The soybean cyst nematode (SCN) causes greater annual yield losses in Kentucky than any other pathogen of soybean.
The last time a formal survey was conducted by the University of Kentucky in 2006 and 2007, approximately 76% of soybean fields in the state were infested with SCN.
Preliminary results from an ongoing SCN survey initiated in 2019 show that approximately 80% of Kentucky fields are infested with SCN.
Although above-ground symptoms, stunting, and yellowing, caused by SCN can be observed occasionally, affected soybean plants generally appear to be healthy.
Unfortunately, “healthy-looking” soybean plants that are infected by SCN can still have up to a 30% yield reduction. Extension plant pathologist, Dr. Don Hershman prepared the following discussion related to the management of SCN.
Management of SCN has gotten much more complex in the last few years since SCN populations have adapted to the use of SCN-resistant soybean varieties.
The primary source of SCN resistance used by commercial soybean breeding programs came from a soybean germplasm line known as “PI 88788.”
This source of resistance was highly effective in managing SCN for several years, but prolific use of soybean varieties with the PI 88788 background has been selected for SCN populations that are able to overcome this source of resistance.
In the 2006-2007 University of Kentucky SCN survey, the PI 88788 source of SCN resistance was not very effective against approximately 60% of the SCN populations in Kentucky, making management of this pathogen much more complex than before.
As complex as it is, the management of SCN is still doable and is important for maintaining and increasing soybean yields. Test your fields to know the number of SCN eggs in your field.
The best times to sample for SCN in your fields are in the fall or in the spring (before planting). A Fact Sheet on sampling for SCN is available on my website at https://daviess.ca.uky.edu/ANR.
Follow the same pattern as fertility sampling, but to 6-8 inches deep and do not air dry. Collect samples from the soybean row only if it was in soybean this year.
Although the University of Kentucky does not currently have an active SCN Laboratory, samples can be sent to the University of Illinois Plant Clinic, the University of Missouri SCN Diagnostics Lab, or Waters Agricultural Lab in Owensboro. Similar to the past two seasons, the Kentucky Soybean Board is continuing to sponsor free SCN testing for Kentucky farmers.
With this program, a limited number of samples for each county can be tested for free. If varieties are available that utilize sources of SCN resistance other than PI 88788 (such as Peking or Hartwig), then rotate the source of resistance every time you plant soybean in a field.
Unfortunately, nearly all the soybean varieties adapted for planting in Kentucky utilize only the PI 88788 source of resistance. However, it is still important to rotate to different resistant soybean varieties, even though they are utilizing the same source of resistance. SCN is good at adaptation, so switching soybean varieties will help.
Rotating fields to a non-host crop, such as corn or grain sorghum, will help reduce SCN populations in fields. Wheat is another non-host crop that may help lower SCN populations by having it in the rotation.
Several years ago, Dr. Don Hershman with the University of Kentucky evaluated the effect of wheat residue on SCN populations. His research found that planting soybeans into fields with standing wheat stubble reduced SCN populations at the end of the growing season.
Consider using a nematode-protectant seed treatment. Several nematode-protectant seed treatment products are now available on the market.
Although the effects of these seed treatments have not always been consistent in field research trials, they are additional tools that can be used along with resistant varieties and crop rotation to help manage this important pathogen.
A multi-state initiative funded by the Soybean Checkoff Program known as the SCN Coalition is helping to promote awareness of the damage caused by SCN and the importance of managing this pathogen. Be on the lookout for information from the SCN Coalition about this important pathogen.
Clint Hardy is the agricultural extension agent for the Daviess County Extension Office. He can be reached at 270-685-8480.