Abstracted from an article by Dean Bohn
Soybean cyst nematodes
are almost invisible without magnification, says George W. Bird, professor and
nematologist with the Department of Entomology at Michigan State University
Extension in East Lansing.
The pest, discovered in Japan in 1934, arrived in North Carolina in 1954. It traveled the Mississippi River to soybean country, where it flourished. The worm appeared in Michigan in 1987 and has reached 39 counties, comprising more than half of the state's soybean crop. Losses can range from five bushels an acre to the entire crop.
Each cyst can hold about 250 eggs. When they drop off the root, they can remain viable in the soil for up to 12 years without a host. Growers can mistake plant damage for nutrient deficiencies, drought stress, herbicide injury or other plant diseases.
The first symptom of nematode injury in the field is circular or oval areas of stunted, yellowed plants. The areas vary in size, often showing a sharp dividing line between stunted and healthy plants, Bird said.
Once present in the soil, the nematodes cannot be eliminated, but they can be managed. The most important factors in fighting infestation are good rotation and increasing soil organic matter, Bird said. Manure also pays off well.
Through the years, scientists have tried to naturally develop soybean cyst nematode-resistant varieties. Ina Michigan field plot, resistant varieties fared much better than susceptible varieties. Nematode-resistant varieties generally have one of three sources of resistance -- Peking, PI (plant introduction) 88788 or PI 437654. Historically, most varieties are derived from PI 88788. Lowest nematode population levels were on Pioneer's 91M80, Dyna Gro's 3221, Asgrow's AG2405, Lathum Seeds' E2611 and Midwest seeds' GR2831 -- all of which had no nematodes.