This article originally appeared in University of Missouri’s Integrated Pest & Crop Management Newsletter and has been reposted with permission. Information on where to submit Missouri soil samples has been omitted.
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:
Limit the size of the area being sampled: 10 – 20 acres is a good target.
Using a bucket and probe or shovel, walk the area in a W or Z pattern, sampling about 8 inches deep between the rows. Take about 20 cores (with a shovel take ¼ cup of soil from near the shovel tip). Mix the cores well into a composite sample, and bag about a pint of it for submission.
Label the plastic bag, avoid storing it in the sun and ship it as soon as possible.
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, or you haven’t had your soils tested for SCN in the last five years, a 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:
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 is used if you feel you may have a corn nematode problem.
Manjula Nathan is an Associate Professor and Director of MU Soil Testing and Plant Diagnostic Service Lab at University of Missouri.