 1942. Coinciding with the continuing increase in soybean acreage in the 1940's and 1950's was a decrease in oat acreage in northern states and a decrease in cotton acreage in the southern states.

SCN damage.

 At present soybean is planted on nearly 60 million acres. In most production areas, rotations which had prevented the buildup of SCN populations were abandoned. In 1965, 8 states were known to have infestations. In 1975, infestations were reported in 14 states. By 1987, 26 states and Ontario, Canada were infested. It is likely that SCN will soon occur in all soybean production areas in the U.S.

 Documenting the economic impact of SCN is difficult because many producers suffer declining yield for several years without knowing that they have SCN. Planting SCN-resistant Forrest soybean in the southern U.S. on farms with known SCN infestations prevented $401 million in crop loss during 1975-1980. The cost of developing Forrest was less than $1 million. If nationwide losses are conservatively estimated at 1 %, SCN cost soybean producers $121 million in 1992 alone. However, as Table 1 shows, losses in infested states often exceed that estimate.

Table 1. Estimated percentage losses of soybean yields due to SCN.