Diagnosis and Management of Soybean Cyst Nematode

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Soybean Cyst Nematode is the most devastating and yield limiting pest of soybean in our region. Since the flood of 1993, soybean cyst nematode infestations are common in many river and creek bottom fields. Eggs can survive in the soil for many years even when a host plant is absent. It is often difficult to identify fields with SCN, because lower yield at harvest may be the only above-ground symptom. Yields may decrease for a number of years before the reduction becomes obvious. Yield loss of 30 percent is possible without any obvious problem until harvest. When SCN is present and plants are under stress, symptoms such as leaf margin or general chlorosis, plant stunting, or under extreme cases, plant death can occur.

The most accurate way of determining whether SCN is present in a field is to have the soil tested in a nematology lab for the presence of SCN eggs. We recommend that fields be sampled in the fall before soybeans are to be planted the next spring. We suggest that SCN-susceptible soybeans be planted no more than once every three times that soybeans are planted, and only if the SCN egg count is below the damage threshold of 500 eggs per cup of soil. If your egg count is greater than 2000 eggs per cup of soil, reduced yield can be expected even with resistant varieties.

Once SCN have been identified on your farm, it is important to manage them. If you have uninfested fields, avoid introducing SCN whenever possible. SCN can spread on anything that moves soil. It is best to till uninfested fields first to avoid spreading SCN in soil on machinery. Rotate soybeans with crops that are not SCN hosts, such as corn, wheat, grain sorghum, rye, alfalfa, or forage grasses. Also plant SCN resistant varieties and rotate sources of resistance. By maintaining plant health and good weed control, the impact of SCN on your soybeans will be minimized. For more information on SCN contact your local Extension office.

Leon Stites, HLStites@oznet.ksu.edu
County Extension Agent, Agriculture
Leavenworth County, Kansas
Kansas State University Research and Extension