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Are you benchmarking your soil’s SCN population?

Because SCN can impact yield, even without showing above-ground plant symptoms, it pays to know what is going on below ground—how big the egg population is and if it is trending up or down. If egg population is going down, your management is working. If egg populations are increasing, your management isn’t.

SCN is a microscopic roundworm that lives in the soil and takes up residence in soybean roots. Female species of SCN invade the roots and extract water and nutrients from the plant. They form egg sacks (cysts) that bulge out of the root and become visible to the naked eye, looking like a small version of a nitrogen-fixing nodule.

You can sample for SCN using a conventional soil probe. Cysts and eggs can be pulled from the soil and cysts can be broken so they expel all their eggs. Cysts contain around 200 to 500 eggs.

SCN distribution is very patchy in a field so it is important to take many sub-samples to increase the possibility of hitting the concentrated areas. Pulling soil samples to collect eggs is much like soil sampling. A soil sampling probe should be used to collect sub-samples in the top 6- to 8-inches. Collect one sample of 12 – 24 soil cores for every 10 acres. Composite a quart of soil without root samples. Samples can be taken at any time; the soil is fit for sampling in spring, summer and fall. Autumn is an excellent time, after corn harvest and going into soybean planting next season.

Sampling patterns are critical to make sure you get a good measurement of egg counts. An egg count of 100 is significantly different from 1,000 or 5,000, so you need a good composite sample because it dictates the urgency of your actions. Conventional management guidelines based on egg count are shown below.

University of Illinois

Sampling for nematodes might appear routine, but proper sampling patterns and protocol are critical for accurate diagnosis.

Do you sample for SCN egg counts? Sampling should become routine, just like soil sampling, so you know how big the population is and how it is trending. You wouldn’t grow corn or soybeans without tracking pH and soil fertility because you know that puts yield at risk. Same goes for SCN.

 Soybean agronomist Daniel Davidson, Ph.D. posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.