Sampling for Soybean Cyst Nematodes (SCN)

Guest Blog Post: Authored by John Wilson, Extension Educator in Burt County.

I recently had a farmer ask me what he needed to do to take the perfect soil sample for SCN? I think he was joking in his search for perfection, but he does ask a good question that I’m asked more all the time, especially at this time of year. What is the proper way to take a soil sample to test for SCN in your field? I think there is both science and art in collecting good soil samples… let me explain!

The science part is pretty easy…

Your sample should be from an area no larger than 40 acres… and less is better.
You need to eat a gallon of ice cream so you have a bucket to put your soil samples in! (OK, you caught me, other buckets will work, but you do need to reward yourself for collecting the soil samples!) On a more serious note, one important thing about buckets (and soil probes)… if you are taking multiple samples, be sure your probe and bucket are clean so you don’t accidentally contaminate other samples from one SCN-positive field, resulting in false positives for SCN in later samples.
You should take a minimum of 20 to 25 soil cores taken randomly across the area being tested,
If the field you are sampling has standing soybean stubble, take your sample just a couple inches to the side of the old soybean row (so you’ll be probing through the old root system and more likely to detect SCN if it is there) and go six to eight inches deep.
If you are sampling in a field that wasn’t in soybeans this year, randomly collect samples across the area to be tested. Samples from these fields that will be planted to soybeans next year can be very important as you place your seed order for next year. You’ll know if you do or do not need to order SCN-resistant varieties. When selecting SCN resistant varieties, don’t forget the other agronomic traits you need (emergence, lodging or chlorosis scores, disease resistance, etc.)
Thoroughly mix the cores you collected and submit the soil sample in bags available at your local UNL Extension office for a free SCN analysis. The cost of the analysis (normally $25/sample) has been covered for you by the Nebraska Soybean Board, your check-off dollars at work for you!
Submit your sample to the Plant and Pest Diagnostic Clinic (address is on the bag) or ask your local UNL Extension staff if anybody is going to Lincoln in the near future and could deliver the sample to the lab for you. That saves you some postage and the samples do not require any special handling (refrigerated, frozen, etc.) until they are delivered to the lab.

That’s pretty straight forward and easy to follow. So you may be asking yourself, “Is he off his meds… what in the world is he talking about when he says there is an art to sampling for SCN?”

When you select those areas in a field you want to sample, it’s important to remember… anything that will move soil will also move SCN. Now it doesn’t take a dirt scraper to move soil in your field… it could be wind, water or wildlife as well as humans and the equipment we take through the field.

Now here comes the “art” part of collecting your soil samples for SCN. With the concept that SCN moves with soil in your mind, think about areas in your field where soil may have moved and be a potential place for SCN to first get established. Here are a few places where you would want to be sure to take a couple cores, just because these are areas where SCN is more likely to be found.

Along a stream that periodically floods. Someone upstream might have had SCN in their field and it washed down to your field.
Low areas where water drains after a heavy rain. Light infestations throughout the field may be concentrated in these low areas where water stands.
Along fence lines. In the past when fall tillage was more common, fences would act like a trip for the blowing soil and SCN could be deposited along old fence rows.
By field entryways or driveways. This is the most likely place for soil from another (SCN-infested) field that stuck to equipment to be shaken loose in the new field.
There are two other areas that I encourage farmers to sample. The first is areas in a field that had a higher incidence of sudden death syndrome (SDS) or brown stem rot (BSR). You can have either of these diseases without having SCN… or you can have SCN without having either of these diseases. BUT, if you have SCN in a field or even part of a field, you are more likely to have SDS or BSR in those areas of the field where SCN is present.

Now the final area to collect a soil sample for SCN is the most common area that I recommend farmers to sample… but it’s so obvious, it’s easy to overlook. Sample where your observations or your yield maps show that soybean yields are not meeting your expectations. This might be a whole field, but more commonly it is an area in the field.

Statements such as “The west end of my field isn’t yielding like the rest of the field and there is not a difference in soil type, compaction, herbicide injury, weed or insect pressure, or other explanation for lower soybean yields. Also, when I plant corn, yields are good across the whole field!” can be the perfect indicator of where to sample for SCN.

In either of these last two situations, higher SDS/BSR or where yields didn’t meet expectations, I recommend farmers take a sample where either of these conditions existed and another sample close by where disease pressure was lower or yields met expectations. This can help you confirm or eliminate SCN as the culprit causing the disease pressure or lower yields.

If both samples come back negative for SCN, you can eliminate it as a cause for these problems.
If both samples come back high for SCN, you know you have SCN and need to manage it, but you also have some other condition that is contributing to these problems.
If the area with higher incidence of SDS/BSR or was lower yielding comes back high for SCN and the adjacent area come backs low, you have identified SCN as the problem and can now start your management plan to lower the level of SCN in your field.

For more information on sampling for or managing SCN, contact your local UNL Extension office or go to: