The soybean cyst nematode (SCN) causes greater annual yield losses in Kentucky than any other pathogen of soybean.
At the time of the last formal survey 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 a new ongoing SCN survey initiated in 2019 show that 84% of Kentucky fields are infested with SCN.
Affected soybean plants generally appear to be healthy. Unfortunately, “healthy-looking” soybean plants that are infected by soybean cyst nematode can still have up to a 30% yield reduction.
Management of SCN has become more challenging 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 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, management of SCN is still doable and is important for maintaining and increasing soybean yields.
The most important step in optimizing the yield potential is testing all of your fields to know the number of SCN eggs you are up against. The best times to sample for SCN in your fields are in the fall or in the spring before planting.
Although the University of Kentucky does not currently have an active SCN Laboratory, samples can be sent to either the University of Illinois Plant Clinic or the University of Missouri SCN Diagnostics Lab. Similar to last season, 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. Call the Daviess County Cooperative Extension Service Office at 270-685-8480 for more information about the limited free SCN testing program.
Resistant varieties should be rotated. 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, most of 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 a field. Wheat is another non-host crop that may help lower SCN populations by including 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. More information about the SCN Coalition is available on their website at https://www.thescncoalition.com/. Be on the lookout for information from the SCN Coalition about this important pathogen.
Free Soil Testing
The Daviess County Cooperative Extension Service currently has a grant with The Daviess County Soil and Water Conservation District to cover the cost of soil samples in Daviess County. Information on collecting soil samples can be found on our website at https://daviess.ca.uky.edu/soil.
Clint Hardy is the agricultural extension agent for the Daviess County Extension Office. He can be reached at 270-685-8480.