Harvest is the perfect time for checking your fields for SCN. Know your number!

Published: October 25, 2021

Soybean harvest has already kicked off in Missouri and it is important that farmers test their fields for soybean cyst nematode (SCN). The SCN is the most yield-limiting pathogen of soybean across North America. This nematode penetrates and feeds on soybean roots (Figure 1) impairing the plant's ability to absorb water and nutrients, decreasing their yield potential. Soybean stunting and yellowing of the leaves are the classic aboveground symptoms caused by SCN. These symptoms can occur in patches or throughout a whole field when the nematode population density is high and SCN is widely distributed. However, soybean fields showing no symptoms of SCN can have up to 30% reduction in yield, making sampling the only way to identify a problem that you might not actually see. It is also important to point out that SCN eggs can survive in the soil for years without a host, only infecting when soybean is once again grown in that field. Sampling soybean fields to check SCN egg counts periodically (every three years) is the only way to monitor whether the SCN populational densities are under control.

Figure 1 Soybean cyst nematode females feeding on soybean roots.

Right after harvest is the best time of year to take soil samples for SCN. Nematode levels are highest following a soybean crop and at the end of the season. High population levels will increase the chance of detecting the nematodes in your field. Since SCN egg counts are only as good as the sample taken, here are some suggestions to take into consideration when sampling for SCN:

1. Divide your field into 20- to 40-acre management zones.
2. In each zone, take 20 soil cores 6-8 inches deep in a zig-zag pattern and thoroughly mix the cores together into one composite sample per zone (bring a bucket to aid in the mixing process). Bag about a pint of the composite sample for submission.
3. Label the bag (Field zone ID, crop rotation and other pertinent details). Avoid storing it in the sun and ship as soon as possible.
4. Fill out a submission form (available at https://scndiagnostics.com/links/sample_submission_form.pdf).

FREE SCN egg counts for Missouri farmers (two samples per farmer) are available as part of the SCN Coalition through the Soybean Checkoff. More information about your FREE SCN egg counts or SCN sampling can be obtained through MU Extension by contacting your local extension office or the SCN Diagnostics lab directly at scndiagnostics@missouri.edu or 573-884-9118.