Some problem pests just keep raising their ugly heads each season, and that’s certainly true for Soybean Cyst Nematode (SCN). Despite a lot of work and effort on the part of university Extension and company researchers, this endemic pest continues to take a big bite out of soybean yields across the Midwest—to the tune of over $1 billion annually, according to the U. S. Department of Agriculture.
Farmers know the typical signs that SCN is present in a field--plants are stunted, yellow and scraggly. In severe cases, SCN can destroy 80% of a field’s yield potential. University of Illinois research shows that when SCN goes undetected in fields--where symptoms aren’t present--it can still sap yields by 15% to 30%.
Terry Niblack, a noted expert on SCN at the Ohio State University, says sampling fields during fall, post-harvest, is the best time to evaluate the pest’s presence. The results can help you determine what kind of soybean varieties your fields need for next season.
She recommends testing every field where soybeans will be grown in 2018. Each soil sample you submit to the lab should be a composite of at least 20 cores, taken in a zigzag pattern across a field at a depth of 8” to 10”. For large fields, collect samples from at least two random 5-acre sections with similar soil types and crop histories. Gathering samples takes some time, but the more samples you take the more accurate the results.
Keep the subsamples from each field together and mix them up in a bucket. Then fill a 1-qt. plastic bag with each mixed subsample and mail it to a qualified laboratory for analysis. Make sure you provide the specified information your lab requests. The old saying of “garbage in, garbage out” applies here. Also don’t delay in mailing your samples into the lab, because old samples or samples that sat in the back of a hot pickup won’t provide accurate test results.
The lab report will then provide you with a population count, telling you the number of cysts or, preferably, the number of eggs per 100 cc of soil.
If you are already managing for SCN and aren’t making any headway with the use of resistant soybean varieties, consider having the lab perform an SCN Type test which characterizes an SCN population. From this test you’ll find out how effective the resistance source is in your varieties. For instance, PI 88788 is the resistance source in about 97% of all commercially available SCN-resistant soybean varieties. If your SCN populations are overcoming PI 88788, you’ll need to determine whether you can access soybean varieties with other lines of resistance, protect resistant varieties with seed treatments, or whether you want to continue growing soybeans in those fields.
Noted SCN expert, Greg Tylka at Iowa State University, evaluates SCN-resistant varieties for yield and effects on SCN population densities. You can consult his lab’s SCN-resistant soybean variety trials at http://www.plantpath.iastate.edu/tylkalab/iowa-state-university-scn-resistant-soybean-variety-trials.