Soybeans planting is just weeks away, and it is important that you test your fields for Soybean Cyst Nematodes(SCN) now before planting. SCN is a major concern to growers throughout the state. These parasitic round worms invade the plant roots and suck nutrients from the plants, decreasing their ability to produce adequate yields. The challenge with preventing SCN is that infected plants do not easily express symptoms. Fields can sustain up to 30% yield loss due to SCN without displaying any symptoms, making sampling the only way to identify a problem that you might not actually be seeing. Producers often ignore the possibility of SCN because they plant resistant varieties, but it is important to realize that SCN can adapt to the resistance lines if the same source is used year after year. It is important to check SCN egg counts periodically (every three years) to see if the egg counts are increasing.
Although typically fall is a good time to check fields for SCN because the results will be available for use in making decisions and plans for the next growing season, especially in terms of crop rotation and soybean variety selection, it is still not too late to sample the fields now ahead of planting. Since SCN egg counts are only as good as the sample taken, here are a few tips for sampling for SCN:
The SCN Egg Count test is what most soybean growers would need. If you notice a field that is slipping in yield, had high egg counts years ago to sample or you haven't had your soils tested for SCN in the last five years, a $15 SCN Egg Count test is a worthwhile investment that can offer peace of mind and save considerable yield loss. If results indicate that the egg count is medium or high, you may want to sample your other fields.
The HG Type race test would be for the grower who has high egg counts after growing resistant lines for years. This test indicates the HG type (or race) of SCN in the field, and what sources of resistance would be good to choose when buying seed. The website below offers a comprehensive listing of the "sources of resistance" for commercial soybean lines: http://www.ag.uiuc.edu/~wardt/cover.htm
The Complete Nematode Analysis test is a count of the worm stages of all the plant parasitic nematodes in the sample. (It does not give an SCN egg count.) This test would be important for growers in SE Missouri who may have the Root Knot nematode as well as SCN.
The Extension Nematology Lab has a website has more information on how to sample, the tests we provide, and how samples are actually run in the lab. A submission form can also be downloaded from the site. http://soilplantlab.missouri.edu/nematode. The turn around time for the lab is typically 3-5 to working days.
For management decisions regarding SCN please refer the University of Missouri Extension Guide on Soybean Cyst Nemtode: Diagnosis and Management. This guide can be downloaded at http://muextension.missouri.edu/xplor/agguides/crops/g04450.htm
REVISED: December 1, 2011