Sampling to determine if SCN is responsible for poor yields


Recommended technique: Collect soil samples and have them tested for the presence of SCN.

When to sample
Fall is often the best time to sample as you review harvest data. Take samples from the harvested soybean field, either in a zig-zag pattern or as part of a grid sample, as described below.

How to sample
The equipment you need for sampling soil for SCN is the same equipment you use for taking a soil sample for soil nutrient analysis: a soil probe, a bucket, and a plastic or plastic-lined soil bag. Sample the top 6 to 8 inches of soil.

Where to sample
You'll want to take 10 to 20 cores in a 20 acre area. If the field is larger, break the field into 20 acre units and take 10 to 20 cores per unit. Use a zig-zag pattern to collect the soil cores.

OR, if you are already collecting soil samples on a 2.4 or 2.5 acre grid pattern, collect two extra cores from every 8 or 9 grid cells, and place those extra cores in a separate bag for SCN testing.

Photograph of farmer taking soil samples   Areas that are suggested to sample from
There is a greater likelihood of discovering SCN if soil cores are collected within the root zone of the soybean crop that was harvested.   You may also want to include samples from a suspect, or high risk area such as the field entrance

No matter what sampling pattern you use, the more cores you take, the better the estimate of SCN population density across the field. SCN is tiny, it is not uniformly distributed and it doesn't move far on it's own. Also, each SCN female produces 200 or more eggs in a cluster. Therefore, SCN tends to be very aggregated or clustered in fields and soil sample results tend to be highly variable.

You may also want to include samples from a suspect, or high risk area, such as

  • near a field entrance
  • areas that have been flooded at one time
  • areas of high soil pH (greater than 7)
  • areas where weed control isn't quite as good
  • areas where the yield seemed to be a little low the last time soybeans were grown
  • along fence lines where wind-blown soil accumulates.

Mixing and packing the soil sample
Bulk the cores in a container and mix thoroughly. Take the time to mix the sample. The better the sample is mixed the better it represents the whole field.

Put 1 to 2 pints of the thoroughly-mixed soil in a plastic bag and label it with an indelible marker. Don't put a paper label inside the bag. The moist soil will make it unreadable by the time the sample reaches the lab. 

The sample doesn't really require any special handling. You'll want to keep the sample at room or field temperatures. Keep the sample out of the sun or hot truck cab until you are ready to pack and ship it. Pack the samples in a box for shipment to a qualified soil lab. Cushion the samples with packing material so the bags don't break open during shipping.

Labeling bags for soil samples   Demonstration of how to cushion bags to prevent them from breaking open
Label bags on the outside.  

Cushion the bags so they don't break open.

Where to send the sample
Send samples to:
Plant and Insect Diagnostic Clinic
327 Bessey Hall
Iowa State University
Ames, IA 50011
(515) 294-0581

Include the Plant Nematode Sample Submission Form which you can download here» (pdf format)

If you do not live in Iowa, check here for links to your state nematologist or county extension office for  assistance in finding the nearest plant diagnostic clinic. Some private labs also offer SCN testing, but not all soil fertility labs are trained to test for SCN - make sure your lab can test for SCN before shipping the sample. 

What to do if SCN is detected
Many labs report SCN eggs or eggs and juveniles per volume of soil, while other labs report the number of cysts. Cyst and egg counts are not directly comparable but keep in mind that a low cyst count does not equal a low egg count since each cyst can contain hundreds of eggs.

If you find out you have SCN, don't panic. Although SCN is a serious soybean pest, it can be managed profitably. Extension personnel and publications can help explain your test results and make management recommendations based on those results. See Interpreting SCN Soil Testing Results (pdf format).