Sampling to determine if SCN is responsible for poor yields

The equipment you need for sampling soil for SCN is the same equipment you use for taking a soil sample for soil nutrient analysis Photo credit:Greg Tylka, ISU

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. Take cores from within the root zone or from within the interrow area.

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

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 or M-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.

 

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.

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 lays 200 or more eggs in clusters. Therefore, SCN tends to be 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.

 

Where to send the sample
University or Extension plant diagnostic clinics or University nematologists usually offer SCN testing. Check here for a state diagnostic clinic in your area. 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. 

 

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. The various details to consider when interpreting results of soil tests for SCN are explained in Interpreting SCN Soil Testing Results (pdf format, Iowa State University)

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