Sampling to evaluate the success of an SCN management program

Cysts of the soybean cyst nematode. Many testing labs report SCN eggs, or eggs and juveniles per volume of soil, while other labs report the number of cysts. Photo credit: Terry Niblack, University of Illinois

Recommended technique: Collect soil samples and have the SCN population densities determined.

When to sample
You can take a soil sample to check on the progress of a SCN management plan at almost any time of the year. But if you want to monitor the effectiveness of your SCN management program over several years, you should sample at the same point in the management program each time (say after a year of resistant soybeans or nonhost crop).

Generally avoid sampling frozen or saturated soil since these samples are harder to process and that may affect the accuracy of the results obtained. Fall is often the best time to sample as you plan for the next crop year.

ISU plant pathologist and nematologist Greg Tylka explains how to sample soil for SCN in the fall. Click on image to view the video. Video credit: Iowa Soybean Association

How to sample

Sample the top 6 to 8 inches of soil. Take cores from within the root zone or from within the interrow area.

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.

The more cores, the better the sample
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, SCN lays it's eggs in clusters. Therefore, SCN tends to be aggregated or clustered in fields and soil sample results tend to be highly variable.

 

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 as described the Diagnostic Tools: How to send a Sample. Cushion the samples with packing material so the bags don't break open during shipping.

 

Where to send the sample

University or Extension plant diagnostic clinics or University nematologists usually offer SCN testing. Check these links to state diagnostic labs for a testing location in your state. 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. 

Make sure you include your name, address and phone number with your sample. Including cropping history of the field, symptoms of problems observed and cropping plans for the next season are helpful in making recommendations for management if SCN is confirmed. Often there is an Information Request Form that can be printed out from the clinic web site. 

For more information, read Interpreting SCN Soil Testing Results  (pdf format)

Adapted from SCN Symptoms and Soil Sampling slide set, courtesy of Greg Tylka, Iowa State University.
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